Creep, recrystallisation and anelasticity of hcp-metals

Metals and alloys with the hexagonal close pack (hcp) structure (e.g. magnesium, zinc, cobalt) are important industrial materials. Hexagonal titanium and zirconium alloys are key materials in the aerospace and nuclear energy sector. Creep properties are key to their success as well as often being the limiting factor. Iron adopts the hcp structure above ~11GPa and the energy to sustain the Earth's magnetic field comes from crystallization of the liquid iron outer-core into hexagonal close pack (hcp)-iron. The properties of the Earth's inner-core are inferred primarily from the speed and attenuation of cyclic, seismic waves as they transverse the core.

The extreme conditions needed to stabilize hcp iron (>12 GPa) and those of the Earth's inner core (>250 GPa, >5500 K) mean that comparatively little is known about its creep behavior or its response to cyclic deformation. In this project the student is studying the experimental systematics of hcp metals and alloys to both creep and small amplitude cyclic (sinusoidal) deformation as well as diffusion and annealing tests at elevated temperatures. Initial experiments will be conducted on magnesium using a 1 atmosphere high temperature creep apparatus. The mechanical data from the tests will be combined with scanning electron microscope (SEM) and electron microprobe analysis (EPMA), to understand the crystallographic and material processes that occur in their experimental samples. The work will progress to other samples and higher pressures.

The response of metals and alloys to small amplitude cyclic loading is important for both understanding of the Earth's inner-core and material forming and industrial processes.