Study On Strengthening And Toughening Of Ti(C,N)-Based Cermets By Pre-Solid Solution Treatment Of Binders

Ti（C,N）cermet is widely used in cutting tools because of its excellent red hardness,wear resistance,fracture toughness and chemical stability,while Ti（C,N）cermet,as a substitute material for WC-CO cemented carbides,has relatively low transverse fracture strength and toughness.Because the tool material is generally used in high temperature environment,improving the oxidation resistance is to increase its service life guarantee.Therefore,it is of great significance to improve the strength,toughness and chemical stability of cermets at high temperature.Cermets are mainly composed of hard phases that provide high hardness and metal phases that bond hard particles.However,at present,Ni or Co is generally used in the metal phase,and the study of other metals as bonding phases is not common.In this paper,Ni base solid solution powder with different elements were firstly prepared,and then these solid solution powders were used as bonding phase to sintered Ti（C,N）cermet.The effect of solid solution on microstructure and properties of cermets was analyzed by XRD,SEM,EDS and TEM.The conclusions are as follows:Firstly,the Ni base solid solution powders with different Ti contents were prepared by mechanical alloying.The results show that relatively fine and almost spherical Ni-Ti alloy powders can be prepared by mechanical alloying.At the early stage of ball milling,Ni and Ti undergo cold welding,and the particles are large and flake.At this time,the distance between Ni and Ti atoms is shortened,and it is easy to produce solution.At 24 h of ball milling,the solution of Ti in Ni is basically complete.The Ni-Ti solid solution prepared by mechanical alloying can not only improve the wettability of ceramic particles,but also refine Ti（C,N）ceramic particles in the sintering process.In the bonding phase,and the solution in advance active elements can improve the wettability,reasons are as follows:（1）improve sinter bonding phase of alloy element content,reduce the solid-liquid surface tension,（2）to form a relatively complete,uniform thickness of ring forms,（3）in the metal bonding phase and nanometer thickness of adsorption layer is formed between ceramic particles.In addition,the adsorption layer can hinder the diffusion process and the surrounding high-density dislocation,which can hinder the growth of ceramic particles and refine particles.When 3 wt.%Ti is dissolved in the bonded phase in advance,the grain size is fine,the wettability is the best,the flexural strength of cermet reaches 2356.8MPa,the fracture toughness reaches 14.33 MPa·m^1/2,and the hardness is 88 HRA.With the increase of the solution amount,more carbides are dissolved in the bonded phase,and the relative density decreases.Bending strength and toughness decrease,hardness increases.Ti（C,N）base ceramics were prepared by Ni-Ti-Cr solid solution and Ti（C,N）base ceramics.The relatively small and nearly spherical Ni-Ti-Cr alloy powder prepared by mechanical alloying can refine cermet ceramic particles and improve the mechanical properties and oxidation resistance of cermet.The surface microstructure of Ti（C,N）cermet is typical core/ring structure,and the fracture mode is a mixed fracture combination of large ceramic particles transgranular fracture and small particles pulled out dimple fracture.When the mass ratio of Ni:Ti:Cr is 91:3:6,the comprehensive performance of cermet is the best,bending strength,fracture toughness and hardness are 2120.3 MPa,15.41 MPa·m^1/2 and 88.9 HRA,respectively.In the cycle oxidation experiment,the oxide layer formed is more dense,both the oxidation weight gain and the peel peeling are relatively less.After 60 h cyclic oxidation of Ti（C,N）cermet,the oxide skin is dominated by Ni O,with a small amount of Ni Cr₂O₄ and Ni Ti O₃.Ti O₂ is mainly embedded in the Grain boundary of Ni O,and then Cr element is enriched in the interior,which can effectively absorb oxygen atoms and play a role of layer to layer connection and transition.In the cyclic oxidation process,when the oxide film falls off,Ni and Cr will absorb oxygen atoms and quickly form a dense oxide film,which will hinder the further oxidation of cermets.