Influence of SiC particles and post-heat treatment on the properties of Ti-6Al-4V-based surface nanocomposite fabricated by friction stir processing

Abstract

Friction stir processing was used to successfully fabricate a Ti-6Al-4V-based surface nanocomposite with a uniform dispersion of SiC reinforcement particles (FSP). Reinforced SiC particles showed good interfacial bonding with the matrix material. Microstructural modification after FSP and post-FSP heat treatment in terms of grain refinement and reinforcement behavior of SiC particles was investigated using an optical microscope (OM), scanning electron microscope (SEM), and electron back-scattered diffraction (EBSD). Microhardness test, Charpy impact test, and pin-on-disc wear test were carried out to measure the hardness, impact toughness, and tribological behavior of fabricated surface composites, respectively. Fully β-transformed microstructure comprising a mixture of fine basket-weave lamellar α/β and ultrafine martensite α′ was evident in the FSPed stir zone. The incorporation of SiC reinforcement resulted in additional microstructure refinement during FSP due to Zener pinning and particle-stimulated nucleation (PSN) caused by SiC particles. Nearly two-fold improvements in microhardness and wear resistance, whereas a slight but noteworthy improvement in impact toughness was observed. Enhancements in mechanical and wear properties were primarily ascribed to the combined effect of microstructural refinement, formation of martensite (α′), and dispersion strengthening (Orowan Mechanism).