Room Temperature Creep of a Tin-Lead Solder Wire under Self-Weight

Creep tests using a simple jig have been performed on 63 wt.% tin-37 wt.% lead solder wires of diameters 1 mm and 2 mm at room temperature (23°C). Coils containing 5 or 10 rings were allowed to creep under their own weight for 60 minutes. It was noted that for either of these diameter wires, the coil with 10 rings had significantly large vertical displacements as compared to those with 5 rings. In each particular coil, the highest vertical displacements were in the bottom rings. The overall maximum vertical displacement was 76.5 mm and this was in a bottom ring of the 2 mm diameter wire with 10 rings. However, in all cases, the amount of horizontal displacement was negligible. The bottom ring of the 2 mm diameter wire had the largest initial strain of 0.151 at 5 minutes and final strain of 0.546 at 60 minutes; this was in the coil with 10 rings. Although no consistent pattern in change between the initial and final diameters was noted for the rings in any coil even after 24 hours of creep, it was quite apparent that in a majority of cases a change in diameter occurred. The main factor responsible for the observed creep is attributed to the weight of the rings in the coils rather than capillary flow.

On the Room-Temperature Creep Behavior and Its Correlation with Length Scale of a Litao3 Single Crystal by Spherical Nanoindentation

Relying on nanoindentation technology, the room-temperature creep behavior of a LiTaO3 single crystal in the typical orientation (01 1 ¯ 2), i.e., Y-42° plane was investigated. Three kinds of spherical tips with the radii of 0.76, 2.95 and 9.8 μm were respectively applied to detect nanoindentation length scale effect on creep deformation at both elastic and plastic regions. Superficially, both creep displacement and rate were nearly linearly increased with increasing holding depth and independent of tip size, which could be ascribed to the simultaneously enlarged holding strain and deformation volume beneath the indenter. At a similar holding strain, creep deformation, i.e., creep strain and strain rate were more pronounced under smaller spherical tips. Strain rate sensitivities of creep flows under different spherical tips and holding strains were also estimated. The potential room-temperature creep mechanism of LiTaO3 under high shear compression stress was discussed.

Room-Temperature Creep Behavior and Activation Volume of Dislocation Nucleation in a LiTaO3 Single Crystal by Nanoindentation

The crystal orientation effect on mechanical heterogeneity of LiTaO3 single crystals is well known, whilst the time-dependent plastic behavior, i.e., creep is still short of understanding. Relying on nanoindentation technology, we systematically studied room-temperature creep flows at various holding depths (100 nm to 1100 nm) in three typical orientations namely the X-112°, Y-36° and Y-42° planes. Creep resistance was much stronger in the X-112° plane than the others. In the meanwhile, creep features were similar in the Y-36° and Y-42° planes. The orientation effect on creep deformation was consistent with that on hardness. The nanoindentation length scale played an important role in creep deformation that creep strains were gradually decreased with the holding depth in all the planes. Based on strain rate sensitivity and yield stress, the activation volumes of dislocation nucleation were computed at various nanoindentation depths. The activation volumes ranged from 5 Å3 to 23 Å3 for the Y-36° and Y-42° planes, indicating that a point-like defect could be the source of plastic initiation. In the X-112° plane, the activation volume was between 6 Å3 and 83 Å3. Cooperative migration of several atoms could also be the mechanism of dislocation activation at deep nanoindentation.