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Showing papers in "Materials Transactions in 2002"


Journal ArticleDOI
TL;DR: In this paper, a review of the formation and properties of bulk glassy alloys is presented, where the authors show that the instability of the liquid phase of metallic alloys below melting temperature is a universal phenomenon, making the formation of a crystalline phase of the bulk metallic alloy unavoidable.
Abstract: For thousands of years, metallic alloys have been among the most important materials used by mankind, and their importance as engineering materials remains as great now as ever. Without exception, all bulk metallic alloys used to date consist of crystalline materials with three-dimensional periodic atomic configurations. The instability of the liquid phase of metallic alloys below melting temperature had been thought to be a universal phenomenon, making the formation of a crystalline phase of the bulk metallic alloy unavoidable. In order to prevent transition from a liquid to a crystalline phase, extremely high cooling rates of the order 10 6 K/s are required and the alloys exhibiting critical cooling rates of 10 5 to 10 7 K/s are known as amorphous/glass forming alloys. 1, 2) As a result of the requirement for rapid cooling, amorphous alloys have usually been produced in a thin sheet form with thicknesses below 0.05 mm. The conventionally accepted concept that the supercooled liquid phase of metallic alloys is always unstable has been broken through by the recent successes in forming bulk glassy alloys in a number of transition metal-based alloy systems using the copper mold casting technique. 3‐5) In recent years, studies of the stabilization of metallic supercooled liquid and the resulting bulk glassy alloys have been significant not only for fundamental science but for engineering applications as well. In this paper we review our recent results on the formation and properties of bulk glassy alloys.

293 citations


Journal ArticleDOI
TL;DR: In this article, a low-rigidity type titanium alloy, Ti-29Nb-13Ta-4.6Zr was designed, and then the practical level ingot of the alloy was successfully fabricated by Levicast method.
Abstract: The low rigidity type titanium alloy, Ti–29Nb–13Ta–4.6Zr was designed, and then the practical level ingot of the alloy was successfully fabricated by Levicast method. The mechanical and biological compatibilities of the alloys were investigated in this study. The following results were obtained. The mechanical performance of tensile properties and fatigue strength of the alloy are equal to or greater than those of conventional biomedical Ti–6Al–4V ELI. Young’s modulus of the alloy is much lower than that of Ti–6Al–4V ELI, and increases with the precipitation of α phase or ω phase in the β matrix phase. The compatibility of the alloy with bone of the alloy is excellent. Low rigidity of the alloy is effective to enhance the healing of bone fracture and remodeling of bone. The bioactive coating layer of hydroxyapatite can be formed on the alloy.

271 citations


Journal ArticleDOI
TL;DR: In this article, the tensile properties of martensitic alloys were investigated to provide superelasticity for biomedical applications as a function of heat treatment and Sn content.
Abstract: Martensitic transformation and tensile properties of 4 to 5 mol%Sn-doped Ti–16 mol%Nb alloys consisting of biocompatible elements were investigated to provide superelasticity for biomedical applications as a function of heat treatment and Sn content. Martensitic transformation (bcc to orthorhombic structure) is accelerated at such quenching conditions that the bcc parent phase is slightly decomposed. Martensitic transformation temperature decreases rapidly with increasing Sn content. In-situ optical microscopic observation on cooling and heating indicates that the martensite is thermoelastic, corresponding to small temperature hysteresis between the martensitic and the reverse transformations, which is determined by differential scanning calorimetry. By controlling the heat treatment condition and Sn content, large superelastic strain is obtained at room temperature.

238 citations


Journal ArticleDOI
TL;DR: In this paper, a new Cu-based bulk glassy alloys with large supercooled liquid region and high mechanical strength were found to be formed in Cu-Zr-Al ternary system.
Abstract: New Cu-based bulk glassy alloys with large supercooled liquid region and high mechanical strength were found to be formed in Cu-Zr-Al ternary system. The large supercooled liquid region exceeding 70 K was obtained in the composition range of 40 at%Zr at 2.5 at%Al, 37.5%Zr to 47.5%Zr at 5%Al and 42.5%Zr at 7.5%Al. The largest ΔT x was 74 K for Cu 55 Zr 40 Al 5 and Cu 50 Zr 42.5 Al 7.5 alloys and the highest T g /T l was 0.62 for the former alloy. The alloys with large ΔT x values above 70 K were formed into a bulk glassy rod form with diameters up to 3 mm by copper mold casting and the glassy alloy rods exhibit high compressive strength of 1885 to 2210 MPa and Young's modulus of 102 to 115 GPa combined with elastic elongation of 1.60 to 1.95% and plastic elongation of 0 to 0.4%. The addition of 2.5 to 7.5°%Al to Cu-Zr alloys was very effective for the increase in glass-forming ability as well as the stabilization of supercooled liquid. The effectiveness can be interpreted on the basis of the concept of the formation of the unique glassy structure in special multi-component alloys with the three empirical component rules.

225 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present measurements of magnetostriction on Fe1−x Gax, 0.13 ≤ x ≤ 0.24, (Galfenol).
Abstract: Fe–Ga alloys, in which the α-Fe structure is maintained, are rich sources of high strength, low cost magnetostrictive alloys for transducer and vibration reduction applications. Although the magnetostriction of Fe itself is very low, when a relatively small fraction of the Fe atoms are replaced by Ga, the magnetostriction, (3/2)λ100, increases greatly. Until recently, the highest magnetostriction was found with the replacement of Fe by Al (Alfenol). In this paper, we present our measurements of magnetostriction on Fe1−x Gax , 0.13 ≤ x ≤ 0.24, (Galfenol). With the substitution of 19% Ga for Fe in Fe1−x Gax , a 12-fold increase in magnetostriction to ∼ 400 ppm occurs, even though Ga is non-magnetic. In these alloys, the saturation magnetizations remain high, Ms ∼= 1.7 T, and the Curie temperatures are far above room temperature, TC ∼= 700◦C. In most alloys studied, the magnetostrictions and magnetizations are fully saturated in fields less than 24 kA/m, even under compressive stresses >100 MPa. For x = 0.24 (near Fe3Ga), an anomalous increase in magnetostriction with temperature occurs with a peak magnetostriction above room temperature. Small additions of Ni and Mo to the binary Fe–Ga alloys decrease the room temperature value of λ100.

193 citations


Journal ArticleDOI
TL;DR: In this article, a new Ni-based bulk glassy alloys with high strength and good ductility were synthesized for the first time in Ni- Nb-Ti-Zr base system by the mold-clamp or copper mold casting method.
Abstract: New Ni-based bulk glassy alloys with high strength and good ductility were synthesized for the first time in Ni- Nb-Ti-Zr base system by the mold-clamp or copper mold casting method. The bulk glassy Ni 53 Nb 20 Ti 10 Zr 8 Co 6 Cu 3 alloy has a rod shape with diameters up to 3mm or a sheet shape with thickness up to 1 mm. The glass transition temperature (T g ) and the supercooled liquid region defined by the difference between T g and crystallization temperature (T g ). ΔT x (= T x - T g ) are 846 and 51 K, respectively, and no distinct change in T g . T x and ΔT x with sample diameter is seen. The Ni-based alloy is located in the vicinity of eutectic composition and has a high reduced glass transition temperature (T g /T m ) of 0.67. The Ni-based bulk glassy alloy also exhibits good mechanical properties. i.e., tensile fracture strength of 2700 MPa, tensile fracture elongation of 2. 1%, compressive fracture strength of 3010 MPa and compressive fracture elongation of 2.4%. It is noticed that the tensile fracture strength is the highest among all bulk glassy alloys developed up to date. The success of synthesizing the new Ni-based bulk glassy alloy with good mechanical properties is promising for future uses as a new type of high strength material.

172 citations


Journal ArticleDOI
TL;DR: In this article, the glass-forming ability of Ti-Zr-Hf-Cu-M (M=Fe, Co, Ni) alloys was examined by melt-spinning and copper mold casting methods.
Abstract: The glass-forming ability of Ti–Zr–Hf–Cu–M (M=Fe, Co, Ni) alloys was examined by melt-spinning and copper mold casting methods. New Ti20Zr20Hf20Cu20Ni20 bulk glassy rod of 1.5 mm in diameter was formed by copper mold casting. The Tx and Tg of the glassy rod were 711 K and 658 K and Tg/Tm was 0.57. The bulk glassy alloy can be characterized by equal concentration of constituent elements without distinct host component. It is confirmed that more multicomponent glassy systems have a better glass-forming ability as compared with simpler alloy systems. The glassy alloy rod also exhibits good mechanical properties which are similar to those for ordinary glassy alloys. The finding of this alloy system may provide a new synthesis method of bulk glassy alloys.

169 citations


Journal ArticleDOI
TL;DR: In this article, a new Fe-based bulk glassy alloys were synthesized in the (Fe 0.75 B 0.15 Si 0.10 ) 100-x Nb x system by copper mold casting.
Abstract: New Fe-based bulk glassy alloys were synthesized in the (Fe 0.75 B 0.15 Si 0.10 ) 100-x Nb x system by copper mould casting. The maximum diameter of the bulk glassy alloy rod was 0.5 mm at I at%Nb, 1.0 mm at 2 at%Nb and 1.5 mm at 4 at%Nb. No glass transition is observed at 0 at % Nb, but the addition of Nb causes the appearance of glass transition before crystallization. The glass transition temperature (Tg) and crystallization temperature (T x ) of the bulk glassy rods were 815 K and 858 K, respectively, for the 1 at%Nb alloy, and 835 K and 885 K, respectively, for the 4 at%Nb alloy. The reduced glass transition temperature (T g /T l ) defined by the ratio of Tg to the liquidus temperature (T l ) was measured as 0.56 at I at%Nb, 0.57 at 2 at%Nb and 0.61 at 4 at%Nb. There is a tendency for T g , ΔT x (= T x - T g ) and T g /T l to increase with increasing Nb content. The effect of Nb addition can be interpreted in the framework of the three component rules for the formation of bulk glassy alloys and the stabilization of supercooled liquid. The Fe-B-Si alloy satisfies the three component rules by the addition of Nb. The bulk glassy alloy rods exhibited good soft magnetic properties, i.e., high saturation magnetization (I s ) of 1.47 to 1.51 T, low coercive force (H c ) of 2.9 to 3.7 A/m and Curie temperature of 593 to 684 K. The high I s and low H c , as well as the formation of bulk glassy alloys in the simple alloy system are promising as a new type of soft magnetic bulk alloy.

162 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied copper oxidation at 623-1073 K under 0.1 MPa O 2 using a commercial 99.9999% pure copper and found that the growth of Cu 2 O is predominant and it obeys the parabolic law at 6 23-773 K.
Abstract: In reviewing the results reported for copper oxidation at intermediate temperatures from 573 to 1173 K, the oxidation mechanism at the lower part of this temperature range and the reason for the change in activation energy with decreasing the temperature remain unclear. To make it clear, copper oxidation is studied at 623-1073 K under 0. 1 MPa O 2 using a commercial 99.9999% pure copper. The oxidation kinetics is essentially parabolic, and the activation energy decreases from 111 kJ/mol at 873-1073 K to 40kJ/mol at 623-773 K. The growth of Cu 2 O is predominant and it obeys the parabolic law at 623-773 K, as well as the case at 873-1073 K. In addition to grain boundary diffusion of copper along the fine and thin columnar Cu 2 O grains, the non-protective CuO whisker layer, which cannot keep the oxygen potential constant at the Cu 2 O/CuD interface, should be responsible for the decrease in the activation energy at 623-773 K.

135 citations


Journal ArticleDOI
TL;DR: In this paper, the martensitic and magnetic transitions of Ni 54 Ga 27 Fe 19 alloy were investigated by differential scanning calorimetry and X-ray powder diffraction and with a vibrating sample magnetometer.
Abstract: The martensitic and magnetic transitions of Ni 54 Ga 27 Fe 19 alloy were investigated by differential scanning calorimetry and X-ray powder diffraction and with a vibrating sample magnetometer. The alloy is martensitically transformed from a L2 1 to a martensite phase with a 14M (7R) structure. The ferromagnetic transition is also accompanied by the martensitic transformation from a paramagnetic parent phase to a ferromagnetic martensite phase in the temperature interval between M s (= 293 K) and M f (= 274 K). The Ni-Ga-Fe system is promising as a ferromagnetic shape memory alloy.

127 citations


Journal ArticleDOI
TL;DR: In this paper, a bulk glassy Ni-based alloys with high fracture strength exceeding 2700 MPa were prepared in Ni60Nb40−x−yTix Zry system by copper mold casting.
Abstract: Bulk glassy Ni-based alloys with high fracture strength exceeding 2700 MPa were prepared in Ni60Nb40−x−yTix Zry system by copper mold casting. The glassy alloys with distinct glass transition were obtained in the wide composition range from 0 to 35%Ti and 0 to 30%Zr and the largest supercooled liquid region before crystallization was 76 K for Ni60Nb15Ti10Zr15. The maximum diameter was 2 mm for Ni60Nb20Ti15Zr5 and the glass transition temperature (Tg), crystallization temperature (Tx) and reduced glass transition temperature (Tg/Tl) of the bulk glassy alloy were 841 K, 898 K and 0.61, respectively. The Young’s modulus (E), compressive fracture strength (σc,f) and compressive fracture elongation (ec,f) were 156 GPa, 2770 MPa and 2.4%, respectively, for the bulk alloy. There is a tendency for fracture strength to increase with increasing E , Tg and liquidus temperature (Tl). It is therefore interpreted that the high strength is due to strong bonding nature among the constituent elements.

Journal ArticleDOI
TL;DR: In this article, the authors compared the performance of single-roller drive rollers and normal rolling on AZ31 Mg alloy and found that the rollers with weaker texture leads to twining and lower planar anisotropy.
Abstract: Mechanical properties and press formability at room temperature of AZ31 Mg alloy processed by single roller drive rolling were compared with those of the one processed by normal rolling. The single roller drive rolled specimens showed the weaker intensity of (0002) texture. As a result of tensile tests, there was no difference in unidirectional elongation between them. However, results of conical cup tests show that the press formability of the single roller drive rolled specimen was rather better. The planar anisotropy was lower and twins were observed for the single roller drive rolled specimen, indicating that the weaker intensity of texture leads to twining, resulting in the lower planar anisotropy.

Journal ArticleDOI
Tetsuya Uda1
TL;DR: In this article, the rare earths in the neodymium magnet sludge were extracted by chlorination with FeCl 2, and activated carbon was used as a de-oxidation reagent.
Abstract: A large amount of neodymium magnet sludge is generated during the manufacture process. Because the sludge is considerably contaminated by oxygen, it is difficult to reuse it as it is. The present basic study has been carried out to establish efficient recycling process of the sludge. The rare earths in the neodymium magnet sludge were extracted by chlorination with FeCl 2 . An activated carbon was used as a de-oxidation reagent. Metallic iron in the sludge was not chlorinated because the iron monochloride is not stable. The extracted rare earth chlorides were easily separated from Fe-alloy and the excess of FeCl 2 by vacuum distillation. In this study, 96% of neodymium and 94% of dysprosium in the sludge were extracted into chloride phase. By the vacuum distillation, a mixture of neodymium and dysprosium trichlorides of 99.2% purity was recovered with the rare earth element's yield of 76% for the charged sludge. In addition, it was confirmed that the rare earth chlorides can be converted to the corresponding oxides by a pyrohydrolysis reaction accompanied by a formation of HCl gas. The HCl gas can chlorinate metallic iron to FeCl 2 . Therefore, a new recycling process for rare earth magnet waste can be realized as a chlorine circulation type process. During the process, only carbon and water are consumed, and there are no toxic pollutants. Moreover, the obtained rare earth oxide can be directly used as raw material in the oxide electrolysis, which is the conventional industrial reduction process for rare earth metal production.

Journal ArticleDOI
TL;DR: Using pure Ti powder with particle sizes from 300 to 500 μm prepared by the plasma rotating electrode process (PREP), porous pure Ti compacts for biomedical applications were synthesized by powder sintering, and microstructures and mechanical properties of the compacts were investigated in this paper.
Abstract: Using pure Ti powder with particle sizes from 300 to 500 μm prepared by the plasma rotating electrode process (PREP), porous pure Ti compacts for biomedical applications were synthesized by powder sintering, and microstructures and mechanical properties of the compacts were investigated in this study. Porous compacts having porosity of 19-35 vol% are successfully fabricated by controlling sintering condition. It is found that Young's modulus and compressive yield strength decrease linearly with increasing porosity, and porous Ti compacts having porosity of about 30-35 vol% exhibit identical Young's modulus of human bone.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the effect of active flux on the Marangoni convection in the welding pool, and showed that the depth/width ratio of the weld pool was closely related to the oxygen content in the pool.
Abstract: Active flux can modify the fusion zone geometry dramatically in GTA welding (A-TIG). In the present study, in order to investigate the effect of the active flux on the Marangoni convection in the welding pool, bead-on-plate specimens are made on SUS304 stainless steel pre-placed with single active flux, Cu 2 O, NiO, Cr 2 O 3 , SiO 2 and TiO 2 by the GTA process. Weld pool cross-sections and the bead surface morphology are analyzed by optical microscopy after welding. The oxygen content in the weld metal is measured using a HORIBA EMGA-520 Oxygen/Nitrogen Analyzer. The results showed that the depth/width ratio of the weld pool was closely related to the oxygen content in the pool. The oxygen content in the weld metal increases with the quantity of fluxes, Cu 2 O, NiO, Cr 2 O 3 , SiO 2 and TiO 2 . However, for the TiO 2 oxide flux, the highest oxygen content in the weld metal is below 200 ppm. As the oxygen content in the weld metal is in a certain range of 70-300 ppm, the depth/width ratio increases to 1.5 to 2.0 times. Too low or too high oxygen content in the pool does not increase the depth/width ratio. The oxygen from the decomposition of the flux in the welding pool alters the surface tension gradients on the weld pool surface, and hence, changes the Marangoni convection direction and the weld pool penetration depth.

Journal ArticleDOI
TL;DR: In this article, the influence from precipitation fraction on precipitate coarsening and hardening kinetics was accounted for quantitatively, which allowed the hardening quantification to be carried out in a more accurate manner.
Abstract: Quantification of precipitation hardening is a challenging subject as it demands combined knowledge of precipitation strengthening mechanism and precipitate growth/coarsening kinetics. Having not seen many attempts on developing new theories in recent years, the authors are aware of the fact that many existing concepts and developed theories are sometimes even neglected or misused. This article therefore aims to describe overview on some aspects which have not been fully addressed and/or misused. Recent developments in this subject include an accurate determination of the equilibrium precipitate fraction and interparticle spacing. The influence from precipitation fraction on precipitate coarsening and hardening kinetics was accounted for quantitatively, which allows the hardening quantification to be carried out in a more accurate manner. In addition, difficulties in quantification of precipitation strengthening effects in commercial systems are discussed. Advanced theories on dislocation precipitate interaction mechanisms are required to improve the accuracy in quantification of precipitation hardening to a high level.

Journal ArticleDOI
TL;DR: In this paper, the surface oxide film on 316L stainless steel after polishing in water consists of iron and chromium oxides containing small amount of nickel, molybdenum, and manganese oxides.
Abstract: The purpose of this study was to characterize the surface oxide films on 316L austenitic stainless steel located in various environments to estimate the reconstruction of the film in human body. Five kinds of specimens were prepared according to the following methods: polished in deionized water, autoclaved, immersed in Hanks’ solution, immersed in cell culture medium, and incubated with cultured cells. X-ray photoelectron spectroscopy (XPS) was performed to estimate the compositions of the surface oxide film and substrate and the thickness of the film. Surface oxide film on 316L steel after polished in water consists of iron and chromium oxides containing small amount of nickel, molybdenum, and manganese oxides. The surface oxide contained a large amount of OH − . Calcium phosphate was formed on/in the film after immersion in the Hanks’ solution and medium and incubated with the cells. Sulfate is adsorbed by the surface oxide film and reduced to sulfite and/or sulfate in cell culture medium and with culturing cells. The results in this study suggest that nickel and manganese are depleted in the oxide film and the surface oxide changes into iron and chromium oxides containing a small amount of molybdenum oxide in human body.

Journal ArticleDOI
TL;DR: In this paper, the defect levels of neutral and charged oxygen vacancies in MgO, ZnO, Al2O3 and SnO2 have been calculated by a first principles plane-wave pseudopotential method.
Abstract: Formation energies of neutral and charged oxygen vacancies in MgO, ZnO, Al2O3, In2O3 and SnO2 have been calculated by a first principles plane-wave pseudopotential method. Two kinds of polymorphs, i.e., an ordinary phase and a high-pressure or an hypothetical negative pressure phase, have been chosen in order to see the effects of crystal structure. Supercells composed of 54 to 96 atoms were employed, and structural relaxation around the vacancy within second nearest neighbor distances was taken into account. Defect levels were obtained from the difference in total energies of the neutral and charged supercells that contain a vacancy. Ionization energies of the vacancy were calculated as the difference in the bottom of the conduction band and the defect levels. They are found to be proportional to band-gaps with a factor of approximately 0.5, which are prohibitively large for the n-type conduction.

Journal ArticleDOI
TL;DR: In this article, the entropy change caused by a magnetic field, ΔS mag, was estimated on the basis of the Maxwell relation, and the results indicated that MnAs 1-x Sb x is a promising material for a working substance in magnetic refrigeration near room temperature.
Abstract: Magnetization of MnAs 1-x Sb x was measured as functions of temperature and magnetic field for 0 < x ≤ 0.4. The entropy change caused by a magnetic field, ΔS mag , was estimated on the basis of the Maxwell relation. The ΔS mag for 0 ≤ x ≤ 0.3 in a field change of 5 T reaches 25-30 J/K kg, which exceeds that of other materials by a factor of 2-4. The substitution of Sb for As can tune the Curie temperature between 230 K and 315 K without any significant reduction of ΔS mag , The large ΔS mag originates in a paramagnetic to ferromagnetic transition induced by a magnetic field. These results indicate that MnAs 1-x Sb x is a promising material for a working substance in magnetic refrigeration near room temperature.

Journal ArticleDOI
TL;DR: In this article, the authors measured interlamellar spacings ranging from 0.18 to 0.5 µm and derived the solidification front velocities and cooling rates at different positions in the as-cast samples.
Abstract: by optical microscopy and scanning electron microscopy. From the measured interlamellar spacings ranging from λ = 0.18 to 0.5 µm, the solidification front velocities and the cooling rates at different positions in the as-cast samples are derived. The decisive effect of the diameter of cast rods is confirmed. For a centrifugal casting technique, the maximum cooling rate decreases from 730 to 95 K/s when the diameter increases from 2 to 5 mm. Moreover, it is revealed that the local cooling rates decrease significantly from the bottom towards the top of the rods. From the estimated cooling rates at a fixed rod diameter the centrifugal casting technique is assessed as superior to other methods applied, namely copper-mould casting and suction casting. The estimated cooling rates are compared with literature data for glass-forming alloys.

Journal ArticleDOI
TL;DR: In this paper, a simple numerical scheme is presented to simulate partial equilibrium solidification with complete interstitial and negligible substitutional solute back diffusion in multi-component and multi-phase systems.
Abstract: A simple numerical scheme is presented to simulate partial equilibrium solidification with complete interstitial and negligible substitutional solute back diffusion in multi-component and multi-phase systems. Based on this scheme, a computing tool capable of using Thermo-Calc databases directly has been developed for the estimation of solidification behavior of steels and other interstitial-containing alloys. Agreements between calculated and experimental as well as DICTRA results have been obtained on the microsegregation, fraction of eutectic, and freezing range of several steels. This suggests that the partial equilibrium assumption and proposed numerical scheme are reasonable and satisfactory, and confirms that the carbon back diffusion plays a very important role in the solidification of steels.

Journal ArticleDOI
TL;DR: In this paper, the authors showed that the glass transition temperature (Tg), crystallization temperature, supercooled liquid region (ΔT x = T x -T g ) and reduced glass transition temperatures (T g /T m ) of the Ca-Mg-Cu system can be obtained.
Abstract: New bulk glassy alloys were formed in the Ca-Mg-Cu system by the copper mold casting method. The maximum rod diameter (d max ) for the formation of a glassy phase was 2mm for Ca 67 Mg 19 Cu 14 and above 4 mm for Ca 57 Mg 19 Cu 24 . The glass transition temperature (Tg), crystallization temperature (T x ), supercooled liquid region (ΔT x = T x -T g ) and reduced glass transition temperature (T g /T m ) are 387 K, 407 K, 20 K and 0.60, respectively, for the former alloy and 404 K, 440 K, 36 K and 0.64, respectively, for the latter alloy. There is a tendency for d max to increase with increasing ΔT x and T g /T m . Young's modulus (E) and compressive fracture strength are 38 GPa and 545 MPa, respectively, for the Ca 57 Mg 19 Cu 24 alloy rod with a diameter of 2 mm. The success of synthesizing bulk glassy alloys in the simple metal (Ca) base system makes it important as a basic alloy system for examining fundamental chemical and physical properties of bulk glassy alloys.

Journal ArticleDOI
TL;DR: In this paper, it is suggested that the rusts formed on mild steel and weathering steel are composed of the crystalline α-FeOOH, γ-FeOH and an X-ray amorphous phase, which gives no peak to the Xray diffraction pattern.
Abstract: The rusts formed on mild steel (15-year exposure) and weathering steel (32-year exposure) exposed to an industrial environment have been characterized by means of X-ray diffraction technique and 57Fe Mossbauer spectroscopy. By using an X-ray diffraction method, it is suggested that the rusts formed on both steels consist of the crystalline α-FeOOH, γ-FeOOH and an X-ray amorphous phase, which gives no peak to X-ray diffraction pattern. The amount of the X-ray amorphous phase exceeds 50% of the total amount of the rust. The 57 Fe Mossbauer spectra observed at 10 K indicate that the rust contains only α-FeOOH, γ-FeOOH and Fe 3-δ O 4 (γ-Fe 2 O 3 ) for mild steel, and only α-FeOOH and γ-FeOOH for weathering steel. The X-ray amorphous substance in the rust layer formed on mild steel possesses the structures of mainly α-FeOOH showing superparamagnetism owing to its small particle size, and Fe 3-δ O 4 (γ-Fe 2 O 3 ). They are contained both in the inner rust layer and in the outer rust layer. The X-ray amorphous phase in the rust layer formed on weathering steel is mainly α-FeOOH.

Journal ArticleDOI
TL;DR: In this article, the ball shear strength of BGA joints during isothermal aging was studied with Sn-35Ag-075Cu solder on three different pads at temperature between 70 and 170°C for times ranging from 1 to 100 days.
Abstract: The ball shear strength of BGA solder joints during isothermal aging was studied with Sn–35Ag–075Cu solder on three different pads (Cu, electroless Ni–P/Cu, immersion Au/Ni–P/Cu) at temperature between 70 and 170°C for times ranging from 1 to 100 days The reliability of solder ball attachment was characterized by mechanical ball shear tests As a whole, the shear strength of BGA joints decreased with increasing temperature and time The shear strength for both the immersion Au/Ni–P/Cu and electroless Ni–P/Cu pads was consistently higher than that of the Cu pad for all isothermal aging conditions The fracture surface showed various characteristics depending on aging temperature, time, and the types of BGA pad The P-rich Ni layer formed at the interface between (Cu, Ni)6Sn5 and Ni–P deposits layer after aging, but fracture at this interface was not the dominant site for immersion Au/Ni–P/Cu and electroless Ni–P/Cu pad

Journal ArticleDOI
TL;DR: The shape memory properties of Fe-Mn-Si-based alloys containing Nb and C are further improved by pre-rolling of the solution-treated austenite and the subsequent ageing treatment.
Abstract: The shape memory properties of Fe-Mn-Si-based alloys containing Nb and C are further improved by pre-rolling of the solution-treated austenite and the subsequent ageing treatment. For an Fe-28Mn-6Si-5Cr-0.53Nb-0.06C (mass%) alloy, 90% of an initial 4% strain is recovered on heating without any previous training treatment, if the alloy in austenitic state is rolled by 6-14% at 870 K and aged at 1070 K for 10 min to produce NbC precipitates. In the same condition, the alloy develops shape recovery stresses of 255 MPa and 295 MPa for 6% and 14% pre-rolling, respectively, when initially deformed by 4.5%. TEM observations indicate that these improved shape memory characteristics are related to a fine distribution of NbC precipitates in the fcc matrix and their interaction with stacking faults.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the transport properties of the obtained (Bi 1-x Sb x ) 2 Te 3 samples with various Sb alloying contents and showed that the sample's transport properties are quite sensitive to the Sb content.
Abstract: Mechanical alloying followed by pulse discharge sintering (MA-PDS) has been employed to develop the bulk (Bi 1-x Sb x ) 2 Te 3 thermoelectric materials with various Sb alloying contents. Substitutional solid solutions of (Bi 1-x Sb x ) 2 Te 3 are formed in the whole Sb content range by MA-PDS process. The sintered compacts are dense and have refined microstructures. Systematic investigations on the electrical, thermal and thermoelectric properties reveal that the transport properties of the obtained (Bi 1-x Sb x ) 2 Te 3 samples are quite sensitive to the Sb alloying content. At room temperature, the samples with x 0.57, the samples become p-type. The pure constituents of Bi 2 Te 3 and Sb 2 Te 3 as well as the Sb-poor, n-type samples exhibit the room-temperature figure of merit of the order of 1.0 x 10 - 3K -1 . High values of figure of merit have been obtained in the Sb-rich, p-type samples. The maximum value of 3.35 x 10 -3 K -1 is attained at x = 0.80, which corresponds to the carrier concentration and Hall mobility of 1.95 x 10 19 cm -3 and 207 cm 2 /Vs, respectively.

Journal ArticleDOI
TL;DR: In this article, a homogeneous melting state without any crystalline inclusions was achieved in an arc melt furnace by using a ladle arc-melting-type furnace and squeeze cast method to produce crystalline inclusion-free Zr 50Cu30Ni10Al10 bulk amorphous alloy sheets.
Abstract: A homogeneous melting state without any crystalline inclusions was achieved in an arc melt furnace by using a ladle arc-melting-type furnace. Molten alloy for pouring can be melted completely by arc heating just above the mold in a pseudo float melting (PFM) state. We combined a ladle arc-melt-type furnace and the squeeze cast method to produce bulk amorphous alloy sheet with a single amorphous phase structure, thereby successfully producing crystalline inclusion-free Zr 50Cu30Ni10Al10 bulk amorphous alloy sheets. The tensile strengths of the Zr50Cu30Ni10Al10 bulk amorphous alloys exceeded 1800 MPa, and the bending deflection of the alloys was improved by a factor of 10 using the PFM process.

Journal ArticleDOI
TL;DR: In this paper, the interfacial reaction and mechanical properties of lead-free alloys/Cu joints were investigated under thermal exposure conditions, and the activation energy of the growth of Cu-Zn compounds at the joint interface was determined to be approximately 70 kJ/mol.
Abstract: The interfacial reaction and mechanical properties of Sn–Zn lead-free alloys/Cu joints were investigated under thermal exposure conditions. In the solder layer, Zn phases reacted with Cu and were transformed to Cu–Zn compounds with increasing exposure time. The microstructure change caused decreasing Vickers hardness of the solder layer. At the joint interface, although Cu–Zn compounds formed first, the formation of Cu–Sn compounds occurred with increasing exposure time. Simultaneously, the disappearance of Cu–Zn compounds and void formation occurred. The activation energy of the growth of Cu–Zn compounds at the joint interface was determined to be approximately 70 kJ/mol. That value is close to the activation energy of the diffusion of Zn in Sn crystal.

Journal ArticleDOI
TL;DR: In this paper, a magnesium solid solution with a novel long periodic hexagonal structure was formed for a Mg97Zn1Y2 (at%) alloy in a rod form prepared by extrusion of atomized powders at 573 K as well as in a melt-spun ribbon form.
Abstract: A magnesium (Mg) solid solution with a novel long periodic hexagonal structure was formed for a Mg97Zn1Y2 (at%) alloy in a rod form prepared by extrusion of atomized powders at 573 K as well as in a melt-spun ribbon form. The novel structure of the rod alloy had an ABACAB-type six layered packing with lattice parameters of a = 0.322 nm and c = 3 × 0.521 nm. The Mg phase in the extruded rod alloy had fine grain sizes of 100 to 150 nm and included cubic Mg24Y5 particles with a size of about 10 nm at volume fractions below 10%. The density (ρ) was 1.84Mg/m 3 . The tensile yield strength (σy) and elongation of the rod alloy were 610 MPa and 5%, respectively, and the specific strength defined by the ratio of σy to ρ was 330 MPa/(Mg/m 3 ), being the highest among all metallic alloys. The σy is 2.7 to 8 times higher than those for conventional high-strength Mg-based alloys. The excellent mechanical properties are due to the combination of fine grain size, new long periodic hexagonal solid solution, homogeneous dispersion of fine Mg24Y5 particles inside the nano-grains and the absence of the second precipitates along the grain boundary. The new Mg-based alloy is promising for future uses in many fields.

Journal ArticleDOI
TL;DR: In this paper, the mechanism of new grain evolution can be a deformation-induced continuous reaction, that is continuous dynamic recrystallization (CDRX), and a model for CDRX is discussed in detail comparing with previous several models.
Abstract: New grain evolution taking place during superplasticity was studied by means of tensile tests as well as metallographic observation for a unrecrystallized coarse-grained 7075 aluminum alloy. Grain boundary sliding (GBS) frequently takes place even on the layered high angle boundaries (HABs) parallel to the tensile axis and brings about rotation of subgrains near the HABs and subsequently in grain interiors. The misorientations of (sub)grain boundaries evolved in the pancaked grains increase accompanied by a randomization of the initial texture, followed by development of new grains with HABs. This indicates that unrecrystallized and pancaked grain structure developed by cold rolling is an important prerequisite not only for the appearance of superplasticity, but also for the dynamic evolution of new fine grains. It is concluded that the mechanism of new grain evolution can be a deformation-induced continuous reaction, that is continuous dynamic recrystallization (CDRX). A model for CDRX is discussed in detail comparing with previous several models.