EFFECT OF HEAT INPUT AND POST WELD HEAT TREATMENT ON THE PHASE TRANSFORMATION TEMPERATURE OF TIG-WELDED NiTinol SHEETS

Abstract

NiTinol Shape Memory Alloys (SMA) are becoming one of the ideal choices for biomedical industries due to their unique properties such as Shape Memory Effect (SME), Super Elasticity (SE) and Biocompatibility. In the process of making complicated biomedical implants, welding processes play a vital role. In this work, an attempt was made to study the effect of heat input and Post Weld Heat Treatment (PWHT) on the TIG-welded NiTinol SMA. TIG welding was carried out on 1-mm thick NiTinol sheets. With increase in heat input, there was a significant variation in Phase Transformation Temperature (PTT) of welded samples. The variation in PTT is attributed to the formation of intermetallic phases such as Ti2Ni, Ni3Ti and NiTiO3 and coarse grain formation. Electron Back Scattered Diffraction (EBSD) analysis on the weld revealed that the average grain size of parent material was increased from 9.92851[Formula: see text][Formula: see text]m to 48.292345[Formula: see text][Formula: see text]m after the welding process. The PWHT was carried out on the best weld characteristic sample. PWHT did not produce significant effect on PTT. Austenite start and finish temperature slightly decreased after PWHT, whereas slight drift towards the positive side was noticed in martensite start and finish temperature.