Refining microstructures and enhancing mechanical properties of Inconel 718 weldment via fast-frequency double pulsed waveforms adopting in FFP-TIG

Raising the frequency of pulsed welding current in conventional tungsten inert gas (TIG) welding would stim-ulate the arc to stir the molten metal and thus refine microstructures and enhance mechanical properties of Inconel 718 (IN-718) weldment. In the high-frequency pulsed welding waveform, scholars are usually focused on the high-frequency pulses distributing above the low-frequency pulses while seldom considering the large space inside the low-frequency pulses to accommodate the high-frequency pulses. A fast-frequency double pulsed (FFDP) waveform is proposed to apply in fast-frequency pulsed TIG (FFP-TIG) welding. The effect of FFDP waveform modulation on the stirring of the molten pool and grain refinement was studied. The electromagnetic effect of FFDP waveform concentrated the welding energy and caused the increasing depth and decreasing width of IN-718 weldments, which enhanced the cooling rate during the solidification and formation of the weldments. Besides, the melt IN-718 within molten pool would be stirred due to the Marangoni effect induced by FFDP waveform. The increasing cooling rate and inducing stirring effect synergistically acted and thus refined the microstructures of IN-718 weldments, with the minimum size being 35.15 and 0.59 mu m for irregular polygonal equiaxed grain and strip Laves phase, respectively. The tensile strength and the corresponding elongation of IN -718 weldments at high temperature (700 celcius) achieved 91% and 209% of the base metal. Current work provides an important direction towards the fabrication and development of high-reliability IN-718 weldment with good mechanical performance in high-temperature.