Investigation of microstructural, mechanical and thermal properties of rapidly solidified Ni–7 wt% Si alloy

This paper presents a systematic study on the microstructure, solidification behavior, tensile-strength and microhardness of rapidly solidified Ni–7Si alloys by using the melt-spinning technique. The microstructures of Ni–7Si alloys were characterized by SEM and the phase composition was identified by XRD analysis. The phase transition during the solidification process was studied by DTA under an Ar atmosphere. The resultant melt-spun ribbons had various microstructures ranging from dendrite to equiaxed grains, and finally to a very homogeneous structure, depending on the solidification rate. The tensile-strength and microhardness of the specimens were examined at room temperature. It was found that both the tensile-strength and microhardness of the melt-spun ribbons were strongly dependent on the solidification rate. Vickers microindentation tests were performed on the samples with different peak loads at room temperature. It was found that the microhardness and effective elastic modulus values increased with the solidification rate and these values showed peak load dependence.

► The solidification behavior is closely related to the composition of Ni–7 wt% Si alloy. ► The α-Ni phase is the stable phase for this composition. ► Tensile strength increase with increasing solidification rate. ► The hardness value of RS alloys at 80 m/s is greater than other RS alloys. ► Undercooling has a strong impact on refinement in microstructure.