Materials Science Forum Vol. 941

Abstract: The precipitation sequence of an Al-Mg-Si alloy with silicon excess was determined between 150°C and 300°C by combining ThermoElectric Power measurements and Transmission Electron Microscopy observations. From these studies, an experimental Isothermal Transformation Curve could be proposed in the investigated temperature range. After calibration of a model of KWN type allowing the simultaneous precipitation of two types of metastable rod-shaped precipitates to be taken into account, the same type of curve could be obtained and the yield strength evolution of the alloy during isothermal ageing treatments could be predicted.

Abstract: Cu-Pd-Ag alloy is widely used in electronic device applications due to its relatively low electric resistance. To obtain higher strength wire, age-hardening is usually conducted to this alloy wire. However, the detailed hardening mechanism of Cu-Pd-Ag alloy was not clarified enough. In the present paper, we investigated the microstructure and hardness of the Cu-Pd-Ag alloy wire with aging treatment. Original alloy contained many rods with an Ag-rich α phase extended along the wire direction in a Cu-rich α phase matrix. After heat treatment of 623K with 1 hour, the matrix was transformed to the β phase contained many elongated α₂ phases as nanolamellar structure. Many β’ phase precipitated in the rods. Hardness measured with nanoindentation test showed that the matrix had a higher value than that of the rods. In the Cu-Pd-Ag alloy wire, the nanolamellar structure of the matrix was revealed to contribute to the hardening of the wire.

Abstract: Severe Plastic Deformation (SPD) process is one of methods for obtaining UFG-Al. It was reported in SPD-processed Al alloy that the extra-hardening due to work hardening caused by accumulated dislocation in the grains. In Al-Mg alloy, Mg decreases the stacking fault energy in this alloy, and dislocation tends to accumulate in the grains. In this study, Al-Mg alloy with various Mg contents were processed by Equal-Channel Angular Pressed (ECAP) which was one of SPD and annealed after processed ECAP. The relationship between Mg content and magnitude of extra-hardening was investigated. In ECAPed Al-3mass%Mg alloy, it was thought that extra-hardening was caused. Magnitude of extra-hardening was increased with increasing Mg content.

Abstract: In a previous study, the damping capacity gradually increased with increasing annealing time and temperature in AZ31. Also, at damping capacity test under similar conditions, AZ61 with a higher solute content showed a more rapid microstructure change than AZ31. In this study, it was investigated damping capacity on various aluminum concentration conditions in order to damping capacity that was influenced by microstructure and solute content. Three types such as pure Mg, AZ31 and AZ61 alloy of specimens were rolled at 673K with a rolling reduction of 30%, respectively. The annealing were conducted at various temperature and time. In this study, static recrystallization was occurred under all annealing conditions. The hardness gradually decreased until 60 minutes after the heat treatment. All annealing conditions, the damping capacity gradually increased with increasing annealing time and temperature. Especially, damping capacity and C₁ value were increased with a decreasing of solute content.

Abstract: A metastable β-titanium alloy, Ti15Mo was subjected to equal channel angular pressing (ECAP). The resulting microstructure of the material is inhomogeneous consisting of micrometer size β-grains with deformed bands containing ultra-fine β-grains. The ECAP-deformed sample was subjected to thermal treatment in order to elucidate the difference in morphology of the α-phase precipitation in deformed and non-deformed materials. The α-phase formation is accelerated in areas with higher concentration of lattice defects. The detail investigation by transmission electron microscopy revealed equixed α-phase formation in deformed bands. In the transition area between deformed band and β-matrix grain boundary α-phase forms while in the interior of the β-grains the α-phase precipitation is suppressed.

Abstract: Uniaxial compression tests are carried out in the M1 magnesium alloy at 723K under a strain rate of 5.0x10^-2s^-1 up to a strain of-1.3. Microstructure observation shows that grain distribution is heterogeneous and coarsened grain is observed in all deformation conditions. Mean grain size tends to decrease with increasing strain. Dynamic recrystallization and grain growth are occurred during deformation. (0001) texture which shown at annealed state is weakened with increasing strain, and texture component changed from (0,0) to (24,0) during deformation. The recrystallized grains have no strong preferred orientation about (0001), similar to the grains of growing.

Abstract: Anodic oxidation of Mg-Li-Al alloys using phosphoric acid-based bath were processed to obtain the corrosion-proof surface coating. The specimen oxidized at low voltage anodically dissolved without the formation of oxidized film. Anodic oxidation film could be formed at higher voltage due to thin layer preferentially formed on tthe active surface, this layer develops to stable thick film. There were no significant differences in film thickness between LA141 and LA143 alloys.

Abstract: In previous study, it was investigated texture formation behaviour of high-temperature plane strain compression test at 723K, under a strain rate of 5.0. It was found that the main texture component and it was sharpness vary depending on deformation conditions. To clarify the characteristic of texture formation behaviour, it is necessary to investigate at various deformation condition. Therefore, in this study, is investigating the influence or texture formation behaviour and strain, strain rate at 673K. Three kinds of specimens with different initial textures were machined out from a rolled plate having a <0001> texture. The plane strain compression tests were conducted at a temperature 673K, and a strain rate of 5.0, with strain between-0.4 to-1.0. After compression tests, the specimens were immediately quenched in oil. The texture evolution was conducted by the Schulz reflection method using Cu Kα radiation and EBSD. Before the deformation, {0001} of specimen A was accumulated in the center of pole figure. The {0001} of specimen B was accumulated at the RD direction. The {0001} of specimen C was accumulated TD direction. As a result, work softening is observed in all the cases at the true stress – true strain curve for three types of specimens. After deformation, the maximum pole density of increases with increasing strain. In this study, it was found that the stable orientation was (0001)<100> and (0001)<110> during deformation.

Abstract: Ni-Cr binary alloys containing high amount of Cr demonstrate gamma/alpha-Cr lamellar structure by discontinuous precipitation (DP) reaction from grain boundary. The mechanism of DP reaction is caused by supersaturated Cr in the gamma phase. Supersaturated Cr concentration influences the driving force for the DP reaction and the lamellar spacing. Moreover, the Ni-based alloys with high Cr, containing Al, significantly increase the hardness and strength due to the very narrow lamellar structure. Al addition brings on Ni consumption in the matrix by precipitation of the gamma prime phase. Therefore, Cr supersaturates dramatically in the matrix. The wrought Ni-Cr-Al alloy, Ni-38Cr-3.8Al (mass%) , reaches extremely high tensile strength, which is over 2 GPa, after annealing treatment. Even though chemical composition of Ni-38Cr-3.8Al is simple, the microstructure is complex because it consists of the gamma/alpha Cr lamellar structure with the fine gamma prime particles. Therefore, in this study, we investigated the influence of Cr concentration on the cellular precipitation behaviour. In order to understand the influence of Cr concentration, Ni-34, 36 and 38Cr-3.8Al alloys were prepared. Forged bars were subjected to solution treatment in the gamma single phase region. Subsequently, the alloys were aged from 873K to 1073 K for various times. The cellular precipitation reaction is suppressed by a decrease in Cr concentration, particularly at low temperature annealing treatment condition. The hardness is low in lower Cr concentration alloys in all range of annealing treatment temperature. These results indicate that Cr concentration remarkably affects the driving force for the DP reaction.

Abstract: The essential objective of this work is to establish the influence of grain size and thermo-mechanical conditions on the activation energy for super plastic flow (Q_SPF) in Ti-6Al-4V alloy by applying the quantum mechanics and relativistic model (QM-RM) proposed by Muñoz-Andrade, in the framework of the unified physics. The QM-RM allows the direct determination of the Q_SPF in advanced materials at instantaneous thermo-mechanical material working conditions. By applying, the QM-RM on the experimental results reported previously by some authors, it is shown for grain size of 6.1μm, that the calculated Q_SPF for grain boundary sliding is about 193 and 178 kJ/mol, at 850°C with an efficiency of power dissipation, η=0.65. These results are in closed agreement with the values of 204 and 174 kJ/mol reported previously for grain boundary self-diffusion energy of α-Ti. Nevertheless, for grain size of 0.6μm the calculated Q_SPF is 142 kJ/mol at 650°C, with an efficiency of power dissipation, η=0.61. As well, in order to understand the phenomenology and mechanics of SPF in Ti-6Al-4V alloy, the variation of the activation energy with the temperature; stress and strain rate is analyzed in association with coupled mechanisms during SPF, such as grain boundary sliding, cooperative grain boundary sliding and self-accommodation process related to the microstructure. In summary, the results of Q_SPF obtained in this work, by the QM-RM are in closed agreement with results reported previously by using the theoretical and conventional methodology set up by Mohamed and Langdon.