Microstructure and high-temperature mechanical properties of Inconel 718 superalloy weldment affected by fast-frequency pulsed TIG welding

Inconel 718 (In-718) alloy has excellent high-temperature mechanical properties and is a strategic material in the military industry, but its high-temperature mechanical properties may decrease due to the comprehensive negative effects of grains and Laves phase coarsening during processing and application. In this paper, a fast-frequency pulsed tungsten inert gas (FFP-TIG) welding process was proposed, and two different waveforms were introduced: fast-frequency double-pulsed (FFDP) waveforms and fast-frequency single-pulsed (FFSP) waveforms. By studying the weld morphology, microstructure and mechanical properties of In-718 alloy weldments, the results showed that FFP-TIG welding reduces heat input, promotes molten pool flow, refines grains and other effects, thereby improving the high-temperature tensile strength of In-718 alloy weldments. FFDP waveforms have a better effect on grain refinement than FFSP waveforms due to the reduction in average heat input and the enhancement of stirring molten pool. The minimum average grain size and Laves phase size of the FFP-TIG weldment were 38.14 μm and 1.133 μm, respectively. Similarly, the high-temperature tensile strength of FFP-TIG weldments reaches a maximum of 685.54 MPa, which was 90.9 % of the base metal strength.