Formation and temporal evolution of modulated structure in high Nb-containing lamellar γ-TiAl alloy
Formation and temporal evolution of modulated structure in high Nb-containing lamellar γ-TiAl alloy
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DOI：
10.1016/j.actamat.2018.11.041
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发表时间：
2019-02
期刊：
影响因子：
9.4
通讯作者：
G. Ren;C. Dai;W. Mei;Jian Sun-;S. Lu;L. Vitos
中科院分区：
文献类型：
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作者：
G. Ren;C. Dai;W. Mei;Jian Sun-;S. Lu;L. Vitos
利用透射电子显微镜（TEM）结合第一性原理研究了Ti− 45 Al − 8. 5 Nb层状合金中调制结构的形成和时间演化。结果表明，富Nb的O相作为调制结构的组成成分，在α_2层中在650 °C以下是稳定的。O相变体的形貌从初始退火时的低体积分数的薄板状转变为长时间退火后的高体积分数的矩形/正方形，并且由于它们的弹性相互作用，在变体与两个正交惯习面的相交处出现重新转变的α2，以下称为α2-β晶。600 °C时Nb在O相与α 2之间的分配系数约为2。由O相的生长动力学推导出Nb在α 2层中的扩散系数约为（1.3 ± 0.2）× 10− 22 m2 s − 1。O相对α 2层片和γ/（α2+O）层片组织具有显著的沉淀硬化效应，其原因是由于α2→O相变产生的弹性应变能细化了α 2层片，并在调制层片和相邻的γ相之间引入了界面。
The formation and temporal evolution of the modulated structure in a lamellar γ-based Ti−45Al−8.5Nb alloy have been investigated by transmission electron microscopy (TEM) in combination with first-principles theory in this work. The results show that the Nb-rich O phase as a constituent of the modulated structure is thermodynamically stable below 650 °C in the α2lamellae. The morphology of the O phase variants changes from thin plate-like shape with a low volume fraction at initial annealing to rectangle/square shape with a high volume fraction after a prolonged annealing, and the retransformed α2, named as α2-ІІhereafter, emerges at intersections of the variants with two orthogonal habit planes due to their elastic interactions. The partitioning coefficient of Nb between the O phase and α2is about 2 at 600 °C. The diffusion coefficient of Nb derived from growth kinetics of the O phase is about (1.3 ± 0.2) × 10−22m2s−1in the α2lamellae. Significant precipitation hardening effect of the O phase has been revealed for the α2lamellae and γ/(α2+O) lamellar microstructure, which is supposed to be attributed to refining the α2lamellae associated with elastic strain energy from the α2→O phase transformation and introducing the interface between the modulated lamella and adjacent γ phase.