Effects of Sequential Operation with Heat Treatment and Mechanical Milling on Work Hardening for Superalloy GH4169

Engineering components are usually manufactured with sequential production processes. Work hardening due to previous production processes affects the machinability of the workpiece in subsequent operations. In this research, the surface work hardening of a workpiece manufactured by two sequential processes with heat treatment/milling (HT + M) and milling/heat treatment (M + HT) of superalloy GH4169 was investigated. First, the surface microstructure characteristics, including plastic deformation and grain size of the machined workpiece surface processed by the two sequential processes, were quantitatively presented. Then, the microhardness on the machined workpiece surface and its cross-section was measured and analyzed. Finally, a surface microhardness calculation model considering twin boundary deformation was proposed. Here, we also present the microstructure evolution principle of the machined workpiece surface by the two sequential processes. It was found that the degree of work hardening of HT + M machining was 179%, whereas that of M + HT was only 101%. The research results can be applied to the optimized selection of process sequence for manufacturing superalloy GH4169.

Highly localized upper mantle deformation during plate boundary initiation near the Alpine fault, New Zealand

Peridotite xenoliths entrained in magmas near the Alpine fault (New Zealand) provide the first direct evidence of deformation associated with the propagation of the Australian-Pacific plate boundary through the region at ca. 25–20 Ma. Two of 11 sampled xenolith localities contain fine-grained (40–150 mm) rocks, indicating that deformation in the upper mantle was focused in highly sheared zones. To constrain the nature and conditions of deformation, we combine a flow law with a model linking recrystallized fraction to strain. Temperatures calculated from this new approach (625–970 °C) indicate that the observed deformation occurred at depths of 25–50 km. Calculated shear strains were between 1 and 100, which, given known plate offset rates (10–20 mm/yr) and an estimated interval during which deformation likely occurred (<1.8 m.y.), translate to a total shear zone width in the range 0.2–32 km. This narrow width and the position of mylonite-bearing localities amid mylonite-free sites suggest that early plate boundary deformation was distributed across at least ~60 km but localized in multiple fault strands. Such upper mantle deformation is best described by relatively rigid, plate-like domains separated by rapidly formed, narrow mylonite zones.

Experimental investigation of precession driven flows in a triaxial ellipsoid

<p>Precession driven flows are relevant for geo- and astrophysical fluid dynamics as well as industrial applications. In the context of planetary core dynamics, they are attributed to the generation of magnetic fields and/or anomalous dissipation. While precession driven flows have been frequently studied in a cylindrical, spherical or spheroidal container shape, the geometry of a triaxial ellipsoid, representing the geophysical case of core mantle boundary deformation in a tidally locked planet, has received less attention.</p><p>Here, we present results from an experimental study in a triaxial ellipsoid. The main focus of our study is on the base flow of uniform vorticity and we report a good agreement between experimental data and existing semi-analytical models. The amplitude of the time averaged uniform vorticity displays a hysteresis loop as a function of the precession forcing and we demonstrate that this observation depends on the ellipticity of the container. Our study also comprises experiments where the boundary layer is expected to be in a turbulent state. Therefore, we discuss the applicability of an effective damping coefficient in the semi-analytical models to account for the dissipation in a turbulent boundary layer. </p>

Asymptotic behavior of repeated eigenvalues of perturbed self-adjoint elliptic operators

A variational characterization for the shift of eigenvalues caused by a general type of perturbation is derived for second order self-adjoint elliptic differential operators. This result allows the direct extension of asymptotic formulae from simple eigenvalues to repeated ones. Some examples of particular interest are presented theoretically and numerically for the Laplacian operator for the following domain perturbations: excision of a small hole, local change of conductivity, small boundary deformation.