大塑性变形制备的非晶镍钛形状记忆合金的晶化

摘要

Based on the local canning compression, severe plastic deformation (SPD) is able to lead to the almost complete amorphous nickel-titanium shape memory alloy (NiTi SMA), in which a small amount of retained nanocrystalline phase is embedded in the amorphous matrix. Crystallization of amorphous NiTi alloy annealed at 573, 723 and 873 K was investigated, respectively. The crystallization kinetics of the amorphous NiTi alloy can be mathematically described by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. NiTi SMA with a complete nanocrystalline phase is obtained in the case of annealing at 573 K and 723 K, where martensite phase transformation is suppressed due to the constraint of the grain boundaries. Crystallization of amorphous NiTi alloy at 873 K leads to the coarse-grained NiTi sample, where (001) martensite compound twin is observed at room temperature. It can be found that the martensitic twins preferentially nucleate at the grain boundary and they grow up towards the two different grains. SPD based on the local canning compression and subsequent annealing provides a new approach to obtain the nanocrystalline NiTi SMA.%局部包套压缩大塑性变形能够实现镍钛形状记忆合金的完全非晶化，其中少量残留的纳米晶相分布在非晶基体上。研究非晶镍钛合金在573、723和873 K退火条件下的晶化机制。采用约翰逊-迈尔方程描述非晶镍钛合金的晶化动力学行为。在573和723 K的退火条件下，可以获得具有完全纳米晶相的镍钛形状记忆合金，在该纳米晶镍钛形状记忆合金中，马氏体相变由于晶界的约束而受到了抑制。在873 K的退火条件下，非晶镍钛合金的晶化产生了晶粒粗大的镍钛形状记忆合金样品。在室温条件下的粗晶镍钛样品中，可以观察到马氏体复合孪晶，而且发现马氏体孪晶在晶界优先形核，并且向两个不同的晶粒内部长大。局部包套压缩大塑性变形结合后续退火工艺为制备纳米晶镍钛形状记忆合金提供了一种新的途径。