The effect of laser welding process parameters on the mechanical and microstructural properties of V-4Cr-4Ti structural materials.

Abstract

V-Cr-Ti alloys are among the leading candidate materials for the frost wall and other structural materials applications in fusion power reactors because of several important advantages including inherently low irradiation-induced activity, good mechanical properties, good compatibility with lithium, high thermal conductivity and good resistance to irradiation-induced swelling and damage [1]. However, weldability of these alloys in general must be demonstrated, and laser welding, specifically, must be developed. Laser welding is considered to be an attractive process for construction of a reactor due to its high penetrating power and potential flexibility. This paper reports on a systematic study which was conducted to examine the use of a pulsed Nd:YAG laser to weld sheet materials of V-Cr-Ti alloys and to characterize the microstructural and mechanical properties of the resulting joints. Deep penetration and defect-free welds were achieved under an optimal combination of laser parameters including focal length of lens, pulse energy, pulse repetition rate, beam travel speed, and shielding gas arrangement. The key for defect-free welds was found to be the stabilization of the keyhole and providing an escape path for the gas trapped in the weld. An innovative method was developed to obtain deep penetration and oxygen contamination free welds. Oxygen and nitrogen uptake were reduced to levels only a few ppm higher than the base metal by design and development of an environmental control box. The effort directed at developing an acceptable postwelding heat treatment showed that five passes of a diffuse laser beam over the welded region softened the weld material, especially in the root region of the weld.

Effect of laser welding on mechanical properties of 70/30 Cu-Ni alloy welds

“…3 Recent studies were carried out on materials such as aluminum alloys, magnesium alloys, titanium alloys, and stainless steel for the evaluation of mechanical and metallurgical properties of laser welded joints. [4][5][6][7][8][9] It has been reported that the effects of CO 2 laser beam welding (LBW) process parameters (2.5 kW laser power, 5.5 m/min welding speed, and 21.5 mm focal position) showed an improvement in mechanical properties of AZ31B magnesium alloy due to the formation of very fine grains in weld region and uniformly distributed finer precipitates. 4 A pulsed Nd:YAG laser to weld 4-mm-thick V-Cr-Ti sheets achieved good welding under an optimum combination of laser parameters including focal length of lens, 1.6 kW pulse power, welding speed (0.15-0.6 m/min), and argon shielding gas.…”

“…4 A pulsed Nd:YAG laser to weld 4-mm-thick V-Cr-Ti sheets achieved good welding under an optimum combination of laser parameters including focal length of lens, 1.6 kW pulse power, welding speed (0.15-0.6 m/min), and argon shielding gas. 5 Pulse energy, duration, and peak power play major role in improving mechanical properties during the welding of 3-mm-thick Ti-6Al-4V by using Nd:YAG pulsed laser. 6 Ti-6Al-4V (5.1-mm-thick) sheets were welded efficiently by laser welding of 4 kW power at various welding speeds (0.7-1.5 m/min) using a spot diameter of 0.45 mm, focal length of 200 mm, and flow rate of argon of 23.6 L/min.…”