Heat Treatment of In Situ Laser-Fabricated Titanium Aluminide

Abstract

Direct energy deposition (DED) via laser processing, operated under standard conditions with a localised shielding gas, is a potential method for the manufacture of the γ-TiAl alloy. The freedom of operation, which includes the production of components via in situ melting of elemental powders, makes this method economically attractive. The goal of this study was to optimise the mass flow rates that lead to gamma phase formation during laser in situ melting of Ti and Al. A 3 kW Nd:YAG laser was used to melt Ti and Al elemental powders. Single clads were produced on Ti6Al4V substrates under localised argon shielding. The samples were heat-treated to promote microstructural homogenization and to provide thermal stress relief, after which they were characterized. Lamellar and duplex microstructures were obtained; depending on the Al feed rate and heat treatment temperatures. The Vickers microhardness was found to be predominantly dependent on Al content and the amount of twinning present. X-ray diffraction detected a proportional increase in the intensity of the γ phase peak with an increase in Al content, while α2 peaks were dissolved and the twin γ-Ti3Al5 peaks diminished slightly. An alloy produced in this work achieved the target microstructure and properties associated with superior ductility and tensile strength in these materials, indicating that the technology has future potential in the production of Ti-Al materials for applications such as structural components or thermal barrier coatings.

Keywords

• γ-Ti-Al
• laser
• manufacture
• heat treatment
• microstructure