Macro/microstructure evolution and mechanical properties of Ti33.3Al alloys by adding WC particles

In order to improve mechanical properties of binary TiAl alloys, Ti33.3Al (weight percent, hereafter in wt%) alloys with different WC particles content (1.5%, 3.0%, 4.5%, 6.0%, 7.5%) were prepared by vacuum arc melting. The phase constitution, macro/microstructure evolution and mechanical properties were investigated systematically. XRD results showed that WC disappeared and Ti2AlC phase appeared after adding WC particles because of WC reacting with Ti and Al. In addition, the lattice parameters of α2 phase increased due to the solid solubility of interstitial carbon atoms and substitutional tungsten atoms. For microstructure, rod-like Ti2AlC particles formed when WC content was more than 3.0%, and the length diameter ratio of Ti2AlC particles increased when WC content was 7.5%. It was found that the shape changing of Ti2AlC was in accordance with the morphology of lamellar colony, which indicated Ti2AlC firstly formed during solidification. The microstructure changed from coarse columnar to fine equiaxed and the average size of lamellar colony decreased from 189.7 to 66.5 µm with increasing WC content. Tungsten segregated and formed a little B2 phase in the lamellar colony when the WC content was more than 6.0%. Compressive testing showed that the strength and the strain were improved from 1847 to 2324 MPa and from 25.7% to 28.5%, respectively. The Vickers hardness of Ti33.3Al alloys was also improved by the addition of WC. The improvement of mechanical properties was caused by the grain refinement, solid solution of carbon and tungsten atoms, reinforcement of Ti2AlC phase and a little B2 phase.