Microstructural investigation of WC reinforced Ti-6Al-4V matrix surface composite fabricated via additive friction stir processing

Abstract

Additive friction stir processing (AFSP) was effectively utilized to fabricate defect-free WC reinforced surface composite on Ti-6Al-4V substrate. Uniform distribution of fragmented WC particles was achieved in the composite layer. Completely β transformed microstructure, containing lamellar α/β structure coupled with ultrafine martensite α′ was observed in stir zone of FSPed Ti-6Al-4V. The addition of WC reinforcement during AFSP has led to additional microstructure refinement; as a consequence of Zener pinning and particle stimulated nucleation caused by fragmented WC particles. More than two times improvement in hardness and wear resistance was noted in WC reinforced Ti-6Al-4V (surface composite) fabricated by AFSP compared to base metal Ti-6Al-4V. Despite a little drop in hardness value, post FSP heat treatment of WC reinforced surface composite has brought about a significant increase in impact toughness.