Microstructure and properties of Ti(C, N)–TiB2–FeCoCrNiAl high-entropy alloys composite cermets

Abstract

The FeCoCrNiAl high-entropy alloys (HEA) was used as binder of the Ti(C, N)–TiB2 composite cermets. The Ti(C, N)–TiB2–FeCoCrNiAl HEA composite cermets were successfully fabricated by mechanical alloying (MA) and vacuum hot-pressing sintering (VHPS) at different sintering temperatures. The microstructure, room-temperature hardness, fracture toughness, bending strength, high-temperature hardness and oxidation behavior were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Vickers hardness testing, indentation method, three point bending method, high-temperature vacuum hardness testing and cyclic oxidation. For the Ti(C, N)–TiB2-HEA composite cermets, apart from Ti(C, N) and TiB2 phases, also a minority Fe2B were detected in the XRD patterns. TEM observation revealed that the structure of the HEA binder was a solid solution where the Ti(C, N) and TiB2 were tightly bound. The Ti(C, N)–TiB2 composite cermets with a Ni/Co binder was selected as a reference. The experimental results indicated that the composite cermets with the HEA binder possesses excellent oxidation resistance. This is attributed to the formation of a continuous and dense external oxide scale and TiO2 layer that effectively impede inward oxygen transport, which leads to a remarkable improvement in the oxidation resistance. The Ti(C, N)–TiB2-HEA composite cermets sintered at 1500 °C showed excellent fracture toughness of 7.9 ± 0.1 MPa.m1/2. And the Ti(C, N)–TiB2-HEA composite cermets sintered at 1550 °C showed excellent hardness and bending strength of 1977.3 ± 20 HV10 and 768.6 ± 20 MPa, respectively. The high-temperature hardness of the HEA binder composite cermets was 993.7 ± 30 HV20, which was superior to the Ni/Co binder value of 668.1 ± 30 HV20 at 1000 °C.