Microstructural, microhardness and electrochemical properties of heat-treated LENS in-situ synthesized Ti–Al-x(Mo, Si) alloys

Abstract

So as to explore the opportunity of property enhancement of TiAl-based alloys, studies of microstructural evolution after processing with heat treatments are to be expected. Therefore, the objective of this present study is to investigate how additions of silicon (Si) and molybdenum (Mo) as alloying elements affects the microstructure, microhardness, corrosion behaviour, and wear properties of Ti–Al-x(Mo, Si) alloys made from constituent elemental powders through in-situ alloying laser engineered net shaping (LENS) technique. The influence of the feed rate of Si powder (0.1 rpm, 0.2 rpm and 0.3 rpm) on Ti–Al-xMo was studied at 0.1 rpm and 0.2 rpm Mo feed rate, respectively. Heat treatment at 1200 °C for 15, 30, and 60 min was performed after LENS in-situ alloying, and furnace cooling (FC) was the final step. The microstructure of the produced alloys was analyzed via Scanning electron microscopy (SEM) fitted with energy dispersive spectroscopy (EDS). Using a tribometer and a potentiodynamic polarization test, the alloys' wear characteristics and corrosion behaviour were studied. Based on the results, it was noticed that microhardness values decrease after heat treatment for all the samples produced. Owing to the combined effects of Mo and Si, both the β _o-TiAl and ζ -Ti ₅Si ₃ phases lead to solid precipitation hardening and solution strengthening at the grain boundaries. The XRD analysis confirmed γ, α ₂, α, β _o and ζ-Ti ₅Si ₃ phases occurrence in the as-built alloys. The LENS fabricated alloys demonstrated improved wear properties and marginally change in corrosion behavior after heat treatment.