Tungsten-based composite materials were synthesized by using tungsten powder,nickel powder, iron powder and casting wax,and then tungsten-based composite material parts with a certain shape and size were prepared by fused 3D printing forming technique.The appropriate printing parameters were determined and the precision of the printed parts was evaluated.The results show that the viscosity of tungsten- nickel-iron-paraffin composite material with 85% solid content is stable with temperature changing, which can maintain the stability and fluidity of the material inside the printing cavity,and obtain a higher solid content of the part at the same time.The composites with the solid contents of 80%,85% and 88% have a uniform density distribution inside the cavity,and their melt has certain stability and uniformity inside the printing cavity.The appropriate printing parameters are as follows:printing temperature of 130~ 132℃,supply pressure of 124.11~151.69kPa,printing ring distance of 1.1mm,and layer height of 1.24 mm.The precision of the parts printed with the above method is low,which is mainly affected by the discharge mode and program control.

The 90W-Ni-Fe alloy parts were fabricated by 3D cold printing using military-grade tungsten powder,nickel powder and iron power as the raw materials.The effects of binder and solid contents on the viscosity of metal slurry were studied,and the microstructure uniformity of the green body was also investigated. The debinding and sintering process was optimized according to TG-DTA curves,and the morphology, metallographic microstructure and density of the sintered body were analyzed.The results show that the W-Ni-Fe metal slurry with 4% binder and 70%~75% solid is the most suitable for 3D cold printing. The microstructure of the green body is uniform in the vertical direction,the metal particles are uniformly filled in the three-dimensional network structure composed of PVB,and solid particles are uniformly distributed without obvious settlement.In the printing process,the thickness of the green body nonlinearly grows,the width is unstable,and therefore the curing rate of the slurry still needs to be improved.After the green body was degreased and sintered at 1440℃ for 2h,the sintered body with 16.26g/cm^3 density is obtained,and its relative density is as high as 94.83%.

Mo-Cu plates were prepared by tape-casting technique,combined with debinding-sintering process.Then the Mo-Cu ultrathin sheets were acquired by rolling and annealing.The X-ray diffraction (XRD),carbon sulphur analyzer,metallographic microscope,density gauge and microhardness tester were used to characterize the phase,composition,microstructure and the Vickers hardness of Mo-Cu ultrathin sheet at different conditions.XRD analysis shows that only the characteristic diffraction peaks of Mo and Cu were found in Mo-Cu ultrathin sheets,and no new phase was formed.The carbon sulphur analysis shows that the sheets debinding completely,only with the carbon content of 0.01809%.The relative density and the Vickers hardness of the Mo-Cu ultralthin sheet were 98.42%and 266,respectively,which were improved by rolling-annealing technique.

The effect was studied of heat treatment temperature on microstructure of Ti-42.5Al-4Nb-1Mo-0.2 Balloy for internal combustion engine.The results show that the alloy has nearly lamellar microstructure in the as-cast state,mainly composed of fine lamellar clusters and B2 phase andγphase around the lamellar clusters.The quenched alloys at 1200℃ and 1250℃ have similar microstructure.With the quenching temperature is increased to 1300℃,γphase in quenched microstructure disappears,and there are some long rod-shaped fine α2 grains in B2 grains.After heat treatment at 1200℃ and cooling to room temperature, the alloy has the microstructure of α2/γ lamellar clusters,B2 phase andγphase.When the heat treatment temperature is up to 1250℃,the number ofαgrains and α2/γ lamellar clusters begins to increase, and their size also gradually increases.When the heat treatment temperature rises to 1300℃,the alloy has nearly lamellar fine α+β microstructure.

The effects were investigated of Ta and Zr contents on the microstructure and damping properties of theβ-type titanium alloy Ti-36 Nb-xTa-yZr-0.3 Oby metallographic analysis and dynamic thermomechanical analysis(DMA).The results show that Ta and Zr addition has no effect on the grain size of the alloy.Ta addition results in the dipole shape factor of the alloy increased and the damping value improved,but the relaxation activation energy and the critical temperature almost have no change and therefore the peak temperature and the peak width have no significant change.The addition of Zr has little effect on the dipole shape factor of the alloy,and the damping value is basically unchanged,but the relaxation activation energy and the critical temperature increase,leading to increased peak temperature and peak width.

The thermal compression tests of Ti-B25 alloy were conducted on Gleeble 3800 thermal simulator under the conditions of 800~1000℃ temperature,0.01~10s^-1 strain rate and 70% strain.The results show that in the initial deformation stage of Ti-B25 alloy,the flow stress increases rapidly with the increase of strain.However,after reaching the peak value,the flow stress begins to decrease and gradually stabilizes, showing a steady flow characteristic.During high temperature deformation,both steady stress and peak stress decrease significantly with the increase of temperature and the decrease of strain rate.Through regression processing of the data,the functional relationships are fitted between the thermal deformation activation energy Q,the structural factor A,the stress index nor the stress level parameterαand the strainε, and then the constitutive equation of the alloy during high temperature deformation is obtained.

CaO-doped BaZrO3powder was synthesized with solid-state method at 1 400 ℃ using BaCO3, ZrO2 and CaO powders as the starting materials.And then CaO-doped BaZrO3 ceramic sheet was prepared by cold isostatic pressing and solid-state sintering at 1 750℃ for 6h.The titanium-rich alloy Ti3Ni was melted on the ceramic sheet by vacuum induction melting.The effect was investigated of CaO dosage on the microstructure of CaO-doped BaZrO3 ceramic sheet and its interfacial reaction with Ti3Ni alloy.The results reveal that part of CaO is dissolved in the BaZrO3 lattice to form Ba1-xCaxZrO3,and the remaining CaO is uniformly distributed in the Ba1-xCaxZrO3 matrix.The increase of CaO dosage results in the increase of the particle sizes of Ba1-xCaxZrO3 matrix and CaO.When CaO dosage(molar fraction)is 15%and 20%,the thickness of the etched layer of the ceramic sheet by Ti3Ni melt is about 32μm and 11μm,respectively.The crystal structure of BaZrO3is modified by CaO doping,and its thermodynamic stability is also improved, which conducive to the application of BaZrO3 refractory material in the field of active metal smelting.

Diamond/copper composites with different contents of lanthanum were prepared by spark plasma sintering(SPS).Phase composition,interfacial microstructure and elemental distribution of the composites were characterized by XRD,SEM and EDS.Relative density and porosity of the composites were tested with drainage method.The interfacial electronic state density and atomic distance variation of the lanthanum-containing diamond/copper composites were calculated based on first-principles density functional theory. The calculated results show that the electronic state density of La and Cu has a wide pseudogap near the Fermi level,and the bonding ability between La and Cu is strong.After energy optimization by periodic plate model,the atomic spacing between La and Ti or Cu is significantly reduced,and the atomic spacing between La and Cu in the system is smaller,showing that the rare earth La and Cu matrix have stronger affinity. The experimental results show that a large amount of La is dissolved in the copper matrix,promoting the formation of Cu2La phase.With the increase of La content,the defects such as cracks and holes in the interface of the composites gradually decrease,and the relative density of the composites is gradually improved.The porosity of the composite without La is 3.48%,while the porosity of the composite with 7% La is decreased to 0.42%.The doped La in diamond/copper composites can effectively reduce the interface defects.

Stress-strain curve and microstructures of a Nb-based alloy with low-density and high-strength were studied.The results show that the alloy almost keep the original microstructures and there was no obvious dynamic recovery and dynamic recrystallization occurrence in case of the alloy compressed under the strain rate of 10s^-1 with the deformation temperature of 1 000℃.During the processing,the alloy was not easy to soften,the deformation resistance of the alloy was large,and it was not easy to carry out plastic deformation. However,under the strain rate of 0.1s^-1,dynamic recovery had been occurred in the microstructures of the alloy even at the deformation temperature of 1 000℃,work hardening during deformation can be counteracted by softening caused by dynamic recovery,the deformation resistance of the alloy was decreasing,and the plastic deformation can be carried out.With the deformation temperature increasing,the dynamic recrystallization was gradually occurred and the plastic deformation was more likely to be carried out.

Micro-crystalline alloys which produced by rapid solidification technologies could have better properties than as-cast alloys.Some Sm-Fe alloys were prepared under different cooling rates in the vacuum rotary quenching furnace.The microstructure and phase composition of the microstructure were studied and gas nitridation was carried out.The results show that with the increase of rapid cooling rate,the segregation of elements in the alloy decreases,and the microstructure of the alloy changes from coarse dendrite to microcrystalline.When the cooling rate reached to 24.0m/s,the alloy with a microcrystalline microstructure could be obtained.The grain growth tendency of microcrystalline Sm-Fe alloy is very small under the condition of direct nitriding of the alloy at 420℃.The grain size is small and the grain boundary area increases,which makes the effective nitriding points increase and promotes the diffusion of nitrogen atoms. However,nitrogen atoms are mainly distributed at grain boundaries in the form of nitrogen compounds, resulting in uneven nitridation between grain boundaries and grain interiors.