In situsynchrotron high-energy X-ray diffraction analysis on phase transformations in Ti–Al alloys processed by equal-channel angular pressing

Abstract

Mixtures of 47-Al and 53-Ti powders (atomic %) have been consolidated using back pressure equal-channel angular pressing starting with both raw and ball-milled powders. In situ synchrotron high-energy X-ray diffraction studies are presented with continuous Rietveld analysis obtained upon a heating ramp from 300 K to 1075 K performed after the consolidation process. Initial phase distributions contain all intermetallic compounds of this system except Al, with distribution maxima in the outer regions of the concentrations (alpha-Ti, TiAl(3)). Upon annealing, the phase evolution and lattice parameter changes owing to chemical segregation, which is in favour for the more equilibrated phases such as gamma-TiAl, alpha(2)-Ti(3)Al and TiAl(2), were followed unprecedentedly in detail. An initial delta-TiH(2) content with a phase transition at about 625 K upon heating created an intermediate beta-Ti phase which played an important role in the reaction chain and gradually transformed into the final products.

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

“…Controversially, a large pressure dependence has been reported by Errandonea et al [48], which Zhang et al refute and interpret as a response to deviatoric stresses, occurring in their diamond-anvil cell. In alloys, especially titanium aluminides, lattice parameters and c/a ratios of both γ-and α 2 -phases depend strongly on the composition of each phase, which varies as a function of temperature and segregation in multi-phase systems [31,57,58]. Increasing 2c/a ratios of {1.60333, 1.60432, 1.60476} with increasing Al content in single-phase α 2 Ti-{24, 28.4, 33.3}Al have been measured by Dubrovinskaia et al [59].…”

“…Such an fcc-Ti structure has been predicted by ab initio simulations [60,61], but it is energetically unstable and has not been experimentally observed. As a theoretically-postulated phase, it can be asymptotically used to interpret experimental data, such as for interpolating lattice parameters by Vegard's law [57]. Lattice parameters (a,b) and lattice strain (c,d) with linear fits y = a + bp; axis ratios (e,f); super-structure peak intensities, plotting ratios of super/main peak at pressure, normalized to the super/main peak at ambient pressure (g); and phase-fractions (h, superimposed to e).…”

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

“…For in situ investigations of the phase transformation behavior of titanium aluminides, high-energy X-ray diffraction (HEXRD) has evolved into a powerful and versatile tool [48,50,51,[63][64][65][66]. At synchrotron radiation sources, a white X-ray beam is produced by the deflection of charged particles, either electrons or positrons, by means of a bending magnet or an insertion device, i.e., a wiggler or an undulator, as shown in Figure 4 [67].…”

Estudo <i>in situ</i> da solubilização e do envelhecimento da liga &beta;-metaestável Ti-5Al-5Mo-5V-3Cr-1Zr usando difração de raio-X com luz síncrotron de alta energia

“…Tal efetividade e acuracidade permitem a obtenção de dados únicos e esclarecedores com respeito aos fenômenos de transformação da fase, motivo pelo qual essa técnica vêm ganhando força no segmento metalúrgico [28,[28][29][30]. Além disso, a literatura apresenta poucos resultados detalhados sobre a cinética de transformação de fase in situ na liga Ti-5Al-5Mo-5V-3Cr-1Zr em função da temperatura e tempo de envelhecimento.…”

“…Alguns trabalhos merecem destaque pela relevância e pioneirismo do uso de luz síncrotron na caracterização ligas metálicas em termos de processamento mecânico, termomecânico e transformação de fase, como os de Reimers et al [76], Liss e colaboradores [28][29][30]77,78,81], Malinov e colaboradores [24,82], Aeby-Gautier e colaboradores [7,23,27], Requena e colaboradores [5,11,66,75] e Jones et al [6] e Pinto e colaboradores [83][84][85] . Por meio da técnica de HEXRD, Aeby-Gautier et al [7] observou a formação da fase α" na liga…”