Effect of microstructural evolution and elevated temperature on the mechanical properties of Ni-Cr-Mo alloys

This paper characterizes the impact of solidification rate on the morphology and type of microstructural and mechanical properties of a nickel-based superalloy with a nominal composition of Ni-25Cr-18Mo (at.%) in a wide cooling range (5-100 K/s). The microstructures of the alloys were identified by scanning electron microscopy (SEM) and the phase composition was examined by X-ray diffractometry (XRD). The phase transitions during the solidification process were investigated by differential thermal analysis (DTA) under an Ar atmosphere. It was found that the final microstructure of Ni-25Cr-18Mo alloy mostly depends upon the solidification rate; the microstructures evolve from a coarse dendritic structure to a refined dendritic structure. The mechanical properties of Ni-25Cr-18Mo alloys were examined by using Vickers and Rockwell hardness tests at room temperature and at elevated temperatures from 400 °C to 800 °C. It was found that the hardness values of the samples were connected with the cooling rate and test temperatures.