Characteristics of laser In-situ alloyed titanium aluminides coatings

Abstract

The use of titanium aluminides as high temperature materials in the aerospace and automobile industries is becoming a reality since their early research and development in 1955. Their mechanical properties at elevated temperatures make them attractive in spite of their poor ductility at room temperature. The progress on their production using powder metallurgy processes seem to be significantly positive; at least on microstructure tailoring and mechanical properties. This research work sought to study the in-situ alloying of the elemental Ti and Al using laser metal deposition (LMD) process. The effects of laser power on the microstructure evolution, composition and micro-hardness were evaluated on the as-produced TiAl coatings. The results indicated that lamellar microstructures formed at 1.0, 1.3 and 1.5 kW laser powers while at 2.0 kW a refined dendritic structure was observed. The phase composition by XRD concluded the presence of TiAl(sub3), TiAl, Ti(sub3)Al(sub5), and the oxide phases of Ti and Al. Generally, the Ti(sub3)Al(sub5) phase is indicative of high temperature process during TiAl processing while TiAl(sub3) is known as a twinning phase to TiAl. The average HV(sub0.3) values for 1.0, 1.3, 1.5 and 2.0 kW coatings were 327(sub0.3), 281(sub0.3), 333(sub0.3) and 367(sub0.3), respectively. These hardness values are indicative of the presence of TiAl/TiAl(sub3).