Materials Science Forum Vols. 638-642

Abstract: Recently, a centrifugal mixed-powder method has been proposed as the processing technique of functionally graded material (FGM) containing fine solid-particles. In this study, Cu-based FGM containing SiC particles was fabricated using this technique. Although the density of SiC is smaller than that of Cu, these SiC particles are successfully distributed on surface of the cylindrical FGM. From this result, it is clear the movement of solid particle in powder mixture during casting is small. Therefore, the gradual distribution of the solid particle can be formed by the control of the volume fraction of solid-particles in powder mixture. Also, it is found that smaller SiC particle can improve the hardness on the surface of the FGMs effectively rather than larger one. In this study, the assignment of the centrifugal mixed-powder method was suggested from the obtained results.

Abstract: The magnetic pressure seam welding is one of the candidate methods to join thin sheet smart and multifunctional materials. In this research, to examine the mechanism of magnetic pressure welding from a dynamic viewpoint, numerical simulation of the impact was carried out by using a commercial Euler-Lagrange coupling software MSC.Dytran (MSC.Software) as a first step of the computational studies, where the joint between Fe and Al was employed according to the previous experimental researches. From the serial numerical results, it was found that the increase of temperature at the joint interface was not enough to melt Al or Fe in the range of collision velocity and angle studied in this report. Also, it was revealed that the very large mean stress occurred at the interface which could be considered as the pressure at joint interface and Al moved with high velocity along the interface. Moreover, it was found that there were two patterns of plastic strain distribution near the joint interface depending on the collision velocity and collision angle. Finally, it can be concluded that the plastic strain pattern might be related to the success of magnetic pressure seam welding.

Abstract: ZnO is heat-resistant and inexpensive, and the raw material of which is abundant, it is considered to be a good candidate thermoelectric material. Usually, a low-resistance n-type ZnO sintered body is obtained by doping 0.5-5 mol% Al2O3 followed by burning at a high temperature of approximately 1673K. However, this high-temperature burning has drawbacks, such as high power consumption and an increase in thermal conductivity with grain growth. Under these circumstances, we attempted to address these disadvantages. When ZnO was burned with Al as a dopant in an electric furnace at a temperature as low as approximately 1473K, ZnO with relatively good thermoelectric properties was obtained. In addition, the Al-doped sample showed lower electric resistance (332 K: 6.85×10-4Ωcm) than the Al2O3-doped sample, as determined on the basis of the resistance temperature characteristics of these samples. The causes of this low resistance may be as follows: 1) the metal-Al-mediated sample was densified by burning at a low temperature of approximately 1473K and 2) the Al distribution to the entire region of the ZnO bulk, resulting in the spread of Al solid-solution regions in the ZnO. We also found that the thermal conductivity decreased (973 K: 3.66 Wm-1K-1) in the Al-doped sample.

Abstract: Two kinds of pure titanium specimens, i.e., the first one is prepared by the ingot metallurgy (I/M) process and the second one is prepared by the metal injection molding (MIM) process were used in this experiment, and their corrosion behavior under stress has been investigated in several aqueous solutions by Slow Strain Rate Tensile (SSRT) test. Ti MIM specimen showed the larger maximum stress and the lower maximum stain than I/M Ti specimen in the deionized water. Both Ti I/M and MIM specimens indicated good corrosion resistance in the aqueous solution of 2.5 kmol/m3 H2SO4 + 0.2 kmol/m3 NaCl in which SUS304 stainless steel showed SCC, and showed the decrease of the maximum stress and the maximum strain in the aqueous solutions of CH3OH + 0.1 kmol/m3 HCl, where the brittle fracture appearance was more remarkable with an decrease of H2O in the solution.

Abstract: Lithium sulfide (Li2S)-carbon composite positive electrodes were prepared by the spark-plasma-sintering (SPS) process for use in rechargeable lithium batteries. By the SPS treatment of Li2S and acetylene black (AB) blended powder, the strong binding between the active materials and the carbon powders were formed. Such contact effect improved the electrochemical performance of the cells with liquid electrolytes (1M LiFP6/(EC+DMC)), probably due to the increase in conductivity of the positive electrodes, though the samples prepared by the ball-milling process showed no significant capacity in the electrochemical tests.

Abstract: The shape memory composite (SMC) with shape memory alloy (SMA) and shape memory polymer (SMP) was fabricated, and the two-way bending deformation and recovery force were investigated. The results obtained can be summarized as follows. (1) Two kinds of SMA tapes which show the shape memory effect and superelasticity were heat-treated to memorize the round shape, respectively. The shape-memorized round SMA tapes were sandwiched between the SMP sheets, and the SMC belt was fabricated. (2) The two-way bending deformation with an angle of 56 degrees is observed during heating and cooling. (3) If the SMC belt is heated and cooled by keeping the form, recovery force increases during heating and decreases during cooling.

Abstract: The Mn3XN(X=Zn, Cu, Sn) compounds and their solid solutions with anti-perovskite structure were prepared by solid state reaction. Their magnetic transition and simultaneous abnormal thermal expansion behaviors were studied by SQUID and variable temperature X-ray diffraction. The lattice contraction was found in Mn3Cu0.5Sn0.5N and Mn3Zn0.5Sn0.5N during the magnetic transition process, however not in pure Mn3XN(X=Zn, Cu, Sn). The mechanism is discussed, combined with the different doping effects. It seems that the lattice contraction behavior is sensitive to the number of valence electrons at the X site in Mn3XN series.

Abstract: Training effect in the Fe-Mn-Si shape memory alloy is known as useful method to improve the shape memory effect. In this study, the training effects on damping capacity in Fe-20mass%Mn and Fe-20.5mass%Mn-12.5mass%Cr alloys have been investigated. As training treatments, the thermal training (only thermal cycling) and the thermo-mechanical training (thermal cycling with rolling deformation) are carried out. Internal friction was measured at room temperature using a free-decay method. Moreover, the behavior of dislocations was observed by TEM. Both training treatments improve the damping capacity of the Fe-Mn alloys with increasing the number of treatment. Strong training effect was found for the specimens trained by the thermo-mechanical training. The main training effect by thermal cycles is concluded to be due to size effects, while the size effects and volume fractional effects of martensite phase affect the damping capacity of the thermo-mechanically trained alloys. These training methods can improve both damping capacity and strength of Fe-Mn alloys.

Abstract: The ferritic oxide dispersion strengthened alloys (ODS) are manufactured using the mechanical alloying process. The development of a coarse grained microstructure during the recrystallization has been noted and discussed by a number of authors but, the mechanism of grain control remains uncertain. Recent work has emphasized the large influence of non-uniformities on the development of the recrystallized microstructure. The purpose of the present work was to study the effect of non-uniform plastic strain on recrystallization of Fe-base ODS alloy named MA 957.

Abstract: Coherent two-phase microstructures consisting of ordered precipitate and disordered matrix phases sometimes exhibit a phase-separation, which brings the split and/or the decelerated coarsening of precipitates. When the coherent two-phase microstructure of A1+L12 (+’) in Ni-base alloys are aged inside the two-phase region of A1+L12 , the L12 precipitate sometimes exhibit a phase-separation and A1 phase newly appears and grows in each L12 precipitate. Phase-separations of the same type to the above also take place due to ageing of coherent two-phase microstructures of A2+D03 and A2+B2 in Fe-base alloys: D03 and B2 precipitates sometimes exhibit phase-separations and A2 phase newly appears and grows in both precipitates. These types of phase-separation take place under the influence of chemical free energy. In the course of further ageing, the new disordered phases of A1 and A2 change their morphology in various ways depending on the elastic constraint: i.e. the morphology of new A1 or A2 phase is influenced by the elastic energies and the surface energy.