A resistance ratio method for alloy homogeneity control

A simple and rapid method has been developed for the homogeneity control of binary alloys in which the alloying element is in solid solution. This is based on the well-known resistance ratio method for the characterization of high-purity metals, but using resistances determined under liquid nitrogen rather than liquid helium. Resistances are measured by the four-point method using a sample holder for up to eight wire samples, connected to a high precision resistance meter. The sensitivity of the resistance ratio to the composition depends on the matrix and alloying elements, but can be high for dilute alloys, decreasing as the concentration increases. It is also influenced by lattice defects and impurities, which prevent absolute measurements of the composition. Two examples of use are given: cobalt segregation was detected in casting of V-1% Co alloy and was confirmed by neutron activation analysis, and homogeneity checks were carried out on a series of Cu-Cr alloys containing 8 to 60 ppm Cr with a precision of 4 ppm Cr (standard deviation) or better. (orig.)