Effect of heat treatment on diffusion, internal friction, microstructure and mechanical properties of ultra-fine-grained nickel severely deformed by equal-channel angular pressing

Severe plastic deformation via equal-channel angular pressing was shown to induce characteristic ultra-fast diffusion paths in Ni (Divinski et al., 2011). The effect of heat treatment on these paths, which were found to be represented by deformation-modified general high-angle grain boundaries (GBs), is investigated by accurate radiotracer self-diffusion measurements applying the 63Ni isotope. Redistribution of free volume and segregation of residual impurities caused by the heat treatment triggers relaxation of the diffusion paths. A correlation between the GB diffusion kinetics, internal friction, microstructure evolution and microhardness changes is established and analyzed in detail. A phenomenological model of diffusion enhancement in deformation-modified GBs is proposed.

Damping properties of open cell microcellular pure Al foams

Damping behaviours of the open cell microcellular pure Al foams fabricated by sintering and dissolution process with the relative density of 0·31-0·42 and the pore size of 112-325 μm were investigated. The damping characterisation was conducted on a multifunction internal friction apparatus. The internal friction (IF) was measured at frequencies of 1·0, 3·0 and 6·0 Hz over the temperature range of 298-725 K. The measured IF shows that the open cell pure Al foam has a damping capacity that is enhanced in comparison with pure Al. At a lower temperature (∼400 K), the IF of the open cell pure Al foams increases with decreasing relative density, with decreasing pore size and with increasing frequency. The IF peak was found at the temperature range of 433-593 K in the IF curves. It is clear that the IF peak is relaxational type and the activation energy associated with the IF peak is about 1·60 ± 0·02 eV. Defect effects can be used to interpret the damping mechanisms.

Prestressed natural fibre spun yarn reinforced polymer-matrix composites

Abstract We report that a prestressing technique similar to that traditionally used in prestressed concrete can improve the mechanical performance of flax fibre spun yarn reinforced polymer-matrix composites. Prestressing a low twist yarn not only introduces tension to the constituent fibres and compressive stress to the matrix similar as in prestressed concretes, but also causes changes to the yarn structure that lead to the rearrangement of fibres within the yarn. Prestressing increases the fibre packing density in yarn, causes fibre straightening, and reduces fibre obliquity in yarn (improved fibre alignment along yarn axis). All these changes contribute positively to the mechanical properties of the natural fibre yarn reinforced composites. Crown

Development of hybrid composites for automotive applications: effect of addition of SEBS on the morphology, mechanical, viscoelastic, crystallization and thermal degradation properties of PP/PS-xGnP composites

In this article, we report on a simple and cost effective approach for the development of light-weight, super-tough and stiff material for automotive applications. Nanocomposites based on PP/PS blend and exfoliated graphene nanoplatelets (xGnP) were prepared with and without SEBS. Mechanical, crystallization and thermal degradation properties were determined and correlated with phase morphology. The addition of xGnP to PP/PS blend increased the tensile modulus at the expense of toughness. The presence of xGnP increased the enthalpy of crystallization and enthalpy of fusion of PP in the blends, without affecting segmental mobility and thermal stability. Addition of polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) improved the toughness of PP/PS blends, but decreased the stiffness. The incorporation of xGnP into this ternary blend generated a super-tough material with improved stiffness and tensile elongation, suitable for automotive applications. It is observed that the presence of SEBS diminished the tendency of agglomeration of xGnP and their unfavorable interactions with thermoplastics, which in turn reduced the internal friction in the matrix.