The shape memory effect in equiatomic TaRu and NbRu alloys
The shape memory effect in equiatomic TaRu and NbRu alloys
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DOI：
10.1016/s1359-6462(98)00303-0
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发表时间：
1998-09-15
影响因子：
6
通讯作者：
Vandermeer, RA
中科院分区：
文献类型：
--
作者：
Fonda, RW;Jones, HN;Vandermeer, RA
形状记忆合金能够在变形后恢复到其原始形状，方法是通过热弹性转变（单向效应）加热解孪合金，或通过卸载发生应力诱导相变的合金（超弹性效应）。 Chang 和 Read 首次在 AuCd 合金中观察到形状记忆效应 (SME) (1)，但直到 Buehler 等人开发出 NiTi 合金后才观察到形状记忆效应 (SME)。形状记忆合金的重要商业应用成为可能 (2, 3)。目前的 NiTi 合金通常仅限于室温约 200 C 内的应用，另外两种商业上重要的形状记忆合金 Cu-Zn-Al 和 Cu-Al-Ni 合金也是如此 (4)。然而，这些当前的形状记忆合金并不适合燃气轮机、火箭发动机、汽车发动机和核反应堆环境中设想的潜在高温 SME 应用，这些应用需要相稳定性和高于 300 C 的转变温度。NiAl (5, 6)、(Ni, Pt) Ti (7) 和 (Ni, Pd) Ti (8) 合金均已在高温下展示了 SME（形状记忆转变高于 250 C），但只有 (Ni, Pd) Ti 合金具有足够有吸引力的机械性能，足以维持当前作为潜在高温形状记忆合金的兴趣 (9)。 NiAl 在室温下是脆性的，并且被限制在低于约 300°C 的温度，以避免负责形状记忆效应的相降解 (9, 10)，而 (Ni, Pt)Ti 在转变温度高于约 300°C 的组合物中变脆 (7)。我们在本文中报告了基于铌-钌和钽-钌的近等原子成分的新型形状记忆合金的开发。这些合金表现出超过 1000°C 的形状记忆转变温度，因此是迄今为止已知的最高温度的形状记忆合金。这些合金的形状记忆效应已在弯曲和压缩中得到证明。近等原子 Nb-Ru 和 Ta-Ru 合金的相变已通过电阻率 (11,12,13)、高温 X 射线衍射 (11,14,15) 和原位透射电子显微镜 (16) 研究。根据这些数据（和（17, 18））确定的相图如图 1 所示。这些合金的高温 ß 相具有 B2 有序 (CsCl) 立方结构，在冷却过程中发生轻微的四方变形，形成 ß 相 (15)。进一步冷却后，一些组合物会进一步转变为单斜 ß 相 (16)。
Shape memory alloys have the ability to return to their original shape after deformation either by heating the detwinned alloy through a thermoelastic transformation (one-way effect) or by unloading one in which the stress-induced phase transformation has occurred (superelastic effect). The shape memory effect (SME) was first observed by Chang and Read in AuCd alloys (1) but it was not until the development of NiTi alloys by Buehler et al. that important commercial applications for shape memory alloys became possible (2, 3). Current NiTi alloys are typically limited to applications within about 200 C of room temperature, as are the Cu-Zn-Al and Cu-Al-Ni alloys, the other two commercially important shape memory alloys (4). These current shape memory alloys, however, are not suitable for potential high-temperature SME applications envisioned for gas turbine, rocket engine, automotive engine, and nuclear reactor environments, which demand phase stability and transition temperatures above 300 C. Alloys of NiAl (5, 6),(Ni, Pt) Ti (7), and (Ni, Pd) Ti (8) have all demonstrated the SME at elevated temperatures (with shape memory transitions above 250 C), but only the (Ni, Pd) Ti alloys possess sufficiently attractive mechanical properties to sustain current interest as potential high temperature shape memory alloys (9). NiAl is brittle at room temperature and is limited to temperatures less than about 300 C to avoid degradation of the phase responsible for the shape memory effect (9, 10), while (Ni, Pt) Ti becomes brittle at compositions with transition temperatures above about 300 C (7). We report in this paper the development of a new class of shape memory alloys based on near-equiatomic compositions of niobium-ruthenium and tantalum-ruthenium. These alloys exhibit shape memory transition temperatures in excess of 1000 C and as such are the highest temperature shape memory alloys yet known. The shape memory effect in these alloys has been demonstrated in both bending and compression.The phase transitions of near-equiatomic Nb-Ru and Ta-Ru alloys have been studied by electrical resistivity (11, 12, 13), high-temperature x-ray diffraction (11, 14, 15), and in-situ transmission electron microscopy (16). The phase diagrams determined from these data (and (17, 18)) are shown in Figure 1. The high-temperature ß phase of these alloys has a B2-ordered (CsCl) cubic structure which undergoes a slight tetragonal distortion during cooling to form the ß phase (15). Upon further cooling, some compositions experience an additional transformation to the monoclinic ß phase (16).