We used a three-dimensional Monte Carlo method to investigate subgrain growth with different initial values for average grain-boundary misorientation, and found that abnormal grain growth emerges for relatively large average misorientation, with remaining cases revealing an exponential kinetics of subgrain growth. We also found that the growth exponent was ˜4.4, and that it was virtually independent of the average misorientation. Self-similarity of the misorientation distribution was observed during growth.

The evolution of microstructure in an Fe-0.67%C steel used for railway wheels has been investigated. To elucidate the mechanism of the ultrafine microstructure which is formed on the railway wheels tread surface, we have experimentally reproduced the same microstructure using uniaxial compressive deformation and subsequent annealing at 873 K. The deformation conditions required for ultrafine microstructure formation are the initial strain rate of 1 (=100) s-1 and total strain of 0.7. The mechanism of microstructural refinement is not the primary recrystallization but continuous recrystallization, i.e., the recovery process associated with the rearrangement of accumulated dislocations during deformation and annealing at temperatures between 773 K and 873 K. The recovery process never occurs at temperatures lower than 773 K. Primary recrystallization which involves the nucleation and growth of new ferrite grains takes place at temperatures higher than 873 K.

TiAl polysynthetically twinned (PST) crystals were deformed under plane strain condition, in which the anisotropic macroscopic deformation of PST crystals is restricted with a channel die, in order to clarify the deformation behavior of TiAl/Ti3Al lamellar structure under constraint conditions. TEM analysis of deformation modes together with the Taylor analysis reveals that all TiAl orientation variants deform to yield the relaxed-constraint-type plastic strain, where three shear strain components are not zero for each TiAl variant but are macroscopically compensated to zero by the existence of twin-related TiAl lamellae at the early stage of deformation. The Taylor analysis assuming the relaxed constraint conditions is found to be adaptable for predicting the operative deformation modes in TiAl at the early stage of deformation and also for correlating quantitatively the stress-strain behavior of PST crystals under external constraint with those under the unconstraint condition.

Transmission electron microscopy (TEM) and specialized dislocation-density based crystal-plasticity formulations and finite-element schemes were used to investigate the effects of nano-sized precipitates and micro-sized Mn-bearing particles on the behavior of Al-Cu-Mg-Ag alloys. By accurately representing crystallography and the morphology of the different precipitates, accurate predictions can be obtained that indicate that the nano-sized Ω and θ’ precipitates promote ductility and toughness by inhibiting shear-strain localization; whereas the micro-sized dispersed particles intensify localization. Collectively, the precipitates and dispersed particles, however, promote the strengthening of the alloy.

A microfracture testing technique was applied for investigating the fracture properties of Mg-Zn-Y alloys with a long-period stacking ordered (LPSO) phase. Microsized cantilever beam specimens with dimensions ≈ 10×20×50 μm3 were prepared from Mg-Zn-Y alloys by focused ion beam (FIB) machining. Notches with widths of 0.5 μm and depths of 3.5–5 μm were also introduced into the specimens by FIB machining. In this study, three types of Mg-Zn-Y alloys―Mg99.2Zn0.2Y0.6, Mg97Zn1Y2, and Mg88Zn5Y7―were used. Fracture tests were successfully conducted using a mechanical testing machine for microsized specimens at room temperature. The fracture toughness values (KIC) could not be obtained as the specimen size was too small to satisfy the plane strain condition. Hence, provisional KQ values were considered. The KQ values of the Mg97Zn1Y2 alloy were 0.8–1.2 MPam½, and those of the Mg88Zn5Y7 alloy were 1.2–3.0 MPam½. As the fracture in the Mg99.2Zn0.2Y0.6 alloy specimen occurred in a ductile plastic deformation, it was impossible to evaluate KQ values of this specimen. The increasing volume fraction of the LPSO phase indicates that the fracture toughness of Mg-Zn-Y alloys increases in LPSO phase.