The Suppression of Liquation Cracking in the Repair Process of Non-Weldable K447a Superalloys by Laser Surface Remelting-Assisted Laser Cladding

Abstract

Nickel-based superalloys with high Al + Ti content are essential materials for manufacturing components such as turbine blades in aerospace engines. However, liquation cracking in the heat-affected zone (HAZ)1 has proven difficult to overcome due to its extremely poor weldability, becoming a significant obstacle to advancing additive repair and remanufacturing technologies for superalloy castings. In this study, we innovatively proposed a new method for additive repair through laser cladding by utilizing a laser remelting process to pretreat the surface of K447A castings. The results showed that the remelted buffer layer (RBL) obtained through pretreatment increased the cracking stress threshold of the liquid film in the HAZ and reduced the thermal stress sustained by the liquid film, effectively mitigating liquation cracking during the repair process of superalloy castings with high Al + Ti content. The fluid capillary flow model and the Stefan-Reynolds model for viscous fluid separation were used to analyze the stress on the liquid film in the HAZ. The thickness of the liquid film, the dendritic size, and the duration of applied force were discovered to impact the cracking stress threshold, with liquid film thinning being the primary factor in raising the threshold of the RBL. Furthermore, the RBL raised the initial liquefaction temperature and reduced the range of liquefaction temperatures, directly leading to a reduction of the total thermal stress sustained by the liquid films. Additionally, the refinement of dendrites in the RBL increased the number of liquid films within a single grain, thereby reducing the strain sustained by individual liquid films. This resulted in strain relaxation between the dendrites, further decreasing the tendency for cracking in the liquid film. By simulating the separation process of the liquid film under ultra-high temperature tensile testing at 1300°C, experimental results confirmed that the tensile strength of the RBL’s liquid film was increased by 192.3% compared to cast substrate, significantly alleviating strain concentration during the stretching process. This study provided new insights and experimental data for additive repair of non-weldable superalloy castings.

Keywords: Non-weldable superalloy, Liquation cracking, laser cladding, Laser surface remelting