Densification mechanism of Ti-Al-Nb alloys pressurelessly sintered from Al-Nb master alloy powder for cost-effective manufacturing

Pressureless sintering is a cost-effective method to fabricate shaped Ti-Al-Nb alloy components in the aerospace industry. However, the sintering pores in the Ti-Al-Nb alloys led to inferior mechanical properties when using elemental Al powder as the raw material. By completely replacing the Al powder with the Al-Nb master alloy powder, the pores were substantially reduced in the pressurelessly sintered Ti-22Al-17.5Nb (at %) alloy, accompanied by the improvement of the tensile strength. We investigated the densification me-chanisms by implementing the isothermal quenching experiments at 500-1200 degrees C. In the Ti/Al/Nb compact, the pores originated from the melting of Al and the Kirkendall effect at the interfaces of the Ti3Al and Nb particles. The transitions of Ti + 3Al-* TiAl3 and alpha 2-* B2 determined the porosity of the sintered alloy. In the Ti/Al-Nb/Nb compact, the Kirkendall pores at the Ti/Al3Nb interfaces were reduced since the diffusion of Al in Ti was retarded. The accelerated diffusion of Nb in Ti3Al suppressed the Kirkendall effect at the Nb/Ti3Al interfaces and promoted the formation of the B2 phase. The ripening of the B2 grains further contributed to the densification of the sintered alloy.(c) 2022 Elsevier B.V. All rights reserved.