Research progress at home and abroad is reviewed of preparation of WC-Co composite powders by spray conversion and cemented carbides with tungsten-cobalt base or tungsten-cobalt-carbon base. The routes,methods and process parameters are mainly discussed for preparing WC-Co composite powders and cemented carbides as well as the alloy properties,to provide research ideas and methods for preparation of cemented carbides with WC-Co composite powders prepared by spray conversion. WC-Co composite pow ders with short process flow, uniform component distribution, low impurity content, narrow particle size distribution,small grain size and low cost can be obtained by continuous optimization and improvement of preparation processes and methods.

WC-6 Co cemented carbide was prepared by spark plasma sintering using WC-6 Co composite powder with different morphology and WC-6 Co mixed powder prepared by traditional wet milling as raw materials.The microstructure,mechanical and physical properties of the cemented carbide were characterized by SEM,microhardness tester,densitometer,cobalt magnetometer and coercive magnetometer.The results show that there are many residual pores in WC-6 Co cemented carbide with density of only 14.21 g/cm3 prepared by SPS and using the spherical composite powder prepared by spray conversion,low-temperature calcination and in-situ synthesis as the raw material.The density of the alloy prepared by wet milling of spherical composite powder for 48 hslightly increases,but its hardness and toughness are lower.The microstructure is uniform and the porosity is reduced of the alloy prepared by SPS and using the loose WC-6 Co composite powder prepared by spray conversion,low-temperature calcination,short time ball milling and in-situ synthesis or WC-6 Co mixed powder prepared by traditional wet milling as raw materials,respectively.The densities of the two groups of alloys increase to 14.77 g/cm3 and 14.73 g/cm3,the microhardnesses increase to 2 045 kg/mm2 and 1 929 kg/mm2,and the toughnesses are 8.76 MPa/m1/2 and 9.29 MPa/m1/2,respectively.

The effect of deep cryogenic treatment on the wear resistance of WC-10Co lathe tool was studied with TC4 titanium alloy as the processed piece. The hardness and microstructure of the lathe tool were ana lyzed and tested by hardness tester,SEM and XRD. The research results show that the wear resistance of the lathe tool can be greatly improved by deep cryogenic treatment(DCT). With the increase of the turning length,the advantage of DTC lathe tool becomes more obvious. After deep cryogenic treatment, the hard ness of the lathe tool is slightly increased,the bending strength and toughness are significantly improved, and the microstructure is not obviously changed. The peak of WC in the XRD pattern of DTC lathe tool shifts to right, indicating that the compressive stress of WC decreases and the tensile stress of Co binder phase decreases,which is advantageous for increasing the strength of the alloy.

Using La(NO3)3 and Co(NO3)2 as raw materials,rare earth perovskite LaCoO3 powder was prepared by citric acid complexation and ammonium carbonate precipitation,respectively.Products were characterized by SEM,XRD,specific surface area analyzer and laser particle size analyzer.The results show that the rare earth perovskite LaCoO3 powder can be prepared by calcination above 600℃,and the surface structure is the flocculent structure of honeycomb foam.With the increase of calcination temperature,the surface will be sintered at different degrees.The sample prepared by citric acid complexation has high purity,stronger sintering resistance and smaller particle size,the efficiency of catalytic denitrification is over 90%.

The oxide layer thickness and oxidation products during the forging process of TaW12 alloy were characterized by optical microscopy and XRD technology,and the macro-oxidation behavior were investigated.The results show that during unprotected forging,the surface of the alloy absorbs a lot of oxygen,resulting in seriously powdered surface and harden sub-surface,with the oxidation depth of about 300~400μm,and the oxidation product is Ta2O5.The oxidation of the alloy could be greatly reduced by the ladle sheath or coating protection in the forging process,which has the best coating effect and the oxidation loss is reduced within 3%.

Using Ni-6 B-53.3 Mo as basic materials,Mo2NiB2-based cermets with different La2O3 doping concentration(0%,0.3%,0.6%,0.9%,1.2%)were prepared by vacuum hot-pressed sintering at 970℃.The effects of La2O3 doping concentration on the microstructure and friction and wear properties of Mo2NiB2-based cermets were investigated by high temperature vacuum friction and wear tester,surface profiler,laser confocal microscopy and X-ray diffraction.The results show that with the increase of La2O3 content,the wear rate and friction coeffiction of Mo2NiB2-based cermets are increased first and then decreased under the same load at room temperature.The wear rate and friction coefficient of Mo2NiB2-based cermets doped with 0.3%La2O3 are the highest and doped with 1.2%La2O3 are the lowest.The effects of load on wear resistance of Mo2NiB2-based cermets is obvious,the wear rate and friction coeffiction decrease with the increase of load.As temperature increases,the wear rate of La2O3 doped Mo2NiB2-based cermets decreases first and then stabilizes gradually,and the friction coefficient decreases first and then increases.

To study the effect of annealing treatment on microstructures and hardness of Al1.5CrCuFeMnTi high entropy alloy,the as-cast alloy was prepared by vacuum arc melting,and the morphology,crystal structure,composition distribution and hardness of the alloy obtained under isothermal annealing treatment at different temperatures were characterized by using methods of X-ray diffraction,scanning electron microscope and Vickers hardness tester.The results show that the as-cast Al1.5CrCuFeMnTi alloy is composed of an ordered and a disordered solid solution with a body-centered cubic structures,which forms a typical dendritic structure,and the characteristic of modulated structure is also observed in as-cast alloy.After annealing at 945℃,a Laves phase rich in Al,Cr and Mn with complex structure is formed.After annealing at 980℃,the Laves phase is transformed into FCC solid solution with Cr as matrix.Annealing treatment is conducive to the release of residual internal stress in as-cast alloys,which reduces the hardness of the alloys to about HV450.

C/C-ZrC-SiC composites were prepared by precursor infiltration and pyrolysis using poly-meric organic zirconium precursor(POZ)and polycarbosilane(PCS)as precursor.Thermogravimetric behavior,phase conversion and microstructure of Zr-Si mixed precursors during pyrolysis were studied by thermal gravimetric analyzer,X-ray diffraction and scanning electron microscope,and the microstructure and ablation behavior of the composites were analyzed in detail.The results indicate that when Zr-Si mixed precursors is heated from room temperature to 1 200℃,ZrC precursor transforms to inorganic ZrO2.When the pyrolysis temperature rises to 1 600℃,ZrO2 can be reduced to ZrC ceramics by carbothermal reduction reaction.The transition temperature of the SiC crystal is 1 200~2 000℃.The microstructure of the C/C-ZrC-SiC composites after ablation shows that the prepared composites exhibit good ablation resistance.

Biomass-derived carbon materials are widely applied for energy storage due to their excellent properties such as renewability,low cost,good conductivity and stability.The common preparation methods of biomass-derived carbon materials(pyrolysis,activation,hydrothermal method)and the latest progress of modified biomass-derived carbon(heteroatom doping,noble metal loading)in lithium-air batteries,sodium-ion batteries and lithium-sulfur batteries were reviewed.The challenges and future development directions of biomass-derived carbon in next generation batteries were discussed.

The characteristics were introduced of three kinds of nitriding processes for preparing alloy ribbon by melt bottom blowing nitrogen,top blowing nitrogen at high pressure and non-equilibrium solidification of rare earth alloy melt,and the factors affecting nitriding effect were discussed.The problems existing in the nitriding process of rare earth alloys and the research direction in the future were prospected.