Materials Science Forum Vols. 783-786

Abstract: The gold alloys are used in jewelry for their aesthetic appearance and inertia to the environment. In jewelry a hardness superior to 300 HV is desirable to facilitate the final machining and reduce the wear of the final product. The maximum hardness that can be obtained with the standard 18 carats gold (Au₇₅-Ag_12.5-Cu_12.5 (wt%)) through a combination of heat treatment and cold working is about 290 HV. Gold-based bulk metallic glasses (BMGs) are an alternative as they present unique properties in comparison with crystalline counterparts, especially easy thermoplastic processing combined with a high hardness. Pd-base BMGs are another solution, due also to their attractive features.An Au₄₉Cu_26.9Si_16.3Ag_5.5Pd_2.3 (% at.) and a Pd₄₀Cu₃₀Ni₁₀P₂₀ (% at.) bulk metallic glasses were fabricated by a copper mould suction casting technique in an argon atmosphere. In the as-cast state hardness, shear modulus and hardness are high (HV_0.3= 360 and 530 in the Au-and Pd-base BMGs, respectively). Various heat treatments have been performed to modify the microstructural state. Formation of crystalline particles induces an increase of both shear modulus and hardness but a drastic decrease in toughness and therefore this formation should be absolutely avoided during casting or thermo processing.

Abstract: In this article, we show principles and advantages of anomalous x-ray scattering in combination with neutron scattering and reverse Monte Carlo modeling to characterize structures of non-crystalline materials, in particular, metallic glasses. Then, we briefly introduce examples of our recent applications to Pd₄₀Ni₄₀P₂₀ and Zr₆₃Ni₂₅Al₁₂ bulk metallic glasses having good glass-forming abilities.

Abstract: The amorphous alloy films of ZrCu and AgMgAl, layers deposited by co-sputtering was utilized as the metallic layer in the bi-layer structure transparent conductive electrode of ZrCu/ITO and AgMgAl/ITO deposited on the PET substrate using magnetron sputtering at room temperature. In the transmittance performance, the 30 nm ITO/3 nm ZrCu and 30 nm ITO/15 nm AgMgAl films could show the optical transmittance of 73 % and 70% at visible light of 550 nm wavelength and maintain the stable transmittance of 70~75% from visible light to infrared region. Meanwhile, the 30 nm ITO/9 nm ZrCu and the 30 nm ITO/15 nm AgMgAl films could show the better sheet resistance of 136 Ω/sq. and 135 Ω/sq. respectively. In addition, compared with the ITO film, the current metallic glasses were utilized as the metallic layer in the bi-layer structure transparent conductive electrode showed the better bending properties. The relative change of resistivity is below 0.4, significantly lower than that of the commercial PET/ITO product. The ZCI would exhibit lower variation in resistance owing to short crack propagated in the amorphous alloy of ZrCu layer after 10000 cycles bending test.

Abstract: Amorphous alloys have many superior properties such as high tensile strength,anticorrosion and easy soft-magnetism, but few amorphous alloys have been used as final productsbecause they lack plasticity at room temperature. Thus, we have developed a new amorphous alloyrolling method. Although the amorphous alloy was brittle at room temperature, it has deformedplastically by semisolid rolling under hydraulic stress. After being subjected to ultrarapidcooling-thermal spraying, amorphous alloy strips were rolled with a ditch roll in the viscoelasticregion below the glass transition temperature. Using this rolling method, we successfully preformedstrips for use in fuel cell separator. This rolling technique is based on the principle of stress-inducedstructural relaxation under hydraulic stress.

Abstract: Monolithic uniform nanoporous Cu (NPC) ribbons with a ligament/pore size of 10-25 nm are successfully synthesized by chemical dealloying the Cu₅₀Zr₅₀ and Cu₅₀Zr₄₅Al₅ metallic glasses in 0.5 M HF for 7 min. It is found that the length scale of ligaments/channels can be tuned by simply alloying 5 at.% Al to the Cu-Zr binary glassy alloys. The current signal of the NPC-supported MnO₂ composite electrode is remarkably enhanced as compared to that of pure MnO₂ powders. These new findings greatly raise the hope for possible applications of NPC as a new type of electrode substrates or an advanced sensor in green and new energy technology.

Abstract: By using the Mg₆₅Zn₃₀Ca₅ amorphous powder prepared by ball-milling of the master alloy or its mixture powders, we produced Mg₆₅Zn₃₀Ca₅ bulk amorphous alloy and its composites by a spark plasma sintering process. The microstructure and corrosion properties of the prepared Mg₆₅Zn₃₀Ca₅ bulk amorphous alloy and its composites were investigated. The bulk amorphous alloy and its composites exhibited a high relative density and high corrosion resistance than commercial Mg alloys.

Abstract: Thermal processing of materials in external magnetic field is employed in order to produce a controllable uniaxial anisotropy and to tailor a domain structure in the series of soft magnetic FeCo-and FeNi-based amorphous/nanocrystalline alloys. Examples of our recent work on the utilization of both longitudinal and transverse magnetic field annealing for tuning the shape of hysteresis loops as well as the giant magnetoimpedance (GMI) characteristics are briefly presented. The beneficial effects of a heat treatment under magnetic field are discussed in terms of the improved application-oriented properties of these soft magnetic alloys.

Abstract: It was reported that micrometer-sized ductile crystalline phases can improve the ductility of Zr-based bulk metallic glasses. The present authors reported the synthesis of bulk metallic glass composites by a process combining cooling slope casting and suction casting for Zr_66.4Nb_6.4Cu_10.5Ni_8.7Al₈ alloys. This study aims to investigate basics of Zr-based metallic glass matrix composites with semisolid structure. As a result, it was found that the Zr-based metallic glass matrix composites with very uniform semisolid structure can be produced by heat treatment process at semisolid region. Moreover, it was found that experimental results can be explained by the pseudo-binary phase diagram.

Abstract: Zr-Cu-Al bulk metallic glass matrix composite with the intermetallic compound ZrCu (B2) phase was fabricated. The effect of the ZrCu phase on mechanical properties and deformation behavior of the composite was investigated by compressive test. Also, phase transformation behavior of the ZrCu phase was analyzed by X-ray diffraction. Furthermore, macroscopic shape memory behavior was investigated using the composite by three point bending test. As the results, it was found that the mechanical properties of the composite depend on the volume fraction of the precipitated ZrCu phase. Compressive strength and yield stress of the composite decrease with increase of volume fraction of the ZrCu phase. On the other hand, plastic strain increases with increase of volume fraction of the ZrCu phase. In addition, it was confirmed that a stress-induced martensitic transformation of the ZrCu phase occurs by compressive stress loading. Furthermore, it was found that the composite with high volume fraction of the ZrCu phase exhibits shape memory effect.

Abstract: T.M.C.P.(Thermo Mechanical Control Processing) has been widely used to improveplastic formability in steel strips. We have produced interstitial free steel(IF steel) strips and ferriticstainless-steel strips through T.M.C.P. rolling method. Optimizing conditions of hot rolling, hotrolled annealing, cold rolling and cold rolled annealing, we developed texture prediction model. Wecan predict rolling texture accurately using the conventional Taylor model. Moreover, we preciselypredict recrystallization texture classifying the total number of microscopic􀀁 slips which arecalculated using the Taylor model. We consider that these calculated results provednucleation-oriented model and two types of recrystallization and grain growth mechanisms exit inour studies. One mechanism is that grains which had the small total number of microscopic slips arepreferred orientation for the hot rolled and annealed ferritic stainless-steel strip. The othermechanism is that grains which had the high total number of microscopic slips are preferredorientation for the cold rolled and annealed IF steel strip.