Effects Of SiC Particles And Whiskers On The Microstructure And Properties Of Ti(C,N)-based Cermets

Ti（C,N）-based cermets have high hardness and good oxidation resistance at high temperature.It is widely used in cutting tools,molds and wear-resistant parts.However,compared with cemented carbide,its lack of strength and toughness.In addition,due to its work in the face of high temperature,high friction and high corrosion and other harsh environment,so in addition to mechanical properties,also should consider its high temperature oxidation resistance,wear resistance and corrosion resistance.SiC particles（SiC_p）have good chemical stability,low thermal expansion coefficient and excellent wear resistance,generally can be used to enhance the strength of ceramic materials.The SiC whiskers（SiC_w）have the advantage of high elastic modulus,which can be used to improve the toughness of ceramic materials.In this paper,SiC_p and SiC_w were added to Ti（C,N）-based cermets by powder metallurgy process.The effect of addition on microstructure and properties of cermets was systematically studied.In this paper,the effects of different SiC_p content on microstructure,mechanical properties and high temperature oxidation resistance of 32 wt.%Ni cermets were studied.The experimental results show that the cermets consists of black core phase,white inner rim phase,gray outer rim phase and gray white binder phase.The bending strength,hardness and fracture toughness of cermets increase first and then decrease with the addition of SiC_p.The cermets containing 2.0 wt.%SiC_p have the best comprehensive mechanical properties,and their bending strength,hardness and fracture toughness are 2370.3 MPa,88.5 HRA and 15.2 MPa.m^1/2,respectively.Compared with the cermet without SiC_p,the cermet increases by 21.5%,2.3%and15.8%,respectively.The main reason is that the addition of SiC_p inhibits the dissolving and precipitation reaction of hard phase particles,which reduces the size of black core phase and refines the grain size.Too much SiC_p will destroy the integrity of the"core-rim"structure.The cermet with 2.0 wt.%SiC_p has fine grain and complete structure of black core,white inner rim and gray outer rim,and has good relative density.In the high temperature oxidation experiment of cermets at 800℃,it is found that the addition of SiC_p can effectively improve the high temperature oxidation resistance of cermets,which is mainly due to SiC_p can reduce the cracking of the oxide film.Prevent O element from entering the cermet matrix to avoid oxidation of the internal matrix.Subsequently,the synergistic effect of SiC_p and SiC_w on the microstructure and properties of cermet was systematically studied by adding different mass ratios of SiC_p and SiC_w to Ti（C,N）-based cermets when the total SiC was 2.0 wt.%.The experimental results show that with the increase of SiC_p/SiC_w,the density and bending strength increase,the hardness increases,and the fracture toughness decreases slightly.When the amount of SiC_p is 1.5 wt.%and the amount of SiC_w is0.5 wt.%,the comprehensive mechanical properties of cermets are the best.The bending strength,hardness and fracture toughness of cermets are 2520.8 MPa,88.0HRA and 16.56 MPa.m^1/2,respectively.Compared with the cermets without SiC_p,it increased 29.3%,1.7%and 26.2%,respectively.This is mainly attributed to the smallest grain size,the most complete"core-rim"structure and the most uniformly distributed binder phase.The effect of SiC_p on grain refinement of cermets is stronger than that of SiC_w.The addition of SiC_p can significantly refine the grain size of cermets,obtain a complete"core-rim"structure,and obviously improve the flexural strength of cermets.The whisker bridging and whisker pull-out of SiC_w can effectively improve the fracture toughness of cermet.Finally,the effects of SiC_p on structure and properties of 25 wt.%Ni cermets were studied.The experimental results show that the cermets with 1.0 wt.%SiC_p have excellent comprehensive mechanical properties,and their flexural strength,hardness and fracture toughness are 2020 MPa,90.5 HRA and 12.2 MPa.m^1/2,respectively.The wear resistance of cermets increases first and then decreases with the addition of SiC_p,and cermets containing 1.0 wt.%SiC_p have the best wear resistance.The corrosion resistance of cermets decreases with the addition of SiC_p.The main reason is that with the addition of SiC_p,the content of alloying elements in the binder phase decreases,the white rim phase and white particles rich in W and Mo appear,and the existence of holes reduces the corrosion resistance of cermets.