Investigation of the microhardness and the electrical resistivity of undercooled Ni-10 at.% Si alloys

Ni-10 at.% Si alloys (Ni and Si of purity of 99.99%) were prepared by arc melting method under argon atmosphere in a water-cooled copper hearth with a non-consumable tungsten electrode and titanium getter. Spherical-shaped Ni-10 at.% Si alloy melts are undercooled in a containerless electromagnetic levitation apparatus. The effects of undercooling (ΔT) on the microstructure, electrical resistivity (ρ) and microhardness (HV) were investigated. The experimental results reveal that with the increase of the undercooling of the melts from 16 to 110 K, the microstructures undergo transition from coarse dendritic morphology to ultra fine dendritic morphology. The measurements of microhardness of the samples were performed by using a microhardness test device. The dependence of microhardness on undercooling was analyzed and it has been found that with increasing the undercooling the HV increases. Variations of electrical resistivity of the Ni-10 at.% Si alloy with the temperature in the range of 300-800 K were also determined by using a standard d.c. four-point probe technique. The resistivity of samples increases with increasing temperature and undercooling.