Tribological investigations of wear resistant layers developed through EDA and WEDA techniques on Ti6Al4V surfaces: Part II – High temperature

Abstract

This work investigates the potential of electrical discharge machining assisted alloying (EDA) and wire-electrical discharge machining assisted alloying (WEDA) techniques in developing tribo-adaptive layers on Ti6Al4V (Ti64) surfaces. The bare Ti64 (BTi64), electrical discharge machined and alloyed Ti64 (ETi64), and wire-electrical discharge machined and alloyed Ti64 (WETi64) specimens are subject to in-situ wear testing at high-temperature conditions (200 °C, 400 °C, and 600 °C). The SWR and CoF curves of the ETi64 follow reverse trends, with the former demonstrating a decrement with the rise in temperature. The WETi64 specimens develop phenomenal wear resistance at 200 °C and 400 °C (due to excessive formation of protective oxides) but possess similar wear response to that of BTi64 during dry sliding at 600 °C (assisted by layer spalling and delamination). The material removal mechanism of BTi64, ETi64, and WETi64 specimens shift from abrasive wear to delamination, composite wear (abrasive + oxidative) to oxidative wear, and oxidative wear to delamination, respectively, with increment in temperature during dry sliding at low load conditions (50 N). For ETi64, the recast layer (RL) over the substrate aided in achieving improved tribological characteristics by imparting stability to the developed oxides (TiO, TiO2, Ti8O15, and Fe2O3) at elevated temperatures. In the EDA process, the high carbon diffusion into the RL and low cooling rates led to the formation of hard phases in the form of carbides (TiC and Ti24C15) and microstructural transitions to ∝p and α′-phases, respectively, improving the wear-resistant characteristics of the substrate.