Studies on the weld integrity, formability and microstructural evolution of grade 2 titanium sheets of laser beam welding process

Abstract

Titanium alloys have been utilized in several structural applications such as automobile industries, aerospace, nuclear power plant, chemical and petroleum sectors. Titanium welding is a challenge due to its high reactivity with atmospheric oxygen when operating under high temperature. Laser beam welding process is found to be a suitable technique for welding of titanium alloys and is preferred over plasma arc welding, gas tungsten arc welding etc. In this study, the Nd:YAG laser welding was used to join the grade 2 titanium of 1.6 mm thickness sheets. From the experimental bead on trials, the input parameters significantly governing the process were identified. The experimental trials were performed on butt joint configurations for beam power of 1100 W and welding speed of 200 mm min−1. The radiography results show that the weld bead has no volumetric defects such as lack of fusion and penetration, porosity and inclusions. The laser-welded joints were subjected to uniaxial tensile, bend, Erichsen cupping, micro hardness, light microscope, energy dispersive x-ray spectroscopy (EDS) and scanning electron microscope fractography. The butt joint displays enhanced tensile strength, bending, formability and hardness value. Non-uniform microstructures were observed in the welded joint due to the unequal thermal cycle experienced in the laser welding. Entrapment of oxygen and nitrogen in weldment were observed in EDS elemental analysis which increases the strength and hardness of the weldments. The retained α phase of base metal and growth of β phase in weldment were observed in x-ray diffraction (XRD) analysis. The fractured specimen has a large amount of dispersive fine dimples which indicates that ductile type of fracture due to micro-void coalescence.