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

Sadiq Abiola Raji; Abimbola Patricia Idowu Popoola

doi:10.1016/j.heliyon.2024.e25519

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

Heliyon. 2024 Feb 2;10(4):e25519. doi: 10.1016/j.heliyon.2024.e25519. eCollection 2024 Feb 29.

Authors

Sadiq Abiola Raji¹, Abimbola Patricia Idowu Popoola¹

Affiliation

¹ Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, P.M.B. X680, Pretoria, South Africa.

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-Ti₅Si₃ phases lead to solid precipitation hardening and solution strengthening at the grain boundaries. The XRD analysis confirmed γ, α₂, α, β_o and ζ-Ti₅Si₃ phases occurrence in the as-built alloys. The LENS fabricated alloys demonstrated improved wear properties and marginally change in corrosion behavior after heat treatment.

Keywords: Beta phase (β-TiAl phase); Heat treatment; Laser engineered net shaping (LENS); Laser in-situ alloying; Microhardness; Titanium aluminide alloys; Titanium silicide (ζ-Ti5Si3).