Fabrication And Research On Microstructure And Properties Of TiB₂/18Ni300 Composites

18Ni300 maraging steel is widely used in aerospace,military industry,mold manufacturing and other industries because of its high strength,good machinability,weldability and excellent formability.Steel-based materials have great research value in wear resistance.According to the research idea of introducing ceramic phase into metal matrix to enhance wear resistance,TiB whiskers are formed in situ by controlling sintering process,and the added ceramic particles can form hybrid enhancement effect with whiskers,thus improving the wear resistance of materials.In this paper,18Ni300 alloy powder with average particle size of 53-106μm,10μm Ti powder and 5μm TiB₂ powder were used as reaction raw materials,and 18Ni300 matrix composites with reinforcing phase content of 3 wt.%and 5 wt.%were prepared by ball milling and hot pressing sintering.By adjusting sintering temperature,reinforcing phase content,solution temperature,aging temperature and aging time,the microstructure analysis,phase identification and aging process of the composites were studied by scanning electron microscope（SEM）,electron probe microanalyzer（EPMA）,Rockwell hardness tester and X-ray diffractometer（XRD）.Hardness,compressive strength at room temperature,elastic modulus,friction and wear properties of the material were tested,and the strengthening and wear resistance mechanism were analyzed.Microstructure analysis shows that the microstructure of sintered 18Ni300 alloy and 3 wt.%and 5 wt.%18Ni300 matrix composites are single-phase martensite,but18Ni300 alloy contains a small amount of retained austenite.The matrix structure in the extruded and heat-treated 18Ni300 alloy,3 wt.%and 5 wt.%18Ni300 matrix composites are martensite,and when the aging temperature is higher than 550℃,there is reverse austenite.The morphology and distribution of reinforcing phase in sintered,extruded and heat-treated materials have not changed,needle-like TiB whiskers are in-situ generated,and granular TiB₂.After studying the preparation technology of composite materials,the best speed of ball milling and mixing powder is 220 rpm;The optimum sintering temperature of18Ni300 alloy is 1360℃,and the optimum sintering temperature of 3 wt.%and 5wt.%18Ni300 composites is 1225℃.The 18Ni300 powder was tested by DSC and DIL.the in-situ reaction temperature was 1235℃,and the phase transition starting and ending temperatures were 610℃and 748℃,respectively.The mechanical properties test results show that with the increase of sintering temperature,the compressive yield strength of sintered 18Ni300 composites increases.Compared with the sintered state,the hardness of the composites after hot extrusion treatment is improved by 5%-8%,and the elastic modulus is improved after hot extrusion treatment.After heat treatment,the hardness of 18Ni300 composites increased greatly.After solid solution treatment at 820℃/1h and aging treatment at 480℃/3h,the hardness of18Ni300 alloy,3 wt.%and 5 wt.%18Ni300 composites increased by 42%,36%and40%,respectively.After heat treatment,the change trend of compressive yield strength is opposite to that of hardness.In terms of hardness,the hardness value,compressive strength,elastic modulus and density tend to increase with the increase of the content of reinforcing phase.The results of friction and wear show that the wear resistance of 18Ni300composites with 3 wt.%and 5 wt.%ceramic phase is obviously higher than that of matrix alloy.The wear mechanism of matrix alloy is adhesive wear,and the wear mechanism of 3 wt.%and 5 wt.%18Ni300 matrix composites is abrasive wear.The wear-resistant mechanism of composites is that high-strength and high-hardness martensite matrix can provide work hardening,TiB2 particles can resist external pressure and lubricate the surface,and whiskers can transfer load to inhibit the cracking of the surface hardening layer.