Preparation And Properties Of Dual-scale Mo-12Si-8.5B-ZrO₂(Y₂O₃) Composite

Mo-Si-B three-phase alloy has the advantages of high melting point,high strength,excellent high temperature mechanical properties and high temperature oxidation resistance.It is expected to become a new type of ultra-high temperature structural material to replace the traditional nickel-based superalloy,and has broad applications in the aerospace field.However,the mechanical properties and high temperature oxidation resistance of Mo-Si-B alloys need to be improved.This paper proposes to use nano-ZrO₂(Y₂O₃)to strengthen and toughen Mo-12Si-8.5B alloy,using homemade nano-Mo-ZrO₂(Y₂O₃)powder,micron Mopowder,Sipowder and B powder as raw materials to construct a dual scale of coarse and nanocrystalline With the microstructure of grain distribution,Mo-12Si-8.5B-ZrO₂(Y₂O₃)composite material is prepared by spark plasma sintering technology,and it is expected to achieve the purpose of improving its comprehensive mechanical properties.The main conclusions are as follows:(1)Prepare MoO₃-ZrO₂(Y₂O₃)composite powder by sol-gel method,and obtain better quality precursor powder through optimized process parameters(PH=1,citric acid content 1.2 times the mass of ammonium molybdate);The best process for calcination of precursor powder is to obtain evenly distributed MoO₃-ZrO₂(Y₂O₃)composite powder after550?×5h,and then reduce at 750?for 3h to obtain nano-level and high purity Mo-ZrO₂(Y₂O₃)composite powder.When kept for 3h,the initial temperature of MoO₃reduction to Mois 550?.(2)Mo-12Si-8.5B-ZrO₂(Y₂O₃)composite materials with single-scale and dual-scale microstructures were successfully prepared using different proportions of micro/nano Mopowder,Sipowder and B powder through SPS technology,The sintered composite material is composed of three phases of?-Mo,Mo₃Siand Mo₅SiB₂.As the content of nano-molybdenum in the composite increases,the hardness,flexural strength and fracture toughness of the composite material increase first and then decrease.Among them,when the content of nano powder is 30wt%,the composite has the highest hardness(9.75GPa),bending strength(629.6MPa)and room temperature fracture toughness(10.61MPa·m^1/2),which is attributed to the FG?-Mozone helps to increase the strength,and the CG?-Mozone has good ductility.All Mo-12Si-8.5B-ZrO₂(Y₂O₃)composites after sintering showed a mixed mode of transgranular and intergranular fracture.(3)With the increase of the content of nanometer ZrO₂(Y₂O₃),the relative density of the Mo-12Si-8.5B-ZrO₂(Y₂O₃)sintered body gradually decreases.When the content of ZrO₂(Y₂O₃)is in the range of 1.5?2.5wt%,the composite has a higher hardness(9.76?9.98GPa),flexural strength(672?678MPa)and room temperature fracture toughness(12.68?12.82MPa·m^1/2).When oxidized at 800?,the higher the content of ZrO₂(Y₂O₃)(5?10wt%),the better the oxidation resistance of the composite;while at high temperatures of 1000?and 1200?,the lower the content of ZrO₂(Y₂O₃)(0.5?2.5wt%)MSBZ composites have better oxidation resistance than composites with high ZrO₂(Y₂O₃)content(5%?10wt%).In the friction and wear experiment,when the ambient temperature is lower than 400?,the MSBZ2.5 composite has a low wear rate in the air and good wear resistance.The wear mechanism is mainly adhesive wear and oxidative wear;When the ambient temperature is higher than 400?,the wear rate of the composite in vacuum is low,and the wear resistance is better.The wear mechanism is mainly adhesive wear and plow wear;Compared to the vacuum atmosphere,the composite in the air is due to friction and oxidation form a MoO₃ film with a low friction coefficient,which reduces the minimum friction coefficient to 0.28.