The enhanced range of temperature for coefficient of low thermal expansion, electrical and thermal conductivities of Cu substituted Fe-Ni invar alloys

Six alloys of Fe65Ni35-xCux(x = 0, 0.2, 0.6, 1, 1.4, 1.8 at.%) have been prepared by conventional arc-melting technique and characterized by utilizing high temperature x-ray diffraction (HTXRD) technique at a range from room temperature to 773 K for determination of phase, lattice parameter (a), coefficient of thermal expansion (alpha(T)), mean square amplitude of vibration ((u) over bar (2)), characteristic Debye temperature (Theta(D)), electrical resistivity (rho) and thermal conductivity (kappa). The studies showed that these alloys form face centered cubic structure (fcc) throughout the investigated temperature range. The values of alpha(T) were found to be comparable to those for conventional Fe-Ni invar alloys but have increased temperature span to a significant extent. The mean square amplitude of vibration ((u) over bar (2)) and Debye temperature were found to remain almost unchanged in the invar temperature range, whereas the electrical and thermal conductivity were found to improve.