Microstructural Characterisations of Welded Shape Memory Alloys

Abstract

Today, with the development of technology, different welding methods were applied for different alloys. In this work, changing of functional properties after using welding methods for NiTi alloy samples were aimed. However, two different welding methods were employed for the same alloy and results were compared to each other and commented on them. In the present study, samples were welded with TIG and Laser welding and their cross section of welded zone was examined. Then these samples were examined in optical microscope and SEM. The advantages and disadvantages of both welding methods were reported. The basic distinction of TIG and laser welded samples examined in microscope were the scale of HAZ (Heat Affected Zone) of TIG welded samples. Nevertheless, due to more thermal input was applied for materials in TIG welded parts, more molten materials were detected, or heat effects were attained in this practice. In laser welding, heat input was less, and this could be recognized from the observed micrographs. When SEM figures were investigated, While HAZ was obviously distinguished from border of welding bath and the base metal was been separated from HAZ too. The twin structures were not observed in optical microscope; for that reason, they were investigated in SEM to see these twins in laser welded area.