Influence Of NbC Additions On Microstructure And Mechanical Properties Of Coated Cermet Insert Materials Bonded By High-entropy Alloy

Owing to the excellent wear resistance,relatively low fraction coefficient and superior chemical stability,Ti(C,N)-based cermets have been broadly applied in many fields,especially in machi ning industry and wear resistance parts.However,when confronted with the more and more severe service condition such as dry machining or high-temperature,the performance degradation of conventional binders produces a great limitations of application.The excellent combination of high temperature hardness and thermodynamic stability makes the high entropy alloys(HEA)a potential candidate to substitute the conventional binder.However,most HEA bonds have insufficient wettability with respect to the ceramic phase,resulting in relatively poor comprehensive mechanical properties of Ti(C,N)-HEA cermets at room temperature,thereby weakening the high-speed cutting of Ti(C,N)-HEA cermets and wear resistance.In view of the above problems,this paper adopts Co Cr Fe Ni(HEA)as the new binder phase,and uses NbC to modify Ti(C,N)-HEA cermet,and researchs the influence of NbC additions on microstructure and wear resistance of Ti(C,N)-HEA cermets.At the same time,to further improve the wear resistance of Ti(C,N)-HEA cermet,PVD coating technology is used to deposit TiAlN coating on the surface of cermet,and revealed the high-speed cutting and high-temperature wear mechanism of the coated Ti(C,N)-Co Cr Fe Ni(HEA)cermets,which lay the foundation of the theory and application in the early stage for the development of coated Ti(C,N)-HEA cermets with good comprehensive mechanical properties at room temperature and excellent high-temperature performance.By optimizing the content of NbC,Ti(C,N)-15%Co Cr Fe Ni(HEA)-18%WC-6%Mo₂C-x%NbC cermet substrates were successfully prepared.Different NbC content will change the"core-ring"microstructure of Ti(C,N)-HEA cermet.This change is mainly due to the slow diffusion effect of the Co Cr Fe Ni HEA binder phase and the grain nucleation position caused by the addition of NbC change.Adding 3 wt.%NbC can optimize the comprehensive mechanical properties of Ti(C,N)-HEA cermet.When the addition amount of NbC is 3 wt.%,the relative density of the cermet is98.13%,the hardness is 1853HV,the strength is 1544MPa,and the fracture toughness is 9.93MPa·m^1/2.To further improve the wear resistance of cermets,PVD coating technology is used to deposit a relatively smooth and dense columnar crystal TiAlN coating on the surface of cermets.The coating thickness ranges from 0.72?m to 1.37?m,the grain sizes are 17nm-27nm,the coating hardness are 3800-4100HV_0.02,and the average bonding force of the coatings are 41N-79N.The amount of NbC added in the substrate has a certain effect on the grain size and internal stress state of the coating,which changes the hardness of the TiAlN coating,thereby affecting the bonding force of the coating.When the NbC content in the substrate is 9 wt.%,the coating hardness is the highest 4062 HV_0.2.The average bonding forces of the 4 groups coatings are 62.75N,78.5N,71.8N and 41.5N,respectively.The TiAlN coating of 3 wt.%NbC Ti(C,N)-HEA cermet has better overall performance,with a coating thickness of 1.37?m,a grain size of 17.49 nm,a bonding force of 78.5N,and a hardness of 3910HV_0.2.The results of dry-cutting GCr15 steel test and high-temperature friction and wear test show that:the inserts with 3 wt%NbC has the lowest flank wear value and shows better wear resistance when processing GCr15 steel.Additionally,the minimum coefficient of friction and minimum wear rate obtained at 3 wt%NbC additions are0.198,4.14×10^-6mm³/N·m,respectively.Based on the uniform microstructure and excellent mechanical properties,due to the existence of a stable friction lubricating layer,the high temperature wear resistance of 3 wt.%NbC cermet is further improved.After the coating process,the flank wear value and wear rate of the coated Ti(C,N)-HEA cermet with 3 wt%NbC are significantly less than that of the uncoated Ti(C,N)-HEA cermet with 3 wt%NbC content and coated Ti(C,N)-Ni cermet samples,and the synergistic effect of the substrate and TiAlN coating endow it with excellent cutting wear resistance.