Fatigue deformation microstructure

Examples of dislocation structures after fatigue deformation appear in a series of microstructures (Figs. 7.55-7.59) obtained by TEM. Subramanian [27] claims that these dislocation substructures are similar to that of unidirectionaUy-stressed MgO. The micrographs presented below are of single-crystal magnesia which underwent a large number of cycles (in the millions) of low strain amplitude. The maximum strain was about 0.1 % per cycle. The characteristics of the dislocation structure in MgO, having a rock-salt structure, is as follows ... 

TEM observations were performed in the as-received and deformed samples in order to reveal the effects of microstructure on the fatigue response of the studied alloy. Fracture surfaces of the deformed fatigue test specimens were comprehensively examined in a scanning electron microscope (JEOL JSM6500F) equipped with field emission gun to determine the macroscopic fracture mode and characterize the fine-scale topography and microscopic mechanisms governing fatigue fracture. 

It is interesting to observe the curved slip lines on the fractured surface of the nanocrystalhne 3Y-TZP ceramic, where the role played by the dislocations in the plastic deformation is evident. Also note the appearance of the curved slip lines that resemble the microstructures observed in metals (the beach markings see, for example, Polakowski and Ripling). These lines represent hiatuses between working and rest periods during fatigue in metals (see Fig. 7.44). 

The two remaining sections describe the fundamental fatigue and creep properties of the Pb-free solders. The properties of the bulk solder, as well as those of solder joints, are highlighted. The relevance of bulk solder properties stems from the need to develop constitutive models that predict the long-term reliability of the solder interconnections. Each section will summarize quantitative data, as well as address microstructural considerations pertaiiung to deformation in Pb-free solder compositions. 

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