Experimental study on the grain evolution induced by thermal characteristics during oscillation laser welding of IN718

Abstract

• Grain morphology was significantly improved during oscillation laser welding. • Two-color pyrometer was used to measure the cooling rate and temperature gradient. • Effect of thermal behaviors on grain distribution was investigated. • Tensile strength and ductility rate of IN718 joint were simultaneously strengthened. An oscillation laser beam was conducted to refine the grain size of IN718 welded joint. The thermal characteristic differences between non-oscillating and oscillating laser welding and their influence on the microstructure and mechanical properties were investigated using a two-color pyrometer. The experiment results showed that the grain size reduced from 291.03 μm(0 Hz) to 171.27 μm(150 Hz) and the crystalline orientation weaken. The derivation of temperature cycle curve indicated the cooling rate in the center and edge of molten pool(150 Hz) increased by 64.4% and 111.9%, and the temperature gradient decreased from 218.5 0 C/mm(0 Hz) to 73 0 C/mm(150 Hz), which illustrated an increase in constitutional supercooling zone width and the nucleation sites to refine grain size. The tensile load and ductility rate of oscillation laser-welded IN718 joint were simultaneously improved.