In situ study of dynamic recrystallization and hot deformation behavior of a multiphase titanium aluminide alloy

Abstract

Hot-compression tests were conducted in a high-energy synchrotron x-ray beam to study in situ and in real time microstructural changes in the bulk of a β-solidifying titanium aluminide alloy. The occupancy and spottiness of the diffraction rings have been evaluated in order to access grain growth and refinement, orientation relationships, subgrain formation, dynamic recovery, and dynamic recrystallization, as well as phase transformations. This method has been applied to an alloy consisting of two coexisting phases at high temperature and it was found that the bcc β-phase recrystallizes dynamically, much faster than the hcp α-phase, which deforms predominantly through crystallographic slip underpinned by a dynamic recovery process with only a small component of dynamic recrystallization. The two phases deform to a very large extent independently from each other. The rapid recrystallization dynamics of the β-phase combined with the easy and isotropic slip characteristics of the bcc structure explain the excellent deformation behavior of the material, while the presence of two phases effectively suppresses grain growth.

Quantum Beam Science—Applications to Probe or Influence Matter and Materials

“…Generally, neutron beams are larger and penetrate further, while high-energy synchrotron X-rays are of high brilliance and focused. They enable, respectively, fine statistical averaging, as needed for texture analysis and quantitative phase analysis in even coarse-grained material [23], versus single and multiple-grain studies scanned locally in a poly-crystalline matrix [24]. The complementarity in scattering contrast is exemplified by titanium aluminides, where the Ti scattering length for neutrons is negative while Al is positive, emphasizing large structure factors for superstructure reflections that describe atomic order.…”

In Situ Characterization Techniques Based on Synchrotron Radiation and Neutrons Applied for the Development of an Engineering Intermetallic Titanium Aluminide Alloy

“…In TiAl alloys, for instance, the disordered β phase is known to improve hot workability at elevated temperatures [26,76,77], while the ordered β o phase has a negative impact on ductility at ambient temperature [78], as well as on creep strength at service temperature [29]. Consequently, the experimental determination of ordering temperatures is of great interest.…”

“…In transmission geometry, Debye-Scherrer rings will, for example, appear on an area detector. If a monochromatic beam impinges only on a small number of crystallites, be it due to a small beam cross-section or due to a coarse-grained microstructure, information on individual crystallites can be extracted from the resulting reflection spots, which sit on the according positions on the Debye-Scherrer rings [77]. In this regard, three-dimensional X-ray diffraction microscopy (3DXRD) has emerged as a powerful technique enabling the tracking of reflections of individual grains over time [100][101][102][103].…”

In Situ High-Energy X-ray Diffraction during Hot-Forming of a Multiphase TiAl Alloy

“…AT plots can reveal some unique, direct information which cannot be gathered by other methods, for example, different stages of texture formation during deformation or different predominant deformation mechanisms [29]. AT plots are suitable for single-phase materials, like Mg alloys [30], and multiphase alloys, as long as no overlapping reflections are used, and reflections with a low multiplicity, like 002-α.…”

“…After 30% deformation, see Figure 4c,f, the intensity accumulation at preferred orientations is clearly visible which indicates the formation of the deformation texture. A simple and effective way to illustrate the crystallographic evolution during deformation is through the use of azimuth angle vs. time plots (AT plots) as introduced by Liss et al [20,29]. Such diagrams are constructed from a specific unrolled ring that is repeatedly plotted from the sequence of diffraction ring images that are collected over increasing time.…”