Revealing the tempering embrittlement in a medium entropy alloy containing carbon atoms

In general, annealing treatment is frequently used to recover the ductility of high/medium entropy alloys after deformation. However, the present work demonstrates that the ductility of a CoCrNiVC medium entropy alloy could be substantially reduced after the tempering process, which is similar to the tempering embrittlement in some steels. Numerous carbides with chromium enrichment are formed at the shear bands and grain boundaries during tempering at 700 °C for 30 min. The carbides embedded at grain boundaries result in a localized strain concentration during plastic deformation, facilitating the nucleation of the micro-cracks. The segregation of carbon at the grain boundary decreases its cohesion energy, accelerating the propagation of cracks and the development of intergranular fracture.