High-temperature deformation behavior of a gamma TiAl alloy—Microstructural evolution and mechanisms

Abstract

The present investigation was carried out in the context of the internal-variable theory of inelastic deformation and the dynamic-materials model (DMM), to shed light on the high-temperature deformation mechanisms in TiAl. A series of load-relaxation tests and tensile tests were conducted on a fine-grained duplex gamma TiAl alloy at temperatures ranging from 800°C to 1050°C. Results of the load-relaxation tests, in which the deformation took place at an infinitesimal level ( ഡ 0.05), showed that the deformation behavior of the alloy was well described by the sum of dislocation-glide and dislocation-climb processes. To investigate the deformation behavior of the fine-grained duplex gamma TiAl alloy at a finite strain level, processing maps were constructed on the basis of a DMM. For this purpose, compression tests were carried out at temperatures ranging from 800°C to 1250°C using strain rates ranging from 10 to 10 Ϫ4 /s. Two domains were identified and characterized in the processing maps obtained at finite strain levels (0.2 and 0.6). One domain was found in the region of 980°C and 10 Ϫ3 /s with a peak efficiency (maximum efficiency of power dissipation) of 48 pct and was identified as a domain of dynamic recrystallization (DRx) from microstructural observations. Another domain with a peak efficiency of 64 pct was located in the region of 1250°C and 10 Ϫ4 /s and was considered to be a domain of superplasticity.

Comparison of titanium silicide and carbide reinforced in situ synthesized TiAl composites and their mechanical properties

“…They found that it is due to BrittleeDuctile transition in the alloy and is dependent on the strain rate. The transition temperature corresponding to the strain rate used in this study is approximately 750 C. The occurrence of pronounced softening would point to the likely occurrence of dynamic recrystallization, with the fine-grained microstructure developed being similar to those reported by others [12,13]. These alloys showed limited deformability up to 600 C, but they became considerably softer and highly deformable as the temperature increased to 800 C. Agote et al [5] reported similar findings through their test in tension on alloys having matrix composition (Ti-48Al-2Cr-2Nb) that exhibited pronounced softening only at high temperature of 750 C.…”

High-temperature deformation and grain-boundary characteristics of titanium alloys with an equiaxed microstructure

“…Meanwhile, the strength of the dislocation slip barrier was reported to decrease considerably as such microstructural changes occurred. A similar phenomenon has also been observed for a TiAl-base alloy [39], whose grain size becomes finer with imposed strain due to dynamic recrystallization. After straining, the relative amount of dislocation-glide increased and that of dislocation climb decreased.…”

Hot Deformation Behavior and Microstructural Evolution of PM Ti43Al9V0.3Y with Fine Equiaxed γ and B2 Grain Microstructure

“…Similar results in terms of processing maps were reported for other TiAl alloys [50][51][52][53]. The hot processing map of Ti45Al8Nb2Cr2Mn0.5Y [54] indicated that the deformation mechanism for a higher efficiency of power dissipation (η ≥ 0.55) was DRX, corresponding to a temperature range of 1000-1200 • C and a strain rate range of 0.001 s −1 -0.01 s −1 at 50% strain.…”