Deformation of lamellar γ-TiAl below the general yield stress

Abstract

The occurrence of plasticity below the macroscopic yield stress during tensile monotonic loading of nearly lamellar Ti-45Al-2Nb-2Mn(at%)-0.8vol% TiB 2 at both 25 °C and 700 °C, and in two conditions of lamellar thickness, was measured by digital image correlation strain mapping of a remodelled Au surface speckle pattern. Such initial plasticity, not necessarily related to the presence of common stress concentrators such as hard particles or cracks, could occur at applied stresses as low as 64 % of the general yield stress. For a same applied strain it was more prominent at room temperature, and located as slip and twinning parallel to, and near to or at (respect.

Creep-Induced Phase Instability and Microstructure Evolution of a Nearly Lamellar Ti–45Al–8.5Nb–(W, B, Y) Alloy

“…4b, the interfaces are kind of unsharp in the bright-field electron micrographs, which is due to that the dislocations were assembled at the α 2 /γ and γ/γ interfaces. During the creep test, the deformation occurred mainly in the γ lamellae [12,18] and these dislocations were generated from the lamellar interfaces [19]. This suggests that the stress concentration induced by lamellar interfaces have caused the interfaces to be both high energy sites and stress concentrators, which are consistent with the result reported by Edwards et al [18].…”

“…3). As also described in the literature [18][19][20], the glide of ordinary dislocations with Burgers vectors b= < 101] and b =< 112] is the primary deformation mode. From the selected area diffraction (SAD) pattern of the area A, the adjacent γ lamellae are in a true-twin relationship, which is the same as in the as-cast microstructure.…”

“…During the creep test, the deformation occurred mainly in the γ lamellae [12,18] and these dislocations were generated from the lamellar interfaces [19]. This suggests that the stress concentration induced by lamellar interfaces have caused the interfaces to be both high energy sites and stress concentrators, which are consistent with the result reported by Edwards et al [18]. When the stress concentration was enhanced, microcracks would be generated at interfaces between the lamellar plates, leading to the splitting of lamellar plates (as shown in Fig.…”

An Advanced TiAl Alloy for High-Performance Racing Applications

“…The UTS of the undeformed condition behaves contrary to the measured R p0.2 , as shown in Table 1, and exhibits a moderate increase followed by a decrease at 700 • C and 800 • C. This effect is attributed to the higher elongation and, therefore, a higher UTS is obtained. The following decrease with increasing temperature of the UTS as well as R p0.2 in all conditions is ascribed to the higher mobility of thermally activated dislocations and the possibility of grain boundary sliding [44][45][46][47][48]. A clear tendency towards higher yield strength values with increasing deformation degree was observed, as shown in Figure 2a.…”

“…This effect is attributed to the higher elongation and, therefore, a higher UTS is obtained. The following decrease with increasing temperature of the UTS as well as R p0.2 in all conditions is ascribed to the higher mobility of thermally activated dislocations and the possibility of grain boundary sliding [ 44 , 45 , 46 , 47 , 48 ].…”