Abstract:Using Cu-coated carbon fiber cloth (CFC) as reinforcement and Ti-6Al-4V (TC4) as matrix, the Cu-coated CFC/TC4 composite is fabricated by spark plasma sintering. The interface morphology, phase microstructure, phase distribution and mechanical properties of CFC/TC4 are characterized. Results show that carbon fibers are uniformly distributed in Cu-coated CFC/TC4. CuTi, Cu and very little TiC are distributed along the interface between fibers and matrix. Possessing slightly better plasticity than TC4, the yield strength and compressive strength of Cu-coated CFC/TC4 are obviously enhanced. The electroplated Cu plays important roles: (1) markedly decreases the sintering temperature of Cu-coated CFC/TC4; (2) significantly improves the wettability and interfacial bonding between carbon fibers and TC4 matrix, giving explanation to the increase of mechanical properties of Cu-coated CFC/TC4; (3) effectively inhibits the excessive generation of brittle TiC compared with uncoated CFC/TC4 composite, explaining the maintaining of good plasticity of Cu-coated CFC/TC4.

Abstract:Microstructure quantitatively analysis is significant for building the relationship between microstructure and properties, especially the ageing precipitation kinetics in aluminum alloys. A core parameter (aspect ratio) was introduced to describe the morphology change of precipitation. Aspect ratios of T1-plate precipitates in Al-Cu-Li-Zr alloys, S-plate precipitates in Al-Cu-Mg alloys and β-rod precipitates in Al-Mg-Si alloys were quantitatively analyzed. Results indicated that aspect ratios of precipitates increased at the early stage of ageing, then reached the peak and finally decreased slowly. The soft-impingement theory and HHC theory were introduced to model the ageing kinetics. Thermodynamics and kinetics parameters of different precipitates were also calculated in the model. Simulate results of different precipitates agree well with the experimental results.

Abstract:_{:Impulse pressuring diffusion bonding (IPDB) of TiC cermet to stainless steel 06Cr19Ni10 using Ti-Nb interlayer was carried out in an attempt to reduce the bonding time and alleviate the detrimental effect of interfacial reaction products on bonding strength. Successful bonding was achieved at 890℃ under a pulsed pressure of 2~10MPa within a duration of only 4~12min, which was notably shortened in comparison with conventional diffusion bonding. Microstructure characterization revealed the existence of the σ phase with a limit solubility of Nb, (β-Ti, Nb) phase, and solid solution of Ni in α β-Ti in the reaction zone. Maximum shear strength of 110MPa was obtained when the joint was bonded for 10min, indicating a robust metallurgical bonding was achieved. Upon shear loading, the joints fractured along the remnant Ti/ α β-Ti interfaceand extended to the interior of TiC cermet in a brittle cleavage manner. This technique provides a highly promising bonding method of TiC cermet and steel.}

Abstract:ZnO/Graphene nano-films were directly prepared on Cu substrate via a low pressure chemical vapor deposition (LPCVD) and sol-gel method. The effects of the annealing temperature on the structural, morphology, the chemical state and component, and optical property of these ZnO/Graphene nano-films were investigated. The XRD patterns demonstrate that the ZnO/Graphene nanostructures exhibit the hexagonal wurtzite structure and the crystalline quality increases with increasing the annealing temperatures from 500 to 700 ℃. When the annealing temperature reaches at 700 ℃, SEM analysis shows that sample ?lm exhibits dense and uniform grains and smooth surface and the average grain size of film deposited 3 layers is about 35.7 nm. The PL measurement confirms that ZnO/Graphene nano-film deposited 3 layers at the annealing temperatures of 700℃ has an better optical performance, which due to the higher crystalline quality and lower defect concentration.

Abstract:The quality of 3D printing parts obtained by means of droplets deposition depends strongly on the mechanism of the interaction between the molten metal droplets and the substrate to be covered. The effects of various parameters such as impact velocity, substrate temperature, droplet diameters, specific heat, thermal conductivity, latent heat on the maximum spread factor during impacting and spreading with solidification of a molten droplet onto an aluminum surface under different parameters was studied. The free surface of the droplet was tracked by the volume-of-fluid (VOF) method. The simulation model was based on the N-S equations and the energy equations which include convection and phase change. These equations were coupled with the Level Set function to track the interface between molten particles and surrounding air. The maximum spread factors were obtained and were in agreement with the experimental data available in the literature.

Abstract:Yttria stabilized zirconia (YSZ) nanocrystals were prepared by hydrothermal synthesis and were calcinated at different temperatures and with different isothermal hold time. X-ray diffraction via whole powder pattern modeling approach is used to study the grain growth as well as the evolution of grain size distribution of YSZ nanocrystals. Results show that YSZ nanocrystals start to grow along with the grain size distribution broadening at temperature about 300℃. The grain growth rate and the grain size distribution of YSZ nanocrystals are dependent on the calcination temperature and the isothermal hold time. The grain growth exponent and the active energy of grain growth were calculated. Grain rotation induced grain coalescence is suggested as the predominant way of grain growth of YSZ nanocrystals.

Abstract:The microstructural characterization and interfacial shear tests of Ti/Steel bimetallic clad sheets were taken to study the interfacial bonding mechanism during explosive welding process. The wavy interface with several vortexes forms between the dissimilar metal matrixes due to the interface deformation. A significant metal flow of steel matrix caused by the severe plastic deformation induces the continuous vortexes in the interface. The TEM and XRD analysis clarify that the nanoscale interfacial interlayer contains solid solutions and a small amount of intermetallic compounds. The shear strength of the interface along the explosive welding direction is enhanced by the wavy interface. The fracture of the bonding interface presents the ductile features on the vortex and while brittle features on the smooth interface.

Abstract:Single crystal superalloys have been prepared by adopting the grain selector and seeding technique in a high temperature gradient directional solidification furnace. The orientation characteristics were measured by XRD. Results indicated that for the grain selector method, the crystal solidification began at the cooling plate with random nucleation, and through mutual competitive growth at the starter block. The grains entered the spiral selector, and finally the single crystal superalloys which were close to <001> direction were obtained. By using the seeding technique, by epitaxial growth of partially melted seed crystals, single crystal superalloys which have the same orientation as the seed crystal were obtained.

Abstract:Temperature of cooling roller is a key issue affecting the quality of the amorphous ribbon. To this end, heat flux distribution acting on cooling roller outer wall calculated by fluid dynamics software Fluent, cooling roller steady temperature field analyzed with Finite Element Method by heat flux boundary conditions, obtained the cooling roller inner and outer wall temperature distribution, and discussed the temperature of cooling roller as cooling roller thickness and water passage height. The results show that cooling roller outer wall temperature decreases with roller thickness and the cooling water passage height decreased; Cooling roller inner wall temperature decreases with roller thickness increased and the cooling water passage height decreased. Meantime, the appropriate roller thickness and passage height selected to keep cooling roller both inner and outer wall temperature within the certain range. The study result provided theoretical support for cooling roller design and optimization.

Abstract:In this study, WC-12Co powder with nano WC grain size was used to deposit wear resistant coatings by AC-HVAF (Acukote High Velocity Air-Fuel) spray system. The phase compositions and micro-structure of the coatings were examined. The microhardness, fracture toughness and wear resistance were investigated. According to the X-ray Diffraction (XRD) analysis, the principal phase was WC, and its decomposition products were not found. The sprayed coating has a porosity lower than 1% and the grain sizes of coatings were among 80-100 nm which contributed to an average microhardness as high as 1940.3 HV0.3 on the surface and 1662.1 HV0.3 on the cross-section. At the load of 1.5 kg and rotational speed of 1198 r/min of WC counter body, the nano-sized coatings showed a 40% lower average weight loss and a stable friction coefficient of 0.26-0.28 (micron-sized coatings: 0.25-0.4 ) in the dry wear conditions. It was concluded that the sprayed nano structural WC-12Co coatings had a better wear resistance.

Abstract:The microstructural evolution of a high Zn-containing Al-Zn-Mg-Cu alloy during homogenization was investigated by optical microscopy, differential scanning calorimetry, scanning electron microscope and X-ray diffraction. A homogenization kinetic equation deriving from a diffusion kinetic model was established to confirm the optimum homogenization parameter. The results showed that severe segregation exists in the as-cast alloy. The non-equilibrium eutectics consisted of α(Al), Mg(Zn,Cu,Al)₂, S(Al₂CuMg), θ(Al₂Cu) and Fe-enriched phases. In present work, no transformation from Mg(Zn,Cu,Al)₂ to S(Al₂CuMg) phase occurred during homogenization and Mg(Zn,Cu,Al)₂ phase directly dissolved into the matrix. θ(Al₂Cu) phase dissolves into the matrix over homogenization. Fe-enriched phases still existed after homogenization, Zn and Mg elements in Fe-enriched phases were reduced or even disappeared by prolonging the holding time. In consistent with the results of homogenization kinetic analysis, the proper homogenization parameter was 440 oC×12 h 468 oC×24 h.

Abstract:Operating temperature waves nearly melt temperature of molten eutectic NaCl-MgCl₂ which is thermal storage media at medium-high temperature. But corrosion behavior of the molten salt on metal at different temperature is not clear. Corrosion behavior and mechanism of the molten salt on Fe-14Cr-Mn alloy were studied by immersion salt corrosion method at 718K, 768K and 818K. Results show that corrosion rate increased lightly with the corrosion temperature. Corrosion kinetics characteristics obey linear law (slop is about k=-4.806E-4). At the early stage of corrosion, there was lots of vacuoles-shape, while a large number of pot hole formed after corroding 80h. Corrosion products are mainly Fe, Fe-Cr and MgO. Corrosion mechanism as follows: Absorbed oxygen on molten salt surface and oxygen atom that introduced in the form of moisture-absorbed MgCl₂ is depolarizing agents. Chloride of Cr and Mn is got when oxide of Cr and Mn react with Cl_-. The chloride of Cr and Mn with water (for example CrCl₃.6 (H₂O) and MnCl₂.n (H₂O)) that has low melting point will escape from corrosion system. In addition, there is a salt crust that is composed of MgCl₂. (H₂O) ₆, NaCl and MgO on molten salt upper surface, while NaCl coexists with NaMgCl₃ inside mixture salt. The study laid the foundation for the study of corrosion-resistant alloy in molten NaCl-MgCl₂.

Abstract:Silver copper oxide composites were prepared by the in-situ synthesized method. The samples were conducted by Accumulative Roll-bonding (ARB) at the temperature of 973K. The phase composition of AgSnO2 composite materials and the mechanical properties of the samples after ARB process were characterized by X-ray diffraction and optical microscope. The results show that accumulative roll-bonding produces a significant effect on the degree of homogenization AgSnO2 composite micro-structure. The density, hardness, resistivity of 4-passes ARB processed AgSnO2 composite material was studied, and the main factors affected the properties of the samples was discussed.

Abstract:In the investment casting of shifting fork,hot crack is the common defact.in order to analysis the hot cracking in the investment casting,The ProCAST software is adopted, the fork investment casting process is simulated,The filling field,temperature field and stress field is analysised, the cause of crack is predicted. The result shows that: as the local area is received larger tensile stress from around, the shrinkage cavity appears, leading to crack.By reducing the pouring temperature,increasing preheating temperature of the shell, increasing chamfer angle of the fork, the casting stress can be reduced, the crack can be avoided.

Abstract:The SrFe12O19 ferrites with different amount of Bi2O3 additive were prepared by hot press sintering process at a low fired temperature of 870 °C compatible to the LTCC (low temperature co-fired ceramics) technology, and their low temperature sintering characteristics were investigated, including the crystal phase composition, sintering density, porosity, and magnetic properties. The results show that the addition of Bi2O3 promotes the formation of SrFe12O19 phase structure and increases the sintering compactness and magnetic properties for the ferrites fabricated at 870 °C. The ferrites with Bi2O3 content from 2 to 4 wt % exhibit a compact microstructure with sintering density higher than 4.65 g?cm-3 and porosity lower than 10%, which contributes to the enhanced saturation magnetization Ms and intrinsic coercivity Hci above 252.4 kA?m-1 and 312.9 kA?m-1, respectively. Moreover, the potentiality of the SrFe12O19 ferrites for use in microwave LTCC circulators is also discussed based on their low temperature sintering characteristics.

Abstract:Laser additive repairing technique was performed to repair the damaged aeroengine turbine blades made of K465 nickel-based superalloy. The cracks characteristics and cracking mechanism of the laser additive repaired K465 superalloy were investigated. The cracks were eliminated successfully by taking some effective measures. The results showed that the cracks originated from the heat affected zone of the laser additive repaired specimens, and extended to the repaired zone along the grain boundaries. The continuous liquid film was derived from the liquation of larger γ′ particles at the grain boundaries and γ-γ′ eutectics appeared during grain boundary liquation. Stress field simulation results obtained using the Ansys software demonstrated the existence of large thermal stresses at the zone between the substrate and the molten pool. Through preheating the substrates synchronously and adopting the optimized processing parameters, the laser additive repaired specimens with the structure of single track and multi layers without any cracks were obtained.

Abstract:Low-density C/C composite was modified with Mo2C interlayers through molten salt method. The formation mechanism of Mo2C layers was analyzed; the effects of flux composition and reaction temperature on the abrication of Mo2C interlayers were studied; the influence of Mo2C-modification on the microstructure of C/C composite was also observed. Results show that the reaction between ammonium paramolybdate and C for the formation of Mo2C layers is mainly consist of three steps: decomposition from ammonium paramolybdate to MoO3, reduction of MoO3 to MoO2, carbonization of MoO2 to Mo2C. The appropriate flux of LiCl–KCl and the suitable reaction temperature as 1000℃ is determined according to the experimental results. Flower-like Mo2C layers are formed and then continuous Mo2C layer cover the surface of C phase with the increase of reaction time and temperature. The Mo2C/C interface showcases good bonding state. The pyrolytic carbon phase near the interface shows high order degree as the result of catalytic graphitization and stress graphitization. Modification of Mo2C interlayer for the C/C composite can facilitate the infiltration of Cu and its joining with Cu.

Abstract:In order to study the effect of electromagnetic stirring on melt pool solidification, a three-dimensional magnetic-thermal coupling numerical simulation was conducted on the process of single-pass laser melting TA15 titanium alloy with and without the magnetic field based on the finite volume method. The influence of electromagnetic field on temperature field, flow field, temperature gradient and solidification rate were analyzed. Then the numerical simulations were verified by experiment method. The results of numerical simulations showed that the melt pool maximum flow velocity increased by 20%, which promoted the function of heat exchange resulting in going down of the highest temperature of melt pool and temperature gradient on solid-liquid interface, and meanwhile the small rise in solidification rate, which were good for columnar-to-equiaxed transition at the top of melt pool. The experiment results indicated some equiaxed grains were generated at the top of melt layer with the magnetic field. Electromagnetic force was enlarged with an increase of the distance from magnetic field center, which causes equiaxed grain zone had a tendency to expand. The numerical simulations were in good agreement with the experimental results.

Abstract:The hot deformation behaviors of β-CEZ alloy in the temperature range of 800~1000℃ and strain rate range of 0.001~10s-1 have been studied by hot compressing testing on a Gleeble-3800 simulator at the deformation degree of 0.7. The high temperature deformation behavior, the flow instability and the deformation mechanism in α β phase field and β phase field were studied by the true stress-true strain curves and processing map, which were established based on experimental data and Prasad criterion. The results shows that under the experimental conditions, β-CEZ titanium alloy shows two kinds of softening mechanism: dynamic recovery and recrystallization. The flow stress decreases continuously in α β phase field after the peak stress, decreases slightly and then tends gradually toward a constant value β phase field. The domains with high value of the efficiency of power dissipation (η) at α β phase field is 850~890℃/0.01~0.05s-1, which is the spheroidization of α lamellae area. And the domains with high value of the efficiency of power dissipation (η) at β phase field is 940~980℃/0.2~0.6s-1, which is the dynamic recrystallization area. The domains of flow instability are 800~850℃/0.1~10s-1, 850~900℃/0.1~5s-1 and 900~1000℃/1~10s-1. The manifestations of the flow instability at the α β phase field is the adiabatic shaer band, at the β phase field is the non-uniform deformation.

Abstract:In order to obtain the essence of the nucleation phase and its variants selected of secondary α. Electronic backscatter diffraction (EBSD) has been employed to study the relationship between the crystal orientation, geometric growth direction, quantity, distribution of secondary α-phase and β-phase grain boundaries properties on nearly β-type Ti-1300 alloy. The alloy was equilibrated for 2 h at 910℃ and handled by water quenching. The alloy occurs a certain percentage of <110> 70.5° special boundaries. The alloy was slowly cooled in the furnace since 910℃, it has a significant relationship between the secondary α phase which from β→α phase transformation and β-phase grain boundaries properties. Common β/β grain boundary generated orientation is not unique, which has little effect on the nuclear of the Self -α phase grain boundary α phase variations, its relatively small number of both sides of since grain boundary α phase. The α phase grain boundary was generated by the common β/β grain boundary, its orientation was not unique. The common β/β grain boundary has little effect on the nuclear of the Self-α phase grain boundary α phase variations, and there are small number Self-α phase grain boundary both sides the α phase grain boundary. Both sides of the β grain which boundary is special high angle grain boundaries (<110>70.5°) have the same (110) plane. The orientation of the α phase grain boundary is favor for the formation of the heterogeneous nucleation of the Self-α phase grain boundary, which causes selective growth of the α variant on both sides in grain boundary; Special small-angle grain boundaries (<110>10.5°) also can cause α variant’s selective growth, but it is different from high-angle grain boundaries, the selective growth may only occur on one side of the grain boundary.

Abstract:The hot compression curves of Nb bulk materials were measured by Gleeble-3500 thermal simulation machine. The flow stress behavior and the deformation microstructures of the materials were analyzed at the temperature range of 350-480 ℃ and the strain rate range of 0.001-10 S_-1. It is shown that the flow stress reduces with the increasing of the deformation temperature and the strain rate. The elongated grains coarsen with the decreasing of the temperature. And dynamic recovery occurs during the hot compression. The soften mechanism also works by the dynamic recovery. Moreover, the constitutive equation of the strain rate affected by the temperature, strain and the hot deformation activation energy was deduced by the help of the modified hyperbolic sine function of Arrhenius and factor of Zener-HolIomon parameters. The simplified relation was adopted to fit the curves of the flow stress versus the strain at different temperature resulting in good effect.

Abstract:By means of the tests of creep performance and the measurements of internal friction stresses, the effective creep parameters of the [001]-, [011]- and [111]-oriented single crystal nickel-base superalloys after being crept to steady-state stage under the conditions of high temperatures/low stresses along [001], [011] and [111] orientations respectively, and their relationship with the creep performance and deformation mechanism have been studied. Results show that, with the increase of creep temperatures and decrease of applied stresses, the internal friction stresses of the three alloys decrease. Under the same conditions, the order of the internal friction stresses is σi[001] > σi[111] > σi[011]. The inclined and continuous “roof”-type γ channels in the [011]- and [111]-oriented alloys before and after creep are responsible for the low internal friction stress and poor creep resistance of the two alloys. The effective creep activation energy of the [001] oriented alloy is Qe[001]= 281.32 KJ/mol, indicating that the deformation mechanism during steady-state creep stage is the dislocation climb controlled by element diffusion. The effective creep activation energy of the [011]-oriented alloy is Qe[011]= 139.74, and the low value is related to the open ? matrix channels possessing small resistance for dislocation slip. The effective creep activation energy of the [111]-oriented alloy is Qe[111]= 182.61 kJ/mol, and the relatively larger value compared to that of the [011]-oriented alloy is related to the lamellar γ’ rafts and the cross slip of dislocations in the [111]-oriented alloy.

Abstract:The effect of lanthanum-cerium mischmetal on the kinetics and the microstructure of the super-cooled austenite continuous cooling transformation in 20MnCrNi2Mo wear-resistant cast steel by L78 RITA quenching thermal dilatometer, QUANTA-400 scanning electron microscope, JEM-2100 transmission electron microscope and so on. The ICP-MS inductively coupled plasma mass spectrometry was used to measure the amount of rare earth solid solution and the JEM-2100 transmission electron microscope was utilized to probe the existential state of the solid-solution rare earth. The action mechanism of the solid-solution rare earth was analyzed combined with the measurement of the interface diffusion coefficient of La. The results show that the CCT curves are moved to the bottom right, the hardenability is improved and the twin substructure in lath martensite is increased due to the effect of the rare earth. The trace amount of solid-solution rare earth can exist in grain boundary, dislocation and other crystal defects. They can reduce the grain boundary energy, block the diffusion channels and then defer the nucleation and growth of the new phase. So the phase transformation and the microstructure are influenced.

Abstract:Compound modification of Al-25% Si alloy with P-Cr-Ti is utilized to study the change of the solidification microstructure and the effect mechanism of Cr and Ti elements. The results indicate that primary Si in the solidification microstructure decreases by 12.24%~51.65% in the Al-25% Si alloy modified by the compound modifier P-Cr-Ti compared with simple phosphorus modification, and the distribution of the primary Si is more uniform. The Cr and Ti elements in the Al-25%Si alloy mainly appear as compounds including TiAl₃, Ti₇Al₅Si₁₂, Al₇Cr and Al₁₃Cr₄Si₄, while a minor amount of P exists in the compounds containing Ti. Compounds containing Ti appear as long strips. Compounds containing Cr, which distribute among the primary Si, appear as granular or short rods. The number of the compounds containing Cr and Ti is increased with the increase of the cooling rate. The TiAl₃ phase initiated by Al-6.5%Ti alloy wanders in the melt during the modifier process. The {110} crystal of TiAl₃ phase becomes the nucleation basal of the Si phase, causing the primary Si to precipitate continuously and to refine the primary Si with a limited refining ability. Compounds containing Cr formed among the primary Si prevent the growth and gather of the primary Si during the solidification, which leads to the distribution of the primary Si more even.

Abstract:Experimental object of this paper is the solution-aging and solution-large deformation (compression,ECAP)-aging of 7085 aluminum alloy. Through the tensile testing machine and scanning electron microscope (SEM) to test the tensile properties and fracture analysis. Internal dislocation density, low angle grain boundary and high angle grain boundary of 7085 aluminum alloy under different states were characterized through X-ray diffractometer (XRD) and Electron Back Scattering Diffraction (EBSD) .Combined tensile test measured yield strength, strengthen the contribution of the large deformation strengthening aluminum items of the quantitative calculation.The results show that, compared with conventional solution-aging treatment, the solution-large deformation - aging treatment can significantly refine grain size, increase the number of low angle grain boundary, prompt uniform distribution of precipitated phase so as to advance yield stress. Especially, Equal Channel Angular Pressing (ECAP) is more effective than compression in improving overall performance. Large deformation processing of 7085 aluminum alloy also makes a lot of internal accumulation of dislocations, large deformation processing was improving performance mainly depends on the alloy dislocation strengthening and small-angle grain boundary strengthening, alloy internal solid solution strengthening and second phase strengthening has been weakened by large deformation processed.

Abstract:Because of its superior high-temperature creep strength in combination with good workability and low cost compared to its Ni-Co-Cr based counterparts, GH 2984 alloy is evaluated to be a candidate material for applying as superheater/ reheater in 700℃ ultra-supercritical coal-fired power plants. At such high temperature (up to 700-760℃), the corrosion behavior of the alloy in steam is of great concern mainly due to the thickness of the oxide scales that are formed. In the present work, the oxidation behavior of GH 2984 alloy in pure steam at 750℃ has been investigated by using scanning electron microscope and X-ray diffractometer. The results show that a single Cr2O3 layer is formed with minor TiO2 solid soluted in it. Ti and Al are internally oxidized into TiO2 and Al2O3, respectively, preferentially along grain boundaries in the alloy underneath the Cr2O3 scale. The oxidation kinetic of the alloy observes a parabolic law. Investigation on the morphology evolution figures out that Cr2O3 blades formed initially which decreased in number and length and finally evolved into short rod-like ones with increasing oxidation time. The reason for the Cr2O3 nodules and blades formation and the oxidation mechanism of GH 2984 alloy in pure steam is discussed in detail.

Abstract:In this paper, the Ag-doped titania nanotube arrays was successfully fabricated by steps of preparation of titania nanotube arrays on the surface of pure titania and the Ag-doped technology of thermal drive, which has excellent bioactive and antibacterial performance. The researches show that the mechanism of thermal drive Ag-doped is the collaboration of thermal decomposition of silver nitrate in the limited space with the phase transition of titania at low temperature. After being soaked in saturated silver nitrate and annealed at 300℃, the titania nanotube arrays can realize not only the low temperature phase transition from amorphous to rutile, but also the low temperature decomposition of silver nitrate within it.

Abstract:TiCN coatings have been deposited on 304 stainless steel by newly developed cathodic arc deposition enhanced by additional electric field. The effect of the current of additional electrode on cathode arc discharge, film microstructure, cross-sectional morphology, wear resistance and adhesion between film and substrate have been investigated. The experimental results show the plasma density has been substantially increased after introduction of additional electrode in the chamber and the substrate current is improved by nearly 100%. Only a properly higher current of additional electrode may effectively decrease the crystal size and make the film structure much denser, consequently the critical load of deposited films has been enhanced. The sample deposited at a 30A-current of additional electrode possesses the highest adhesion force between film and substrate (HF1), best wear-resistance featured by narrowest wear track. The friction coefficient may decrease by 33% compared to the sample fabricated without the assistance of additional electrode. In summary cathodic arc deposition enhanced by additional electric field is an effective tool to fabricate TiCN films.

Abstract:In the present study, ZrC nanocrystalline coating was synthesized on Ti-6A1-4V alloy as bipolar plates for PEMFC by a double glow discharge plasma technique. The microstructure of as-prepared ZrC coating was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Electrochemical measurements were carried out on a CHI604D electrochemical workstation in the simulated PEMFC anodic and cathodic environments. The hydrophilicity and interfacial contact resistance of the ZrC nanocrystalline coating were also evaluated. The microstructure of as-prepared ZrC coating consists of deposited layer and diffusion layer. The 10 μm thick deposited layer shows a dense columnar microstructure, composed of equiaxed grains with an average grain size of ~12 nm, whereas the 4 μm thick diffusion layer with the gradient distribution of alloying elements offers a smooth transition of mechanical properties, which is beneficial to improve the adhesion strength of the ZrC coating on the Ti-6A1-4V substrate. The Ecorr of the as-deposited ZrC nanocrystalline coating is obviously higher than that of Ti-6A1-4V alloy in a simuiated PEMFC environment. At applied cathode ( 0.6 V) potential for PEMFC, ZrC nanocrystalline coating is in passive region, and the passive current density is four orders of magnitude lower than that of Ti-6A1-4V alloy. At applied anode (-0.1 V) potentia, ZrC nanocrystalline coating exhibits the characteristic of cathodic protection. The results of OCP and EIS showed that the higher the temperature, the worse the corrosion resistance of bipolar plates. And the temperature corrosion susceptibility of ZrC nanocrystalline coating is obviously lower than Ti-6A1-4V alloy. Moreover, ZrC nanocrystalline coating can effectively improve conductivity and hydrophobic nature of Ti-6A1-4V alloy bipolar plate.