Research on the formation mechanism of thermal crack for laser welding of IC 10 alloy

In this paper, the IC10 alloy joints are prepared by laser welding. The effect of process parameters on thermal crack is discussed, and the formation mechanism of welding thermal crack in different types during laser welding of IC10 alloy are analyzed by micro means. The microstructure, element distribution and phase composition of the thermal cracks are studied. When the laser scanning direction is perpendicular to the grain growth direction of the substrate, the crack sensitivity is greater. With the increase of laser power and the decrease of shielding gas flowing, the crack sensitivity is also greater. A faster welding speed could cause thermal stress and increase crack sensitivity. The choice in an appropriate laser scanning speed range could effectively control the tendency of crack formation. According to the analysis of the formation mechanism of different cracks, the results of SEM and EDS showed that IC10 alloy was susceptible to crystallization cracking due to the high content of low melting point eutectic between grains and grain boundaries, and the tendency to produce liquefaction crack becomes greater when coarse carbides precipitate, both types of cracks belong to the thermal cracks caused by liquid films. In IC10 alloy, ductility dip cracking (DDC) is thermal crack caused by the sharp drop of intergranular plasticity, which is closely related to the state of grain boundaries and interstitial phase precipitated from grain boundary. The crack susceptibility of DDC cracks is easier to control than the above mentioned two type thermal cracks.