Metal Additive Manufacturing Of Titanium Aluminides From Blended Elemental Powder

Abstract

Titanium aluminide is considered a key material for high performance gas turbines for aircraft engines, manufacturing of engine valves and a variety of automotive applications. This is due to the attractive high oxidation resistance and strength retention of the Titanium aluminide alloy at high temperatures. The limitations of the conventional methods of manufacturing Titanium aluminide alloy components with precise geometry and near net shape functional characteristics have limited the usefulness of the Titanium aluminide alloys. However, additive manufacturing (AM) methods such as direct metal laser sintering (DMLS) have proven to have the capacity to uncover the full potential of the Titanium aluminide alloy by producing components with complex shapes. The aim of this study was to determine the feasibility of using a blend of elemental Ti and Al powders in a DMLS system, to make parts that have comparable or better geometric, functional and microstructural properties to that of the conventionally processed titanium. In this, study Ti6Al and Ti46Al alloys were investigated, using blends of elemental powders of Ti and Al. Single tracks were manufactured and single layers were built using a wide range of process parameters to determine the optimum process parameters for use in building good Titanium aluminade parts. Finally, two three-dimensional (3D) samples were built from Ti6Al (low Al content) and Ti46Al (high Al content). The Ti6Al sample was built at the optimum parameters of laser power 150W and scanning speed 1.2m/s and the Ti46Al sample was built at the optimum parameters of 170W laser power and 0.1m/s scanning speed as identified in this study. The Ti46Al 3D sample was not a success and further analysis could not be completed as the 3D sample collapsed. The Ti6Al sample was a success, showing good overlapping of the single layers forming the 3D part. Good penetration depth of the single layers was achieved, complete melting and homogeneity of the powder were achieved, and finally, a good dense 3D part with α+β microstructure was achieved. A 2% loss of Al in the produced 3D part of Titanium aluminide alloy, which was attributed to the differences in thermo-physical properties between the powders (Ti and Al). The process of rescanning improved the homogeneity and promoted complete melting of the powder. Improving the mixing method of the powders prior to in-situ alloying improved the homogeneity of the alloy by reducing Al rich zones in the Ti matrix. A 2% Al loss allowance should be considered in further studies to ensure that the resultant alloy would meet the required compositional specification.