Microstructure And Properties Of La₂O₃ Doped With Mo₂NiB₂ Based Cermets

The properties of ternary boride-based cermets has the advantages of both metal and ceramic in the terms of performans,and the preparation process is easy and the cost is cheap,which is widely used in the fields of wear resistance,corrosion resistance,high temperature and oxidation resistance.It has good development prospects in the fields of hard material production,aerospace,coatings,and has important research value.Among them,Mo₂NiB₂-based cermets has good mechanical properties and good properties such as excellent abrasion resistance,corrosion resistance,high temperature resistance,oxidation resistance,electrical conductivity and thermal conductivity,and has huge development potential in the study of functional materials.However,because it has poor sintering activity and toughness,which seriously affected the improvement of its comprehensive performance and restricted its development.So the purpose of improving the comprehensive performance of Mo2NiB2-based cermets can be achieved by adjusting the element ratio and adding grain inhibitor.According to different Mo/B atomic ratios,Mo₂NiB₂-based cermets doped with La₂O₃?0,0.3%,0.6%,0.9%,1.2%?were prepared by vacuum hot press sintering technology,which were used Mo powder,Ni powder,B powder and La₂O₃ powder.The effect of the phase composition,microstructure,mechanical properties and wear resistance of La2O3 doped Mo₂NiB₂-based cermets have been studied.The effects of doped La₂O₃ on the chemical composition of the material were simply studied.The results show that when Mo/B=1,the material doped with La2O3 produce Ni-based bonding phase,Mo₂B phase and orthorhombic Mo₂NiB₂ phase.When Mo/B=0.9,orthorhombic Mo2NiB2 phase,Ni-based bonding phase,MoB phase,and Ni3B phase were generated in Mo₂NiB₂ based cermets doped with different contents of La₂O₃.When the Mo/B=0.8,in the system results in the formation of orthorhombic Mo₂NiB₂ phase,Ni-based bonding phase,and Ni3B phase in the material.Different Mo/B atomic ratios produced different phases.La₂O₃ can promote the transformation of the Mo₂B phase,MoB phase,Ni₃B phase into Mo2NiB2 phase.By studying the effect of different content of La₂O₃ on the microstructure and properties of the material,it was found that the doped La₂O₃ can inhibit the grain growth,the grain size was small,and the hard phase particles were uniformly distributed.The effect was best when the doping amount of La₂O₃ is 0.6%,When the La₂O₃ doping content exceeded 0.6%,the grain size increased,the hard phase particles were no longer uniformly distributed,and the suppression effect was reduced.La2O3 can improve the bending strength,hardness,compressive strength,wettability and density of the material,lead to a decrease in fracture toughness.The bending strength and hardness of the material were good when the La2O3doping content was 0.6%.When Mo/B=0.9,the bending strength and hardness were 1056.3MPa and 923.5HV.When Mo/B=0.8,the bending strength and hardness were 1150.06 MPa and 904.5 HV.When Mo/B=0.9,the highest fracture toughness of the material was 17.49MPa·m^1/2.By studying the effect of load and temperature on the wear resistance of material doped with La₂O₃.It was found that at room temperature,when the load was 700 g,900 g,1100 g.With the load increased,the formation of particles on the surface of the material produced lubrication.The friction coefficient was the smallest at Mo/B=0.8,the load is 1100 g,and the doping amount of La₂O₃ was 0.6%,which was 0.373.At 600?,700?,and 800?,the effect of doping La2O3 on the friction coefficient of the material was different.As the temperature increases,the abrasive particles attached to the surface of the wear scar during the friction process can produce lubrication after being heated,thereby reduced the wear.The degree of wear on the material and the wear resistance were improved.At Mo/B=0.8 and800?,the friction coefficient of the material was the smallest when it was undoped with La₂O₃,which was 0.333.