Anomalous effect of nitrogen flow ratio on mechanical properties of NbMoTaW:(N,O) medium entropy alloy films

Abstract

In this work, nanocrystalline NbMoTaW:(N,O) thin films were prepared by magnetron sputtering. The effect of nitrogen flow ratio [RNN2/(N2 + Ar)] ranging from 0 to 0.5 on the microstructure and mechanical properties of as-deposited films is investigated. It is found that the microstructure and the mechanical properties are both dependent on RN. The structures of NbMoTaW:O films and NbMoTaW:(N,O) films are body-centered cubic and face-centered cubic, respectively. With increasing RN, the hardness of the film reduces first and then increases, showing an anomalous effect of RN on the mechanical properties compared with previous results. The anomalous effect origins from the phase transformation, dislocation density and grain boundary hardening. The surface roughness and residual stress havelittle influence on the mechanical property.