Abstract
An anomaly which occurs in annealing in the temperature range between 250°C and 450°C was investigated with commercial Cu-Ni-Zn alloys. The electric resistance and its temperature coefficient of cold-drawn wires and of wires which were water-quenched and furnace-cooled from 500°C were measured at 21°C and −196°C. (1) The electric resistance of cold-drawn wires increased gradually in the temperature range between 100°C and 300°C during isothermal annealing. (2) Its reaction was of second order and its activation energies were 2.5 kcal/mol and 25 kcal/mol at 100°∼200°C and 200°∼300°C, respectively. (3) During isochronal annealing process, both cold-drawn wires and water-quenched wires showed maxima of electric resistance and of its temperature coefficient between 250°C and 450°C. (4) but in these wires, an effect of over-aging on electric resistance and monotonous increase of its temperature coefficient were observed in a long-time or high-temperature isothermal annealing. (5) Etching bands were observed under an electron microscope only on a surface of the specimen which showed high electric resistance. From these results it seemed difficult to explain the anomaly in nickel silver alloys only with the mechanism of ordering. Therefore the author suggests that segregation of Zn atoms to stacking faults may explain the above and some of the recent experimental results.
