NiTi shape memory alloys (SMAs) are widely applied as a smart material in many areas. Its unique properties, such as high ductility, corrosion resistance, shape memory effect, and superelasticity, attracted much attention to this material. However, the NiTi SMAs are unfavorable in machining operations. Chip formation characteristics provide a favorable factor in analyzing the machining mechanism and then providing support to improve the processing technology. Experiments on turning NiTi SMAs at different cutting speeds varied from 7.5 m/min to 125 m/min was performed in this paper, and the feed rate was 0.15 mm/r and the depth of cut was 0.2 mm. The shape and microstructure of the chip were analyzed to reveal the material flow behavior in the chip. Together with the change of micro-hardness and the differential scanning calorimetry(DSC) curves of NiTi SMAs, this paper presented that the martensitic phase transformation plays an important role in the material flow behavior, and thus influence the formation of the chip. When the cutting speed is lower, strain hardening is a primary driving force for the material flow in the chip. The thermal softening effect and degree of martensitic transformation increase with an increment in cutting speed and this coupled effect promoted the material softening. Furthermore, the critical cutting speed and the shear angle for the formation of the serrated chip were depicted from the experimental data, which resulted in the cutting speed of 40 m/min and the shear angle of 45°.

NiTi形状记忆合金（SMAs）在许多领域被广泛用作智能材料。其独特的性能，例如高延展性，耐腐蚀性，形状记忆效应和超弹性，引起了人们对该材料的广泛关注。但是，NiTi SMA在加工操作中是不利的。切屑形成特性为分析加工机理提供了有利因素，然后为改善加工技术提供了支持。本文进行了将NiTi SMAs的切削速度从7.5 m / min改变为125 m / min的实验，进给速度为0.15 mm / r，切削深度为0.2 mm。分析芯片的形状和微结构，以揭示芯片中的材料流动行为。结合NiTi SMAs的显微硬度变化和差示扫描量热（DSC）曲线，提出马氏体相变在材料流动行为中起着重要作用，从而影响切屑的形成。当切削速度较低时，应变硬化是切屑中材料流动的主要驱动力。随着切削速度的增加，热软化效果和马氏体相变程度也增加，并且这种耦合效应促进了材料的软化。此外，从实验数据中可以看出形成锯齿状切屑的临界切削速度和剪切角，切削速度为40 m / min，剪切角为45°。本文提出马氏体相变在材料流动行为中起着重要作用，从而影响了切屑的形成。当切削速度较低时，应变硬化是切屑中材料流动的主要驱动力。随着切削速度的增加，热软化效果和马氏体相变程度也增加，并且这种耦合效应促进了材料的软化。此外，从实验数据中可以看出形成锯齿状切屑的临界切削速度和剪切角，切削速度为40 m / min，剪切角为45°。本文提出马氏体相变在材料流动行为中起着重要作用，从而影响了切屑的形成。当切削速度较低时，应变硬化是切屑中材料流动的主要驱动力。随着切削速度的增加，热软化效果和马氏体相变程度也增加，并且这种耦合效应促进了材料的软化。此外，从实验数据中可以看出形成锯齿状切屑的临界切削速度和剪切角，切削速度为40 m / min，剪切角为45°。应变硬化是芯片中材料流动的主要驱动力。随着切削速度的增加，热软化效果和马氏体相变程度也增加，并且这种耦合效应促进了材料的软化。此外，从实验数据中可以看出形成锯齿状切屑的临界切削速度和剪切角，切削速度为40 m / min，剪切角为45°。应变硬化是芯片中材料流动的主要驱动力。随着切削速度的增加，热软化效果和马氏体相变程度也增加，并且这种耦合效应促进了材料的软化。此外，从实验数据中可以看出形成锯齿状切屑的临界切削速度和剪切角，切削速度为40 m / min，剪切角为45°。