Abstract

In this paper we studied thermal stability of Ni75Cr7Si7.5Mn10.5 and Ni80.5Cr4.2Si6.5Mn5B3.8 glass coated microwires with metallic nucleus diameters ranging between 10 pro and 20 mu m using electrical resistance measurements, X-ray diffraction and DSC methods. Electrical resistance was measured during Joule heating of the sample i.e: flowing the DC current. X-ray diffraction was used to determine the crystalline structure in as-prepared microwires. It was found that electrical resistance per length, rho, depends on the sample geometry. Besides this dependence is opposite for Ni75Cr7Si7.5Mn10.5 and Ni80.5Cr4.2Si6.5Mn5B3.8 glass coated microwires. Such dependences have been related with effect of rapid solidification conditions on the grain sizes and consequently on grain growth process during annealing. Temperature coefficient of resistivity in the case of Ni75Cr7Si7.5Mn10.5 microwires is much smaller (about 5 times smaller). Considerable dependence of the current density for beginning of phase transition on metallic nucleus diameter has been attributed to the thermal transfer conditions. Efficiently of joule heating for the case of thinner microwires is smaller and the current density for achieving the phase transition-higher. (C) 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim (C) 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim