Materials & Design (Jun 2022)
The subsurface deformed region and superficial protective tribo-oxide layer during wear in a non-equiatomic CoCrFeNiV high entropy alloy
Abstract
In the present work, the tribological performance of V10Cr10Fe45Co30Ni5 high entropy alloy (HEA, at%) and its relationship with the subsurface deformed area and the superficial tribo- layer were investigated. After dry sliding in reciprocation motion at applied loads of 2–15 N, surface and subsurface regions of the samples were investigated using SEM and TEM analyses, respectively. At an applied load of 2 N, dislocation activity was the subsurface deformation mechanism. The superficial depth-dependent gradient ultrafine microstructure containing the BCC phase decorated with the retained FCC phase, as well as mechanical nano-twins were formed when the applied load was increased to 5 N. By further increase in applied load (10 N), these twins were replaced with elongated FCC /BCC grains. At an applied load of 15 N, a friction-induced heterogeneous microstructure including two individual regions of extremely ultrafine and ultrafine grains was detected in the subsurface region of the worn sample. The simultaneous effects of grain refinement, dislocation-mediated plasticity, and martensitic phase transformation, along with hetero-deformation-induced strengthening, enhanced the hardenability of the subsurface during sliding wear. The formation of the protective superficial tribo-oxide layer triggered by the mechanical support of the substrate resulted in the outstanding tribological performance of the V10Cr10Fe45Co30Ni5 HEA.
