Preventing microcracks between directed energy deposited Hastelloy X and IN792 substrate by adding IN625 buffer layer

Abstract

Recently, laser-based additive manufacturing (AM) has emerged as a promising method for repairing complex-shaped components. Although small heat-affected zones and high degrees of freedom expand the processing window for AM, microcrack initiation can occur depending on the combination of parent materials. In particular, frequent microcracking has been observed in additively manufactured Hastelloy X (HX) despite its extensive use in hot components for gas turbine systems. To mitigate this issue, Inconel (IN) 625 was deposited as a buffer layer before the deposition of HX to prevent elemental diffusion between HX and IN792 substrate. Consequently, the IN625 buffer layer reduced the W migration from the IN792 substrate to the HX deposit layer, suppressing segregation at the grain boundaries. In addition, the enhanced Nb content in the HX deposit layer, owing to the high Nb content in the IN625 buffer layer, stabilized the primary carbides in the interdendritic region. By combining these two effects, microcracking was suppressed when the IN625 buffer layer was placed between the IN792 substrate and the HX deposit layer. The suppression of microcracks near the interface delayed crack initiation and propagation during tensile tests, resulting in greater elongation with the IN625 buffer layer compared to the specimens without it. This finding highlights the critical role of selecting the deposit layers in influencing microcrack initiation in partially repaired components, suggesting that designing a sequence of deposit layers can be an effective strategy for AM without extensive alloying modifications for additive manufacturing.