Solid State Phenomena Vols. 124-126

Abstract: Molten Mg alloys burn rapidly in air if not protected. In order to handle molten Mg safely, the molten metal should be protected from oxidation by covering the surface with flux or protective gases. Sulfur hexafluoride (SF6) gas is widely used for Mg alloy as a cover gas and has proved to be a successful inhibitor. However, the use of SF6 gas is limited because of its high cost and its significant impact on global warming potential (GWP). Therefore, SF6 gas is being replaced by alternative protection gases such as tetrafluoro ethane (HFC-134a) and 3M NovecTM 612. These gases are less expensive and have lower GWP, compared with SF6 gas. Recent studies show that there has been another attempt by adding CaO into Mg alloys to manufacture CaO added AZ31Mg alloy in terms of increasing ignition temperature and reducing protective cover gas amount during melting and casting. This paper discusses effect of CaO on ignition and oxidation behaviors of AZ31 Mg alloy as well as on surface roughness and mechanical properties of AZ31 Mg alloy extruded bars.

Abstract: This research has been performed to investigate the effect of ageing onto the grain refinement of 82wt%Cu-13.5wt%Al-4.5wt%Ni-0.1wt% misch metal alloy with ageing temperature and time. The variation of transformation temperature with ageing has been found to be heavily dependent on ageing time and temperature. In the second reversed transformation cycle, the temperature of Ms point decreases with ageing time at 300
, but no variation at 100
. The temperature of As point increases with ageing time at both temperatures. After the second reversed transformation cycle, the transformation temperature does not show any significant changes in martensitic phase with ageing, the temperature of Ms point being the same afterwards. Parent phase after ageing appears to show M18R and N2H martensitic phases depending on the ageing time and temperature. It is also found that α and γ2 phases are formed only at the condition of 300
and 24h.

Abstract: This paper investigates the effect of Bubbling and AlCuP on primary Si size in Al-18%Si alloy. Bubbling process and AlCuP treatment are effective for refining primary Si in hypereutectic Al-Si alloy. Both the bubble and AlCuP can be used as nucleation sites of primary Si. Many nucleation sites can make the size of primary Si decreased. So, this experiment suggests that the mix using of bubbling process and AlCuP treatment are more effective for nucleation site of primary Si. For deciding the optimum treatment order, the experiments are processed 3 kinds of order with varying stirring time and holding temperature; 1)AlCuP treatment and then bubbling process, 2)simultaneously using of bubbling process and AlCuP treatment, 3)bubbling process and then AlCuP treatment.

Abstract: Ni-3at.%W alloy tapes for YBCO coated conductor were fabricated by powder metallurgy process including powder compaction, cold isostatic pressing(CIP), cold rolling and annealing for recrystallization. The Ni-3at.%W tapes annealed in an atmosphere of 96%Ar and 4%H2 mixing gas were characterized by X-ray pole figures, orientation distribution function(ODF) and optical microscopy(OM). The Ni-W alloy tapes were heat-treated at 700~1000°C for the development of cube texture {001}<100>. The texture analysis indicated that as fabricated tapes have a sharp cube texture after annealing at 900 and 1000°C. Also, thoroughly recrystallization takes place for the annealed tapes at the both temperatures and the average grain size of the two tapes is about the same, which is about 35㎛.

Abstract: The influence of solidification rates and Cr equivalents on the formation of the ferrite was studied by directional solidification in mod. (9-12)Cr-1Mo steels. It was found that the volume fraction of ferrite increased as increasing Cr equivalent and solidification rate. The volume fraction of the ferrite showed much higher at low solidification rates with the planar or cellular interface than that at high solidification rates with the dendritic interface. The volume fraction of ferrite in solidification microstructure showed much higher than that in extruded and heat-treated alloys. It depends on not only solidification rate and Cr equivalent but also the solidification fraction. At low solidification rates, there occurs segregation because the solid/liquid interface was planar or cellular, and it makes composition change with solidification fractions. The formation of ferrite has been discussed with Cr equivalent and solidification rate.

Abstract: To synthesize a crystalline-glass composite in a Cu-based bulk metallic glass, the monotectic reaction was used. The (Zr-Sn-Pb)-rich crystalline phase was found to coexist with the (Cu-Ti-Ni)-rich glassy phase during the process of quenching from the melt in the (Cu47Ti33Zr11Ni6Sn2Si1)100-x+Pbx=1,2 system. Microstructures consisting of uniformly dispersed crystalline particles in the amorphous matrix were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). Compressive tests demonstrated that the fracture strain of the sample with a Pb content of 1 at% was three times higher than that of the sample with no Pb.

Abstract: MC decompositions during thermal exposure have been investigated in three conventional cast Ni-base superalloys, GTD111, IN738LC, and CM247LC. MC decomposition in GTD111 and IN738LC depends on exposure temperature. While MC decomposed into M23C6 at 982°C, η formed from MC after exposure at 927°C and 871°C. Ta and Ti separated from MC during thermal exposure made η phase to form instead of γ'. The decomposition of the MC in CM247LC depends on their morphology and position. Segregation during casting process affected the morphology and composition of MC type carbide in this alloy. Acicular M6C was found near scriptal MC in the dendrite. Blocky MC near γ-γ' eutectic decomposed into M23C6. Both M23C6 and M6C can be found on grain boundary after thermal exposure in CM247LC.

Abstract: The degree of preference of thin anatase TiO2 films prepared by CVD for the <112> orientation was enhanced by pretreating the soda-lime glass substrates with a plasma. The relationships between the preferred orientation and plasma pretreatments were investigated. It was founded that the TiO2 films on the plasma pretreated soda-lime glass substrates exhibited a higher degree of preference for the (112) orientation than those without the pretreatment. To confirm the effect of the plasma pretreatments on the soda-lime glass substrates, TOF-SIMS, contact angle measurement and TEM were used to determine the changes in the components, surface energy and crystallinity of the substrates, respectively. It was found the components added as network modifiers, such as Na+, Ca2+, and K+ ions, was depleted in the surface region of the substrates after the plasma pretreatment, and that the surface energy of the substrates was increased. Finally, it was observed that the substrate surface was changed from an amorphous phase to polycrystalline. To sum up, it was assumed that the surface of the soda-lime glass substrates with their partially crystalline, namely poly-crystalline, structures artificially induced the thin anatase TiO2 films to develop with a <112>-preferred orientation. In conclusion, the plasma pretreatment of the glass substrate caused the TiO2 thin films to exhibit a higher preference for the <112> orientation, thereby optimizing their photocatalytic efficiency.

Abstract: Series of TiCrN wear resistant coatings have been known to be superior to other coatings in protecting tools which may be damaged corrosion, oxidization, abrasion and hardness of mold materials. The corrosion and oxidation resistance of TiN/CrN(TiCrN) multilayer coatings is better than that of single TiN and CrN coatings. TiCrN coated layer was formed by coating a layer of TixCr1-xN by non-stoichiometry. In this study, TiCrN coated layer by R.F magnetron sputtering was executed heat treatment each other temperature by tube furnace. And then surfaces of coated layer and cross sections were observed by FE-SEM and XRD. Corrosion resistance tester measured characterizations of coated layers. When the temperature increased, TiN was partially transformed to Ti2N and TiNX, and CrN was also transformed to Cr2N. The formation of non-stoichiometric phases decreased corrosion resistance.

Abstract: Mg97Zn1Y2 alloy powders were prepared from gas atomization process, followed by consolidation using spark plasma sintering (SPS) process. The atomized Mg97Zn1Y2 alloy particles were entirely spherical in shape and dendrite microstructure. The compacts sintered by SPS process have values more than 99% of theoretical density. The compressive yield strength was decreased as sintering temperature increased. It is found that the compressive strength showed the maximum value of 303MPa at the sintered specimen under load of 250MPa at 350°C.