Microstructural and mechanical properties of binary Ni-Si eutectic alloys

Abstract

In the present work, Ni-Si eutectic alloys with nominal compositions of Ni80Si20, Ni70Si30, Ni55Si45 and Ni45Si55 (Ni and Si with the purity of 99.99%) were prepared by arc melting method under vacuum/argon atmosphere. The effects of Si/Ni ratio on the microstructural properties, thermal transformation behavior, micro-hardness and magnetic properties of the Ni-Si eutectic alloys were investigated. These alloys were characterized by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), differential thermal analysis (DTA), Vickers microhardness measurement and Vibrating Sample Magnetometer (VSM). The phases expected according to Ni-Si phase diagram for conventional solidified eutectic Ni-Si alloys are considerably consistent with phase detected by XRD in this study. The quantitative results confirm that the chemical composition of the alloys very close to eutectic compositions and the microstructures are in typical lamellar eutectic morphology. The maximum microhardness value of 1126 HV obtained for Ni70Si30 alloy which has highest melting temperature amongst Ni-Si eutectics. The microhardness values decreases with increase of Si/Ni ratio. Ni80Si20 and Ni55Si45 alloys are soft ferromagnetic, Ni70Si30 and Ni45Si55 alloys are paramagnetic with no magnetic saturation. (C) 2014 Elsevier B.V. All rights reserved.