Superplastic Deformation Mechanisms of Superfine/Nanocrystalline Duplex PM-TiAl-Based Alloy

Abstract

Abstract:In this paper, the equiaxed superfine/nanocrystalline duplex PM-TiAl-based alloy with (γ + α 2 ) microstructure, Ti-45Al-5Nb (at %), has been synthesized by high-energy ball milling and vacuum hot pressing sintering. Superplastic deformation behavior has been investigated at 1000 • C and 1050 • C with strain rates from 5 × 10 −5 s −1 to 1 × 10 −3 s −1 . The effects of deformation on the microstructure and mechanical behaviors of high Nb containing TiAl alloy have been characterized and analyzed. The results showed that, the ultimate tensile strength of the alloy was 58.7 MPa at 1000 • C and 10.5 MPa at 1050 • C with a strain rate of 5 × 10 −5 s −1 , while the elongation was 121% and 233%, respectively. The alloy exhibited superplastic elongation at 1000 and 1050 • C with an exponent (m) of 0.48 and 0.45. The main softening mechanism was dynamic recrystallization of γ grains; the dislocation slip and γ/γ interface twinning were responsible for superplastic deformation. The orientation relationship of γ/γ interface twinning obeyed the classical one: (001) γ //(110) γ .

Creep behaviour of equiaxed fine-grain γ-TiAl-based alloy prepared by powder metallurgy

“…Microstructure of TiAl alloys significantly affects the high-temperature properties. The two-phase ( γ + α 2 ) alloys usually have better mechanical properties than single-phase γ alloys or α 2 alloys, because the uniformly distributed α 2 phase is acting as the reinforcement of γ phase [9,10], including the mechanisms of reinforcement of γ phase through α 2 interfaces [11,12]. TiAl alloys with such microstructure, which are commonly known as γ -TiAl base alloys, generally possess the best combination of room-temperature toughness and high-temperature strength [13].…”