Revealing the Effects of Friction Stir Processing on the Microstructural Evolutions and Mechanical Properties of As-Cast Interstitial FeMnCoCrN High-Entropy Alloy

The present study aims to investigate the effect of friction stir processing (FSP) on the microstructural evolutions and mechanical properties of a nonequiatomic interstitial high-entropy alloy (HEA). To achieve this, an as-cast FeMnCoCrN interstitial HEA undergoes FSP to modify the as-cast microstructure and investigate the resulting effects on mechanical properties. The grain size, sub-boundaries, martensite fraction, and accommodated strain exhibit a gradient from the base metal (BM) to the stir zone (SZ). As a result of FSP, the average grain size in the upper SZ is significantly decreased from approximate to 700 mu m in BM to 1.5 mu m, which is around 500 times finer than that of the BM. Furthermore, the martensitic transformation in a single metastable face-centered-cubic phase specifically occurs in the thermomechanical-affected and heat-affected zones. Continuous and geometric dynamic recrystallizations triggered by FSP lead to the development of a refined equiaxed microstructure. This gradient microstructure, in turn, plays a pivotal role in achieving significantly improved mechanical properties when compared to the as-cast microstructure. Remarkably, the yield strength doubles, the ultimate tensile strength increases from 548 to 852 MPa, and ductility increases by 16%. The present study deals with exploring the unique microstructural evolution and mechanical properties of a friction-stir-processed FeMnCoCrN nonequiatomic high-entropy alloy through various characterization techniques. The effect of friction stir processing along with nitrogen as a solute element on the phase stability of the metastable FCC matrix is also investigated.image (c) 2024 WILEY-VCH GmbH