Microstructure and cracking behavior of Ni3Al-based IC21 alloy fabricated by selective laser melting

Understanding the formation mechanism of microstructure and cracking behavior of Ni3Al-based IC21 alloy fabricated by selective laser melting (SLM) is of great importance to promote its development and application in advanced aeroengine field. In this study, SLM was applied to Ni3Al-based IC21 for the first time and cubic IC21 alloy samples were prepared by SLM and their microstructure was characterized. The average primary dendrite arm spacing (PDAS) is only 700 nm due to the extremely high cooling rate in the molten pool, which is three orders of magnitude smaller than that in traditional directional solidified parts. The microstructure consists of the long striped gamma and gamma' phase in the dendritic trunk and the granular NiMo phase particles at the interdendritic regions and grain boundaries. This unique microstructure of aligned gamma and gamma' phase is distinct from the cubic gamma' phase precipitated in gamma matrix in conventionally manufacturing since PDAS was significantly refined to a scale of precipitated phase, thus the solid-state transformation of gamma to gamma' occurs epitaxially from the long striped peritectic gamma' phase at interdendritic regions. The solidification cracking appears at high angle grain boundaries (HAGB) with dendritic morphology, where Mo, Ta and Re elements are enriched and many granular NiMo phase forms. Decreasing content of Mo element is a method to reduce NiMo phase at grain boundary which can eliminate crack.

Automated summary

Understanding the microstructure formation and cracking behavior is crucial for the development and application of Ni3Al-based IC21 alloy fabricated by selective laser melting (SLM) in the aeroengine field. In this study, SLM was used to prepare Ni3Al-based IC21 alloy samples, characterized by a unique microstructure with reduced primary dendrite arm spacing (PDAS) and aligned gamma and gamma' phases. Solidification cracking occurred at high angle grain boundaries (HAGB) enriched with elements Mo, Ta, and Re, and decreasing the content of Mo was found to eliminate cracks at grain boundaries.