Abstract:This paper concentrates on the forming of a hollow wide-chord titanium fan blade with complex geometries by a more efficient and simple way. A new two-layer process based on hot forming and diffusion bonding is developed. An essential approach for optimal blank design is proposed. The presented process employed a more reliable and controllable method to construct the internal ribbons, instead of the complicated superplastic forming in contemporary multi-layer approaches. To evaluate the practicability, the numerical method is used to investigate the thickness uniformity, structural integrity and skin defects of forming results by ABAQUS. A series of experiments were conducted to validate the simulation results. The Ti-6Al-4V alloy was adopted as the forming material, and blanks optimal designed by the proposed approach were used. The scaled-down version of the hollow wide-chord fan blade was successfully formed without defects. In addition, it is observed that the experimentation and simulation agree well.

Abstract:In this thesis, a fluorine-doped hydroxyapatite (FHAP)/Micro-arc oxidation (MAO) composite coating is deposited on commercially pure titanium (CPTi) surface through micro-arc oxidation and electrochemical deposition (ED) technique. Simulative Hank"s solution is used to test the electrochemical corrosion resistance of uncoated CPTi substrate and coated samples. The impact of MAO interface layer on the micro-structural, mechanical property, and electrochemical property of coating is studied in this article. Results show that the deposited HAP/Ti, FHAP/Ti and FHAP/MAO/Ti coated samples dramatically improved the anticorrosion of the CPTi substrate in the simulative Hank"s solution. However, the mechanical properties testing show that FHAP/Ti coating has a poor bonding strength of 10.7 MPa compared to that of FHAP/Ti coating with a MAO interface layer (18.1 MPa). Furthermore, the contact angle of the FHAP/MAO/Ti coating with deionized water is approximately 35.8°, which is more beneficial to promote cell attachment and proliferation.

Abstract:In this study, R60702 plate and TA2 plate were successfully bonded together by explosive welding. The microstructure, element diffusion, microhardness changes near the bonding interface before and after heat treatment were investigated utilizing optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and microhardness tester. The mechanical properties and fracture morphology in initial and heat treated states were examined as well. The results demonstrate that after explosive welding, the explosively welded bonding interface shows a wavy appearance, obvious deformations and short element diffusion. The microhardness values decrease gradually with the increasing distance from the interface due to the diminishing deformations. After heat treatment, a diffusion layer and recrystallization occur in the microstructure. The overall microhardness values, the tensile strength and shear strength decrease while the plasticity and ductility are improved compared with the initial state. The explosively welded R60702/TA2 composite plate shows a good bending performance after heat treatment.

Abstract:Four fretting modes exist in ball-on-flat contact according to the direction of relative motion, i.e. tangential, radial, rotational, and torsional fretting. Torsional fretting in a physiological medium is one of the main reasons that artificial joints fail. A new test system was successfully established for torsional fretting in a liquid medium at a constant temperature in a torsional mode with a ball-on-flat contact. The torsional fretting experiments were conducted on Titanium alloys against Zirconium dioxide ceramic balls in a saline solution at 37°C, and the torsional fretting running behaviors and damage mechanisms were discussed in detail. The results showed that the dynamics behaviors were strongly depended upon the torsional angular displacement amplitude and the number of cycles. A running condition fretting map (RCFM) was established, which included 3 fretting running regimes: a partial slip regime (PSR), a mixed fretting regime (MFR), and a slip regime (SR). No damage was observed on the contact center and only slight scratch and wear were observed on the contact edge in the PSR. The damage zone extended to the contact center and the sticking zone (which exhibited no damage) contracted to the contact center with increases in the number of cycles, and some oxidation wear and damage presented on the contact edge region in the MFR. The damage mechanisms were primarily the result of abrasive wear, oxidation wear and adhesion wear in the SR.

Abstract:The influence of Si content on mechanical properties of Ti-6Al-2Zr-1Mo-1V titanium alloy at room temperature and 500℃ was studied. The fracture morphologies and microstructures were analyzed by scanning electron microscope (SEM) and transition electronic microscope (TEM). The nucleation and growth of silicide were related to the mechanical properties. It was shown that the tensile strength and high-temperature enhance performance were improved when Si was added from 0.04wt% to 0.14wt% in the Ti-6Al-2Zr-1Mo-1V alloy; the ductility is almost unchanged; impact toughness and plane strain fracture toughness were decreased. The alternation tendency from ductility to brittle fracture can be found with the addition of Si, the radial region enlarged, and the area of fibrous region and shear lip minified. When the content of Si is less than 0.09wt%, the Si elements are dissolved in α and β phase and increase strength, solid solution strengthen mechanism is the main mechanism. On the other hand, the silicide precipices along phase boundary when the content of Si reaches 0.14%wt, which led a combined strengthening by solution and precipitation.

Abstract:Ti-45Al (at %) and Ti-45Al-0.3Y (at %) samples were fabricated by vacuum hot-press sintering (VHPS). The influence of Y additions and VHPS process parameters on the microstructure and mechanical properties of TiAl-based alloys were analyzed using x-ray diffraction (XRD), optical microscopy (OM), back-scattered electron (BSE) imaging, compression and hardness testing. Optimized sintering parameters were 42 MPa at 1400℃ with holding time of 90 minutes. Samples prepared under these conditions had uniform and fine grains with a duplex microstructure which consisted of γ phase and γ+α2 lamellar colonies. The reaction between γ-TiAl and α2-Ti3Al reached completion at a hot-press temperature of 1400℃ and holding time of 240 minutes. Unfortunately, significant grain growth occurred under these conditions. The addition of Y had an obvious effect on grain and interlamellar spacing refinement contributing to an increased mechanical strength of the alloy.

Abstract:An aluminized coating of TiAl3 was prepared on Ti-6Al-4V alloy by hot-dip aluminizing and subsequently high-temperature diffusion at 650 ℃. Dry sliding wear behavior was conducted for the aluminized Ti-6Al-4V alloy against GCr15 steel on a pin-on-disc wear tester. The morphology, phase and composition of worn surface of the HDA coatings were characterized by SEM, XRD, EDS and XPS. The wear mechanism was also explored. The research result demonstrated that with an increase of sliding velocity, the wear loss of the aluminized Ti-6Al-4V alloy decreased to a lower value at 0.75 m/s, then increased to the highest at 2.68 m/s and finally decreased to the lowest at 4 m/s. At different sliding velocities, the wear loss increased with an increase of load. Tribo-layers were identified to notably affect the wear behavior and mechanism. At 4 m/s, oxide-containing tribo-layers (TiO and TiO2) possessed an obvious wear-reduced function; conversely at 2.68 m/s, no-oxide ones did not show the protection from wear. Compared with uncoated Ti-6Al-4V alloy, the aluminized coating improved the wear resistance of the titanium alloy under various conditions, especially 4 m/s. The improved wear performance was suggested to be attributed to Ti-Al coating and tribo-oxide layer.

Abstract:This study developed a new preparation process for titanium powder for additive manufacturing- Wire Induction heating Gas Atomization (WIGA). The combination of numerical simulations and experimental investigations was used to investigate the high frequency induction melting of titanium wire. The numerical simulations obtained the optimal parameters of the titanium wire induction melting model. The angle α of the induction coil is 90°. The power output frequency f is 450 kHz. The diameter of the titanium wire was 4mm, and the minimum wire feed speed was 45 mm/s when forming a 15 mm length of metal flow. Under this condition, the critical output power is 34kW when the molten metal generates 350±50°C of superheat. An argon atmosphere protective titanium melting experimental device was established. Through experimental investigations, the minimum TC4 wire feed speed was 50 mm/s when forming a 15 mm length of metal flow，and the error between the experimental and the numerical simulation was 10.0%. Under this condition, the minimum output power of the power supply was 38kW when generating a molten metal with a superheat of 350±50°C, the experimental and numerical simulation errors were 10.5%. The experimental and numerical simulation results proved each other, and the engineering application basis of high frequency induction melting of titanium wire was obtained.

Abstract:For the design of pore structure of titanium alloy implants, most of the current researches are on regular pore structures, while few of them are concerned with the design of gradient pore structures. In this research, two methods of designing circular pores with Planar Center Gradient and Spatial Sphere Gradient are proposed. On this basis, a certain model design of Planar Center Gradient is completed, some samples of titanium alloy gradient pore and regular pore structure implants with a porosity of 75% were fabricated by Selective Laser Melting(SLM), and made microscopic material characterization. Through the test of mechanical properties, the related mechanical data are obtained. Conclusion: The mechanical properties of the gradient pore structure are better than those of regular pores. Under the condition of porosity of 75%, the average elastic modulus of gradient pore sample is 36.25% higher than that of regular pore and the average compressive strength is increased by 29.9%.

Abstract:The plastic deformation mechanisms of the titanium single-crystal nanopillars under both tension and compression were studied with the molecular dynamics simulation method. In this work, the research focuses on two aspects around the microscopic deformation mechanisms: stress-strain analysis and the evolution of atomistic configuration. The results indicate that the {101 ?2} twinning and stacking fault dominate the tension deformation along the [0001] direction. The slip is the principal factor leading to the initial yielding and then the pyramidal slip occurs to coordinate both vertical and horizontal strains for the compression condition along the [0001] direction. Additionally, no twinning is found in compression. Besides the conventional {101 ?2} plane, semi-coherent basal-prismatic interfaces between parent and reoriented crystal were also observed under tensile loading.

Abstract:(Ti_0.5Ni_0.48M_0.02)₈₀Cu₂₀ (M=Fe, Ce and Zr) with 3mm diameter was fabricated by suspend melting under argon atmosphere using a water-cooled Cu mold. The influences of Fe, Ce and Zr on the shape-memory crystalline phase precipitation law in the solidification structure of alloys were studied, and the mechanical behaviors at room temperature and strengthening and toughening mechanism of alloys analyzed as well. The results showed that the as-cast microstructure of (Ti_0.5Ni_0.48M_0.02)₈₀Cu₂₀ (M=Fe, Ce and Zr) alloys are the amorphous matrix and shape-memory crystal phase (B2 undercooled austenite and B19’ thermal martensite) structure. The B2 phase volume fraction precipitates most in M=Fe alloy. In M=Zr alloy, the B19,phase volume fraction precipitates most. The alloys all exihibit good comprehensive mechanical properties, among which M=Ce alloy with the best comprehensive mechanical properties, and the fracture strength, yield strength and plastic strain are 2645Mpa, 1150Mpa and 12.2%, respectively. After alloys fracture with loading, the B2 austenitic phase volume fraction decrease and B19,martensite increase. Moreover, the room temperature deformation behavior of alloys can be described as elastic deformation and strong work hardening after yielding. The work hardening rate and instantaneous work hardening rate are divided into three stages with the change of true strain, and the transformation of B2 to B19" under the compressive stress is the mainly force of alloy strengthening and toughening. The work hardening rate, work hardening exponent and instantaneous work hardening index of the M=Fe alloy are the largest and its work hardening ability is the strongest, the work hardening ability of M=Ce alloy weaker than M=Fe alloy, and M= Zr alloy is the weakest.

Abstract:it is well know that CaTiO₃ is the evitable interphase produced during electrolysis of TiO₂ in molten CaCl₂. Here, the relationship between formation of CaTiO₃ and deoxygenation of TiO₂ and emition of gas on the anode is studied by the intermittent experiments. The results show that the process of deoxygenation from TiO₂ to Ti can be dividied three stages. The first stage is deoxygenantion of TiO₂ and formation of CaTiO₃. The second is deoxyenation and decalcification of CaTiO₃ to Ti₂O including deoxygenation of titanium suboxides. The final stage is deoxygenation from Ti₂O to Ti (2% O). the mole ratio of O_2- and Ca₂₊ and CaTiO₃ is 1:1:1. Cl₂ releases from the anode when CaTiO₃ is formed in the cathode. If the whole electrolysis time from TiO₂ to Ti (2% O) is thought 100%, the cost time of stage I, stage II and stage III is 5.6%,38.9%, 55.5% respectively. Formation of CaTiO₃ and deoxygenation of Ti₂O to Ti are both main factors of the low current effeciency.

Abstract:_{Ti-5Al-3V-3Zr-0.7Cr titanium alloy, a new near α titanium alloy, as a candidate material for pressure hull of fusion reactor was researched detailedly in this paper. Firstly, the flow behavior was analyzed by stress-st rain curves obtained by isothermal compression of Ti-5Al-3V-3Zr-0.7Cr alloy, and it was found that the stress decreased with the increasing deformation temperature and the decreasing strain rate, the extent of softeningfirstincreasedthendecreased after 800℃with increasing deformation temperature at higher strain rates of 0.1 and 1s-1, while it decreased continuously with increasing deformation temperature at lower strain rates of 0.001 and 0.01s-1, and the flow stress dropped rapidly after peak stress presenting the dynamic recrystallization characteristics. Secondly, the constitutive model of Ti-5Al-3V-3Zr-0.7Cr alloy was developed in the form of the hyperbolicSsine and the deformation activation energy was calculated to be about 548.74 kJ/mol. Thirdly, Based on the conventional recrystallized fraction curves, the evolution of recrystallized volume fraction is greatly affected by the strain rates and the deformation temperature. The flow softening of the alloy has been proved to be mainly attributed to the occurrence of DRX. Based on the dynamic materials model and Prasad’s instability criterion, the power dissipation map and instability map of Ti-5Al-3V-3Zr-0.7Cr alloy were constructed at strains of 0.4 and 0.6, the obtained optimal processing windows of Ti-5Al-3V-3Zr-0.7Cr alloy were 750℃/ 0.001-0.01s-1 and 850-900℃/ 0.01-0.1s-1 with the peak efficiencies of 65% and 73% respectively.}

Abstract:Solid particle erosion (SPE) resistance of compressor titanium alloy blade can be enhanced by the hard coatings. But the system of hard coating / soft substrate is easily corrupt by the SPE due to the coatings’ higher brittleness and interface mismatch, so the brittle fracture often occurs at the interface of coating and substrate. In order to improve the hard coatings’ SPE resistance, combining with the plasma ion diffusion and arc ion plating technology, a series of composite coatings with gradient carburized layer and TiN(Ti) coating were synthesized on TC4 alloy. And the influence of structure on composite coating’s properties was studied in detail. The results showed that the hardness and bonding strength of composite coatings were enhanced remarkably, comparing with the monolayer TiN and 12 periods of Ti/TiN hard coatings deposited on TC4 alloy without plasma carburization. The monolayer TiN showed a mechanism of brittle cracking after sand erosion, and the 12 periods of Ti/TiN coating presents morphologies of flaking and erosion pit due to the multilayer toughening effect. After carburization, the coating’s impact toughness was enhanced. The interface fracture of monolayer TiN was restrained. And the composite coating with gradient carburized layer and 12 periods of Ti/TiN coating possessed the best SPE resistance with erosion weight loss rate decreased by more than ten times and showed a mechanism of tough damage, which can be attributed to its higher interface strength and better match of hardness and toughness.

Abstract:The superhydrophobic coatings were prepared on the surface of biomedical Ti-6Al-V alloy by micro-arc oxidation (MAO) and surface modification of fluoroalkyl silane. The effect of voltages on surface morphologies and roughness of the coatings was investigated, and the phase composition and element chemical state of the MAO and hydrophobic treated samples were analyzed to discuss the formation mechanism of the superhydrophobic coating. At the same time, the cytotoxicity and antibacterial property of the superhydrophobic samples were also preliminarily evaluated. The results show that the surface roughness of the coatings increases with increasing the voltages, and the microstructure uniformity of the coatings is optimum at 440 V. After superhydrophobic treatment, the surface roughness of samples decreases slightly compared to the MAO samples, and the contact angles of the samples increase first, and then decrease with increasing the the voltages, reaching the maximum value of 154.9° at 440 V. The MAO coating is mainly composed of anatase TiO2 phase and a little rutile TiO2 phase with a large number of –OH and some phosphorus compounds. While the surface of the superhydrophobic coating contains a large number of CF3, CF2 and Si-O groups.The fluoroalkyl silane is grafted onto the MAO coating through the hydrolytic reaction and dehydration reaction to form the superhydrophobic surface. The superhydrophobic sample belongs to Class 1 non-toxic material, and the cell viability of the superhydrophobic sample has no significant difference from that of Ti-6Al-4V alloy. Moreover, the superhydrophobic sample also has certain antibacterial property, and the antibacterial rate can be up to 93.03% compared to the MAO treated sample.

Abstract:The ingot with 120mm diameter of Ti-25V-15Cr-5Mo-0.25Si-0.08C alloy which is a new type burn resistant titanium alloy with lower cost was produced by vacuum arc remelting in this study. This ingot was forged into bars with 25mm diameter by sheathed extrusion. The microstructures of the ingot and extrusion bars of TF-X alloy were studied. The tensile, thermal stability and creep properties of extrusion bars of TF-X alloy were tested under different conditions. The results show that microstructures of TF-X alloy, which has better ductility in tensile test, were roughly the same as TF550 alloy. In addition, TF-X alloy has higher strength and worse thermal stability than TF550 alloy, and its creep property better than Ti40 alloy was equivalent to TF550 alloy.

Abstract:In this paper, the diffusion behavior of Cu/Ni/Ti atoms at different temperatures was studied by means of diffusion heat treatment. The influence of diffusion process on the structure and corrosion of the coating was also discussed. The results show that the corrosion resistance of the coating surface can be effectively improved with the stable diffusion layer formed by the mutual diffusion of Cu/Ni/Ti atoms. As the thermal diffusion temperature up to 700 ℃, the compact structure of membrane layer, the NixTiy intermetallic compounds and a small amount of CuxTiy intermetallic compounds formed in the diffusion layer, the corrosion resistance of coating on the surface of the best. Temperature to 800 ℃, Kirkendall space grew up together each other, which is formed by the formation of cracks or holes and make coating porous, so as to lower the corrosion resistance, due to Kirkendall effect is triggered by atoms at the interface between Cu/Ni/Ti structure.

Abstract:The microstructure evolution and mechanical properties of Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe alloy after single and duplex aging treatment were studied. The Single aging temperature was 550℃, the duplex aging was pre-aged at 400 ℃ then re-aged at 550℃. The results showed that when the alloy pre-aged at 400℃, the ω phase was precipitated. As the pre-aging time prolonged, the ω phase finally changed to the α phase. Duplex aging was effective to yield the α phase fine dispersion, and the pre precipitated isothermal ω phase provided more uniform nucleation position for precipitation of α phase than single aging so as to improve the alloy tensile strengthen greatly. During pre aging, the isothermal ω phase could precipitate sufficiently so as to provide more advantageous nucleation position to precipitate very fine α phase of acicular style, and the strengthening effect was the same with that of duplex aging.

Abstract:Al-doped Ti/PbO₂ electrodes were prepared by using anodic deposition from solution containing Al (III) cation. Influence of Al-doping on the physicochemical properties of modified PbO₂ coating electrodes was characterized by surface roughometer, scanning electron microscope (SEM), X-ray diffraction (XRD), linear polarization and electrochemical impedance spectroscopy (EIS) techniques, and accelerated life test. The electrocatalytic oxidation degradation behavior of Al-doping PbO₂ electrodes for phenol simulation wastewater was compared. These results show that PbO₂ coatings with smaller size, uniform and dense surface, lower surface roughness and less nodulation defect are obtained when a certain amount of Al₃₊was added into the electrodeposition solution. Al-doping results in increased oxygen evolution potential, improved charge transfer capacity and enhanced electrocatalytic performance for PbO₂ electrodes. Nevertheless, those properties do not uniformly varied with increase of Al₃₊additive amount. When deposited 3h in the bath solution contain 3mM Al₃₊, the electrode prepared has maximum oxygen evolution potential 2.09 V, excellent electrical conductivity, the best electrocatalytic property and the longest accelerated life of 460 h, which is increased by 100h compared with that of the unmodified electrode. The Al-doped Ti/PbO₂ electrodes show good electrochemical oxidation degradation capacity for phenol simulated wastewater. After treatment 180 min the removal rate of phenol is up to 93.6%, and the maximum removal rate of COD can reach 73.6%.

Abstract:The addition of Ni as filler is one of the methods to restrain the crack of TiNi / stainless steel dissimilar material laser welding joint and realize its good connection, but the difference between filler metal Ni and base metal TiNi alloy will form the interface area, the welding heat input has a great influence on the microstructure and morphology of the interface area, which will affect the mechanical behavior of the whole joint. In this paper, TiNi alloy / Ni / 321 stainless steel laser welding joint with thickness of 0.2mm was obtained by using Ni as filler material in laser micro - welding. the effect of laser pulse width on the TiNi side interface of the welding joint was studied. The results show that, the interface zone of TiNi alloy side under different pulse width is composed of TiNi eutectic layer and TiNi3 intermetallic layer with different width.With the increase of pulse width, the average width of TiNi eutectic layer gradually decreases, the average width of TiNi3 intermetallic compound layer increases gradually, and the microhardness of interface zone increases with the increase of pulse width. The change of the melting amount of TiNi and the flow of Marangoni is the main reason that affects the width and microhardness of the interface zone.

Abstract:To improve the bioactivity of surface of titanium and reduce infection rate of implantation, the porous coatings were prepared by ultrasonic micro arc oxidation (UMAO) and Rhizoma drynariae(ERD) coupled by phytic acid .Besides, the structure, surface morphology and performance were investigated. The results indicated that nanoSparticles of drug loading increased with concentration of ERD. The surface of coatings produced PO_43-,P₂O_74- and O=P-O-. The friction coefficient of 12.5 g/L was lower .Also, the coating of 12.5 g/L had a better binding force and was hydrophilic. The potential increased by 0.33-0.45V and self-corrosion current decreased by a order of magnitude for concentration of 12.5 g/L. In conclusion, the corrosion resistance, binding force and bioactivity are improved by drug loading coupled with phytic acid after MAO on the magnesium.

Abstract:By comparing the microstructure, static mechanical properties, tensile fracture and microhardness of laser deposited TC4 / TC11 titanium alloy direct transitional parts in the as-deposited and heat-treated states, the approaches to perfect the microstructure of laser deposition TC4/TC11 alloy so as to improve its integrated mechanical properties were explored,. Results show that after the as-deposited sample undergoes 970℃ heat treatment, its length-width ratio of α laths is less than that of as-deposited and annealed samples. The microstructure on the two sides is featured by basket-weave structure and more even. In addition, the grain boundary α disappears entirely. There is almost no existence of transitive interface, which optimizes the textural parameters of TC4/TC11 titanium alloy. For all the as-deposited, relieved-stress and solution aging samples (optimal heat treatment parameters), their tensile fractures are tough fracture and their fracture sections are all on the side of TC4 titanium alloys. Among them, the strength of solution aging sample is not reduced greatly. Moreover, its plasticity is remarkably enhanced. So it has excellent integrated mechanical properties. When the temperature of the heat treatment raises to 970℃ (optimal heat treatment parameters) microhardness of TC4/TC11 titanium alloys is uniform along the whole transitive interface with minimum differences. At the same time, microhardness changes the most slightly on the matrix and transitive interface.

Abstract:The effects of solution and aging process on the precipitation behavior and mechanical properties of Ti-15V-3Cr-3Sn-3Al titanium alloy were investigated by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that there are a large number of metastable martensite α" phases in the microstructure after solution treatment at 980℃×0.5h. After the aging treatment, the precipitates with different quantities and morphology are formed. With the increase of aging temperature or time, the number of precipitates increases, the morphology changes from irregular aggregation to acicular, and the size and spacing of precipitates also increase. During the aging process, a large number of nano dispersed α phases were precipitated, and the formation of the α/β phase interface hindered the dislocation movement, thus increasing the strength of the alloy. The more and smaller the precipitated phase is, the better the strengthening effect. The plasticity depends mainly on the distribution and number of precipitates on grain boundaries. The morphology of grain boundary α phase has a great influence on the plasticity of the material, and the continuous distribution of grain boundary α phase will seriously damage the plasticity of the material.

Abstract:Solidification temperature range, temperature sensitivity of solid fraction, temperature process window and phase composition and transformation path of Mg-9Zn-xAl(x=2,4,6) were calculated by Pandat calculation, and studied by experiment. The results indicate that the bigger temperature window is conducive to the control and operation of semi-solid forming for Mg-9Zn-xAl alloy, and the temperature sensitivity of solid fraction is all smaller than 0.015. Mg-9Zn-xAl alloy has the different transformation temperature and path of the phase at the different Al addition. α-Mg, MgZn, Mg32(Al,Zn)49 and Al5Mg11Zn4 were formed in all samples, when Al addition is increased to 6%, Mg17Al12 phase was formed. The grain size and roundness of Mg-9Zn-xAl alloys which prepared by self-inoculation rheo-diecasting method are 65.3μm, 56.5μm, 52.2μm and 1.3, 1.19, 1.23 respectively. When the operating temperature is 150℃, the comprehensive strength and deformation are 278MPa, 283MPa, 295MPa and 36.22%, 33.02%, 31.21% respectively.

Abstract:A fine bonded interface is essential for the property of metal matrix composites. In this paper, an innovative method to strengthen boron carbide reinforced aluminum composites (B₄C/Al composites) was studied by liquid stirring technology. The effect of interfacial reaction on the microstructure and mechanical behavior of B₄C/Al composites was revealed by addition of Ti. Through B₄C-Al melt interfacial reaction, Ti element strongly enriched at the interface. A dense and continuous nanoscale layer of TiB₂ was formed on the surface of B₄C particles. Interfacial modification was achieved by interfacial reaction. Due to the formation of TiB₂ layer with good wettability and bonding, interfacial defects were eliminated. Increasing the degree of reaction, such as Ti content and reaction time, the strength of B₄C/Al composites was gradually improved. Severe interfacial reaction introduced lots of nano-scale TiB₂crystals into the matrix, which as in situ second reinforcement also improved the strength of B₄C/Al composites. Fracture behavior of B₄C/Al composites with different interfacial modification was discussed at last.

Abstract:CeO2-free and CeO2-modified aluminide coatings were prepared by aluminizing pure Ni film and Ni-CeO2 film on Ni plate at 620°C, respectively. The effect of the CeO2 addition on the growth rate and adhesion of the alumina scale was investigated at 1000 °C. The results show that the addition of nanometer CeO2 in aluminide coating of δ phase delayed the formation of a continuous α-Al2O3 scale and decreased the growth rate of alumina scale during oxidation. Moreover, the alumina scale adhesion was improved by the addition of nanometer CeO2 due to the smaller cavities formed at the alumina scale/coating interface compared with the CeO2-free one.

Abstract:Design and preparation of various rational silver micro-nanostructures has been recognized as a promising solution for the Surface-enhanced Raman scattering (SERS) signal amplification. Here, a simple wet-chemical method was reported for the synthesis of high-density Ag dendrites structures on silicon wafer by rapidly mixing silver nitrate and hydrofluoric acid aqueous solutions. The reductive Si-H surfaces is oxidized while silver ions are reduced, yielding a final Ag dendrites structure that offers an excellent SERS enhancement. The EDS measurements confirmed the metallic nature of the formed Ag dendrites. Researches also show that the pure and low-cost Ag dendrites were about several micrometers in size and can be rapidly and reproducibly produced in high yield. Importantly, there were no organic contaminants were detected on the surface of the resulting dendrites structure. Additionally, the influence of experimental parameters on the morphology of dendrites was also been investigated, such as hydrofluoric acid concentration, silver nitrate concentration, and the reaction time. Importantly, the fabricated Ag dendrites substrates can be used for accurate and reliable determination of Sudan I, Sudan II, and Sudan III, which indicate that they could have a good future for implementation.

Abstract:Electroformed gold layers were prepared by bidirectional pulse electrodeposition process, with thickness up to 150μm in 20h from cyanide-free bath. Through single variable experiment, which the pulse period was treated as a single variable, we studied the effect of pulse period on the properties of electroformed layer of gold using bidirectional pulse power. Scanning Electron Microscopy, X-ray Diffraction, and Vickers hardness test were used to research the surface mophology, average crystal size and hardness of electroformed gold layers. Results showed the microhardness of electroformed layer of gold is higher when pulse period changes between 45ms and 75ms, which can reach to 117HV0.1. Strong (111) preferred orientation can result in more flat micro surface and higher micohardness of electroformed gold layers.

Abstract:Experimental diffusion data in Ni-rich fcc Ni-Nb-Ti alloys at 1273 K was measured by electronic-probe microanalysis and the interdiffusion coefficients have been determined using Whittle and Green method. The atomic mobilities of Ni, Nb and Ti in Ni-Nb-Ti alloys have been obtained through assessing the interdiffusion data critically with the DICTRA software. Comprehensive comparisons between calculated and experimental diffusion coefficients showed that the atomic mobilities obtained in this work could well reproduce the experimental data. And the validity of the diffusion mobilities was tested by simulating the concentration-distance profiles and diffusion paths in diffusion couples.

Abstract:The objective of this study is to test the feasibility of RuMoC films for its application in seedless Cu diffusion barriers of damascene structure. The compatibility with IC fabrication and thermal stability of RuMoC barriers were investigated. The RuMoC barriers were amorphous at temperatures up to 500 ℃, showing great thermal stability. This is because the Ru-C bonds were well preserved at those temperatures, as revealed by XPS results, which hindered the Ru from crystallizing. A Cu plug of good quality was successfully electroplated on RuMoC barriers and filled the trench without seed layer, and the barrier effectively blocked the diffusion of Cu atom at temperatures up to 500 ℃. The results indicated a great prospect of RuMoC film as seedless Cu diffusion barrier in damascene structure for Cu interconnect.

Abstract:Monofilament AgAu sheathed Bi-2223 tapes were fabricated by powder in tube (PIT) process. The influences of cooling rate during the second heat treatment process (HT2) on the phase composition, microstructures and transport properties of Bi-2223/AgAu tapes were systematically investigated. It was noticed that after the HT2 process, the content of Pb-rich Pb₃Sr_2.5Bi_0.5Ca₂CuO_y (3321) phase increased with the decreasing cooling rate, while the size of CuO phase particles became bigger. With the cooling rate decreasing from 600 °C /h to 1 °C /h, the critical current density, J_c increased from 7 kA/cm₂ to the maximum value of 11.5 kA/cm₂, which increased for 64%. Meanwhile the current capacities in magnetic field of these Bi-2223/AgAu tapes have also been enhanced with slow cooling process, attributed to the improvements of both the intergrain connectivity and the flux pinning properties.

Abstract:To extrusion AZ31 magnesium alloy plate by the constant-strain-rate extrusion techniques, a new constant-strain-rate die was designed. Constant-strain-rate and traditional extrusion were investigated by finite element software Deform-3D separately. Key field variables, metal flow velocity, effective strain, exit temperature and mean stress, were studied systematically using the two type’s dies, during the extrusion processing. Results show that the uniformity of metal flow velocity, effective strain, exit temperature and mean stress are increased by 13.5%, 43.2%, 7.6% and 13.4%, respectively, by the constant-strain-rate extrusion.The effective strain of the plates at the exit of two kinds of dies exhibits gradually increasing trend from the center to the edge and the exit temperature field exhibits a trend that the center keeps stable and the edge gradually reduces. Moreover, the plate at the exit of constant-strain-rate die exhibits lower temperature increment than the plate at the exit of the traditional die. The range of tensile stress of the plate near the die exit is reduced by using constant-strain-rate die and the plate at the exit of constant-strain-rate die exhibit large compressive stress than the plate at the exit of the traditional die.

Abstract:The effects of trace Zr on microstructure and properties of Al-0.8Mg-0.9Si alloy sheets by asymmetrical rolled and its subsequent solution treated were investigated. The results show that the Al3Zr phase is formed in the alloy and dispersed in the matrix. The phases has unobvious effect on the formation of deformation textures Copper{112}<111>, Brass{011}<211>, S{123}<634>, E{111}<110>, F{111}<112> and others during asymmetric rolling process. However, the recrystallization happened during the subsequent solution treatment makes the orientation density of the textures Copper, Brass, S etc. reduce ,while the density of shear textures E and F formed in the asymmetric rolling process enhance due to the insoluble fine phase Al3Zr inhibit recrystallization process to some extent. The structure of trace elements Zr promote plates of the alloy a better comprehensive properties which the tensile strength, yield ratio and elongation were up to 230MPa, 0.49 and 9.5%, respectively, the plastic strain ratio r value increased from 0.7 to 0.84, the value of cup drawing IE increased from 8.94 to 9.84, and the anisotropy degree of ∣Δr∣reduced from 0.15 to 0.04.

Abstract:In order to solve the decarburization problems of WC particles caused by high temperature during detonation spray process, a detonation spraying facility with Laval nozzle was designed. Theoretical and experimental studies on preparing WC coatings via detonation spraying were carried out by introducing that facility. Numerical calculation results based on isentropic flow indicated that the temperature of the carrying gas could be decreased greatly by introducing nozzle, meanwhile, the velocity of the WC particles could also be accelerated up to above 1000m/s. Some pressure sensors were used to test the pressure in the entrance and the exit of the nozzle, the Mach number of the gas was calculated. Laser Extinguish method was employed in the nozzle exit to measure the average velocity of the particles. Both theoretical and experiment results could match each other properly. SEM, metalloscope and XRD were used to characterize WC particles and the coatings. The test results presented that the Laval nozzle could avoid decarburization phenomenon of WC particles effectively. This paper provides a new thought to solve the decarburization problems of WC particles during detonation spraying process.

Abstract:Abstract: Differential scanning calorimeter (DSC) experiments were performed on solid-solution strengthening Ni-base superalloy 625, considering the effects of the alloy state (powder, powder+HIPed and as-cast) and heating/cooling rate (5-10°C/min) on the phase transformation temperatures. The alloys with different states were characterized by FESEM and EPMA. (1) The results indicate that the dendritic arm spacing of the as-cast alloy is 2 orders of magnitude higher than that of the 625 alloy powders, whereas the hot isostatically pressed (HIPed) alloys possess a fine equiaxed grain structures without dendritic segregation. (2) The heating/cooling rates have no significant influence on the onset of matrix melting ( equal to the incipient melting temperature for the solid-solution strengthening superalloy) and onset of solidification temperatures (inflection point), but have an obvious effect on the melting end, matrix mass solidification temperatures (peak position) and solidification end temperature (inflection point) of the alloy. Using the average phase change temperature on heating and cooling curve average method can reduce the influence of DSC experiment or sample conditions and obtain a relatively fixed and comparable phase transformation temperature. (3) The alloy state has obvious effect on incipient melting temperature and the arc shape near soidus temperature of DSC heating curve. The segregation tendency of alloy can be determined by the radian near the solidus reigion of DSC heating curve. The powders and HIPed PM625 alloys with weak segregation tendency exhibit a sharp inflection point in DSC heating curves in the region near solidus temperature, there is only a 5-6°C gap between the onset of matrix melting temperature of the alloy (deviation from the baseline inflection point) and the nominal solidus temperature (tangent-onset intersection). The DSC heating curve of the as-cast IN625 alloy with a high segregation tendency exhibit a larger radian near the solidus region, the difference between the onset of matrix melting temperature and the nominal solidus temperature (tangent-onset intersection) can reach 52°C. The onset of matrix melting temperatures of as-cast 625 alloys are 45°C and 40°C lower than that of the HIPed and powder 625 alloy respectively. The parameter of the process such as HT or HIP should be selected concerning the effect of the alloy state with large radian near solidus region of DSC heating curve on decreasing the incipient melting temperature. The DSC cooling curves for the different state of 625 alloys are similar, which all possess a large radian near the solidus region, because the alloys were completely remelted which eliminated the original microstructure features and re-solidified from the full liquid state.

Abstract:Ultrasonic shot peening (USSP) was used to treat industrial pure zirconium and its tension-tension fatigue properties were studied. The microstructure and surface hardness of the samples were characterized by optical microscopy (OM) and microhardness tester. The grain size, micro distortion and residual stress of sample surface were analyzed by X ray diffractometer (XRD). The results show that：After USSP treatment, the grain size is refined to the nano scale, and the residual compressive stress, surface roughness and hardness of the surface increase with USSP time. The fatigue limit of original industry pure zirconium is 195MPa, USSP treatment can significantly increase the fatigue limit and the maximum fatigue limit of USSP treated 45min is maximum, reaching 220MPa, which is 11.2% higher than original industrial pure zirconium. The lower the maximum loading stress during fatigue loading is, the increase of fatigue life by USSP treatment is more obvious.

Abstract:The graphite sheet (Gr)/6061Al composites with Gr content of 1~25vol.% were prepared by vacuum hot-pressure sintering. The nano-aluminum powders were adopted as cladding materials on the surface of graphite sheet to improve the dispersal uniformity of graphite sheet within aluminum matrix. The graphite sheet dispersed uniformly in the aluminum matrix, and the interface between aluminum and Gr was well integrated without interfacial reaction product being found. The presence of few layer graphene was observed by transmission electron microscopy (TEM). The relative densities of the Gr/6061Al composites with 1~15vol% Gr content are all higher than 90%. The relative densities of the samples were decreased with the increasing of graphite content; and the coefficient of friction(COF) of the samples possess the same trend. The wear rate of the samples with Gr content of 5vol.%, 10vol.%, 15vol.% and 25vol.% are all higher than that with 1vol.% Gr content.An experimental set-up was designed for measuring the self-field losses of Bi2223/Ag HTS tapes using a transport current method.

Abstract:The influence of different treatment processes on microstructure and properties of Cu-Ni-Co-Si alloy were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution electron microscopy (HRTEM). The physical properties were tested as well. The results show that a large number of (Ni、Co)₂Si large phases with orthorhombic structure and few of little (Ni、Co)₂Si phase are found in the Cu-Ni-Co-Si alloy when the alloy is quenched on-line and aged treatment, which is ascribed to the low strength of the alloy. The relation curve between Vickers hardness and aging time exhibit a single peak and the electrical conductivity firstly rapid increase, then slowly raise, finally trended to stable as the aging time rise, when the Cu-Ni-Co-Si alloy is treated by solution and aging treatment and solution, cold deformation and aging treatment, respectively. Meanwhile, a lot of disc-shaped (Ni、Co)₂Si precipitates with orthorhombic structure are found in the above condition. These precipitates with orientation relationship with Cu matrix could be analyzed as 。

Abstract:The study use a company"s production of electroplating nickel plate as the object, studied the mechanics performance of the electrodeposition of nickel:At the same time in order to explore the mechanical behavior of the metal plastic deformation mechanism, in particular, on the different degree of cold rolling deformation.The experimental results show that:Electroplating nickel exist wide crystal,Size is about 0.5μm～1.5μm,At the same time there is growth twin.The average tensile strength from 385 MPa to 461 MPa,In vertical beginningless product direction has reached the lowest (385 MPa); in parallel beginning product direction has reached the highest (461 MPa).

Abstract:Effects of the extrusion temperature on the microstructure of solution-treated Mg-2.0Zn-0.5Zr-3.0Gd alloys were investigated by the metallographic microscope, the scanning electron microscope and the transmission electron microscope. Moreover, the mass-loss measurement and electrochemical corrosion technique were used to investigatethe corrosion behaviors of the alloys in the simulated body fluid. The obtained results showed that the extruded alloys were composed of large deformation grains and dynamic recrystallization grains, while the precipitated phases consisted of nanoscale rod-like (Mg, Zn)₃Gd and granular Mg₂Zn₁₁ phase.With an increase of the extrusion temperature in the range of 340 ℃ to 360 ℃, the volume fraction of dynamic recrystallized microstructure of the extruded alloys gradually raised, but the corrosion rates progressively decreased. When the extrusion temperature was 360 ℃, the alloy had a full dynamic recrystallization, and had a better corrosion resistance with a static corrosion rate of 0.527 mm/y, and behaved with a uniform corrosion. When the temperature increased to 380 ℃, a portion of the dynamic recrystallized grains grew abnormally, which resulted in an increase of the corrosion rate with increasing the extrusion temperature.

Abstract:The applications of tailor friction-stirring welded blanks demand the friction stir welding (FSW) be extended to higher welding velocities. Unfortunately FSW has been traditionally applied at linear velocities less than 500 mm/min and welding parameters and thermal modeling researched and developed at low welding velocities do not directly translate to high-speed linear FSW. Therefore, to facilitate production of high volume aluminum FSW components, in this paper 7075-O aluminum alloy rolled plates of 3 mm thickness were friction stir butt welded at a constant high-travel speed of 1000 mm/min and various tool rotary speeds (1000-1900 rpm) as well as the peak temperature of joint was measured by thermal infrared camera. Effects of tool rotary speed on peak temperature and appearance and cross-sections microstructures and mechanical properties of FSW joints were investigated. The results show that peak temperature of joint increases gradually with increasing the tool rotary speed till 1600 rpm and reaches maximum at 1600 rpm,approximately 500℃. Increase of rotation speed more than 1600 rpm brought about fluctuation of peak temperature form 480 to 495℃ and slightly decreasing tendency. This does not consist with the previous thermal modeling and peak temperature function of welding parameters. With an emphasis on weld quality, the experimental results of cross-sections microstructures indicate that the optimum tool rotary speeds are 1400, 1500, 1600 rpm. Analyzing the mechanism of heat generation about friction, an analytical thermal model of high-travel FSW was developed to estimate the peak temperature in which a variable of friction was created in consideration of the properties of coefficient in the material friction.

Abstract:Mg_96.5Gd_2.5Zn₁、Mg₉₆Gd_2.5Zn₁Ca_0.5和Mg₉₅Gd_2.5Zn₁Ca_0.5Al₁ alloys were fabricated by conventional gravity casting. The influence of Ca and Al elements on the formation of LPSO phase in as-cast Mg-Gd-Zn alloys and the microstructural evolution and the variation in mechanical properties through subsequent solid-solution heat treatment and hot extrusion processing were investigated and the correlation between the microstructural transformation and mechanical behavior was analyzed.

Abstract:In order to obtain a metal coating with excellent corrosion resistance and a simple preparation process is applied to navy vessel corrosion protection, Ni-graphene composite coating was grown on 45 steel substrates by electro-brush plating, Scanning electron microscope(SEM),energy dispersive spectrometer(EDS),atomic electron microscopy(AFM) and Raman spectroscopy were employed to characterize graphene,and morphology of the coatings, The corrosion resistance of Ni-graphene composite coatings was studied by electrochemical experiment and immersion test. Results show that the graphene layers enters the Ni-graphene composite coating, compared with Ni coating, the quality of Ni-graphene composite coating is better. In electrochemical experiments and immersion test, we found that Ni-GE composite coating compared with Ni plating, the corrosion resistance of the former than the latter is 70 mV, the corrosion current density of the former was only 0.34 times that of the latter, the former of the charge transfer resistance is 3.1 times of that for the latter; After immerse 168 h, the weight loss of Ni- graphene composite coating was 0.47 times of Ni plating layer, indicating that the corrosion resistance of Ni- graphene composite coating was obviously enhanced.

Abstract:In present work, the influence of the oxygen content variation on the Dy increment and the coercivity increment in Dy grain boundary diffusion processed (GBDP) Nd-Fe-B sintered magnet was investigated. Various magnets including both high and low oxygen types were processed and the latter one showed higher increments either in Dy contents or in Hcj. Nine specimens with 0wt. % original Dy contents were compared after GBDP, and it was proved that decrease of oxygen is beneficial to Dy content and Hcj increase. Furthermore, Dy content gradient in each GBDP sample showed that the gap between the outer and interior region in low oxygen magnets were narrower. According to the EPMA figures, Dy-rich shells were more continuous and brighter and almost completely surrounded each matrix grains in low oxygen GBDP magnet. The optimization of the microstructure enabled the low oxygen GBDP sample to gain a higher anisotropic field increment. Decrease of oxygen lead to Nd-rich phase surround the matrix phase more homogeneously and continuously, providing a more continuous tunnel for Dy to diffuse into the magnet, ultimately inducing a further enhancements of Dy content and Hcj.

Abstract:Al0.8CoCrFeNiTi0.2 high entropy alloys were prepared by vacuum arc melting and were treated by vacuum annealing at 600 ℃, 800 ℃ and 1000 ℃ for 10h. The microstructure, mechanical properties and corrosion resistance of the as-cast and annealed alloys were studied using XRD, OM, EPMA, hardness tester, universal testing machine, and electrochemical workstation. Microstructure analysis shows that the Annealing treatments have changed the phase composition and microstructure morphology of the alloys. The as-cast alloy consists of BCC and FCC solid solutions, while the 600 ℃, 800 ℃ and 1000 ℃ annealed alloys consist of BCC, FCC and σ phase. In the 800 ℃ annealed alloy, the σ phase precipitates the most. During the annealing process, the single-phase solid solution dendrites in the as-cast shift to the thin layer-flake two-phase mixed structure. In the temperature range of 800 ℃ and below, the higher the annealing temperature, the mixed structure is finer and the composition uniformity is better. But the 1000 ℃-annealed alloy has a large block single-phase solid solution precipitation, causing elements segregation to intensify. Hardness and compression tests show that all of the as-cast and three kinds of annealed alloys have high hardness, yield strength, fracture strength and plastic deformation, showing good comprehensive mechanical properties and resistance to temper softening. The 800 ℃-annealed alloy has the highest hardness, yield strength and fracture strength, but the as-cast alloy have the best plasticity. Electrochemical corrosion tests show that the as-cast and three kinds of annealed alloys all have good corrosion resistance in the 3.5wt.% NaCl solution and 0.5 mol/L H2SO4 solution and the corrosion resistance of the 800 ℃-annealed alloy is best.

Abstract:The MoNbTaW refractory high-entropy alloys were prepared by spark plasma sintering using pure metal powders as raw materials. The effects of technological parameters on the phase, crystal structure, sintering behavior and mechanical properties of MoNbTaW refractory high-entropy alloys were studied. The results show that the single-phase BCC high-entropy alloy can be formed at the sintering temperature of 1800 °C with the holding time of 5 min. The sintering temperature is the most important factor that affects the density, grain size and mechanical properties of the MoNbTaW refractory high-entropy alloy. When the sintering temperature is 2000 °C, the density of the alloy is 99.8 %, and the yield strength is 1314±14 MPa, the fracture toughness is (5～6)MPa.m_1/2. The MoNbTaW refractory high-entropy alloy prepared by spark plasma sintering process have no chemical composition segregation and is a brittle material with the fracture mode of cleavage fracture.

Abstract:Different rare earth La precursors were used to modify Pd/γ-Al2O3 catalyst via incipient wetness impregnation method. C3H8 oxidation performance was studied using powder sample evaluation device and the structures of catalysts were characterized through H2-TPR, XRD, XPS, etc. The results showed that addition of lanthanum effectively promotes palladium dispersion, strengthens Pd-support interaction and stabilizes highly-active Pd2+ species, improving the catalytic activity for C3H8 oxidation. Addition of lanthanum nitrate showed the best promoted-effect in palladium dispersion and stabilization of highly-active Pd2+ species. Compared with Pd/Al2O3, La-modified catalysts showed lower Ts, T50 and T50 values for C3H8 and NO conversion. Lanthanum addition induced changes in metal-support interaction and disperse state of active species play a significant role in enhanced activity for C3H8 catalytic oxidation.

Abstract:Pure molybdenum material was processed by high-pressure torsion（HPT）at room temperature under the applied pressure of 6 GPa with different revolution number of 1, 2 and 5 turns, and the ultrafine-grained molybdenum was obtained. Nanoidentation technology was applied to characterize the mechanical properties of HPT-processed samples as well as the sintered one. The load-displacement curves, hardness and elastic modulus were obtained directly. The stress-strain curves of different samples were obtained base on the finite element simulation by using the software of Abaqus. The results show that the hardness of HPT-processed samples has an obvious increase from 3.02 GPa to 7.80 GPa. Correspondingly, the yield strength increase significantly from 970 MPa to 3370 MPa. Grain refinement and dislocation tangling make the major contribution to the strength improvement. However, there is a gradual decrease in elastic modulus along with the increasing HPT revolutions, which may be due to the dislocation tangling and residual stress. The relationship between stress and equivalent strain during HPT was established based on the stress-strain curves obtained by simulation results, and the hardening behavior during HPT processing was discussed.

Abstract:_{:The effect of temperature, the distance of electrodes, conductive salt concentration, pH values and kinds of additives on the purity and size of indium powder by electrolysis process was studied. The results show that：The optimum process parameters for electrolysis are obtained. (The optimum process parameters for electrolysis as follows: The concentration of In3+ is 30g/L, the current density is 130 A/cm2, continuous electrolysis time is 1 hour, the concentration of NaCl is 80g/L, the distance of electrodes is 5cm, thiourea concentration is 0.3g/L, gelatin concentration is 0.5g/L, pH=2.5 and polyvinylpyrrolidone is 0.2g/L). Under these conditions, the distance of electrodees does not affect the purity of the powder, but affect theparticle size of the powder. The concentration of NaCl has the greatest influence on the purity of the powder.The higher temperature of the electrolyte, the particle size becomes larger and the purity of the powder decreases. The additive of thiourea restraining dendrite growth of the powder. Electrolysis 1 hour under the optimum process parameters, indium powder with a grain size of less than 100μm is obtained. The particle size less than 30μm accounted for 75%, the purity of the powder is 99.98%, and the average current efficiency is 70.10%.}

Abstract:Zirconia nanopowders were prepared via polyzcrylamide gel route with different zirconium salt, including ZrOCl2·8H2O, Zr(SO4)2·4H2O and ZrO(NO3)2·2H2O. Thermogravimetric analysis (TG), differential scanning calorimetry analysis (DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the thermal decomposition process of xerogel, phase compositions and morphologies of zirconia nanopowders. The influence of different zirconium salts on the phase transformation, phase compositions and morphologies of the as-prepared zirconia nanopowders by polyacrylamide gel route were studied. The results demonstrate that zirconium salt affects thermo-decomposing temperature of polyacrylamide gel. When precursor is zirconium oxynitrate, the thermo-decomposing temperature of xerogel is the lowest which is around 530 ℃. When precursors are zirconium sulfate and zirconium oxychloride, the thermo-decomposing temperatures of xerogels are around 573 ℃ and 580 ℃, respectively. Zirconium salt affects the crystallization temperature of zirconia, but the phase transformation of zirconia is similar, which transforms from amorphous to tetragonal and completely converts to monoclinic at 900 ℃. The higher the crystallization temperature of zirconia, the smaller the mean particle size, the more particle agglomeration. The nearly spherical zirconia nanopowders can be prepared and the particle size distribution is within the range of 52~97.4 nm with the above three zirconium salts as precursors.