Enhanced viscous glide creep in disordered β (Cu17Sn13) intermetallic phase with coarse grains

Abstract

High-temperature deformation mechanisms and processing maps of the coarse-grained A2 (disordered BCC) β (Cu17Sn13) intermetallic phase alloy (with the chemical composition of Cu-24.6 wt %Sn) were examined in compression in the temperature range of 843–993 K and strain rate range of 10−3-10 s−1. The β phase exhibited a stress exponent (n1) of nearly 3 over almost the entire strain-rate range at these temperatures. Limited subgrain formation occurred during hot compression. This microstructural feature and the observation of n1 = 3 strongly suggest that solute drag creep is the main high-temperature deformation mechanism. A comparison of the high-temperature deformation mechanisms and behaviors of the BCC β phase and FCC α-solid solution phase (with the composition of Cu–10Sn alloy studied in previous work) shows that both β and α phases exhibit solute drag creep, but β is considerably weaker in strength, and the upper limit of strain rate for solute drag creep is much higher (over 100 times). Solute drag creep at high strain rates in the β phase can be attributed to the high breakaway stresses for dislocations from the solute atmosphere in the presence of a high concentration of Sn solutes in the matrix. The β phase exhibits superior hot workability compared with the α phase according to the processing maps, especially at high strain rates. This is because there is no flow instability regime for the β phase under the investigated testing conditions and the power dissipation efficiency at high strain rates is higher in the β phase compared with the α phase.