Influence of NbC additions on microstructure and wear resistance of Ti(C,N)-based cermets bonded by CoCrFeNi high-entropy alloy

Abstract

Ti(C,N)-based cermets bonded by CoCrFeNi high-entropy alloy (HEA) were reinforced via adding NbC. The microstructure, mechanical properties, cutting performance and high-temperature wear resistance of the cermets were investigated in detail. Due to the sluggish diffusion effect of HEA binder, the fine bright-coreless grains exist in cermet without NbC. The increased addition of NbC causes a increase of the proportion of bright-coreless grains resulted from the change of nucleation sites. The higher relative density resulted from the increased wettability of CoCrFeNi HEA binder to ceramic phase. The hardness increased significantly due to the fined grains and maximized solid solution strengthening effect of CoCrFeNi HEA binder. The fracture toughness enhanced because of the bright coreless-complete rim grains with the less lattice strain. A good comprehensive mechanical properties of cermets was obtained at 3 wt% NbC additions with the relative density of 98.13%, the hardness of 1853 HV and fracture toughness of 9.93 MPa m1/2. Moreover, a small amount of NbC additions may decrease the friction coefficient and improve wear resistance of cermet inserts during machining the GCr15 bearing steel. Additionally, on the basis of uniform microstructure and superior hardness, the high-temperature wear resistance of cermet with 3 wt% NbC was further improved due to the existence of stable lubricant tribolayers. The corresponding average friction coefficient and wear rate are 0.198, 4.14 × 10−6 mm3/N·m, respectively.