H. Jiang

Abstract: The size and crystal orientation of Sn grains in Pb-free, near eutectic Sn-Ag-Cu solder joints were examined. A clear dependence of the thermomechanical fatigue response of these solder joints on Sn grain orientation was observed (Sn has a body centered tetragonal crystal structure). Fabricated joints tend to have three orientations in a cyclic twin relationship, but among the population of solder balls, this orientation triplet appears to be randomly oriented. In thermally cycled joints, solder balls with dominant Sn grains having the particular orientation with the c-axis nearly parallel to the plane of the substrate were observed to fail before neighboring balls with different orientations. This results from the fact that the coefficient of thermal expansion of Sn in the basal plane (along the alpha-axis) is half the value along the c-axis; joints observed to be damaged had the maximum coefficient of thermal expansion mismatch between solder and substrate at the joint interface, as well as a tensile stress modes during the hot part of the thermal cycle. Localized recrystallization was observed in regions of maximum strain caused by differential expansion conditions, and its connection with crack nucleation is discussed.

TL;DR: In this paper, the size and orientation of Sn grains in Pb-free, near eutectic SAC solder joints were examined and a clear dependence of the thermomechanical response of these solder joints on Sn grain orientation was observed.

TL;DR: In this paper, the effects of dislocation substructure evolution and recrystallization on electron and phonon conduction, as well as the interior and surface states, are considered. And the authors design optimal processing paths for cost effective performance using approaches such as hydroforming, which minimizes or eliminates welds in a cavity.

TL;DR: In this article, a tapered wedge niobium specimen was rolled at room temperature with multiple passes in the same direction without lubricant and then annealed at 750°C for 1h.

TL;DR: The overall mechanical properties of the high purity niobium (RRR) sheets, which are used in fabrication of the superconducting accelerator cavities, were investigated in this article.