Creep-Recovery Behavior of Copper Springs at Low Stresses

Copper springs, unlike conventional wires, endure complex stress states such as torsion and bending under sustained thermal and mechanical loads. This study examines the time-dependent creep-recovery behavior of copper springs under low tensile forces at temperatures ranging from 523 K to 623 K, focusing on springs with spring indexes (ratio of mean spring diameter to wire diameter) of 6.4, 8.5, and 9.6. The non-linear Burgers model with a Kelvin solid effectively captures the deformation response and mirrors dislocation nucleation and annihilation kinetics. SEM and TEM imaging reveal that low-angle grain boundaries (LAGBs) act as both dislocation sources and sinks. The non-linear Burgers model with a Maxwell solid is excluded due to its inconsistency with temperature-dependent Young’s modulus. Steady-state creep is governed by dislocation climb and grain boundary sliding, with activation energies ranging from 17 to 21 kJ/mol, consistent with grain boundary and pipe diffusion. The stress exponent remains constant at 2.7 across all spring indices. During transient creep, dislocation glide and rearrangement dominate, accompanied by dynamic recovery and the formation of subgrains. The activation energy for transient creep decreases with increasing spring index. These results offer insight into the microstructural evolution and thermal stability of copper springs, thereby enabling a more accurate prediction of their long-term mechanical performance.