L12-Type Ordered Structures in NiCrAlFe Precision Resistance Alloy

Using the first-principles pseudopotential plane-wave method, the binding energies, density of states and lattice constants of a NiCrAlFe precision resistance alloy were calculated based on the disordered solid solution and L1(2)-type ordered structures. The microstructure of the alloy was analyzed by high-resolution transmission electron microscope (HRTEM). Also, the electrical resistance of the alloy was measured after solid-solution and aging treatment. From the binding energy point of view, the L1(2)-type ordered structure is more stable than the disordered solid solution structure. The calculation results of density of states and partial density of states show that in the L1(2)-type ordered structure, Ni, Cr, Al and Fe atoms bond with each other more strongly than they do in the disordered solid solution structure. Thus the stability of the alloy is improved. In fact, L1(2)-type ordered structure is revealed by HRTEM in the as-aged alloy, and its lattice parameters are close to the calculated results. According to the comparison of density of states at the Fermi level of different structures, the electrical conductivity of the alloy decreases due to the formation of L1(2)-type ordered structure compared with that of the disordered solid solution structure, which is consistent with the experimental results.