Magnesium (Mg) alloys are suitable materials for weight reduction in vehicles because of their low densities and high specific strengths. However, rolled Mg alloy sheets generally exhibit a poor formability at room temperature and thus their applications are restricted. This poor formability is originated from basal slip dominated deformation as well as strong basal texture. It is known that the formability can be improved by suppression of basal texture formation. Thus, large efforts have been devoted to texture control for the purpose of enhancing the room temperature formability. In this paper, recent researches for texture control of rolled Mg alloy sheets are reviewed.0
Thermoelectric(TE) power generation can directly convert waste heat into electric energy. However, one of the bottlenecks for widespread use of TE power generation is toxicity of currently-used TE materials. We focused on Al-based materials as candidate of low-toxicity TE materials. Although Al-based materials have high power factor, the achievement of high TE performance is difficult because of the high lattice thermal conductivity. The aims of the present study are to synthesize Al5Co2 known as a pseudogap intermetallic compound, and to investigate the TE properties. We found that lattice thermal conductivity κlat of Al5Co2 is lower than those of other Al based TE materials, such as Fe2VAl, Al2Ru and Al3V. The κlat of Al5Co2 at room temperature was 7.1 Wm-1K-1. We also found that Fe substitution at Co sites enhances power factor(PF). The maximum PF was ~0.6 mWm-1K-2 at room temperature for Al5(Co0.95Fe0.05)2.
Grain growth behavior and static globularization behavior of the Ti-5Al-2Sn-2Zr-4Cr-4Mo(Ti-17) alloy (with the lamellar starting microstructure and the equiaxed-grained-microstructure) under static heat treatment process were investigated in this work. Rapid grain-growth and static globurarization are exhibited in the 1123HR specimen (with the equiaxed starting microstructure) rather than the lamellar specimen, which is mainly due to the quite difference in fraction of Burgers orientation relationship (BOR) (with coherent relationship) between α and β phases. The interface energy of γαβ at BOR was estimated to be approximately 0.01 J/m2 according to Lifshitz-Slyozov-Wagner(LSW) model. Static globularization behavior of the 1123HR specimen is reasonably explained in relation to the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. Here, similar apparent activation energies were exhibited for both behaviors of grain growth and globularization, indicating the similar rate-limiting mechanism for both these behaviors.
Structural relaxation of amorphous germanium has been examined by molecular dynamics simulations based on the empirical Tersoff interatomic potential. Although the Tersoff potential overestimated both the melting and glass transition temperatures, it was found that this potential can reproduce the behavior of structural relaxation. The potential energy decreased with thermal annealing below the glass transition temperature, but it sometimes increased during structural relaxation. The mean square displacement of atoms also increased at the corresponding period. These changes were attributed to the cooperative atomic motion during structure relaxation. Atomic trajectories revealed that structural changes are induced by spatially- and temporally-inhomogeneous atomic motions: atomic mobile and immobile regions coexisted during structural relaxation.
Ultrasonic guided waves achieve non-destructive inspection of thin plates. However, issues such as large energy leakage and attenuation often plague guided wave inspection of storage tanks and pipes filled with fluid. This study experimentally investigated the non-destructive testing of a water-loaded flat aluminum alloy plate through the application of a quasi-Scholte(QS)wave that propagated along the fluid-plate interface without experiencing attenuation due to leakage. A QS wave was confirmed as having been generated and propagated in a plate loaded with water on the bottom surface using ultrasonic incidence and detection at the top water-free surface. Two-dimensional Fourier transform images of the waveforms revealed reflection of the QS wave from a defect as well as a forward incident QS wave. The visualization results experimentally confirmed—via measurements of waves in water using a laser Doppler vibrometer—that QS waves propagated along a plate surface, while scattered waves were generated by defects.
The undercooling for nucleation and volume fraction of primary (β-Sn) phase has been investigated in Sn-X hypoeutectic alloys where X were Pb, Ag, Al, Bi, Cu and Zn. The purities of raw materials were 4N and the solute content of the alloy was set for the volume fraction of primary phase to be from 0.3 to 0.45, according to the equilibrium phase diagram. Thermal history was measured during solidification of 5 g alloy sample at a cooling rate of 0.05 K/s, with fine K-type thermocouple. The volume fraction of primary (β-Sn) phase was measured on the longitudinal cross section of the sample. When the solute elements were Pb, Ag, Al, Bi and Cu, the undercooling was more than 5K and was large. Furthermore, the volume fraction of primary (β-Sn) was larger than the equilibrium value. On the other hand, when the solute element was Zn, the undercooling for the nucleation of primary (β-Sn) was 0.9 K and quite small. In addition to this, the volume fraction of primary phase agreed with the equilibrium value.
The amounts of calcium carbonate adhered on sheets (PVC, carbon steel, Type 316 stainless steel, and Cu) and coated steels sheets (Cu, Zn, Ni, Ni-P, and Ni-W-P coated steels) were investigated in the synthesis solution. The transformation and crystal growth of the calcium carbonate were different among the materials. The primary form in the adhered polymorphisms was calcite on PVC, carbon steel, Type 316 stainless steel, Cu, and Cu coated steel, and aragonite on Zn, Ni, Ni-P, and Ni-W-P coated steels, and vaterite was not primary form on all materials. The materials, on which the primary form in the adhesion polymorphisms is calcite, showed large adhesion amounts because calcite is stable phase and its solubility is lower than the other polymorphisms. The crystal growths of the specific polymorphisms on some materials were inhibited, and the irregular shapes of their polymorphisms formed: calcite adhered on carbon steel and Ni, Ni-P, Ni-W-P coated steels, aragonite adhered on Zn, Ni-P, and Ni-W-P coated steels became the irregular shape. The comprised elements of the material surfaces were detected at the surface of the calcium carbonate crystals adhered on the materials. The transformation and crystal growth are affected by the elution ions from the material surfaces, and the effects of eluted ions (Fe2+, Cu2+, Zn2+, Ni2+, and ) from these materials were almost same with the ones of previous studies. To reduce the adhesion amount of calcium carbonate, the material comprised of the elements, which shows the inhibitor effects of the transformation and the crystal growths of many kinds of polymorphisms, is better.
The growth process of ω-precipitates was studied for a Ti-20 mass% Mo alloy aged at 673 K. Investigations of the aging time t dependences of precipitate size, precipitate volume fraction, and precipitate number density revealed that the growth process was divided into three stages: the first stage of diffusion-controlled growth, the second mixed stage of growth and coarsening, and the third stage of coarsening. In the first stage, the precipitate size d increased as d2 ∝ t with increasing t, and then the precipitate growth became very slow after a value of d =14 nm was reached at the beginning of the second mixed stage. This is ascribed to the transition from the growth stage to the mixed stage of growth and coarsening, and the collision of neighboring ω-precipitates. After the neighboring ω-precipitates of the same variant collided and then coalesced, the precipitate size increased as d3 ∝ t with increasing t in the mixed stage and the coarsening stage.