Laser micro in situ alloying of c-Ti46.8Al1Cr0.2Si with Manganese

Abstract

Titanium alloys have two primary phases (a + ß) that are attributed to the a-stabiliser (aluminium) and ß-stabiliser (niobium). The latter stabilisers shift a-phase to higher temperature while the former stabilisers shift the ß-phase to lower temperatures. To extend their scope of application, (a + ß)-phase titanium alloys can be micro-alloyed with ß-eutetic elements (Mn, Cr, Si, Co etc) to form intermetallic compounds which are typically referred to as titanium aluminides (Ti-Al). Several intermetallic alloys can be formed in the Ti-Al phase diagram but only (a2)-Ti3Al and ( )-TiAl are stable and of relevance to structural engineering since they can be used in industries spanning across energy, aerospace and tissue-engineering. In this study, a castable -Ti46.8Al1Cr0.2Si pre-alloyed powder, was micro-alloyed with Mn in order to examine if it can improve its tensile properties. When 1–2 at. % Mn is added to Ti-Al alloys, it is able to increase ductility, reduce oxidation resistance and shift the (a2 + )/ to the titanium side and decrease the Al content in the -phase. To effectively ascertain these effects Mn feed rates were varied from 0.2 to 1.0 rpm during the micro-alloying of -Ti46.8Al1Cr0.2Si through in-situ laser deposition to form -Ti46.8Al1Cr0.2Si-(xMn). The produced clads were characterised for chemistry and microstructure using scanning electron microscope. Results concluded that Al content decrease with an increase in Mn from 56 at. % to 49 at. %. Mn of 10.16 g/min had similar properties to the non-Mn alloyed sample. Moreover, it was shown in this work that laser processing decreased the tensile and yield strength of the alloy when compared to the as-cast in previous studies, and that 2.69 g/min and 10.16 g/min are lower and upper Mn values when ductility of the master alloy is to be improved.