Cooling Rate Effects in a Ni-Cr-Based Heat-Resistant Alloy: Microstructure Coarsening and Compression Behavior

Although Ni-Cr-based alloys are widely used in high-temperature applications due to their excellent oxidation, corrosion, and creep resistance, strict control during manufacturing is required to ensure quality and performance. Casting and centrifugal processing must be optimized to minimize defect formation and post-processing requirements. In this context, solidification thermal parameters play a key role in governing microstructural coarsening, defects and resulting properties. Due to the lack of mapping of solidification of this type of alloys, the present study investigates the influence of cooling rate on the microstructure and mechanical behavior of a 25Cr-35Ni-15Co-5W-0.5C alloy solidified under transient heat flow conditions. A wedge-shaped mold was used to generate a wide range of cooling rates within a single casting, followed by detailed microstructural characterization and quantification (optical microscopy, scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy (SEM-EDS), XRD) and mechanical testing (hardness, compression testing). The results show that increasing the cooling rate promotes dendritic refinement and a more refined and uniform dispersion of the interdendritic carbide network, whereas lower cooling rates lead to coarser carbide network formation. Yield compression strength remains weakly affected by coarsening. In contrast, maximum stress and strain hardening are significantly improved in refined microstructures of a 25Cr-35Ni-15Co-5W-0.5C alloy, mainly related to dendritic spacing in the order of 32 μm. Although the FCC γ -Ni dendritic matrix governs strength, a finer carbide distribution enhances compression by increasing matrix/carbide interfaces that hinder dislocation motion, whereas coarser carbides promote stress concentration and strain localization. Microstructural coarsening reduces the strain hardening parameters ( k and n ), lowering the work-hardening capacity up to 0.3 strain. Overall, cooling rate is a key parameter for tailoring the microstructure and mechanical response of Ni-Cr-based heat-resistant alloys, and the relationships established here may support the optimization of casting processes, including centrifugal casting, in which local solidification conditions influence the resulting microstructure.