We compute the dynamic correlations of the nonlocal shear stress at the liquid to glass transition in colloidal dispersions. Whereas Eshelby's elastic pattern is recovered independently of the dynamics, the Goldstone modes of the colloidal glass are diffusive, ω = −iDq 2 , because the transverse momentum is not conserved -excluding propagating transverse sound. Precursors of both, the Goldstone modes and the long-ranged, anisotropic stress correlations, can be observed in the colloidal fluid. The slow diffusive mode dominates the dynamics in the supercooled liquid for wave numbers qξ 1 with a correlation length ξ ∝ τ 1/2 which grows like the square root of the relaxation time τ . Time-and space-dependent stress correlations are anisotropic, decaying like r −5 . These results are derived within a hydrodynamic theory, generalising Maxwell's model to finite wave numbers, after the dynamics has been decomposed into potentially slow modes, associated with the order parameter, and fast microscopic degrees of freedom. Alternatively, hydrodynamic equations, closed by constitutive laws, can be used to predict the linear response of stress to an applied shear flow.

Phase separation of g 0 precipitates determines the microstructure and mechanical properties of nickel-based superalloys. In the course of ageing, disordered g spheres form inside ordered (L1 2 ) g 0 precipitates, undergo a morphological change to plates and finally split the g 0 precipitates. The presence of g particles inside g 0 affects coarsening kinetics and increases alloy hardness. Here we use atom probe tomography to visualize phase separation in a Ni 86.1 Al 8.5 Ti 5.4 alloy in three dimensions and to quantify the composition of all the phases with near-atomic resolution. We find that g 0 precipitates are supersaturated in nickel, thereby driving the formation of g particles and observe a compositional evolution of the g particles, which accompanies their morphological change. Our results suggest that by controlling nickel supersaturation we can tailor the phase separation and thereby the properties of nickel-based superalloys.

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During solidification of Fe-containing Al-Si casting alloys, various different intermetallic phases are formed. As this can have an impact on mechanical properties we investigated phase formation by applying in-situ time resolved synchrotron X-ray tomography. For a commercially pure Al-10Si-0.3 wt.%Fe alloy, phase morphology and spatial arrangement during solidification was revealed with 1°C temperature resolution. We find that many of the intermetallic phases that have been identified as β-AlFeSi phases in previous studies are in fact δ phases. It was found that δ plates mainly nucleate on the eutectic Al and Si. δ phase formation terminates almost simultaneously with the final solidification of eutectic phases. Features of δ phase growth such as impingement, branching and deformation of plates are discussed. The phase separation sequence during solidification is described and explained by the existence of "cells" of residual liquid in which δ phase formation progresses rapidly due to the supersaturation of solute atoms.