Low-Cycle Fatigue of Ultrafine-Grained Aluminum at Low Temperatures

Abstract

Ultrafine-grained (UFG) Al of 99:98$99:99% purity was fabricated by equal channel angular pressing. Fully reversed tensioncompression low-cycle fatigue tests were carried out under plastic strain control at various temperatures between 83 K and 300 K. At 300 K, UFG Al showed rapid cyclic softening. As test temperature decreased, cyclic softening became less significant and at 83 K, UFG Al showed cyclic hardening till saturation. Formation of shear bands and development of dislocation structure were the characteristic features of fatigued specimens. As test temperature decreased, the area fraction of shear bands on specimen surface decreased and at 83 K, shear bands could not be observed. In addition, local grain coarsening occurred except at 83 K. Formation of dislocation cell and wall structures became more frequent at lower temperatures and well-developed dislocation walls were formed in grains as small as 1.5 mm in size at 83 K.

Physics-of-Failure Lifetime Prediction Models for Wire Bond Interconnects in Power Electronic Modules

“…(2) Evidently, thermally activated processes occur during thermal cycling and are more significant at higher temperatures [14], [36], [37]. The occurrence of thermally activated phenomena such as recrystallization during thermomechanical fatigue is not in itself a controversial notion and has been widely reported even for isothermal fatigue conditions [14], [46], [47]. However, its influence on failure is yet to be captured meaningfully by existing PoF models for wire bonds.…”

Stability of Fatigued Dislocation Wall Structure in Coarse-Grained and Ultrafine-Grained Aluminum against Monotonic Tensile Deformation

“…Therefore, the calculated values of ¡ listed in Table 1 are close to the theoretical value. Figure 6 summarizes the experimental results of the inverse channel width under a given stress amplitude for single-crystalline Al, 32,37,53) UFG Al, 39) CG Al and UFG Al in this study. From the slope of the straight line, we find ¡ = 2.1 which is again in good agreement with the theoretically-estimated value.…”

“…We have recently reported that test temperature plays an important role on the fatigue behavior of high purity UFG Al and very fine dislocation wall structure is formed when tested at 83 K in grains smaller than a few micrometers. 38,39) In this study, low-cycle fatigue tests were carried out under plastic-strain control at 77 K using CG and UFG Al, and monotonic tensile tests were performed in succession either at 300 or 77 K after the fatigue tests. From the results of monotonic tensile tests and transmission electron microscopy (TEM), the formation and stability of the fatigued dislocation structure are studied.…”