Abstract:The fourth generation single crystal superalloy DD15 with Re content of 5wt%, 6wt%, and 7wt% was cast in the directionally solidified furnace, while other alloying elements were basically the same in content. The long term aging after full heat treatment was performed at 1100 °C for 1000 h. The stress rupture tests of the alloy were conducted under 1100 °C/137 MPa. The effect of Re content on the microstructure and stress rupture properties of the alloy was investigated. The results show that the size of γ′ phase decreases, the volume fraction and cubic degree of γ′ phase slightly increase with increase in Re content. After long term aging, the γ′ phase coarsens, and the drafting rate, precipitate rate and volume fraction of TCP phase are all improved with increase in Re content. With the increase in Re content, the microstructure stability and the stress rupture life of the alloy decline significantly. The three ruptured specimens all exhibit the presence of TCP phase. The amount of TCP phases increases greatly with increase in Re content. TCP phase can be the site of crack initiation. This is the main reason for the decrease in stress rupture life of the alloy with increase in Re content. The dislocation networks formed at the γ/γ′ interface of ruptured specimen turn denser with increase in Re content. Re has a strong segregation tendency in γ matrix. The partition ratio of Re rises significantly with increase in Re content. The lattice misfit of the alloy becomes larger toward negative with increase in Re content.

Abstract:The low-cycle fatigue performance and fracture damage mechanism of Ni-based single crystal superalloy were investigated at 530 °C. Results show that at 530 °C, the fatigue crack of the single crystal superalloy generally appears on the surface, sub-surface or inside of the sample. When there are casting defects on the sub-surface, fatigue crack will arise preferentially from the defects. Under the condition of large strain amplitude (>0.85%), the alloy shows obvious cyclic hardening behavior during the fatigue cycle, and the cyclic stress response curve tends to be stable when the strain amplitude is lower than 0.85%. The plastic deformation of Ni-based single crystal superalloy is mainly proceeded by slip. At 530 °C, the fracture of single crystal superalloy is mainly caused by octahedral slip mechanism, and the main slip system is {111} <110>. According to the sectional structure characteristics of the fracture, no obvious plastic deformation occurs near the source area. The characteristic of fatigue striation can be seen in the stable extension of the crack, and a lot of cross slip bands exist at the slip step in the rapid crack extension stage. By electron backscattered diffraction analysis, there are obvious plastic deformation on the fracture surface at the junction of different slip planes, and the γ matrix and cubic γ' phase near the fracture surface are seriously distorted. No obvious oxidation is observed on the surface of fatigue fracture at 530 °C .

Abstract:The excellent mechanical properties of nickel base single crystal superalloy are mainly due to its ordered L12 structure γ? (Ni₃Al). In order to study the effect of laser shock γ?, the molecular dynamics model of single crystal Ni₃Al was constructed by molecular dynamics method, and the microstructure evolution behaviors of [100], [110] and [111] were analyzed. The results show that the plastic deformation mechanism of [100] crystal shock is the transformation from FCC phase to BCC phase, and the content of BCC phase increases with the increase of shock pressure; The plastic deformation mechanism of [110] and [111] crystal direction shock is dislocation slip, and the [110] crystal direction slip system is mainly (1)[011] and (11)[01], The [111] crystal slip system is mainly (1)[10] and (11)[101],the dislocations produced are mainly 1/6<112>(Shockley). However, with the increase of impact pressure, the plastic deformation mechanism is the transformation from FCC phase to BCC phase, and disordered structure is produced at the same time.

Abstract:In this paper,we used ?1.2mm ER-GH4169 welding wire to prepare columnar array structure on 5mm thick Q235 carbon steel substrate by CMT-Pin additive technique,and investigated the Pin forming process and tissue characteristics.The results show that when the Ball/Cyl Adaptation parameter is negative,the Pin head shape is Cylindrical;when the Ball/Cyl Adaptation is non-negative,the Pin head shape is Ball;Altitude Adaptation controls the height of Pin growth,and the Pin height is obtained between (2.30~4.96)mm.The microstructure of Pins is divided into Pin axis zone,fusion zone,and base material zone;Pin axis area has a large number of columnar crystals,which grow outward along the axis; in the fusion area,the columnar crystals change from fine crystals to coarse crystals along the Pin axis upward,and the fusion area is a very fine fusion line,with a large number of strips of Laves phase precipitated between the crystals;in the base material area,there is a tissue of light and dark interlayer.

Abstract:The effects of heat treatment on the microstructures and rupture properties at 1070 ℃/140 MPa of a hot-corrosion resistant single crystal superalloy was investigated. The results show that long-term homogenization heat treatment significantly reduces element segregation. With the extension of homogenization time, the area fraction of micropores gradually increases, the average size keeps increasing, and the density of micropores increases firstly and then decreases. With the increase of primary aging temperature, the size of γ" phase enlarge gradually, the area fraction of γ" phase frist increases and then decreases. The stress rupture life of the alloy increases first and then decreases with the increase of the primary aging temperature. When the primary aging temperature is 1100 ℃, the size of the cubic γ" phase is about 370 nm and the squareness is better, the area fraction of the γ" phase is the largest and the stress rupture life is the highest. The stress rupture fracture is characterized by ductile fracture. The carbides and micropores at the sub-grain boundary are the main crack sources that cause the stress rupture fracture of the sample.

Abstract:Laser powder-bed fusion (L-PBF) technology processes unique advantages in building complex-shape alloys. This paper invesgated the microstructure and high temperature low-cycle fatigue behavior of L-PBFed GH3536 superalloy in 855℃, and revealed the influence of heat treatment on microstructure and fatigue performance. By combining with different fatigue life prediction models, the fatigue damage behavior of L-PBFed GH3536 superalloy in various strain amplitudes was further discussed. These results are important for high temperature low-cycle fatigue life prediction and application of additive manufactured samples.

Abstract:In present work the stress rupture property and related microstructure evolution of FB2 rotor steel are investigated by metallographic analysis, scanning electron microscope and transmission electron microscope. The investigation shows that the microstructure of FB2 rotor steel is composed of tempered martensite. Large amount of fine M23C6 carbides precipitates on original austenite grain boundary and in matrix. Decomposition and broaden of martensite lath can be found with prolonging stress rupture duration. The dislocation density decreases at the same time. Meanwhile, the M23C6 carbides located at grain boundary and martensite lath boundary grows. Laves phase gradually grows at original austenite grain boundary and aggregates into a chain distribution. The microstructure evolution at high temperature can apparently influence high temperature stress rupture property. While the FB2 roto steel can still meet the requirement that the stress is higher than 100 MPa after 630℃stress rupture test for 105h.

Abstract:The Maxwell 3D module in Ansys Electromagnetics Suite was used to establish a mathematical and physical model for electromagnetic field in the vacuum arc remelting process of titanium alloy, and the interaction law of current, magnetic field and electromagnetic force in the melting process was analyzed. The results show that the current in the ingot is centripetal and concentrated within 350 mm of the upper part of the ingot. Tangential magnetic field is generated by smelting current and axial magnetic field is generated by stirring current, which are simply coupled. Under the action of smelting current and its self-induced magnetic field, radial and axial electromagnetic forces are generated; the electromagnetic force rotates under the action of the stirring magnetic field, generating tangential electromagnetic force. With the change of smelting current, the tangential component of magnetic field and the radial and axial resultant force of electromagnetic force change linearly. The axial component of the magnetic field and the radial component of the electromagnetic force change linearly with the stirring current.

Abstract:In order to understand the influence of the different aging parameters on the microstructure and mechanical properties of Ti-6Al-3Nb-2Zr-Mo (Ti6321) alloy, the microstructures and mechanical properties under different aging parameters (temperatures ranging from 500 °C to 650 °C, 3–24 h) were investigated by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and mechanical properties tests. The results reveal that the secondary α phase (α_s) is more sensitive to the aging parameters than the primary α phase (α_p). Moreover, the thickness of α_s phase is positively correlated with aging temperature or aging time. As the aging temperature and aging time increase, the segregation of Ti and Al elements in the β transformation phase (β_t) becomes obvious, and the α_s phase changes from fine needle-like to long rod-like. When the alloy is aged at 600 °C for 12 h, the alloy shows good comprehensive mechanical performance. The tensile strength, yield strength, and elongation are 907 MPa, 796 MPa, and 16%, respectively, and the impact energy is 55 J.

Abstract:The corrosive lubricanting environments that TC4 alloy being exposed can result in severe corrosion wear. Corrosion wear experiments were carried out to explore the corrosion and wear mechanisms of TC4 alloy, as well as the synergistic between corrosion and wear. In this experiment, distilled water, artificial acid rain, and artificial seawater were selected as corrosive lubricating media for the GCr15/TC4 friction counterpart. The Anton Paar TRB₃ tester were used for the experiments. The results suggest that the wear mechanisms of TC4 alloy in three water-based media are significantly different. Adhesive wear is most pronounced in distilled water, as well as fatigue delamination dominates in artificial seawater, however, abrasive wear is most significant in acid rain. The wear length, width, depth and volume of the wear profiles in acid rain are greater than those in artificial seawater and distilled water. The wear volume of TC4 alloy in artificial acid rain is larger than that in artificial seawater and distilled water, and it increased linearly with the number of cycles and normal loads. It shows that GCr15/TC4 is the most sensitive to acid rain, as well as suffers the most serious damage. In these three media, the synergistic factor of TC4 corrosion and wear in descending order is artificial acid rain, artificial seawater, and distilled water. The wear loss of TC4 alloy in distilled water is dominated by mechanical factors, while in artificial seawater and acid rain is dominated by corrosion-wear interaction and mechanical factors. The synergistic factor decreases as the load increases, and the influence of mechanical factors on corrosion wear becomes more significant.

Abstract:Additively manufactured TC4 alloy has attracted extensive attention due to its short processing cycle, high dimensional accuracy and good forming quality. However, the research on its high-temperature mechanical properties and corrosion behavior in Cl- containing solution after heat treatment is relatively scarce. In this study, TC4 alloy was fabricated by selective laser melting (SLM). The microstructure, high-temperature mechanical properties and corrosion behavior of TC4 alloy after heat treatment were studied by optical microscope, scanning electron microscope, X-ray diffractometer, universal tensile testing machine and electrochemical testing, and compared with as-cast TC4 alloy. The results show that the phase composition of SLM is the same as that of cast TC4 alloy. The microstructure of SLM TC4 alloy is mainly lamellar (α+β) phase, with an average grain area of about 2 μm2, while the as-cast TC4 alloy shows a typical Widmanstatten structure, and the average grain area is about 276 μm2. Compared with as-cast TC4 alloy, SLM TC4 alloy possesses excellent mechanical properties at both room temperature and high temperature, and the passivation film formed on its surface has better protection performance, resulting in a lower corrosion rate.

Abstract:To reveal the effect of trace W addition on the hot workability of the Mn-containing β-solidifying γ-TiAl, the Ti-42Al-5Mn-0.8W alloy (at.%, the same below) were refined with a vacuum induction furnace. Hot deformation behavior of the alloy was studied at the temperature of 1100~1250 ℃, stran rate range of 0.001~10 s-1 and maximum deformation degree of 70% with thermal simulator. It shows that the range of appropriate thermal processing parameters are 1150~1250℃/0.001~10 s-1 and 1100~1145 ℃/0.001~1 s-1. 0.8 at.% W addition can obviously reduce the peak flow stress of Ti-42Al-5Mn alloy(σp) and steady-state flow stress(σ0.7), and the steady-state flow stress decreases more significantly. The main reason why 0.8 at.% W improves the hot workability of Ti-42Al-5Mn alloy is that on the one hand, the W content is relatively small, and the segregation degree of W element is not obvious under the vacuum induction melting mode with strong electromagnetic stirring; On the other hand, thanks to the fact that the β-stabilizing effect of W is stronger than that of Mn, extending the region of β single phase zone, thus having a wider processing window that can be thermally deformed.

Abstract:Explosively welded Ti/steel clad plates were one-pass warm rolled by 60%, microstructures of the Ti layer and steel layer adjacent to interface were investigated, and shear strength of the one-pass warm rolled clad plates was tested. Results show that the one-pass warm rolling process can cause obvious shear deformation in both the Ti layer and steel layer adjacent to the interface. Because of the shear deformation, the RD-split basal texture forms in the Ti layer. In the steel layer, high fraction of the rotated cube texture and low fraction of the γ fiber texture form. Compared with the common multi-pass rolling method, shear strength of the one-pass warm rolled Ti/steel clad plate is improved because the shear deformation refines the interfacial compounds.

Abstract:In order to reveal the diffusion behavior of Ti/Al interface, the molecular dynamics simulation was applied to study the microscopic diffusion mechanisms of Ti/Al explosive welding interface at the atomic scale. Molecular dynamics model of Ti/Al explosive welding spot was established by Materials Studio (MS). According to the physical process of explosive welding, the simulation of the collision was divided into two stages: the loading stage and the unloading stage. The mean square displacement (MSD), radial distribution function (RDF), and diffusion layer thickness were calculated by LAMMPS, and the diffusion behavior of interfacial atoms at different stages was reproduced by OVITO. Results show that in the loading stage of explosive welding, Ti and Al atoms do not diffuse but only vibrate at the equilibrium position, and the vibration of Al atoms is stronger than that of Ti atoms. The atomic diffusion only occurs in the unloading stage of the explosive welding process. The Ti-Ti bonding energy is too high to break. The Al-Al bonding energy is low, so it is easy to be damaged, resulting in vacancies, gaps and other defects, which promotes the deep diffusion of Ti atoms into the Al substrate lattice while hindering Al atoms from entering the Ti substrate lattice. The simulation result is basically in accordance with EDS experimental result.

Abstract:TiAlN coatings were deposited at various deposition temperatures using vacuum arc ion plating (AIP) for the high performance manufacture. The relationships between deposition temperatures and surface properties were investigated. Results show that surface macroparticles (MPs) decrease in number and size with increasing the deposition temperature because of ion bombardment. When deposition temperature increases, the grain size on the top coating first decreases sharply, and then increases gradually. Furthermore, deposition temperature has little influence on the phase constituents and chemical compositions of the resultant coatings. With raising the deposition temperature, the hardness and adhesion strength first increase rapidly, and then decrease gradually. The deposited TiAlN coating exhibits the highest hardness and the strongest adhesion strength when deposition temperature is set at around 450 °C. The mechanism of the above phenomena is attributed to the variations of microstructure and residual stress between the surface and interface during the deposition process. The resultant coatings have a good thermal stability in air at temperatures up to 900 °C.

Abstract:In order to predict the crack defects in sheet metal bending, an Lemaitre criterion was improved to effectively predict the forming limit in bending while considering the stress triaxiality , the maximum principal stress ratio , and the influence of plastic strain on the damage. Taking 7075-T6 aluminum alloy as the research object, the crack forming in sheet bending was simulated to obtain the criterion parameter so as to determine the cracking threshold. Three point bending test and metallographic test were carried out on 7075-T6 aluminum alloy sheet with 6 mm in thickness. The accuracy of the criterion for crack prediction was verified by comparing the press measure of experimental, simulation and theoretical values. The results show that the improved Lemaitre fracture criterion is 9.7 mm, which is consistent with the results of simulation and experiment. Therefore the improved Lemaitre fracture criterion has a certain accuracy in predicting the crack of bending forming.

Abstract:Al-Cu alloy with wide solidification interval is prone to hot tearing and porosity defects due to insufficient feeding. The effect of hydrogen content on the hot tearing susceptibility (HTS) of Al-xCu alloy was investigated by the constrained rod casting (CRC) mold. Based on analysis of the HTS value, fracture morphology and the microstructure of Al-xCu alloy with different hydrogen contents in the melt, the influence of porosity formation on the hot tearing was analyzed. The results show that the hot tearing susceptibility of the alloy is evidently aggravated, which is caused by grain coarsening and insufficient feeding of liquid phase in the late stage of solidification with the increase in melt hydrogen content. A porosity-based formation mechanism of hot tearing is proposed to explain the interplay between porosity and hot tearing.

Abstract:The effect of Sc addition on the corrosion behavior of as-cast Al-3Cu-1Li alloy in 2 mol/L NaCl acidic solution was studied. The phase compositions of as-cast Al-3Cu-1Li-xSc (mass fraction) alloys were determined by XRD. The microstructures of Al-3Cu-1Li alloy and Al-3Cu-1Li-0.5Sc alloy were observed by FE-SEM/EDS and TEM. The corrosion behavior of the alloy was studied by potentiodynamic polarization, EIS, EN and immersion test, and the corrosion mechanism was discussed. The results show that Cu-rich spherical phases are distributed in the grain of Al-Cu-1Li alloy; Cu-rich spherical phase is reduced, and W phase precipitates at the grain boundary of Al-3Cu-1Li alloys containing Sc. Sc can reduce the corrosion reaction activation energy of the alloys, making the corrosion process easier. With increasing the Sc content, cathode hydrogen evolution rate increases, the self-corrosion current density of the alloy increases, and the corrosion resistance decreases gradually. EN and EIS results show that the surfaces of Al-3Cu-1Li alloy and Al-3Cu-1Li-0.1Sc alloy are in the state of “film rupture-repassivation” during 12 h immersion in the solution, and Al-3Cu-1Li-0.3Sc alloy and Al-3Cu-1Li-0.5Sc alloy have severe intergranular corrosion.

Abstract:The evolution of microstructures and mechanical properties stimulated by long-term service was investigated using a GTD111 blade employed in the first stage rotor blade of a heavy-duty gas turbine. Results show that the microstructures of the blade are mainly composed of γ matrix, γ′ precipitates with two dimensions, γ+γ′ eutectic and MC-type carbides. The microstructural degradation of the blade is closely related to its structural characteristics. Samples from leading edge and middle region of the blade exhibit a relatively lower degree of microstructural degradation, while samples from trailing edge of the blade possess higher degree of microstructural degradation. The ultimate tensile strength (UTS) of the leading edge region is significantly higher than that of the trailing edge region at room temperature, but the UTS of different regions has little difference at 982 °C, which may be related to different deformation mechanisms at higher temperatures.

Abstract:A Fe-16Cr-2.5Mo (wt%) damping alloy was prepared by spark plasma sintering (referred to SPS alloy) and vacuum induction melting followed by forging and annealing (referred to VIMFA alloy). The comparative study on microstructure, magnetic performance, damping capacity and mechanical property of SPS and VIMFA alloys was conducted. Results show that the relatively high compactness of SPS alloy is obtained. The dissolution of Cr and Mo in α-Fe solid solution is obviously promoted and the homogeneity of microstructure of SPS alloy is dramatically ameliorated with increase in sintering temperature and extension in holding time. SPS alloys exhibit relatively lower saturation magnetization but higher coercivity than VIMFA ones. There is still favorable damping capacity for SPS alloys despite it is lower than that of VIMFA one. Furthermore, the damping capacity of SPS alloy slightly rises with increase in sintering temperature and extension in holding time. The SPS alloys possess evidently higher compression strength than VIMFA ones. Also, the compression strength of SPS alloy rises with increase in sintering temperature.

Abstract:The Mg-3Y (wt%) alloy sheet was fabricated by pre-extrusion and subsequent single-pass large strain hot rolling process. The influences of different twinning types on dynamic recrystallization (DRX) and grain structure evolution during large strain hot rolling were investigated. Results show that the alloy undergoes nearly complete DRX during pre-extrusion processing under a low extrusion ratio of 8:1. During subsequent large strain hot rolling processing, deformation twinning, especially the {101} compres-sion and {101}-{102} double twinning, plays an important role in plastic strain accommodation. Moreover, the compression twin and double twin assisted DRX occurs extensively within the grains, and the recrystallization region is extended from the twin interior towards non-twinned regions, greatly relieving the internal stress. Both of processes above promote the formability of the alloy during large strain hot rolling processing.

Abstract:The microstructure of the 7075 aluminum alloy, which was extruded before the preparation of a semi-solid isothermal remelting billet, was studied in this paper along with the effects of isothermal temperature and holding time. The grain coarse-grain law was predicted using the grain-growth model in the JMAK module of DEFORM-3D software. The findings demonstrate that the grain size gradually rises, the grain tends to be rounded, and the liquid content of the grain border increases with increasing isothermal temperature and holding time. During the high solid fraction interval, the grains underwent recrystallization, merged and grown, and liquid phase increased. In the low solid fraction interval, non-recrystallized grains are rarely visible, and Ostwald ripening is the primary mechanism causing the grains to grow quickly. In the semi-solid isothermal remelting grain growth formula, n=3 is a more accurate value. The rate of grain growth is calculated at 55.1 μm3/s, 295.3 μm3/s and 817.9 μm3/s as isothermal temperature rises. Using the energy relation and grain growth formula, the activation energy of the grain boundary migration of the 7075 aluminum alloy was calculated to be 118.6 kJ/mol, with a grain growth rule in the 550-620 °C range predicted. The actual measured value and the expected value are relatively close.

Abstract:This paper studied the effect of residual stress on the reheat cracking susceptibility of Super304H austenitic stainless steel weld metal using the pre-compressed CT specimen method. The plastic strain and dislocation density distribution of weld metal under different residual stresses were analyzed by ABAQUS simulation combined with EBSD characterization. The effect of residual stress on the reheat cracking susceptibility is explained from the aspect of stress-induced precipitation. The results show that CT specimens with high pre-compression force have higher residual stress and are more likely to generate cracks. As the residual stress increases, the tensile strength of the tensile specimen decreases gradually. The high residual stress region of the CT specimen closed to the U-shaped notch root has higher dislocation density and subgrain, promoting the precipitation of the small intragranuar phase, which makes the intragranular hardening more serious, and reheat cracking are easier to occur.

Abstract:Amorphous indium gallium zinc oxide thin film transistors (a-IGZO TFTs) have the advantages of high field effect mobility and high switching ratio, and thus exhibit great potential applications in the fields of active drive display technology, flexible and wearable electronic devices. However, the poor stability of the electronic performances is the key problem restricting its large-scale applications. In this paper, Al2O3 thin films with low oxygen vacancy content were prepared by hollow cathode assistant pulsed laser deposition at room temperature, and used as the passivation layer of a-IGZO TFT devices. In-depth X-ray photoelectron spectroscopy illustrates that oxygen plasma introduced by the hollow cathode inhibits the formation of oxygen vacancies at the Al2O3/a-IGZO interface, which could improve the subthreshold performances of the TFT devices. 180 oC annealing for a-IGZO films could improve the mobility and reduce the threshold voltage shift; Annealing at 100 oC for Al2O3/a-IGZO TFT devices is helpful to reduce the carrier concentration and improve the subthreshold characteristics. The mobility of TFT devices processed by these two combining annealing processes could be as high as 22.8 cm2V-1s-1, and the subthreshold swing is 0.6 Vdecade-1.

Abstract:ZrAl alloy is a potential space material for aerospace. Zr-6Al-0.1B alloy was prepared by vacuum hot pressing sintering. The isothermal compression tests of hot-pressed sintered Zr-6Al-0.1B alloy were carried out under the conditions of deformation temperature 950 ℃ ~ 1150 ℃ and strain rate 0.01 s-1 ~ 1 s-1 using Gleeble-3500 thermal simulation machine. The results show that at the beginning of deformation, the stress increases rapidly with the increase of strain and reaches the peak quickly. Then, the stress decreases continuously with the increase of strain, and there is no stress equilibrium stage. With the decrease of the deformation temperature or the increase of the strain rate, the stress-strain curve shifts to the high stress region, indicating that the hot-pressed sintered Zr-6Al-0.1B alloy is a sensitive material for deformation temperature and strain rate. The Johnson-Cook constitutive model of hot-pressed sintered Zr-6Al-0.1B alloy was established, the temperature sensitivity coefficient D and strain rate sensitivity coefficient C were modified. Through qualitative and quantitative comparative analysis between the predicted value by the model and the tested value, indicating the model has higher prediction accuracy when C is modified alone. This study can provide guidance for the selection of subsequent hot working parameters of hot-pressed sintered Zr-6Al-0.1B alloy, and provide a reliable constitutive model for the corresponding numerical simulation research.

Abstract:In order to solve the problem of poor thermal conductivity of traditional tool coatings with high wear resistance, the (TiAlTaCrZr)N coatings were prepared by DC magnetron sputtering under different nitrogen flow rates. The effects of different nitrogen contents on the microstructure, hardness, adhesion and thermal conductivity of the coatings were studied. With the increase of nitrogen flow rates, the content of N in the coatings increases, and the microstructure of the coatings changes from nanocrystalline to columnar crystal. The hardness of the coatings increases from 11.0 GPa of the TiAlTaCrZr coating to 20.6 GPa of the (TiAlTaCrZr)N coating with 5 SCCM nitrogen flow rate. The adhesion of the coating reaches to the value of 130 N when nitrogen flow is 5 SCCM, and then decreases gradually with the increase of nitrogen contents. The thermal conductivity of the (TiAlTaCrZr)N coating is better than that of the TiAlN coating, but the thermal conductivity decreases with the increase of nitrogen contents. Since the (TiAlTaCrZr)N coating have high thermal conductivity, high adhesion and high hardness, the cutting length of the (TiAlTaCrZr)N coating is 175% higher than that of the TiAlN coating for titanium alloy cutting. It provides a new tool coating with high wear resistance and high thermal conductivity for titanium alloy cutting.

Abstract:The thermal barrier coating prepared by atmospheric plasma spraying was modified by high-current pulsed electron beam. The original coating and the electron beam modified coating were subjected to CMAS corrosion experiments at 1250℃, respectively. The phase composition, microstructure and chemical composition of the original coating and the electron beam modified coating before and after corrosion were characterized by XRD, SEM and EDS, and the CMAS corrosion behaviors and influence laws of the original coating and the modified coating were compared and analyzed. The results show that the surface roughness of the modified coating decreases, and a dense remelting layer with columnar crystals is formed. The surface of the coating has better structural stability and phase stability. After 8 hours of CMAS corrosion, the structure of the modified coating remains intact, and the coating does not fail to fall off, so it has good resistance to CMAS corrosion.An experimental set-up was designed for measuring the self-field losses of Bi2223/Ag HTS tapes using a transport current method.

Abstract:AlCoCrCuFeNi high-entropy alloys (HEAs) were prepared by selective laser melting (SLM). The microstructure and high-temperature oxidation behaviors at 800℃, 1000℃ and 1200℃ were studied. The phase compositions and morphological characteristics of the oxide film were analyzed by X-ray diffractometer (XRD) and scanning electron microscope (SEM). Results indicate that the prepared AlCoCrCuFeNi HEA mainly contains BCC phase, BCC/B2 phase and a small amount of FCC phase, and the microstructure is a non-equilibrium heterostructure composed of long straight columnar dendrite and equiaxed cell structures. The HEAs have good oxidation resistance at three temperatures. The oxidation kinetics curves basically follow the parabolic law. The oxidation rate is determined by a clear dependence on temperature, which increases with the increase of temperature, and obvious voids and cracks appear in the oxide films, which provided channels for diffusion of elements that aggravate the oxidation reaction, resulting in the oxide film peeling becomes more and more serious. The main components of the oxide films are Cr₂O₃, Al₂O₃ and spinel MCr₂O₄ mixed oxides. The denser oxide film can effectively inhibit the matrix from being further oxidized and improve the anti-oxidant properties of SLM-prepared HEA.

Abstract:NbMoTaWZr-HfC composite is composed of high temperature strengthened particles and refractory high entropy alloy. It is difficult to prepare the spherical powder by traditional gas atomization due to its high melting point characteristics. In this work, NbMoTaWZr-HfC spherical powder is successfully synthesized by spray granulation combined with radio frequency plasma spheroidization. The macroscopic properties, phase composition and microstructure of the powder are studied and analyzed. Results reveal that the shape of the composite powder is spherical and the particle size is range from 13.31 to 32.11 μm, D50=19.62 μm. The sphericity, flow rate and bulk density of the spheroidized powder are 0.98、8.9 s/50g，7.20 g/cm3, respectively. Moreover, the main phases of NbMoTaWZr-HfC spherical powder are body-centered-cubic ( BCC )+ ZrO2 + HfC phase and it has dendritic and cellular structure.The elements distribution in the spherical NbMoTaWZr-HfC powder is uniform, while elemental segregation at the dendritic scale region, high melting point elements such as W, Mo, Ta are enriched in the dendrite arm, and low melting point elements such as Nb, Zr are enriched at the interdendritic region, and the Hf are uniformly distributed,

Abstract:In order to explore the effect of Cu on the corrosion resistance of Zr-1Sn-0.35Fe-0.15Cr-0.10Nb (mass fraction, %) alloy in 400 ℃/1000 ppb oxygen-contained super-heated steam, Zr-1Sn-0.35Fe-0.15Cr-0.10Nb and Zr-1Sn-0.35Fe-0.15Cr-0.10Nb-0.05 alloy specimens were corroded in 400 ℃/10.3 MPa/1000 ppb oxygen-contained super-heated steam by a dynamic autoclave. The scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscope were used to characterize the microstructure of the oxide films and the valence state of the alloying element. The results show that the addition of Cu can improve the corrosion resistance of Zr-1Sn-0.35Fe-0.15Cr-0.10Nb alloy; Cu mainly exists in the form of Cu and Cu+ in the oxide film; Cu can promote the transformation of Sn and Sn2+ to Sn4+ and Fe2+ to Fe3+ in the oxide film; The reasons of Cu improving the corrosion resistance of Zr-1Sn-0.35Fe-0.15Cr-0.10Nb alloy are discussed from the aspects that the addition of Cu affects the oxidation behavior of alloying elements and inhibits the formation of pores and cracks in the oxide film.

Abstract:Aiming at the problems of low strength and poor plasticity of magnesium alloys at room temperature, Mg-4Sn-2Al-1Zn alloys were extruded at 250℃ by compound extrusion process, and the microstructure evolution, texture and mechanical properties of the alloys after extrusion were studied. The results show that the grain size of Mg-4Sn-2Al-1Zn alloy can be refined from 45.2mm to 3.1mm by one-step compound extrusion, and the structure is uniform. The hardness and uniformity of the extruded alloy increased, and the yield strength, tensile strength and elongation after fracture were 204 MPa, 287 MPa and 21.0%, which were 140.0%, 91.3% and 156.1% higher than that of the homogeneous state, respectively. Dynamic recrystallization is the main mechanism of grain refinement. Grain refinement and basal plane texture enhancement after extrusion, and the texture expands uniformly in the extrusion direction improves the strength and plasticity of the alloy, and the Mg2Sn phase breakage further improves the mechanical properties of the alloy during extrusion. The above studies show that compound extrusion is a process that can effectively improve the comprehensive properties of magnesium alloys.

Abstract:The medium entropy alloy of CrCoNi has excellent low temperature properties, but its plasticity is poor (<8%) after liquid nitrogen temperature rolling. In this research, arc melting of casted CrCoNi entropy alloy as the research sample, rolling deformation of CrCoNi alloy at low temperature (77K) for three passes, the total deformation was 50%. Then, annealing was carried out at 650 ℃, 700 ℃ and 800 ℃ for 30 minutes. Experimental data show that: CrCoNi medium entropy alloy after rolling and annealing, not material phase structure changed, after annealing. Because of recrystallization, deformation grains become smaller, and generated ∑3 annealing twin in organization. As the annealing temperature increased, the number of recrystallized grains increased, the elongation increased. It can be concluded that through the cold rolling and medium temperature annealing in short time performance controlling, matching the performance of the strength and toughness can be obtained, The efficiency of heat treatment process was improved.

Abstract:Molten oxidation method is an environmentally friendly treatment technology for metallurgical slag, which has attracted an increasing amount of attention in recent years. The isothermal oxidation kinetics of iron-rich molten nickel slag in air atmosphere was studied. The actual melting temperature (liquidus temperature) of modified nickel slag was determined to be 1488 ℃ by high temperature confocal laser scanning microscope (HT-CLSM). The variation curve of Fe_²⁺ concentration with time during isothermal oxidation of molten nickel slag was obtained by isothermal oxidation experiment of tubular furnace. The oxidation reaction order of Fe_²⁺ in molten nickel slag is 1.45~1.26 and the apparent activation energy is 286.83 kJ/mol by differential method and Arrhenius equation. The oxidation kinetics of molten nickel slag is dominated by diffusion control. Based on the Whitman theory and Higbie theory, the diffusion coefficients of oxygen in the melt are estimated to be 2.02′10_^-9 m_²/s~4.42′1010_^-9 m_²/s and 0.75′10_^-9 m_²/s ~3.28′10_^-9 m_²/s, respectively.

Abstract:In this paper, the step fatigue test of CuCrZr copper alloy at 300°C and 400°C was carried out, and the cyclic plasticity behavior was studied from the aspects of cyclic strain amplitude, average strain, average strain rate and energy dissipation rate. It is found that the cyclic soft hardening characteristics of CuCrZr copper alloy and the ratchet effect are affected by the combination of temperature and cyclic stress, and the higher the temperature, the more prone to cyclic softening, and the ratchet effect is more significant. Based on the comparison between the high temperature tensile fracture energy of CuCrZr copper alloy and the total dissipative energy of high temperature ladder fatigue, both are related to temperature, so the high temperature tensile fracture energy is used as a temperature compensation parameter, and a linear damage fatigue life prediction model based on energy method is proposed, and the fatigue life of CuCrZr copper alloy is predicted. Finally, the temperature-related failure mechanism of CuCrZr copper alloy is analyzed based on fracture analysis: fatigue crack failure is prone to occur at lower temperatures, and with the increase of temperature, the ductility failure accumulated by ratchet strain is more likely.

Abstract:In order to balance the strength and ductility of titanium matrix composites (TMCs), in-situ TiC/Ti composites with layered structures have been prepared by graphene oxides (GOs) electrophoretic deposition on pure Ti foils followed by spark plasma sintering (SPS) process. In order to further modifying the mechanical property, the sintered composites were subjected to cold rolling and annealing. The results show that GOs on the surface of Ti foil reacts with Ti matrix to form in situ TiC phases, thus forming TiC/Ti layered composites. With increasing deposition duration, the content of TiC distributed between Ti layers increases. After cold rolling and annealing, the grains of annealed composites are equiaxed, and the TiC still planarly distributed in the composites. The ultimate tensile strength (UTS) and the elongation (δ) of sintered material are 555 MPa and 15% respectively, while the UTS of annealed material is 568 MPa and the δ is 27%. Compared with sintered materials, annealed material achieves good strength-plasticity synergy. In addition, the strengthening and toughening mechanism of composites was discussed based on the analysis of microstructure and fracture behavior.

Abstract:Sm₂Fe₁₇ alloy as the precursor of a potential permanent magnet (Sm₂Fe₁₇N_x) has been paid attention to, but the pure one obtained has been still very difficult until now due to having a distinct difference of melting point between the Fe and Sm metals as raw materials, it impairs seriously the magnetic performance of Sm₂Fe₁₇N_x. In this work, this problem was resolved successfully using a method of molten salt electrolysis. A chronopotentiometry was used at 1160℃ to obtain different thicknesses (17.22 ~ 40.34 μm) of single-phase Sm₂Fe₁₇ alloy as the product on the iron cathode in LiF-CaF₂-SmF₃, simultaneous a cyclic voltammetry and a square wave voltammetry were carried out to reveal the electrochemical behavior of Sm^₃₊. The result shows that the reduction of Sm^₃₊ to Sm^₀ on the iron electrode included two steps. Firstly, a soluble-soluble reaction appears at -0.33 V vs. Cr/Cr₂O₃ corresponds to the electroreduction of Sm^₃₊ to Sm^₂₊. Secondly, results of CV that Sm^₂₊ can be reduced at -0.78 V vs. Cr/Cr₂O₃ on the iron electrode in LiF-CaF₂-SmF₃ melts due to lower activity of metallic samarium in the Sm₂Fe₁₇ alloy than that of samarium metal and makes samarium in Sm-Fe alloy more stable.

Abstract:In order to improve the properties of nano-cermet composite electrodeposited coatings, Ni-TiN-GO (Graphene Oxide) composite electrodeposited coatings were prepared on the surface of alloy steel by multi-step electrodeposition process. Its microstructure, composition, microhardness, wear resistance and corrosion resistance were characterized and analyzed, and determine the most suitable multi-step electrodeposition process. On this basis, the coating was post-treatment, the effect of post-treatment on the corrosion resistance of the coating was studied. The results show that the microstructure and properties of the coating obtained by three-step electrodeposition are the best, good bonding with the substrate and the thickness is 24.6 μm, the coating obtained by three-step electrodeposition has uniform and dense surface, and the grain size is about 20nm, and the grains show double preferred orientation of (111) and (200) planes. The microhardness of the electrodeposited coating is 2249.44HV, and the friction coefficient is 0.8. the wear mechanism is mainly weak abrasive wear. The results of Tafel polarization curve test showed that the corrosion potential of the three-step electrodeposited coating is -0.677V, and the self-corrosion current density is 1.71×10-5A·cm-2, After 96h salt spray test, the morphology of the coating did not change obviously. After post-treatment, the self-corrosion potential of the three-step electrodeposited coating shifted positively to 60mV, and the self-corrosion current density decreased by an order of magnitude.

Abstract:An The development of efficient and stable photocatalytic materials is the key to the application of photocatalytic technology. In this paper, urea, bismuth nitrate and potassium bromide were used as raw materials, BiOBr/g-C3N4 composite photocatalysts (Bix/CN) with different mass ratios were prepared by one-step hydrothermal method. Based on the results of UV-Vis, the calculated ECB values of BiOBr and g-C3N4 were 0.52eV and -1.1eV, while the calculated EVB values of BiOBr and g-C3N4 were 3.38eV and 1.55eV, respectively. Photoelectric catalytic performance tests showed that Bi3/CN had the higher photocurrent density and lower charge transfer resistance. When the visible light irradiation time was 10 min, the total removal rate of RhB by Bi3/CN was 81.35%. The total removal rate of RhB by Bi3/CN decreased only 6% after reused for 5 times, indicating that Bi3/CN had high and stable photocatalytic efficiency for RhB. The improvement of photocatalytic efficiency of compound photocatalyst mainly depended on the effective coupling of the two-dimensional monomers, and the effective interface contact improved the photogenerated electron transfer and carrier separation efficiency. The photocatalytic enhancement mechanism was proposed as that the accumulated electrons on CB of g-C3N4 for generation of ?O2- were the essential reason for the improvement of photocatalytic performance.

Abstract:B2-CuZr phase reinforced amorphous matrix composites usually shows better mechanical properties than those with conventional reinforcing phases due to their unique “transformation induced plasticity” phenomenon. However, the volume fraction, size and distribution of in-situ B2-CuZr phase is difficult to control, and B2-CuZr tends to occur eutectoid decomposition, which limits the widespread application of these materials. The microstructural optimization could be realized via tailoring the casting parameter, the composition and aftertreatment. The present paper will give a review on the microstructural characterization, reinforcing mechanism and microstructural tailoring methods on B2-CuZr phase reinforced amorphous matrix composites.

Abstract:Samarium iron nitrogen compound (Sm2Fe17N3) has become research hotspot of new rare earth permanent magnet materials because of its higher magnetocrystalline anisotropy field and Curie temperature value and less rare earth content than neodymium iron boron (Nd2Fe14B). However, since samarium iron nitrogen will decompose at 600 °C resulting the disappearance of permanent magnetic properties, the conventional high-temperature sintering process is not suitable for the preparation of samarium iron nitrogen sintered magnets and it can only be compounded with polymer materials as plastic magnets, which results in that the magnetic properties of Sm2Fe17N3 cannot be fully exerted. Therefore, the development of low-temperature forming process to prepare all-metal bulk magnets with high density is the key to obtaining high-performance samarium-iron-nitrogen magnets. After more than 30 years of hard work, researchers have developed a variety of low-temperature rapid prototyping processes for preparing samarium-iron-nitrogen magnets, and obtained high-performance magnets with a maximum magnetic energy product of 25MGOe. Starting from the preparation method of magnets, this paper summarizes the current research status and problems of bulk samarium-iron-nitrogen magnets, especially analyzes the phenomenon of coercivity decline in different fabrication methods, and makes prospect for its future development.

Abstract:Electron beam selective melting parts experienced complex thermal history, resulting in multi-scale microstructure. Thermal history data play an important role in analyzing microstructure formation. The complex metallurgical behavior of micro-melting pool makes it difficult to obtain the temperature-time-spatial data by experimental means. As a new technical means, numerical simulation technology provides a new idea for solving this problem. In this paper, the research status of numerical simulation of electron beam selective melting thermal behavior is reviewed from the aspects of mathematical theory of temperature field, simulation process, thermal-mechanical coupling simulation, thermodynamic simulation of molten pool and thermal defect mechanism. The challenges and future prospects of numerical simulation of electron beam selective melting thermal behavior are discussed.

Abstract:Rhenium is widely used as functional materials and ultra high temperature structural materials due to its excellent physical and mechanical properties. A variety of methods has been applied to prepare rhenium materials, in which chemical vapor deposition (CVD) is one of the main technique. The reaction type, deposition condition and effect of rhenium by CVD are briefly introduced firstly in the present paper. Then, the deposition dynamics, microstructure characteristics, mechanical properties and typical applications of CVD rhenium are reviewed, and compared with powder metallurgy rhenium. Finally, several key issues which need to be solved hereafter are put forward, and the directions of further research and applications foreground is prospected.

Abstract:Refractory metal energetic structural materials (ESMs) have good mechanical properties and excellent impact initiated energy release characteristics. However, due to the high melting point of refractory elements, it is difficult to fabricate large size defect-free castings by traditional methods of melting and casting. In this paper, Ti-Zr-Ta refractory alloy powders were prepared by plasma rotating electrode processing technology, and Ti-Zr-Ta refractory metal ESMs was prepared by laser metal deposition (LMD) technology. The microstructure, mechanical properties and impact initiated energy release characteristics of Ti-Zr-Ta refractory metal ESMs were studied. The results show that the densification of Ti-Zr-Ta refractory metal ESMs can be achieved by LMD technology and the density of alloy reaches 98.75 %. The alloy has good mechanical property, the quasi-static tensile stress reaches 1202 MPa. Ballistic gun experiments imply that Ti-Zr-Ta alloy prepared by laser metal deposition can generate quasi-static pressure of 0.144 MPa in 27 L airtight target chamber at the impact velocity of 1202 m/s, which reveals excellent energy release characteristics.