Abstract

Owing to their shape memory effect and pseudoelasticity, NiTi shape memory alloys (SMAs) are widely used as functional materials. Mechanical processes particularly influence the final formation of the product owing to thermal softening and work-hardening effects. Surface integrity is an intermediate bridge between the machining parameter and performance of the product. In this study, experiments were carried out on turning NiTi SMAs at different cutting speeds, where surface integrity characteristics were analyzed. The results show that a higher cutting speed of 125 m/min is required to turn NiTi SMAs based on the evaluation of surface integrity. The degree of work hardening is higher at 15 m/min. Consequently, as a primary effect, work hardening appears on the plastic deformation of the machined samples, leading to dislocations and defects. As the cutting speed increases, the thermal softening effect exceeds work hardening and creates a smoother surface. A stress-induced martensitic transformation is considered during the turning process, but this transformation is reversed to an austenite from the X-ray diffraction (XRD) results. According to the differential scanning calorimetry (DSC) curves, the phase state and phase transformation are less influenced by machining. Subsequently, the functional properties of NiTi-SMAs are less affected by machining.

中文翻译：

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车削后加工的NiTi形状记忆合金的表面完整性演变

摘要

由于其形状记忆效应和拟弹性，NiTi形状记忆合金（SMAs）被广泛用作功能材料。由于热软化和加工硬化作用，机械过程特别影响产品的最终形成。表面完整性是加工参数和产品性能之间的中间桥梁。在这项研究中，对以不同切割速度车削NiTi SMA进行了实验，分析了表面完整性特征。结果表明，根据表面完整性的评估，需要更快的切削速度（125 m / min）来旋转NiTi SMA。加工硬化度较高，为15 m / min。因此，作为主要作用，加工硬化出现在加工样品的塑性变形上，从而导致位错和缺陷。随着切削速度的增加，热软化效果超过了加工硬化，并产生了更光滑的表面。在车削过程中考虑了应力引起的马氏体相变，但是从X射线衍射（XRD）结果可以看出，这种相变被转换为奥氏体。根据差示扫描量热法（DSC）曲线，相状态和相变受机械加工的影响较小。随后，NiTi-SMAs的功能特性受机械加工的影响较小。根据差示扫描量热法（DSC）曲线，相状态和相变受机械加工的影响较小。随后，NiTi-SMAs的功能特性受机械加工的影响较小。根据差示扫描量热法（DSC）曲线，相状态和相变受机械加工的影响较小。随后，NiTi-SMAs的功能特性受机械加工的影响较小。