Quenching studies on mechanical properties of pure gold

Abstract

The effect of quenching from temperatures in the range 500°C–1050°C on the mechanical properties of 99.999% gold wires was studied over the range of cooling rates from 1000° to 60,000°C/sec. The specimens were deformed in tension at various temperatures from liquid nitrogen to 250°C. Upon aging at temperatures of 25°, 60° and 100°C subsequent to quenching, the yield stress was found to increase markedly, depending on the cooling rate and the quenching temperature. No effect was found for a rate of cooling of 1000°C/sec. An increase of the yield stress of six fold occurred upon quenching from 1030°C with a rate of cooling of 60,000°C/sec. The activation energy corresponding to the rate of increase in yield stress was 0.7 eV upon aging at 25–100°C. Variation of the testing temperature from −196°C to 150°C had no effect on the increase in yield stress resulting from quenching and aging. However, a considerable decrease in the yield stress of quenched samples was observed for tests at 250°C. No resoftening was caused by annealing at 250°C for as long as 6 hr. Appreciable softening was observed above 600°C for anneals of 1 hr. The effect of quenching temperature can be divided into three temperature regions when the complication of quenching strains are not present. Region I depends strongly on quenching speed and lies from about 930°C to the melting temperature for a 30,000°C/sec cooling rate; region II lies just below and extends down to 740°C, and region III below 740°C. The dependence of yield stress on quenching temperature in region II gives an activation energy of 1.1 eV.