Creep behavior of eutectic Sn-Cu lead-free solder alloy

• DOI: 10.1007/s11664-002-0098-3
• Publication Date: 2007-04-06T06:46:35Z
• Authors: C. M. L. Wu; M. L. Huang
• Keywords: Burgers vector; Stress relaxation; Atmospheric temperature range

Tensile creep behavior of precipitation-strengthened, tin-based eutectic Sn-0.7Cu alloy was investigated at three temperatures ranging from 303-393 K. The steady-state creep rates cover six orders of magnitude (10-3 - 10-8 s-1) under the stress range of σ/E = 10-4 - 10-3. The initial microstructure reveals that the intermetallic compound Cu6Sn5 is finely dispersed in the matrix of β-Sn. By incorporating a threshold stress, σth, into the analysis, the creep data of eutectic Sn-Cu at all temperatures can be fitted by a single straight line with a slope of 7 after normalizing the steady-state creep rate and the effective stress, indicating that the creep rates are controlled by the dislocation-pipe diffusion in the tin matrix. So the steady-state creep rate, e, can be expressed as e = A Gb/RT(σth/G) exp (-Qc/RT), where Qc is the activation energy for creep, G is the temperature-dependent shear modulus, b is the Burgers vector, R is the universal gas constant, T is the temperature, σ is the applied stress, A is a material-dependent constant, and σth = (σOB√1-kR2, in which σOB is the Orowan bowing stress, and kR is the relaxation factor.