Thermomechanical instability and deformation behavior of βo(ω) phase region in a Ti-43Al-8Nb-0.2W-0.2B alloy under high-temperature rotary-bending fatigue

Phase transformation and deformation behavior of the beta(o)(omega) phase region under high-temperature rotary-bending (HTRB) fatigue condition are studied in the current work. Rotary-bending fatigue tests of a Ti-43Al-8Nb-0.2W-0.2B (at.%) alloy were performed at 800 degrees C under 325, 340, 355 and 370 MPa in atmosphere condition. The quasi-fatigue limit (sigma(-1)) was calculated as 355 MPa [4]. Microstructures were examined using scanning and transmission electron microscopy (SEM &TEM) and thermodynamic calculation was adopt to interpret the phase transition mechanisms. Under HTRB fatigue, the phase transition of omega(o) -> beta(o) occurred and the newly formed beta(o) phase is completely coherent with the pre-existing beta(o) phase. Thermodynamic calculation revealed that a tensile stress could promote the phase transition of beta(o) -> omega(o). The local recrystallization was found at lamellar colony boundary and grain interior, where is consisted of gamma and omega grains. The deformation mechanisms of beta(o) phase might be the dislocation glide on the < 1 1 1 >{1 2 3} system. The dislocations have a strong tendency for slip localization into slip bands. Disordered omega phase was observed in the residual omega(o) phase and it may be a transition state in the phase transformation of omega(o) -> beta(o).

Automated summary

This study investigates the phase transformation and deformation behavior of the beta(o)(omega) phase region under high-temperature rotary-bending fatigue condition. It is found that under this condition, the omega(o) phase transforms into the beta(o) phase, and the newly formed beta(o) phase is coherent with the pre-existing beta(o) phase. Additionally, tensile stress promotes the phase transition of beta(o) to omega(o). The presence of disordered omega phase in the residual omega(o) phase suggests it may be a transition state in the phase transformation from omega(o) to beta(o).