Papers by Author: Munekazu Ohno

Abstract: In a flow forming process of automobile wheels of Al-based alloys, plastic deformation of the rim part is performed by rollers from the periphery side, while the inner periphery is fixed on a steel mandrel and is slightly deformed. Therefore, the rim part has a strain-graded microstructure in the thickness direction. In this study, the effects of the strain-graded plastic deformation on mechanical properties of an Al-Si cast alloy have been investigated. The strain-graded plastic deformation in this study was done by hot rolling of an Al alloy plate together with a steel plate. The two plates were joined at one end in the longitudinal direction and were rolled from the joined edge at 330 oC using a roller with a roll diameter of 200 mm and a rotation speed of 66 per minute. The chemical composition of the alloy was Al-7mass%Si-0.3mass%Mg-0.3mass%Fe. The rolled Al alloy plate had a strain-graded microstructure in the thickness direction; the strain was the highest at the roller side surface and the lowest at the steel plate side surface. The rolling also brought about a Si particle size graded microstructure. The eutectic Si rods were broken by the rolling deformation and the Si particle size was the smallest at the roller side surface and the largest at the steel plate side surface. On the other hand, a normal rolling deformation of the Al alloy plate without the steel plate was also performed for comparison. The rolled sample having the strain-graded and Si particle size graded microstructure exhibited much　more excellent bending strength and ductility compared with the normally rolled sample.

Abstract: Multi-scale simulation of ordering process from electronic, atomistic scales to microstructural scale was carried out by hybridizing Phase Field Method (PFM) and Cluster Variation Method (CVM). The hybrid model was applied to disorder-L10 ordering process in Fe-Pd system. Furthermore, computation of relaxation constants in the PFM was attempted based on Path Probability Method (PPM) which is the time evolution version of the CVM, within a linearized analysis of order-order relaxation process.

Abstract: First principles calculations have been applied in various fields in Materials Science. The authors have been attempting to reproduce a binary phase diagram by combining FLAPW electronic structure total energy calculations with Cluster Variation Method of statistical mechanics. Such a first principles calculation for static equilibrium has been quite successful for a series of Febased alloy systems. Recently, main attention is directed towards the extension of the first principles calculation to phase transformation dynamics by incorporating Phase Field Method. A series of preliminary calculations on disorder-L10 ordering in Fe-Pd and –Pt are satisfactory and the evolution process of Anti-Phase Boundaries was reproduced. In the present report, first-principles calculations of phase equilibria and phase transformation are briefly reviewed. Particular focuses are placed on coarse graining operation which authors developed and and time scaling as a remaining problem.

Abstract: Phase Field Method (PFM) is hybridized with Cluster Variation Method (CVM) to investigate the ordering dynamics of L10-disorder transition at atomistic and microstructural scales simultaneously. For this, coarse graining operation is attempted on the inhomogeneous free energy functional of CVM. The resultant gradient energy coefficient is found out to be dependent on temperature and order parameters, which is in marked contrast to a conventional PFM formalism. Electronic structure total energy calculations for Fe-Pd system are incorporated to the hybridized scheme and the first principles calculation of microstructural evolution process is attempted.