Analysis of SLM Forming Cracking Mechanism of ZGH451 Nickel-Based Superalloy

Abstract:

This study focuses on the selective laser melting (SLM)-formed ZGH451 nickel-based superalloy, revealing the mechanism that solidification liquid films lead to crack initiation and clarifying the roles of alloy elements and texture in forming crack defects. Experimental results indicate that cracks of ZGH451 nickel-based superalloy in the SLM process can be mainly categorized into internal solidification cracks and edge cold cracks. During the late solidification stage, low-melting-point phase liquid films exist between dendrites, and high-melting-point Cr element particles at the solidification front hinder melt feeding. The insufficient feeding and thermal stress between dendrites cause the liquid film's rupture, leading to solidification cracks in the core of the material. In the alloy's contour region, high cooling rates and significant thermal stress lead to residual stress accumulation, which exceeds the material's strength limit or grain boundary cohesion strength, resulting in the formation of cold cracks. When the input laser energy density is below 45 J/mm3, the unfused defects in the alloy are densely distributed along the building direction. Once exceeding 140 J/mm³, the probability of keyhole and pore formation sharply increases. These defects can induce cracks under stress. The more the WC and other carbide particles precipitated between dendrites, the greater the grain misorientation, and the higher the alloy's crack sensitivity. The deposited ZGH451 nickel-based superalloy is mainly composed of γ and γ' phases, with a preferred orientation on the (100) plane. The average aspect ratio of the grains reaches 11.25, and the significant texture exacerbates stress concentration at the grain edges and tips, promoting crack initiation and altering crack propagation direction.