Influence of Casting Defects on Weldability of a Nickel-Based Superalloy

Abstract:

The impact of casting defects on the weldability of K4951 superalloy was investigated using tungsten inert gas (TIG) welding. The as-cast K4951 superalloy samples with prefabricated U-shaped grooves of varying depths and widths were TIG welded, and the microstructures, cracks morphology, and precipitated phases were analyzed using optical microscope, scanning electron microscope, transmission electron microscope, and energy dispersive X-ray spectrometer. The results reveal that the dimensions of casting defects significantly affect the weldability of K4951. Deep defects (greater than 2 mm) lead to rapid crack propagation, while wider defects can moderate the propagation process of cracks. Elemental segregation and the formation of precipitated phases, such as MC carbides, are observed in the fusion zone, contributing to welding cracks. An optimal groove aspect ratio (depth-to-width) between 0.2 and 0.5 minimizes crack formation tendency and enhances tensile strength, resulting in a mixed brittle-ductile fracture mode of joint after high-temperature tensile testing.