We investigate acoustic emission (AE) that arises during the martensitic transition in a polycrystalline specimen of the prototypical superelastic/elastocaloric alloy ${\mathrm{Ni}}_{50.4}{\mathrm{Ti}}_{49.6}$ (at. %) driven using tensile strain. We use two independent AE sensors in order to locate AE events, and focus on contributions to the AE that arise away from the grips of the mechanical testing machine. Significant AE activity is present during the first mechanical loading primarily due to nucleation and growth of wide Lüders-like bands during the forward martensitic transition (imaged using visible light and infrared radiation) that lead to persistent changes in intergranular interactions. AE activity is suppressed during the subsequent reverse martensitic transition on unloading, and in successive loading/unloading cycles, for which the Lüders-like bands narrow and modify intergranular interactions to a much smaller extent. After the first loading, we find that the AE activity associated with the martensitic transition is weak, and we suggest that this is because the elastic anisotropy and strain incompatibility in Ni-Ti are low. We also find that the AE activity becomes weaker on mechanical cycling due to increased retained martensite.

中文翻译：

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多晶Ni50.4Ti49.6超弹性拉伸循环过程中的声发射抑制

我们调查在典型超弹性/弹性热合金的多晶试样中马氏体转变过程中产生的声发射（AE） ${你}_{50.4}{钛}_{49.6}$（at。％）使用拉伸应变驱动。我们使用两个独立的AE传感器来定位AE事件，并专注于机械测试机的抓地力对AE的贡献。在第一次机械加载过程中会出现大量的AE活性，这主要是由于马氏体前向过渡（使用可见光和红外辐射成像）期间宽Lüders状带的形核和生长导致了晶间相互作用的持续变化。在随后的卸载过程中，以及随后的加载/卸载循环中，随后的马氏体逆向转变过程中，AE活性被抑制，为此，Lüders状带变窄并改变了晶间相互作用。第一次加载后，我们发现与马氏体转变有关的AE活性较弱，我们认为这是因为Ni-Ti的弹性各向异性和应变不相容性较低。我们还发现，由于增加了残留的马氏体，AE活性在机械循环中变得较弱。