Fatigue Crack Propagation Micromechanisms in a Cu-Zn-Al Alloy with Pseudoelastic Effect
Fatigue Crack Propagation Micromechanisms in a Cu-Zn-Al Alloy with Pseudoelastic Effect
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DOI：
10.1016/j.mspro.2014.06.062
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
V. D. Cocco;F. Iacoviello;S. Natali;V. Volpe;F. Maiolino
中科院分区：
文献类型：
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作者：
V. D. Cocco;F. Iacoviello;S. Natali;V. Volpe;F. Maiolino
铜锌铝合金具有良好的形状记忆性能，这是由于体心立方的无序结构，在高温下稳定，被称为β相。这些牌号能够通过从β相到B2电池的可逆转变(在适当的冷却工艺后)和通过从B2第二级到DO_3的可逆转变(在其他冷却过程之后)来改变其微观结构。在β-Cu-Zn-Al形状记忆合金中，马氏体相变在室温下不平衡。因此，为了获得马氏体组织，往往需要先进行高温热处理，然后再进行淬火处理。马氏体相既可以通过热诱发自发相变获得，也可以通过其他机制(应力诱导或降温)获得。高温到马氏体相的直接淬火是最有效的工艺，这是因为相变的非扩散特性。马氏体相继承了β相的原子有序。在本工作中，用X射线衍射和光学显微镜观察了一种人造的铜锌铝形状记忆合金的微观结构。这些分析是在“铸态合金”条件下进行的，并在负载条件下进行，以表征合金的行为。此外，还进行了疲劳裂纹扩展试验和断口扫描电子显微镜(SEM)观察，以评估主要的裂纹微观机制。
Cu-Zn-Al alloys are characterized by good shape memory properties due to a bcc disordered structure, stable at high temperature, called β-phase. These grades are able to change their microstructure by means of a reversible transition from β-phase to a B2 cell (after appropriate cooling process), and by means of a reversible transition from B2 secondary to DO3 order (after other cooling processes). In β-Cu-Zn-Al shape memory alloys, the martensitic transformation is not in equilibrium at room temperature. Therefore, a thermal heat treatment at high temperature followed by quenching is often necessary in order to obtain the martensitic structure. The martensitic phases can be obtained either by means of thermally-induced spontaneous transformation, or by means of other mechanisms (stress-induced, or temperature decrease). Direct quenching from high temperature to the martensite phase is the most effective process because of the non-diffusive character of the transformation. The martensite inherits the atomic order from the β-phase.In this work, an artificial Cu-Zn-Al SMA alloy has been microstructurally characterized by X-ray diffraction and Light Optical Microscope (LOM) observation. These analyses have been performed in“as cast alloy” conditions, and under load conditions in order to characterize the alloy behavior. Furthermore, a fatigue crack propagation test and fracture surface scanning electron microscope (SEM) observations have been performed in order to evaluate the main crack micromechanisms.