Martensitic Transformation Under Compression of a Plasma Processed Polycrystalline Shape Memory CuAlNi Alloy

Shape memory alloys (SMA) are attracting considerable attention owing to possible applications from biomedical to aerospace. In particular, CuAlNi alloys present significant advantages associated with low cost, easy processing and superior thermo-electric conductivity over other SMAs such as the NiTi alloys. Characterization of some properties and structural changes caused by martensitic transformation are still open to investigation. The present work evaluated these characteristics in an as-cast plasma processed shape memory Cu-14wt.%Al4wt.%Ni, which was compression tested until fracture. Experimental results showed that an as-cast ingot presents not only chemical and phase homogeneity, but also microstructures composed of grains with martensitic morphology. Martensites β'1 and γ'1, as well as intermediary martensitic R and high temperature β1 were identified by X-ray diffraction tests. It was found that the compressive deformation does not interfere in the phase composition and martensite morphology. However, compression changes the volumetric fractions and crystallographic orientation of the martensites. The mechanical behavior is characterized by an apparent elastic response until the fracture. The fractured surface exhibits brittle aspect like "river patterns" and evidence of intergranular rupture.

形状记忆合金（Shape Memory Alloys, SMA）因覆盖生物医学至航空航天等多领域的潜在应用而受到广泛关注。其中，铜铝镍（CuAlNi）合金相较于镍钛（NiTi）等其他形状记忆合金，具备成本低廉、加工便捷以及优异热电导电性等显著优势。当前，针对马氏体相变引发的部分性能与结构变化的表征研究仍存在探索空间。本研究对经等离子处理的铸态Cu-14wt.%Al-4wt.%Ni形状记忆合金开展了表征，并进行了直至断裂的压缩试验。实验结果显示，该铸态锭坯不仅拥有良好的化学成分与相组织均匀性，其微观组织还由具有马氏体形貌的晶粒构成。通过X射线衍射（X-ray diffraction）测试，成功识别出马氏体相β'1、γ'1，以及中间马氏体R相与高温相β1。研究表明，压缩变形并未改变合金的相组成与马氏体形貌，但会改变马氏体的体积分数与晶体取向。该合金的力学行为表现为断裂前呈现表观弹性响应。断口形貌呈现出类似“河流花样”的脆性断裂特征，且存在沿晶断裂的相关证据。