Evolution of Metastable α₂ Phase in a Quenched High‐Nb‐Containing TiAl Alloy at 800 °C

Abstract

Fast cooling from high temperatures is a common way in heat treatments and hot processing, which could introduce excess metastable α2 phase in the microstructure. Herein, the evolution of the metastable α2 phase in a water‐quenched Ti–45Al–8.5Nb–(W, B, Y) alloy from different single‐phase regions is experimentally studied. After water quenching from the β single‐phase region, Widmanstätten α2, as well as residual βo, γ grains form from β phase and thin γ laths in α2 phase are observed. However, the water‐quenched microstructure from the α single‐phase region consists of equiaxed α2 grains, residual βo, and massive γ phase. When annealing the quenched samples at 800 °C, similar microstructural evolutions are found in both samples quenched from different temperatures. 1) α2 phase transform into α2/γ nanolamellar structure immediately. 2) Recrystallization and discontinuous coarsening occur at the colony boundaries. 3) The nanometer‐scale γ/γT lamellae transformed from α2 grains are also unstable, which merge into thicker γ lamellae, and the interfaces of coarsened γ lamellae become curvy and blurry.

Effects of Solidification Rates on Microstructure Refinement and Elemental Distribution of Ti44Al6Nb1.0Cr2.0V0.1B0.15Y Alloy by Rapid Solidification

“…Referring to previous literature, [9,22,23] the transformation of Ti44Al6Nb1.0Cr2.0V0.1B0.15Y alloy follows L ! L þ β !…”

Peritectic Solidification Kinetics and Mechanical Property Enhancement in a Rapidly Solidified Ti–48 at% Al–8 at% Nb Alloy via Hierarchical Twin Microstructure

“…Many metallic materials undergo peritectic reaction during solidification, such as Ti–Al, Fe–Ti, Ni–Zr, and Cu–Sn alloys and YBa 2 Cu 3 O 7 superconductors. [ 12,13 ] For a peritectic reaction, to begin with, the primary phase precipitates primitively, followed by the formation of the peritectic phase, which is accomplished by reactions between the primary phase and the liquid phase. The peritectic reaction is considered to be controlled by solute diffusion, which cannot proceed thoroughly, especially when the alloy melt is being rapidly solidified.…”