Yoshimasa Takayama

Preferential penetration path of gallium into grain boundary in practical aluminium alloy

The preferential penetration of a liquid metal along grain boundaries (GBs) in polycrystalline metals is a well-known phenomenon. Gallium-decorated GB networks in rolled aluminium alloys have been visualized three-dimensionally using the high-resolution synchrotron radiation computer tomography (SRCT). The distribution of gallium concentration along GBs was measured using X-ray absorption. Statistical correction for blurring was performed to raise accuracy of the measurement, and then compared with orientation mapping by the SEM/EBSP method on the surface of a tomographic specimen. The pancake-like grain microstructure formed by a rolling process causes the anisotropy of penetration direction. Although the gallium penetrated into high-angle GBs, all of the high-angle GBs are not necessarily decorated by the gallium. The reason for this may be explained by considering geometrically possible penetration paths that seem to be dependent on local grain arrangement and GB structure through each path. The dependence of the gallium concentration on the rotation axis of misorientation has been found along the high-angle GBs. Especially, GBs with a specific misorientation (⟨221⟩ as a misorientation axis) showed high gallium concentration.

Analysis of Intragranular Misorientation Related to Deformation in an Al-Mg-Mn Alloy

Intragranular misorientation reflects strain generated during deformation with dislocation glide. The SEM/EBSP (scanning electron microscope/ electron back scatter diffraction pattern) technique provides is “kernel average misorientation (KAM)” as the most appropriate quantity to evaluate the strain or the stored energy for a given point. The KAM is defined for a given point as the average misorientation of that point with all of its neighbors. In the present paper two analyses of the intragranular misorientation using the SEM/EBSP technique for a cyclic deformation at room temperature and a high temperature deformation in an Al-Mg-Mn alloy are reviewed.

Microstructure and texture evolution in titanium subjected to friction roll surface processing and subsequent annealing

Commercial purity and high purity titanium sheets were initially strained by a new technique, named as friction roll surface processing (FRSP). Severe strain was imposed into the surface layer and strain gradient was formed through the thickness of the sheet. The microstructure and texture in as-strained state were investigated by optical microscopy and X-ray diffraction technique. On the surface of the sheets, ultra-fine grains were found to have a sharp texture with a preferred orientation strongly related to the FRSP direction. The evolution of microstructure and crystallographic texture of FRSPed samples during recrystallization were also studied by electron back-scattered diffraction (EBSD) technique after being annealed at selected temperatures and time. The results indicated that the preferred orientations resulting from FRSP and annealing in the surface layer were formed during rolling and its recrystallization textures were reduced by FRSP. In addition, the texture evolved stably without change in main components during the annealing.

AE behaviors evaluation with BP neural network

Abstract This paper reports our experiment on training a three layer forwards neural network with backpropagation algorithm (BP) to memorise acoustic emission (AE) behaviors of magnesium alloy during fatigue test process and perform the mapping from AE behaviors to fatigue crack propagation. This study reveals the potential possibility of using artificial neural networks for automated AE testing. Simulation results are very encouraging and conclusively in favor of this attempt.

COMPUTER SIMULATION OF GRAIN GROWTH IN THREE DIMENSIONS

A Monte Carlo computer simulation has been carried out to study the kinetics of grain growth and the grain size distribution in three dimensions. The model employed is superimposed onto a fcc lattice, which has the least anisotropy among conceivable ones. The temporal evolution of the microstructure during normal grain growth is monitored for both the cross-section and the model itself to investigate the change in grain size distribution. The simulated results indicate the change in the distribution form of grain size during grain growth. Furthermore, it is found that the microstructural evolution including the change depends on the dimension in measurement and the temperature.

Effects of Aging Parameters on the Mechanical Properties in Corson Alloy System with High Contents of Ni and Si

The influences of solution treatments, prior cold drawings and aging treatments on mechanical properties in Corson alloy with high contents more than 8.0 mass% of Ni and Si have been investigated. As a result of the optimization of conditions, the maximum hardness and tensile strength reached 306HV and 968MPa, respectively. Effects of temperatures of solution treatment and aging on the mechanical properties were analyzed based on solid solute concentrations in matrix phase, which were estimated by using the linear analysis and calculated from the electrical conductivity. The solute concentrations were also measured directly by SEM-EDS. Consequently, the precipitation hardening of the alloys was governed mainly by the solute concentrations of Ni and Si in matrix phase in solution treatment. The hardness depended on not only the solute concentrations but also the excess of Ni and Si in the alloys.

Grain Refinement and High Temperature Deformation in Friction Stir Processed Sheets of Magnesium Alloys

Grain refinement and high temperature deformation in two kinds of magnesium alloys subjected to friction stir processing (FSP) have been investigated. One was a rolled sheet of LA141Mg and another was a cast plate of AZ91Mg. FSP was developed by adapting the concepts of friction stir welding to obtain a fine grain size in a stirred zone. Grain refinement was achieved by FSP to give fine grain sizes of 11.4μm and 8.4μm for LA141 and AZ91 alloys, respectively. For LA141 alloy, the maximum stress of the FSPed sample was higher than that of the as-received one in the range of 300K to 523K while the elongation to failure of the former was considerably smaller than that of the latter. On the other hand, the elongation for the FSPed sample of AZ91Mg showed three times larger elongation with a lower maximum stress than the as-received cast one at 523K and 2.8×10-3s-1. Further difference in high temperature deformation for both magnesium alloys was discussed based on microstructural change and stress-strain curves.

Texture Evolution in Titanium and Aluminum Sheets Subjected to Friction Roll Surface Processing and Subsequent Annealing

Titanium and aluminum sheets were directionally strained by friction roll surface processing (FRSP). Severe shear strain was imposed into the surface layer and strain gradient was formed through the thickness of the sheet. The microstructure and texture in as-strained state were investigated by optical microscopy and X-ray diffraction technique. Ultra-fine grains in the surface layer of the titanium sheet were found to have a sharp texture with a preferred orientation strongly related to the FRSP direction. The evolution of microstructure and crystallographic texture of FRSPed samples during annealing were studied by electron back-scattered diffraction (EBSD) technique. Obvious preferred orientations of shear straining were obtained in the surface layer of both materials as a result from FRSP and subsequent annealing.

Microstructure and Mechanical Properties of Titanium Severely Strained by Means of Friction Roll Processing

Severe strain has been introduced to commercially purity (CP) titanium samples by means of friction roll processing (FRP), which represents an alternative severe plastic deformation technique by inducing shear strain. FRP has an excellent possibility of controlling surface microstructure combining with subsequent annealing. The resultant microstructure refinement and texture evolution has been investigated. Hardness of sample was measured to compare mechanical properties of samples before and after FRPed. Parameters including the different indentations given to the sample and sample feeding speed were experimentally conducted to find the optimum condition for investigating effect on microstructure evolution. After subsequent annealing, the evolutions of microstructure and texture were observed by field emission scanning electron microscopy (FESEM) and analyzed by scanning electron microscopy/ electron back scatter diffraction pattern (SEM/EBSP) technique. Transverse texture was found to be the preferred orientation existing in the thin top layer of the sample after FRP and annealed at 823K for 1h.

Constitution of ISO and JIS for Method of Tensile Testing of Superplastic Materials

Method for tensile testing of superplastic materials had been standardized as ISO 20032: 2007, which is based on JIS, Japanese Industrial Standard, H 7501 and H 7505. These standards specify the test specimens of S-and R-types. Recently, the working group organized by Osaka Science and Technology Center, Japan, proposed a revised version of ISO 20032 with several corrections. After systematic review and voting at ISO/TC (Mechanical Testing of Metals) 164/SC2 (Ductility Testing), the second edition of ISO 20032 was published in 2013. Now, a working group has been set for proposing a revised version of JIS corresponding to ISO 20032: 2013. This paper reports the constitution process of these ISO and JIS standards.