Study On Preparation Technology And Microstructure Properties Of Mo₂NiB₂

The effects of alloy composition,pressure forming and vacuum sintering on the microstructure and properties of Ni-Mo₂NiB₂ alloy were investigated.The effects of doping Cr,V and Cr+V atoms on the electronic structure,crystal structure and mechanical properties of Mo₂NiB₂ system were calculated based on first-principles of materials.The effects of different Ni/Cr,Ni/V and Cr/V atomic ratios on the microstructure and properties of Ni-Mo₂NiB₂ alloy were experimentally investigated.The strengthening mechanism of Cr,V and Cr+V combined elements on Ni-Mo₂NiB₂alloy was explored,and the electrochemical corrosion performance of Ni-Mo₂NiB₂alloy doped with Cr,V and Cr+V was investigated,and the corrosion characteristics and corrosion mechanism in nitro-hydrofluoric acid solution were studied.The main findings are as follows:During the formation of Ni-Mo₂NiB₂ alloy,the density and hardness increase with the increase of cold isostatic pressure.The bending strength of Ni-Mo₂NiB₂ alloy increases when the cold isostatic pressure increases to 280 MPa.However,when the cold isostatic pressure is 300 MPa,the bending strength of Ni-Mo₂NiB₂ alloy increases.The bending strength of Ni-Mo₂NiB₂ alloy decreases.With the increase of vacuum sintering temperature in the range of 1230-1330℃,the number of semi-solid phases of Ni-Mo₂NiB₂ alloy changes,the hard phase grows and the sintering neck is formed,the bonding phase of Mo₂NiB₂ phase and solid solution increases,and the bending strength and hardness increase.The bending strength of nitrogen cooled alloy is higher after vacuum sintering at 1260℃.The alloy held for 1 h has higher bending strength and hardness than that held for 0.5 h.The doped Cr in the tetragonal hard phase Mo₂NiB₂ can enhance the crystal stability.When the Ni/Cr atomic ratio of the hard phase is 0.5,the hard phase has the highest bond strength and the most stable structure.Doping V can improve hardness and reduce toughness;Doped Cr+V hard phase structure,V greatly reduces the bonding strength of Cr atom.Mn doping can reduce the bending strength of Ni-Mo₂NiB₂ alloy.The microstructure and properties of Ni-Mo₂NiB₂ alloy doped with Ni/Cr atomic ratio of1.75,2.00,2.25 and 2.50 show that the alloy has the highest bending strength of1378.4MPa and hardness of 72.4 HRA when Ni/Cr atomic ratio is 2.0（Ni/Cr atomic ratio is 0.50 in hard phase）.The distribution of hard phase is uniform and the aggregation of phase structure is less.The microstructure of Ni-Mo₂NiB₂ alloy doped with Ni/V atomic ratio 4.2,3.0,2.2 and 1.6 showed more irregular pores,and the hard phase and adhesive phase gathered and joined,and the bending strength and hardness decreased to a certain extent.The Ni-Mo₂NiB₂ alloy doped with Cr/V atomic ratio of4:0,3:1,2:2,1:3 and 0:4 shows that the bending strength of Cr doped alloy increases,while the bending strength and hardness of V doped alloy decrease.The hard phase and bonding phase of Cr+V doped alloy increase,and the bending strength decreases in different degrees and the hardness increases.When Ni-Mo₂NiB₂ alloy is corroded by HNO₃-HF,the corrosion of Cr doped hard Mo₂NiB₂ phase is greater than that of bond phase.The doped V shows that the corrosion of hard Mo₂NiB₂ is lower than that of bond phase.When Cr+V doped Ni-Mo₂NiB₂ hard phase Mo₂NiB₂ and bond phase compete for corrosion,the minimum weight loss of Ni-Mo₂NiB₂ alloy is 32.78 g/m² when the Ni/Cr atomic ratio is 1.75.When Ni-Mo₂NiB₂alloy is corroded in Na Cl medium,the Cr/V atomic ratio decreases and the corrosion current density decreases.