Superplastic deformation mechanisms of high Nb containing TiAl alloy with (α2 + γ) microstructure
Superplastic deformation mechanisms of high Nb containing TiAl alloy with (α2 + γ) microstructure
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DOI：
10.1016/j.intermet.2016.06.003
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发表时间：
2016-08-01
期刊：
影响因子：
4.4
通讯作者：
Bouzy, Emmanuel
中科院分区：
文献类型：
--
作者：
Cheng, Liang;Li, Jinshan;Bouzy, Emmanuel
本文研究了一种具有细（α 2 + γ）组织的高铌TiAl合金Ti-43.5Al-8 Nb-0.2W-0.2B（at.%）的超塑性变形行为。在850 ℃ ~ 1050 ℃温度范围内，以10（-4）s（-1）的初始应变速率进行热拉伸试验。分析了其力学性能和组织演变规律。此外，为了深入了解变形机制，系统地研究了普通（非超塑性）和超塑性条件下变形过程中织构的演变。结果表明，该合金在1000 ℃下具有良好的超塑性延伸率，应变速率敏感指数m约为0.5，表观激活能Q（app）约为390 KJ/mol。显微组织分析表明，当合金在850 ℃变形时，晶粒明显细化，小角度晶界比例显著增加。同时，织构的特征在于平行于拉伸方向的双纤维成分。所有这些观察结果表明，位错滑移和孪生机制。然而，如果在超塑性条件（1000 ℃）下变形，发现在拉伸过程中，微观结构在晶粒尺寸、形态和晶界特征方面相当稳定，但观察到初始纤维织构（由包套锻造引起）的连续弱化。这被认为是晶界滑动机制的指示。此外，还同时出现了（+）形变织构，虽然这种织构很弱。通过对变形动力学和组织演变的详细讨论，认为滑移/孪晶协调的晶界滑移是超塑性变形的主要机制，γ晶内位错攀移是超塑性变形的速率控制步骤。(C)2016由Elsevier Ltd.出版
In this paper, superplastic deformation behaviour of a high Nb containing TiAl alloy with fine (alpha 2 + gamma) microstructure, Ti-43.5Al-8Nb-0.2W-0.2B (at.%), has been examined and studied by means of hot tension from 850 degrees C to 1050 degrees C under an initial strain rate of 10(-4) s(-1). The mechanical behaviour and microstructure evolution have been characterized and analyzed. Besides, to gain insight into deformation mechanisms, the texture evolution during deformation at ordinary (non-superplastic) and superplastic conditions has been systematically studied. The results showed that, the alloy exhibited impressive superplastic elongation at 1000 degrees C with a strain-rate sensitivity exponent (m) of about 0.5 and an apparent activation energy (Q(app)) value of about 390 KJ/mol. The microstructural characterization showed that, when the alloy was deformed at ordinary condition (850 degrees C), severe grain refinement occurred and the fraction of low-angle grain boundary notably increased. Meanwhile, the textures were characterized by and double-fiber components parallel to the tensile direction. All these observations suggested a dislocation slip and twinning mechanism. However, if deformed at the superplastic condition (1000 degrees C), it was found that the microstructure was fairly stable in terms of grain size, morphology and grain boundary characteristics during tension, but a continuous weakening of the initial fiber texture (resulted from canned-forging) was observed. This was believed to be an indication of grain boundary sliding mechanism. Moreover, the deformation texture ( + )-though is very weak-was simultaneously appeared. According to a detailed discussion on the deformation kinetics and microstructure evolution, it was believed that the slip/twinning-accommodated grain boundary sliding was responsible for superplastic deformation and the dislocation climb inside of gamma grains was the rate-controlling step. (C) 2016 Published by Elsevier Ltd.