Effect of Postweld Heat Treatment on the Microstructure and Cyclic Deformation Behavior of Laser-Welded NiTi-Shape Memory Wires |
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Authors: | C W Chan H C Man T M Yue |
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Affiliation: | (1) Laser Processing Group, Advanced Manufacturing Technology Research Centre, Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hong Kong, P.R. China; |
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Abstract: | NiTi wires of 0.5 mm diameter were laser welded using a CW 100-W fiber laser in an argon shielding environment with or without
postweld heat-treatment (PWHT). The microstructure and the phases present were studied by scanning-electron microscopy (SEM),
transmission-electron microscopy (TEM), and X-ray diffractometry (XRD). The phase transformation behavior and the cyclic stress–strain
behavior of the NiTi weldments were studied using differential scanning calorimetry (DSC) and cyclic tensile testing. TEM
and XRD analyses reveal the presence of Ni4Ti3 particles after PWHT at or above 623 K (350 °C). In the cyclic tensile test, PWHT at 623 K (350 °C) improves the cyclic deformation
behavior of the weldment by reducing the accumulated residual strain, whereas PWHT at 723 K (450 °C) provides no benefit to
the cyclic deformation behavior. Welding also reduces the tensile strength and fracture elongation of NiTi wires, but the
deterioration could be alleviated by PWHT. |
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