Mechanism and inhibition of welding cracks in microplasma arc of Inconel 713LC casting superalloy

Aiming at the problem that the heat-affected zone of Inconel 713LC casting superalloy is prone to cracks during additive welding, this paper adopts microplasma arc welding technology, scanning electron microscope and energy dispersive spectrometer to analyze the micro-morphology of cracks and the distribution of alloy elements. The formation mechanism of cracks in the heat-affected zone is explored, and the crack suppression technology is studied. The result shows that the appearance of welding cracks in the heat-affected zone is mainly due to the dissolution and liquefaction of intergranular carbide and the formation of liquid phase under the influence of welding heat input. At the same time, the grain is heated and grown to promote the original grain boundary to move and then intersect with the liquid phase to form a larger liquid phase. Nb, Mo, Ti and other alloy elements in the grains and grain boundaries are segregated into the liquid phase. Carbides with a size of more than 10 μm are formed after cooling and solidification of liquid phase. Under the action of welding stress, cracks initiate around carbides and propagate along grain boundaries. The number and size of welding cracks increase with the increase of heat input. Reducing the welding heat input through pulse welding, the high temperature residence time in the heat-affected zone becomes shorter, the degree of elements segregation in the alloy is reduced. The growth of harmful carbides in the alloy is slowed down, and the crack formation is inhibited. After the solution treatment of the as-cast base metal, the original element segregation of the base metal are homogenized. The hardness of the base metal decreases and the plasticity is improved, which weakens the enrichment tendency of the alloying elements and reduces the crack sensitivity during welding.