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首页> 外文期刊>Scripta materialia >CHANGE IN Al CONCENTRATION PROFILE RELATED TO THE D0_(19)->L1_0 STRUCTURAL CHANGE IN Ti-Al ALLOYS
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CHANGE IN Al CONCENTRATION PROFILE RELATED TO THE D0_(19)->L1_0 STRUCTURAL CHANGE IN Ti-Al ALLOYS

机译：Ti-Al合金中与D0_（19）-> L1_0结构变化有关的Al浓度分布变化

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摘要

A precipitation reaction is one of the important phenomena in the phase transformation of alloys. A key factor of the reaction is normally the long-range diffusion of atoms occurring in the matrix. Therefore, the kinetics of the precipitation reaction is of interest when the matrix contains a condition that suppresses atomic diffusion. An example of such a case is the L1_0 precipitation reaction in the D0_(19) matrix, which occurs in the hcp->D0_(19)+L1_0 structural change of Ti-Al alloys (1)-(4). The D0_(19)->L1_0 structural change is a change between substitution-type ordered structures, accompanying a change in the Al concentration. Because atomic diffusion generally does not take place so quickly in ordered structures, the mechanism of the L1_0 precipitation in the D0_(19) matrix is worthy of interest.Recently, we have examined the features of the hcp->D0_(19)+L1_0 structural change of Ti-38 approx 40 at. percent Al alloys by transmission electron microscopy (5).and have observed that the structural change is accompanied by the appearance of both the B_(19) metastable state having a band-like shape in the D0_(19) matrix and the subsequent lattice-destructed (LD) state (5). The D0_(19)+L1_0 lamellar structure forms as an equilibrium state as a result of the crystallization of the region into the L1_0 structure. The change can thus be described as hcp->D0_(19)+B_(19)->D0_(19)+LD->D0_(19)+L1_0. An important feature of the LD region is that it has a two-dimensional character both morphologically and crystallographically, which originates from the anisotropy of the D0_(19) structure (6).It is obvious that the kinetics of the precipitation reaction occurring in Ti-Al alloys is different from that of normal reactions. Although amorphization as an equilibrium transition, referred to as inverse melting, has been found in some alloys (7, 8), lattice destruction in the case of Ti-Al alloys is a unique feature. In this paper, we describe the change in the Al concentration profile together with the structural change from hcp to D0_(19)+L1_0 lamellar structures. The chemical compositions of both the B_(19) and the LD regions as well as that of the D0_(19) matrix, all of which appear during the structural change in a Ti-40 at. percent Al alloy, were measured by analytical electron microscopy. On the basis of the experimental data, we discuss not only the role of the B_(19) metastable state in the formation of the LD state but also that of the Al concentration profile for the stability of the LD state in the present reaction.
机译：沉淀反应是合金相变中的重要现象之一。反应的关键因素通常是基质中发生的原子的远距离扩散。因此，当基质包含抑制原子扩散的条件时，沉淀反应的动力学是令人关注的。这种情况的一个示例是D0_（19）基质中的L1_0沉淀反应，该反应发生在Ti-Al合金（1）-（4）的hcp-> D0_（19）+ L1_0结构变化中。 D0_（19）-> L1_0结构变化是取代型有序结构之间的变化，伴随着Al浓度的变化。由于原子的扩散通常不会在有序结构中发生得如此迅速，因此值得关注D0_（19）矩阵中L1_0的沉淀机理。最近，我们研究了hcp-> D0_（19）+ L1_0的特征Ti-38的结构变化约为40 at。 ％的铝合金通过透射电子显微镜（5）观察到，结构变化伴随着在D0_（19）基体中出现带状形状的B_（19）亚稳态和随后的晶格-破坏（LD）状态（5）。 D0_（19）+ L1_0层状结构由于该区域结晶成L1_0结构而形成为平衡状态。因此，该变化可以描述为hcp-> D0_（19）+ B_（19）-> D0_（19）+ LD-> D0_（19）+ L1_0。 LD区的一个重要特征是它在形态和晶体学上都具有二维特征，这是由于D0_（19）结构的各向异性（6）引起的，很明显，Ti中发生了沉淀反应的动力学。 -铝合金不同于正常反应。尽管在某些合金（7、8）中发现了非晶化作为一种​​平衡转变（称为逆熔化），但在Ti-Al合金的情况下晶格破坏是其独特之处。在本文中，我们描述了Al浓度分布的变化以及从hcp到D0_（19）+ L1_0层状结构的结构变化。 B_（19）和LD区域以及D0_（19）基质的化学成分均在Ti-40 at的结构变化期间出现。通过分析电子显微镜测量铝合金的百分含量。根据实验数据，我们不仅讨论了B_（19）亚稳态在LD态形成中的作用，而且还讨论了Al浓度分布对于本反应中LD态稳定性的作用。

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