Thermal creep of copper and copper alloys can be significant at relatively low temperatures, because of copper’s low melting point (0.3 Tm = ^134 °C, Tm is the melting point). Nadkarni51 and Zinkle and Fabritsiev2 compared the 100-h creep rupture strength of copper and several PH and DS copper alloys at elevated temperatures. Copper alloys have significantly higher creep rupture strength than pure copper. Creep rupture strength decreases drasti­cally as temperature increases in PH alloys such as CuCrZr, as well as in pure copper, between 200 and 450 °C. DS alloys such as CuAl25 have superior creep rupture strength even above 400 °C because of their thermal stability at high temperatures.

Li et al?1 summarized steady-state thermal creep data for pure copper and several copper alloys, as shown in Figure 5. Pure copper can suffer significant creep deformation at high temperature even with a very low applied stress. The creep rate of pure cop­per can be as high as ^10-4s-1 at ^100 MPa at 400 °C. The creep resistance of copper alloys is con­siderably higher than that of pure copper. The creep
rates of copper alloys strongly depend on the applied stress and the temperature, and can be described by the Norton power law relation; that is, e = Aan exp(—Q/RT) where e is creep rate, a is the applied stress, n is the stress exponent, Q is the activation energy, R is the gas constant, and T is the temperature. DS copper alloys exhibit unusu­ally high values of the stress exponent, for example, 10-21 in the temperature range of 472-721 °C for GlidCop Al15.52

Because of the time-dependent nature of creep deformation, softening behavior due to overaging and recrystallization must be considered during the creep analysis for PH copper alloys. The creep prop­erties of this class of alloys could be significantly changed during prolonged exposure at elevated temperature.