Influence of aluminium on electric resistivity of nickel-aluminium alloys

Temperature and concentration dependences of electric resistivity of nickel-aluminium alloys in a liquid state have been studied. The type of ρ polytherms is determined by the initial phase composition of alloys. Polytherm hysteresis is associated with the elimination of the influence of the structure and phase composition of solid samples on the melt and the transition of the system to an equilibrium and homogenous state. All this leads to a greater structural ordering of intermetallic compounds. Experimental data show a wave nonlinear concentration dependence of the electric resistivity isotherm of nickel alloys with the aluminium content of up to 35 mass percent. In this concentration region the existence of a solid solution of aluminium in nickel (up to 10 mass percent) is possible, as well as the emergence of intermetallic phases Ni 3Al and NiAl. On the basis of the percolation theory and the model of the microinhomogeneous structure of melts, the wave-like type of isotherms of electrical resistivity of nickel-aluminium melts has been qualitatively explained. Due to different electrical negativity of atoms and the distortion of the electronic and atomic structure of nickel subsystems, the Ni-Al system is overcharged. This leads to local atomic ordering and cluster formation, the ordering nature differs from nickel microregions which are outside the energy field of the charge. An additional factor of dispersion is formed in the system alongside with the formation of clusters for conduction electrons. The increase of the aluminium concentration in the alloy is accompanied by the increase of the number of conduction electrons per atom. Secondly, in accordance with the percolation theory, gradually emerging clusters first create chains and later zones of overlapping thus improving conductivity of alloys containing up to 10 mass percent of Al.