Effect of Temperature on the Fracture Toughness of a NiTiHf High Temperature Shape Memory Alloy
Effect of Temperature on the Fracture Toughness of a NiTiHf High Temperature Shape Memory Alloy
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DOI：
10.1007/s40830-019-00245-2
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发表时间：
2019-12
影响因子：
2.2
通讯作者：
B. Young;B. Haghgouyan;D. Lagoudas;I. Karaman
中科院分区：
文献类型：
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作者：
B. Young;B. Haghgouyan;D. Lagoudas;I. Karaman
系统研究了Ni50.3Ti29.7Hf20高温形状记忆合金的断裂韧性随温度的变化规律。在对应于三种试验条件的五种温度下，对盘形紧凑拉伸试样进行了一组名义上的等温断裂韧性试验：（i）低于马氏体结束温度以获得马氏体的断裂韧性（ii）高于奥氏体中的马氏体开始温度但低于马氏体终止温度（Md，奥氏体不发生转变的温度），以便发现当应力诱发马氏体（SIM）转变在裂纹尖端附近发生时的断裂韧性，以及（iii）高于Md，以获得奥氏体的断裂韧性。裂纹尖端附近的非弹性区的范围进行了检测，使用数字图像相关，并检查了断裂表面。断裂行为是高度温度/相依赖。相变材料的断裂韧性高于奥氏体和马氏体的断裂韧性，即SIM相变是一种增韧机制。这是由于应变硬化行为的差异，在去孪晶，马氏体相变，和塑性变形制度的应力-应变响应，其中SIM转变发生与最低的应变硬化率。这里得到的断裂韧性值低于那些等原子NiTi。
The fracture toughness of Ni50.3Ti29.7Hf20high temperature shape memory alloy was systematically investigated as a function of temperature. A set of nominally isothermal fracture toughness tests were conducted on disk-shaped compact tension specimens at five temperatures corresponding to three thermodynamical conditions: (i) below martensite finish temperature to obtain the fracture toughness of martensite (ii) above martensite start temperature in austenite but below the martensite desist temperature (Md, the temperature above which the austenite does not transform), in order to find the fracture toughness when stress induced martensitic (SIM) transformation takes place close to the crack tip, and (iii) aboveMd, in order to obtain the fracture toughness of austenite. The extent of the inelastic zone near the crack tip was detected using digital image correlation, and the fracture surfaces were examined. The fracture behavior was highly temperature/phase dependent. The fracture toughness of the transforming material was higher than that of austenite and martensite, i.e. SIM transformation acts as a toughening mechanism. This was attributed to the differences in strain hardening behavior in detwinning, martensitic transformation, and plastic deformation regimes of the stress–strain response, where SIM transformation occurs with the lowest strain hardening rate. The fracture toughness values obtained here are lower than those of equiatomic NiTi.