Elemental partitioning,lattice misfit and creep behaviour of Cr containing γ′ strengthened Co base superalloys

Novel Cr containing Co-Al-W base superalloys were studied by atom probe tomography and neutron diffraction. Cr is found to predominantly partition to the γ matrix and decrease partitioning of W to γ′. Furthermore, Cr significantly enhances the γ′ volume fraction, decreases the γ/γ′ lattice misfit and deteriorates the creep resistance. Addition of Ni to the Cr containing alloys affects partitioning of W and Al, further decreases the lattice misfit and results in the formation of irregularly shaped precipitates. Al, W and Cr tend to occupy the ‘B'sublattice in the γ′-A₃B phase (L1₂ type), while Co and Ni reside in the ‘A' sublattice.     

The Effects of Debonding on the Low-Velocity Impact Response of Steel-CFRP Fibre Metal Laminates

The effect of metal-composite debonding on low-velocity impact response, i.e. on contact force–central deflection response, deformation profiles and strains on the free surfaces was studied. We focused on type 2/1 fibre metal laminate specimens made of stainless steel and carbon fibre epoxy layers, and tested them with drop-weight impact and quasi-static indentation loadings. Local strains were measured with strain gauges and full-field strains with a 3-D digital image correlation method. In addition, finite element simulations were performed and the effects of debonding were studied by exploiting cohesive elements. Our results showed that debonding, either the initial debonding or that formed during the loading, lowers the slope of the contact force–central deflection curve during the force increase. The debonding formation during the rebound phase was shown to amplify the rebound of the impact side, i.e. to lower the ultimate post-impact deflection. The free surface strains were studied on the laminate’s lower surface at the area outside the debond damage. In terms of in-plane strains, debonding formation during impact and indentation, as well as the initial debonding, lowered the peripheral strain and resulted in a positive change in the radial strain.     

Features of the Interaction and Phase Formation in the WC–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–C System When Heated in Vacuum and in Argon

Special features of the interactions and phase formations in carbide-oxide mixture WC 33.5 wt % Fe₂O₃ and in the WC–Fe₂O₃–C system when heated in vacuum and in argon have been studied. To add free carbon into carbide-oxide mixture, the K354 soot and saccharose, which dissociated when heated to high-clean carbon. It is established that at the absence of free carbon in the carbide-oxide system the active interaction between carbon of tungsten carbide and oxygen of iron oxide takes place that shows up in the weight loss of the samples. As a results there form the phase of the intermetallide Fe₇, W₆, the phase with a structure of the FeWO₄ and W. The addition of free carbon allows keeping tungsten carbide partly or completely and reducing iron from oxide. At the lack of free carbon some part of the tungsten carbide carbon starts to interact with oxygen and the Fe₃W₃C complex carbide forms in the system, at the excess of carbon the tungsten carbide retained and the bcc-iron forms. The heating in vacuum differs from the heating in argon by two indications: to remove the same amount of oxygen is spent more carbon than in heating in argon; the temperature of the active interaction of carbon with oxygen decreases. The largest (by 300°C) decrease of the temperature is observed when the saccharose is used as the source of free carbon.     

Current-Oscillation Power Growth in a Semiconductor Superlattice with Regard to Interminiband Tunneling

The total power of oscillations of current flowing through a semiconductor superlattice with different gaps between the first and second minibands is discussed. It is demonstrated that, with a decrease in the band gap, i.e., with an increase in the probability of interminiband tunneling, the total current-oscillation power increases when certain voltages are applied to the superlattice.     

Instability of the Flow in a Spherical Layer under Torsional Oscillations of the Inner Boundary

The instability of viscous incompressible fluid flows caused in a thin spherical layer by torsional oscillations of the inner sphere in a thin spherical layer with respect to the sate of rest is studied numerically. It has been established that an increase in the frequency of torsional oscillations leads to a change in the mode of the instability, with a transition from secondary flows in the form of Taylor vortices to structures not observed earlier. The revealed instability is observed in the frequency range from 0.61 to 2.45 Hz or, if the wavelengths are taken relative to the layer thickness, from 0.67 to 1.33.