Loading in 2 Seconds...
Loading in 2 Seconds...
D-DIA (Deformation DIA) High-P and T, homogeneous stress/strain (Durham, Wang, Getting, Weidner)
Rotational Drickamer Apparatus large strain (radial distribution), high P-T (Yamazaki, Xu, Nishihara)
Sample assembly for a rotational Drickamer Apparatus (torsion tests on a thin disk-shaped sample to large strain) Alumina Zirconia MgO
Large-strain shear deformation of wadsleyite
Effects of Phase Transformation Grain-size Crystal structure, bonding Internal stress/strain (“transformation plasticity)
Rheology of deep mantle minerals At present, only results from analog materials are available High-pressure deformation experiments are preliminary Need for direct, quantitative high-pressure studies
A first-order phase transformation is associated with a finite volume change that causes an internal stress/ strain, which may modify the rheological behavior (transformation plasticity).
The role of internal stress In the Orowan equation, the dislocation density may be controlled by the “internal stress”. .
Physical Processes Controlling • the Grain-Size • Grain growth (static: driving force=boundary energy) • Dynamic recrystallization (dynamic: driving force= dislocation energy) • Phase transformation
Driving forces for grain-boundary migration Grain-boundary energy -> grain-growth Dislocation energy -> dynamic recrystallization Chemical energy -> grain-size reduction
Driving forces for grain-boundary migration : grain-boundary energy : dislocation energy
(µmn) A comparison of grain-growth kinetics in olivine and wadsleyite (under nominally “dry” conditions) Log (GS^n-GS0^n)
ln k (m3/s) H*=140+/-20 kJ/mol
r~0.5 q~1 H*~140 kJ/mol
Secondary phase particles have an important effect on grain-growth (Zener pinning). Grain-growth in two-phase mixture is completely different from that in a single-phase aggregates (controlled by the Ostwald ripening). Very few studies have been done on two-phase aggregates (Yamazaki et al., 1996).
Zener pinning When excess energy needed for a moving boundary to pass over secondary particles exceed the driving force for migration, then grain-boundary migration stops. LZ=4a/3f a: size of secondary-phase particles f: the volume fraction of secondary phase particles If the size of the secondary phase particles can increase, then continuing growth is possible.
Kinetics is proportional to the solubility and diffusion coefficient of growing material in the matrix.