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. (October 2022)

• Record Type: Journal Article
• Authors: Yang, Jieren; Wang, Xuyang; Dong, Chengli; Fu, Hengzhi
• Is Part Of: International journal of fatigue. Volume 163(2022)
• Publication Date: 2022-10
• Subjects: TiAl alloy -- Rotary-bending fatigue -- βo(ω) phase -- Thermomechanical instability -- Deformation behavior; Materials -- Fatigue -- Periodicals; Materials -- Fatigue; Periodicals; 620.1122
• DOI: 10.1016/j.ijfatigue.2022.106933
• Languages: English
• ISSNs: 0142-1123

Abstract

Graphical abstract: Rotary-bending fatigue tests of a Ti-43Al-8Nb-0.2W-0.2B alloy were performed at 800 °C under 325, 340, 355 and 370 MPa in atmosphere condition. Under HTRB fatigue, the phase transition of ωo → βo occurred and the newly formed βo phase is completely coherent with the pre-existing βo phase. Thermodynamic calculation revealed that a tensile stress could promote the phase transition of βo → ωo . The local recrystallization was found at lamellar colony boundary and grain interior, where is consisted of γ and ω grains. The deformation mechanisms of βo phase might be the dislocation glide on the 〈1 1 1〉{1 2 3} system. Highlights: The fatigue-induced instability of βo (ω) phase region was verified. The ωo → βo phase transformation is interpreted by thermodynamic calculation. The deformation mechanism of βo phase under HTRB was proposed. Abstract: Phase transformation and deformation behavior of the βo (ω) 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 °C under 325, 340, 355 and 370 MPa in atmosphere condition. The quasi-fatigue limit (σ-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 ωo → βo occurred and the newly formed βo phase is completely coherent with the pre-existing βo phase. Thermodynamic calculation revealed that a tensile stress could promote the phase transition of βo → ωo . The local recrystallization was found at lamellar colony boundary and grain interior, where is consisted of γ and ω grains. The deformation mechanisms of βo 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 ω phase was observed in the residual ωo phase and it may be a transition state in the phase transformation of ωo → βo .