The mechanism and regulation of hot cracking in a new complex-concentrated alloy by a novel integrated directed energy deposition

Improving thermal efficiency in advanced ultra-supercritical coal-fired power plants relies on increased steam temperature and pressure, accelerating the emergence of newly complex-concentrated alloys (CCAs). However, the new developed CCA have a combined Al and Ti content for 4.87 wt.%, which indicates a high susceptibility to hot cracking. In this work, the hot cracking problem for the CCA during the laser deposition process was studied. The eutectic of the matrix and carbides with a low melting point liquefied during reheating process. The hot cracking occurred with local unbearable stress concentration. Based on the above analysis of hot cracking, a novel integrated directed laser deposition method was proposed to flexibly adjust the microstructure evolution and stress distribution by thermal cycles to achieve the control of hot cracks. The microstructure evolution and the control of residual stress are realized by gas quenching and preheating substrates, respectively. The evidence was obtained to show that the coupled process with synchronous gas quenching during preheating can eliminate the hot cracks effectively. More specifically, the preheating process relieved the residual stress, and the local gas quenching simultaneously accelerated the liquid film solidification and reduced carbide segregation. Finally, the sample prepared by the integrated directed energy deposition presented superior overall performance with ultimate tensile strength of 991.84 MPa and elongation of 18.28%. This work provides a meaningful reference for producing crack-free superalloys in metal additive manufacturing.