Elastoplastic Deformation of a Ni3Al-Based Single Crystal Depending on Crystallographic Direction

AbstractAn electronic stopping power model for boron, arsenic, and phosphorus ion implantation into single-crystal Si is reported over the energy range from a few keV to several MeV, for both offand on-axis implant angles relative to the <100> crystallographic direction. Combined with previously developed models for damage accumulation, this model allows physically-based simulation of 3-D profiles over an extremely wide range of implant conditions. In particular, this allows modeling of MeV implants which are being used more and more frequently.

Nanoindentation tests with the aid of acoustic emission monitoring were performed on single crystal MgO (001) plane to investigate the deformation of MgO under high indentation pressures. The results indicated that the deformation of MgO under nanoindentation with a sharp indenter could be classified into three stages: elastic deformation, elastoplastic deformation, and fragmentation. The elastic energy release and fracture occurred could be identified using acoustic emission signals.

Among processes involving plastic deformation, sheet metal forming requires a most accurate description of plastic anisotropy. One of the main sources of mechanical anisotropy is the intrinsic anisotropy of the constituent crystals. In this paper, we present the single-crystal yield criterion recently developed by Cazacu et al. [1] and its application to the prediction of anisotropy in uniaxial tension of strongly textured polycrystalline sheets. Namely, it is shown that using this single crystal yield criterion the Lankford coefficients exist and have finite values for all loading orientations. Moreover, the variation of both the yield stress and Lankford coefficients with the crystallographic direction can be expressed analytically. An application of this criterion to forming a cylindrical cup from a single crystal of (100) orientation is presented. Finally, we show that using this single-crystal model, one can describe well the effect of the spread around an ideal texture component on the anisotropy in uniaxial tensile properties of a polycrystal.

The problem was suggested by Professor G. I. Taylor as being of interest and importance in the phenomena of rupture in a solid, due to the presence of a crack, and the slip in a crystal. In experiments on the distortion of a crystal of aluminium under a tensile stress the conclusion is reached that “…as far as these experiments go, the distortion of a crystal of aluminium under compression is of the same nature as the distortion which occurs when a uniform single-crystal bar is stretched. The distortion is due to slipping parallel to a certain crystal plane and in a certain crystallographic direction, and the choice of which of twelve possible crystallographically similar types of slipping actually occurs depends only on the components of shear stress in the material and not at all on whether the stress normal to the slip plane is a pressure or a tension.”

Single-crystal SnO2 nanofibers have been formed from SnO2 polycrystals via reaction at low oxygen partial pressures. Polycrystalline SnO2 disks coated with Au nanoparticles were exposed to humid H2/N2 at 700 to 800 °C. Single-crystal SnO2 nanofibers formed beneath Au nanoparticles, with the nanofiber length oriented parallel to the [100] crystallographic direction of SnO2. Because this simple process does not require either a separate source of a Sn–O-bearing vapor species located upstream of the substrate or a temperature gradient, single-crystal nanofibers may be formed on large area SnO2-bearing substrates.