Microstructure and mechanical properties of Ti-45Al-2W-xC alloys

The microstructure and mechanical properties of five alloys with nominal compositions of Ti-45Al-2W-xC (in at. %), where x is ranging from 0.4 to 2.0 at.%, were studied. The alloys were prepared by vacuum induction melting in graphite crucibles, followed by centrifugal casting into a graphite mould. The as-cast alloys were subjected to hot isostatic pressing and heat treatment consisting of solution annealing, cooling at a constant rate and stabilisation annealing. The microstructure of the heat-treated alloys consists of equiaxed alpha 2(Ti3Al) + gamma(TiAl) lamellar grains surrounded by gamma grain boundaries with a small amount of beta/B2 particles. The alpha 2-alpha 2 interlamellar spacing lambda decreases with increasing carbon content until a solubility limit of carbon is achieved. The increase in carbon content above the solubility limit leads to the formation of primary Ti2AlC particles during solidification and an increase in the amount of gamma phase at grain boundaries. Vickers microhardness of lamellar grains depends on the carbon content and interlamellar spacing lambda. The studied Ti-45Al-2W-0.8C and Ti-45Al-2W-1.2C alloys show improved creep resistance at 800 degrees C compared to that of the reference carbon-free TiAl-W and carbon-containing TiAl-Nb based alloys with fully lamellar, nearly lamellar, convoluted or pseudo-duplex microstructure.