Study on the Cracks of NiTiNb/TC4 Lap Joints Welded by Micro Laser Welding

Abstract

Dissimilar metal sheets of Ni47Ti44Nb9 (at.%, short for NiTiNb) shape memory alloy and Ti6Al4V (TC4) alloy with the same thickness of 0.2 mm are joined by using micro laser welding technology. The microstructure and crack in the weld are studied by optical microscope (OM) and scanning electron microscope (SEM). The results show that the cracks are easy to generate during the laser lap welding of NiTiNb alloy and TC4 alloy due to plenty of brittle intermetallic compound of Ti2Ni. However, the welding cracks can significantly reduce or disappear by adding filler metal of Ni foil. No-defect joint is obtained when NiTiNb alloy is located on the upper and 50 μm thick Ni foil is added during the lap welding process. The crack sensitivity can be decreased because of finer grains and elliptic boundaries. The shear load of the joint can reach 162 N.