Study On Preparation And Properties Of Novel Ti(C,N)-based Cermet Coated Inserts With High-entropy Alloy Binder

Nowadays,the demands for difficult-to-machine high-performance alloys and the requirements for cutting technique are enhancing.Research on high-performance cutting tool materials is also a trend of the times.Due to low density,high hardness,high chemical stability,high wear resistance,low friction coefficient,and the composition of Ti and Ni,Ti(C,N)-based cermets are regarded as alternative materials for cemented carbides.However,lack of comprehensive mechanical properties and high temperature performance is the main bottleneck restricting the wide application of Ti(C,N)-based cermet cutting tools.In recent years,most of the related researches have been optimized by refining structure of hard phase and complicating composition of hard phase.However,the research on binder optimization is relatively limited and the results are not ideal.Besides,traditional binders Co/Ni are unstable in acidic and high-temperature cutting environments.The cutting inserts are easy to chip,and high-speed cutting performance is poor.Therefore,the search for new Ti(C,N)-based cermet binder is of great significance.Last but not least,tool coating technology is also one of the key technologies to improve the overall performance of tools.At present,more than 90%of cutting tools for high-precision machine tools in developed countries are coated.Therefore,it is also significant to study the matching between coatings and Ti(C,N)-based cermet substrates.This study systematically takes the three key technologies in the field of cutting tool manufacturing(cutting tool materials,coating technology and cutting processing)as the starting point.Innovatively,five-component high-entropy alloy(HEA)CoCrCuFeNi is used as a new binder to solve the shortcomings of traditional binders.The traditional industrial sintering method is used to fabricate Ti(C,N)-HEA cermet tool material with high comprehensive performance.And the effects of CoCrCuFeNi HEA binder on microstructure,basic mechanical properties and high-temperature friction properties of Ti(C,N)-based cermet are studied.Additionally,the coatability of Ti(C,N)-HEA matrix material is studied by physical vapor deposition(PVD)and chemical vapor deposition(CVD)technology under the mature coating process and coating material experimental conditions of cemented carbide.Finally,the cutting behavior and wear mechanism of PVD and CVD coated Ti(C,N)-HEA cermet tools are studied by cutting experiments on H13 die steel.The novel Ti(C,N)-15HEA cermet exhibits excellent microstructure and comprehensive mechanical properties.Compared with conventional Ni binder,CoCrCuFeNi HEA binder has a huge superiority to the inhibition of core-rim grain growth and the formation of submicron white-core grains.Owing to the sluggish diffusion effects,CoCrCuFeNi can inhibit the growth of grains and promote the growth of small(Ti,W,Mo,Ta)(C,N)particles as independent nucleation cores into white core grains.The novel cermet Ti(C,N)-15HEA exhibits higher comprehensive mechanical properties than the traditional cermet Ti(C,N)-15Ni.The hardness is significantly improved.Hence,CoCrCuFeNi HEA binder can significantly improve hardness of cermet while maintaining similar transverse rupture strength and toughness of traditional cermet Ti(C,N)-15Ni.This is also unmatched by traditional binders Ni/Co.The high hardness can be attributed to the solid solution strengthening effect of fine grain strengthening and the high hardness CoCrCuFeNi bonding phase.The good toughness benefits from a large number of submicron white-core grains and less precipitation of brittle phases.Compared with typical black-white-gray core-rim grain,the white-core grain has a simple microphase structure.In other words,the number of interfaces and the complex stresses at the interface are relatively small.Therefore,its toughness is improved.CoCrCuFeNi binder can significantly improve high-temperature friction reduction and wear resistance of Ti(C,N)-based cermet.The inter-steel friction coefficient of Ti(C,N)-15HEA cermet is much lower than that of traditional Ti(C,N)-15Ni cermet.And its wear resistance is2.4-2.6 times of Ti(C,N)-15Ni cermet.The wear mechanism of Ti(C,N)-15HEA cermet at high temperature is mainly the formation and delamination of oxide layer.Under the premise of excellent microstructure,Co Cr Fe Ni Cu binders can adequately exert high-entropy effects at high temperatures.On the one hand,it promotes the formation of a stable lubricant layer.On the other hand,it realizes the high-strength combination with hard phase to avoid generation of abrasive particles.These significantly improve high-temperature friction and wear properties of Ti(C,N)-based cermets.Ti(C,N)-HEA cermet has excellent coatability of PVD TiAlN and CVD TiN/Ti CN/Al₂O₃/TiN.Under the same test method,it can obtain tool coating similar to Ti(C,N)-Ni substrate and can be used.For two TiAlN coatings on the surfaces of Ti(C,N)-Ni and Ti(C,N)-HEA cermet substrates,the microstructures present dense columnar crystal structure without obvious defects.Comparatively,the TiAlN coating on the Ti(C,N)-HEA substrate has finer grains.This is because more nucleation grains can be obtained on the Ti(C,N)-HEA cermet substrate with a finer microstructure,and finally a finer coating can be formed.Moreover,a large number of binder elements such as Cr,Cu,Fe,Ni in the Ti(C,N)-HEA matrix diffuse into the TiAlN coating.Among them,Cu element shows the highest content and diffusion distance in TiAlN coating.The content and diffusion distance of Fe and Ni in TiAlN coating are the second,and Cr is the lowest.Due to the effect of fine-grain strengthening and solid solution strengthening,the hardness of the TiAlN coating on the Ti(C,N)-HEA cermet substrate is relatively higher,reaching 36.97 GPa.The bonding strength of TiAlN coatings on Ti(C,N)-Ni and Ti(C,N)-HEA cermet substrates are both HF1.For CVD TiN/Ti CN/Al₂O₃/TiN coatings,when coated on different substrates,the preferred orientation of each phase shows some differences.The Ti CN and Al₂O₃grains in the CVD coating of Ti(C,N)-HEA cermet substrate are relatively finer.Each layer of the five-layer coating is well connected without obvious defects such as cracks and peeling.Furthermore,Ti(C,N)-HEA cermet's binder elements,such as Co,Cr,Cu,Fe,Ni,diffuse into the CVD multilayer coating.Among them,the diffusion degree of Cu element is the strongest,followed by Co,Cr,Ni,and the diffusion degree of Fe element is the weakest.Due to fine-grain strengthening effect,hardness of the CVD multilayer coating on Ti(C,N)-HEA cermet substrate is slightly higher than that of coating on Ti(C,N)-Ni substrate,reaching 22.62 GPa.The bonding strength of TiN/Ti CN/Al₂O₃/TiN multilayer coatings on Ti(C,N)-Ni and Ti(C,N)-HEA cermet substrates are both HF1.At different cutting speeds(100?150 and 200 m/min),both uncoated and coated Ti(C,N)-15HEA cermet inserts have better cutting wear resistance than the corresponding Ti(C,N)-15Ni cermet inserts.The wear mechanisms of uncoated Ti(C,N)-HEA cermet tools are mainly adhesive wear,diffusion oxidation wear and slight abrasive wear.The wear mechanisms of PVD-coated Ti(C,N)-HEA cermet tools are mainly adhesive wear,abrasive wear and slight diffusion oxidation wear.The main wear mechanisms of CVD-coated Ti(C,N)-HEA cermet tools are:adhesive wear and slight abrasive wear.