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首页> 外文期刊>Shape memory and superelasticity >Tensile Deformation of Superelastic NiTi Wires in Wide Temperature and Microstructure Ranges
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Tensile Deformation of Superelastic NiTi Wires in Wide Temperature and Microstructure Ranges

机译：宽温度和微观结构范围内超弹性NITI线的拉伸变形

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Superelastic NiTi wires were prepared from a single cold worked wire by various electropulse heat treatments. The wires having a wide range of virgin microstructures were subjected to tensile tests until rupture and cyclic superelastic tensile testing in a wide temperature range. The results were complemented by TEM observation of lattice defects created by superelastic cycling. It appeared that the yield stress depends significantly on the wire microstructure and less on the test temperature. The upper plateau stress varies with the microstructure through its effect on the Ms temperature and increases with increasing temperature in accord with the Clausius-Clapeyron equation up to a maximum temperature characteristic for each microstructure. The upper plateau strains exhibit pronounced maxima (12-18%) at test temperatures and microstructures (pulse times), at which the upper plateau stress approaches the yield stress. The instability of cyclic superelastic deformation was found to be inversely related to the difference between the yield stress and upper plateau stress. Cyclic deformation introduces dislocation slip in the microstructure of the cycled wire from the 3rd cycle and promotes formation of {114} austenite twins upon later cycling. These observations were explained by the activation of deformation twinning in oriented martensite and the stress induced B2 => B19' => B2~T martensitic transformation in specific range of microstructures and temperatures. The ductility of the tested wires was observed to vary stepwise with microstructure from ~13 up to ~55% and gradually decreased with temperature increasing above 100°C.
机译：通过各种电热处理从单个冷加工丝制备超弹性NITI线。对具有各种原始微结构的导线进行拉伸试验，直到宽温度范围内的破裂和循环超弹性拉伸测试。通过TEM观察超弹性循环产生的晶格缺陷的结果互补。似乎屈服应力显着取决于线微观结构和较少的测试温度。上部平台应力通过其对MS温度的影响而随着微观结构而变化，随着温度的增加而增加，Clausius-Clapeyron方程达到每个微结构的最高温度特性。上部高原菌株在测试温度和微观结构（脉冲时间）处表现出明显的最大值（12-18％），上平台应力接近屈服应力。发现循环超弹性变形的不稳定性与屈服应力和上平台应力之间的差异成反比。循环变形在第3周期中引入循环丝的微观结构中的位错滑，并在后来循环后促进形成{114}奥氏体双胞胎。通过在定向马氏体中的变形孪晶的激活和应力诱导的B2 => B19'=> B2〜T马氏体转化在微观结构和温度范围内的变形，解释了这些观察结果。观察到测试线的延展性以逐步改变，微观结构从〜13至〜55％逐渐增加，随温度升高到100℃的温度增加。

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