The interaction of borides and longitudinal twinning in polycrystalline TiAl alloys. (November 2017)

• Record Type: Journal Article
• Authors: Edwards, Thomas Edward James; Di Gioacchino, Fabio; Muñoz-Moreno, Rocío; Clegg, William John
• Is Part Of: Acta materialia. Volume 140(2017)
• Page Start: 305
• Page End: 316
• Publication Date: 2017-11
• Subjects: Titanium aluminides -- Deformation twinning -- Electron backscattering diffraction (EBSD) -- Digital image correlation; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2017.08.055
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: In this paper the occurrence of twinning parallel to the lamellae during compression at 700 °C of a polycrystalline nearly lamellar commercial γ-TiAl alloy, Ti-45Al-2Nb-2Mn(at%)-0.8 vol% TiB2, has been studied and shown to lead to the formation of cracks at colony boundaries. However, the occurrence of this longitudinal twinning mode was less common by at least a factor of ten in tests at room temperature. Furthermore, the debonding of colony boundaries caused by the shear strain of longitudinal twinning is exacerbated when the same γ-TiAl variant favourably oriented for twinning occurs repeatedly in the lamellar structure. This effect was caused by the preferential nucleation of certain γ-TiAl variants in the presence of TiB2 boride reinforcement. It is shown that the boride additions increase the probability of double, triple or even higher order multiply stacked γ-variants. This increases the resulting shear strain that must be accommodated and hence the probability of crack nucleation. Graphical abstract: Image 1