Implications of carbon content for the processing, stability, and mechanical properties of cast and wrought Ni-based superalloy Nimonic 105

As the temperature and pressure requirements in land-based turbines for power generation increase, the shift towards more advanced alloys, e.g., Ni-based superalloys, requires improved understanding of their long-term stability and mechanical properties. Additionally, the larger size of the components also presents fabrication and cost-reduction problems. In this study, we investigated Nimonic 105 as a potential rotor material at two carbon content levels - the commonly used maximum of the alloy specification and a lower carbon content variant. Reducing the carbon content presented fabrication challenges, resulting in surface crack formation during hot working. Additionally, a lower M6C carbide fraction was present after fabrication/solutioning, leading to a significantly larger grain size. After the standard aging treatment, similar gamma ' populations formed in the two variants, however the M6C carbides in the high-carbon variant already started transforming to intergranular M23C6. Although we did not observe a noticeable effect on the tensile properties of the two variants, the lower carbon content alloy possessed a superior creep property - mainly due to the larger grain size as the microstructural stability was inferior. Upon prolonged thermal exposure, the M6C carbides in the low-carbon variant further decomposed to intergranular and intragranular sigma and mu precipitates, as opposed to mainly M23C6 as in the high-carbon variant.

Automated summary

With the increasing temperature and pressure requirements in land-based turbines for power generation, the study of high-temperature alloys becomes more important. This study investigated the effect of carbon content on the fabrication and properties of Nimonic 105 alloy. Lowering the carbon content improved the creep property and grain size, but also presented challenges in fabrication. Prolonged thermal exposure resulted in complex carbide phase transformation in the low-carbon variant.