Compositional effect on TCP phase formation in Ru-containing Ni-based single crystal superalloys

Abstract

Abstract. Microstructural instability involving the formation of topologically close-packed (TCP) phases is restricted during the alloy development of Ni-based single crystal superalloys. In this study, the effects of alloying elements including Co, Cr, Mo and Ru on the formation of different TCP phases were investigated in a series of single crystal superalloys. Experimental results showed that more additions of Cr and Mo promoted the TCP phase formation, while Co and Ru played a positive role in improving microstructural stability. It is indicated that σ , P and R phases existed with various morphology and compositions in different experimental alloys during thermal exposure at 1100• C. The content of Co, Cr and Mo in those alloys affected the types of TCP phases significantly, while Ru additions showed a negligible effect. R phase was prone to form in alloys containing high level of Co addition. Meanwhile, the ratio of Cr and Mo content had strong influence on the formation of σ and P phases in alloys containing low level of Co addition. The effects of alloying additions on the elemental partitioning ratios between γ and γ phases contributed to their corresponding influence on TCP phase formation.

Investigation of grain growth and microstructural evolution in electron beam melting additive manufacturing process

“…During dendritic solidification of Ni-based superalloys, the process of solute enrichment leads to variation in partition coefficients of refractory elements. When these solute rich regions are exposed to higher temperatures for longer durations, which happens during ageing or annealing or--as observed in this study--reheating during SEBM process, TCP phases are formed [120,121,123,124,[275][276][277][278]. It is believed that the presence of Laves based TCP phases in as-built specimens is the outcome of the inherent non-equilibrium nature of solidification in AM processes.…”

“…Based on these reflections, it can be inferred that the secondary precipitates present at GBs are C14 Laves phase that has an HCP structure. Several previous studies on Ni-based superalloys have also reported the formation of these phases, and have referred to them as TCP precipitates [120,121,123,124,[275][276][277][278]. These precipitates are generally irregular in shape and form when the alloy is aged at high temperatures for extended periods [278].…”

“…TCP precipitation in Ni-based superalloys depends on the segregation tendencies of microconstituents and the service temperature[120,121,123,124,[275][276][277]. It is important to examine the elemental segregation at the micro-scale to better understand the unexpected TCP precipitation in the SEBM-built superalloy.…”

Microstructural stability of TMS-238™ Ni-base superalloy during long-term exposure at high temperature

“…The precipitation kinetics of Re–Ru–Ni-rich phase is not uniform in the whole sample. Noticeable differences in the evolution of the precipitates were identified for the dendrite core, arm and interdendritic regions, Figure 6(a,b), while in most of the papers [21,22,30] only dendrite cores, as the most critical areas with respect to TCP or HCP phase formation, were taken into account. However, in this study it was shown that even small changes in chemical composition can strongly affect the formation of Re–Ru–Ni-rich precipitates.…”