S0301-3-4 Relationship between crack morphology and microstructure in the creep-fatigue crack propagation of read-free solder

Abstract

Crack propagation tests of lead-free solder were conducted using center-notched plates under three cyclic tension-compression load controlled wave forms: pp wave is fast loading and unloading, cp-h wave is tension-hold and cc-h wave is tension and compression hold. Creep crack propagation rate of cc-h and cp-h wave shape was calculated by the subtraction of fatigue crack propagation rate from total crack propagation rate. The relationship between creep crack propagation rate and creep J-integral showed parallel two lines for cc-h and cp-h wave shares, showing 10 times faster for cp-h than cc-h. Crack morphologies were obtained from SEM and EBSD observation. Macroscopic crack path was perpendicular to loading axis for pp and cp-h, while 45° inclined from loading axis for cc-h. Microscopic crack path was inter-particle zig-zag type for pp wave but rather straight for cc-h and cp-h possibly due to the reduction of crystal orientation between particles which showed recovery or re-crystalization of β-Sn particles. Therefore, microscopic and macroscopic crack morphologies in relation to the micro-structural change may affect the crack propagation rate under creep-fatigue condition.