A high power Nd-YAG laser was used to perform bead-on-plate (BOP) welding on high viscosity Inconel 690 alloy plates of 3 mm in thickness with three different shielding gases (Ar, He, and N 2 ). Adopting a rectangular laser power waveform, four different peak-base power differentials (ÁP) were applied with a constant average power of 1.5 kW. A comprehensive investigation was performed into the influences of the shielding gas, the flow rate, and the value of ÁP on the characteristics of the resulting welds, including the weld morphology, the penetration depth, the plume volume, and the porosity formation. The results showed that the weld penetration depth, the depth-to-width ratio, the weld surface roughness and the degree of weld spattering all increased with increasing ÁP. The choice of shielding gas had a significant effect on the porosity ratio (P r ) of the weld. The weld formed under Ar shielding had the highest P r , while that formed under N 2 shielding had the lowest. Under He shielding, the gas flow rate had a significant effect on the porosity ratio. However, under the higher density gases of Ar and N 2 , the porosity appeared to be insensitive to the flow rate. Finally, an increased ÁP yielded a significant reduction in P r for the welds with higher porosity.

This study investigates the microstructure and corrosion behaviour of alloy 690-SUS 304L stainless steel dissimilar weldments formed by electron beam welding (EBW). Slow strain rate tensile tests (SSRTs) are performed in air and in a 0 . 01M Na 2 S 2 O 3 z1 wt-%NaCl corrosive environment. The microstructure, mechanical properties and corrosion behaviour of the weldments are analysed. Experimental results of this study reveal that the precipitation of chromium carbide is suppressed owing to the effect of rapid solidification of EBW in fusion zone (FZ). In addition, there is no chromium depletion found at the grain boundary at all. The interdendritic region of the FZ contains fine precipitates, which are a mixture of Ti rich phases with a rectangular shape and Cr rich phases with an oval shape. Fewer interdendritic phases are formed in the root than in the cap owing to the higher cooling rate in the root region of the weldment. Fracture tests indicate that all the specimens ruptured in the FZ by SSRTs preformed either in air and or in a corrosive environment. The tensile strength and total tensile elongation of the specimen deformed in the 0 . 01M Na 2 S 2 O 3 z1 wt-%NaCl corrosive environment are lower than those of the specimen deformed in air. Fractographic investigations revealed that the fracture mode, in good accordance with mechanical behaviour and performance, transits from a ductile dimple rupture in the specimens tested in air to a mixed rupture of dimples and corrosion formation on fractured surface which obviously assisted the cracking in the specimens tested in the corrosive environment.