Mechanical and superelastic properties of laser welded Ti-Ni shape-memory alloys produced by powder metallurgy

• Main Authors: Bahador, A., Hamzah, E., Kondoh, K., Kawahito, Y., Junko, U., Bakar, T. A. A.
• Format: Article
• Published: Elsevier Ltd 2017
• Subjects: TJ Mechanical engineering and machinery
• Online Access: http://eprints.utm.my/id/eprint/76472/; https://www.scopus.com/inward/record.uri?eid=2-s2.0-85019742166&doi=10.1016%2fj.jmatprotec.2017.05.019&partnerID=40&md5=5479762342d5b7bf13be94549befd768
• Institution: Universiti Teknologi Malaysia

Tensile test showed that the strength of the welded joints of powder metallurgy Ti–51%atNi shape-memory alloys (SMAs) decreases after disk-laser welding due to the presence of pores and columnar structure in the fusion zone. There was a reduction in the superelastic behavior of the welded joints compared to the base metal. Superelastic properties of specimen LW1 (with welding speed of 6 m/min and laser power input of 3 kW) were close to the base metal after loading and unloading at room temperature. Welded specimens, which were subjected to solution treatment at 1000 °C followed by aging at 500 °C showed an increment in superelasticity properties. Superelasticity improved significantly after heat treatment in all the welded joints except LW2 (with welding speed of 7.5 m/min and laser power input of 3 kW), because it contained high amounts of porosity in the fusion zone. LW1 exhibited the best properties after heat treatment with superelasticity strain increasing up to 7%, which was higher than the base metal. Differential scanning calorimetry (DSC) investigations showed that heat-treated weld seams had similar phase transformation peaks of martensite, austenite, and R phases to the base metal, which may be due to the recovering of Ti3Ni4 precipitates.