Effect of Ta and W Additions on Microstructure and Mechanical Properties of Tilt-Cast Ti-45Al-5Nb-2C Alloy

The effect of Ta and W additions on microstructure and mechanical properties of tilt-cast Ti-45Al-5Nb-2C (at.%) alloy was investigated. Three alloys with nominal composition Ti-45Al-5Nb-2C-2X (in at.%), where X is Ta or W, were prepared by vacuum induction melting in graphite crucibles followed by tilt casting into graphite moulds. The microstructure of the tilt-cast alloys consists of the alpha(2)(Ti3Al) + gamma(TiAl) lamellar grains, single gamma phase, (Ti,Nb,X)(2)AlC particles with a small amount of (Ti,Nb,X)C, and beta/B2 phase identified only in W containing alloy. The EDS analysis shows that Ta segregates into the carbide particles and reduces dissolution of Nb in both (Ti,Nb,Ta)C and (Ti,Nb,Ta)(2)AlC phases. The alloying with W reduces Nb content in both carbide phases and leads to stabilisation of beta/B2 phase in the lamellar alpha(2) + gamma regions. The alloying with Ta and W does not affect the volume fraction of the carbide particles but influences their size and morphology. While the alloying with Ta and W has no significant effect on Vickers hardness and the indentation elastic modulus of the studied alloys, the addition of Ta affects the nanohardness and elastic modulus of the (Ti,Nb,Ta)(2)AlC phase. The addition of W significantly increases the Vickers microhardness of the lamellar alpha(2) + gamma regions.

Automated summary

The addition of Ta and W has significant influence on the microstructure and mechanical properties of tilt-cast Ti-45Al-5Nb-2C alloy. Ta segregates into carbide particles and reduces Nb dissolution, while W stabilizes the beta/B2 phase in the alpha(2) + gamma regions and significantly increases Vickers microhardness.