Microstructural tailoring and property enhancement via friction stir processing of additively manufactured steel and Ti6Al4V alloy

Abstract

Friction stir processing (FSP) has emerged as a transformative solid-state technique for enhancing the mechanical performance and microstructural integrity of metallic materials, particularly in the context of additive manufacturing (AM). This study demonstrates the effectiveness of FSP as a post-processing strategy for two distinct AM systems: wire arc additive manufacturing (WAAM) of low-carbon steel and selective laser melting (SLM) of Ti6Al4V alloy. In the case of WAAM fabricated steel, FSP significantly refined the coarse dendritic microstructure into ultrafine equiaxed grains, resulting in a 21%–24 % increase in hardness and enhanced tensile properties at the overlapping regions. Similarly, for SLM fabricated Ti6Al4V, FSP eliminated the columnar prior- β grains and residual porosity, yielding a homogenous α + β structure with improved strength-ductility balance and reduced anisotropy. These improvements were attributed to the dynamic recrystallization, conversion of low-angle to high-angle grain boundaries, and homogenization of phase constituents induced by FSP. Despite challenges such as tool wear and fixturing complexity, the study confirms that FSP can reliably bridge the performance gap in AM components by healing solidification defects, mitigating anisotropy, and tailoring the local microstructure. The findings position FSP as a versatile and scalable post-processing technique, crucial for advancing high-performance, application-ready components in aerospace, biomedical, and structural applications.