Effect of carbon addition on the microstructure and mechanical properties of Nb-30Ti-18Al alloy

The Nb-30Ti-18Al alloys doped with the amounts of 0 at%, 1 at% and 5 at% carbon were prepared by arc melting and annealing. The effects of carbon addition on the microstructure and mechanical properties of Nbss/Nb3Al in situ composites as well as the strengthening mechanisms were investigated. The results showed that during annealing at 1200 °C, supersaturated Nbss decomposed and Nb3Al phase precipitated in C-free alloy, while carbide decomposed with the precipitation of Nb3Al in C-doped alloys. Furthermore, the orientation relationship of Nb3Al phase and the surrounding (Nb, Ti)C was observed in Nb-30Ti-18Al-5C (NA5) alloy. Additionally, with increasing the carbon content, the compressive strength of alloys at high temperature were improved significantly ascribed to the occurrence of solid solution and volume fraction increase of strengthen phase, while the fracture toughness decreased due to the volume fraction decrease of Nbss.