Crack Mechanism and Control Strategy for Ni₅₈Cr₂₃Fe₁₀W₅Ti₂Ta₁Nb₁ Multi-Principal Element Alloy by Selective Laser Melting

With the increasing sophistication of laser additive manufacturing technology, the need for high-performance alloys suitable for additive manufacturing has grown. Developing new alloys with excellent mechanical properties and good formability has become a critical direction in the field of additive manufacturing, but severe defect-like cracking remains a major concern. Based on a new design concept from the corners of the phase diagrams to the central region, multi-principal element alloys (MPEAs, i.e., high-entropy alloys) have introduced new opportunities for the development of high-performance additive manufactured alloys. Ni₅₈Cr₂₃Fe₁₀W₅Ti₂Ta₁Nb₁ MPEA (containing 0.02%B element, mass fraction) shows great potential for overcoming the severe trade-off between manufacturability and high strength. On the one hand, Ni₅₈Cr₂₃Fe₁₀W₅Ti₂Ta₁Nb₁ MPEA has a yield strength of ~1 GPa and an elongation of ~25%, thus its comprehensive performance is superior to that of most existing MPEAs. On the other hand, because of its slower precipitation kinetics than the IN718 alloy, the main strengthening phase (γ″) of MPEA is stable at 800^oC, and thus it shows promise for eliminating the cracking of the precipitation-strengthened alloys. However, because Ni₅₈Cr₂₃Fe₁₀W₅Ti₂Ta₁Nb₁ MPEA is a newly designed alloy, the effects of multi-principal alloying on its non-equilibrium solidification behavior are unknown, as is the mechanism of this effect, and its cracking behavior under additive manufacturing and corresponding mechanism must be evaluated. This work takes Ni₅₈Cr₂₃Fe₁₀W₅Ti₂Ta₁Nb₁ MPEA as the research object and uses selective laser melting (SLM) technology and advanced characterization techniques to investigate the crack formation mechanism and control path of the alloy under different SLM process parameters. The formability of Ni₅₈Cr₂₃Fe₁₀W₅Ti₂Ta₁Nb₁ alloy under different SLM process parameters was investigated, and the crack formation mechanism of Ni₅₈Cr₂₃Fe₁₀W₅Ti₂Ta₁Nb₁ alloy was revealed. The crack control method was then explored. The results showed that the cracks propagated along the grain boundary of the coarse columnar crystals and preferentially appeared at high-angle grain boundaries (HAGBs). The surface of the cracks presented a smooth and clear dendritic morphology, which is a typical solidification crack. At the terminal stage of solidification, the HAGB regions contain a thin layer of B segregation, which promoted the production of a continuous liquid film, and the liquid film remained stable at HAGB owing to the large grain boundary energy. The residual stress caused by heating/cooling circulation acted on the liquid film and triggered solidification cracking. The relationship between the heat input and the cracking sensitivity was not linear. Cracks cannot be eliminated by simply regulating heat input, and cracks can be suppressed only to a certain extent. The grain boundary density increased, local stress concentration was alleviated, and solidification cracks were successfully eliminated with the addition of TiB₂ nanoparticles.