Effect of Ti2AlC particles on the microstructure and elevated-temperature-deformation properties of g-TiAl alloys

Abstract

The -TiAl intermetallics with and without amount fractions x = 0.3 % of yttrium and with different carbon amount fractions ranging from 0.9 % to 1.6 % were prepared by vacuum-induction melting in a graphite crucible. Different amounts of carbon were obtained by varying the time of melting. The resulting samples had large rod-like carbides with volume fractions 0.6 % to 3.7 % Ti2AlC in the lamellar matrix consisting of the alternating lamellas of -TiAl and 2-Ti3Al phases. It was found that the grain size of the matrix decreases with the increasing volume fraction of Ti2AlC carbides from 430 μm to 35 μm. In addition, finer carbides with a similar composition were observed. Their size was below 1 μm and they appear mainly at the grain boundaries and also inside the lamellar grains. Compression testing revealed that all the samples had a relatively high yield strength at elevated temperature, from 917 MPa to 623 MPa at 600 °C and from 608 MPa to 547 MPa at 800 °C, but the best strength and the best yield strength were found for the sample with the lowest amount of the large rod-like Ti2AlC carbides. From these results it is concluded that the strengthening at an elevated temperature is a result of C in the solid solution and small carbide precipitates rather than of the rod-like Ti2AlC carbides.