Online Lecture by prof. dr. Andy Godfrey

Grain-size dependence of mechanical properties in single-phase metals with a near-micrometer average grain size

Speaker: prof. dr. Andy Godfrey,  Tsinghua University (Beijing).

Title:
Grain-size dependence of mechanical properties in single-phase metals with a near-micrometer average grain size

Abstract:
Grain size control remains a major part of the physical metallurgy of single phase metals, driven by the increase in strength with decreasing grain size as described by the Hall-Petch relationship. Considerable evidence now exists, however, for a transition on mechanical properties as the grain size is reduced to the near-micrometre regime, where a positive deviation from the Hall-Petch relationship is found.
Examples will be given in this lecture based on the use of samples prepared by spark-plasma sintering of powders for a range of metals, where it is possible to achieve samples with near-micrometre average grain-size in a fully recrystallized condition.
In the case of aluminium powders, the native oxide on each powder allows also the effect of heterogeneity in grain size and spatial arrangement to be studied, by mixing of powders with different average sizes.
The spatial variation of plastic deformation at the grain scale has been explored in these samples by digital image correlation combined with electron backscatter diffraction measurements of the same area during in-situ deformation in a scanning electron microscope, providing correlated information on local displacement gradients and crystal lattice rotations.

Investigation of the mechanical properties of these samples raises questions about the nature of plastic yielding in single phase metals, motivating in-situ deformation experiments using X-ray synchrotron radiation to allow measurements in 3D of the mesoscale pattern of plastic slip.

This session was chaired by prof. Leo Kestens (Ghent University – TU Delft).