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Some Fe-rich amorphous alloys of Fe–B–P–Si and Fe–B–P–Si–C systems were found to exhibit simultaneously good soft magnetic properties with high-saturation magnetization values near 1.7 T, which are higher than those for previously reported Fe-based amorphous and glassy alloys, in addition to rather good amorphous ribbon formability, good bending ductility, and rather high corrosion resistance. The corrosion resistance increased with increasing P content, accompanying by the increase in thermal stability of the amorphous phase. The decrease in the outer surface velocity of the wheel, which results in the increase of ribbon thickness, also causes an improvement of surface smoothness of the melt-spun amorphous alloy ribbons. The syntheses of new high-saturation Fe-based soft magnetic amorphous alloys without any other transition metals hold promise for future extension of Fe-based soft magnetic amorphous materials.
It is widely accepted that oxygen will severely deteriorate the glass-forming ability (GFA) of an alloy. In this work, we report that the GFA of a Fe76Si9B10P5 glassy alloy can be significantly improved (the critical diameter for fully glass formation is increased from 1 to 3 mm) under oxygen casting atmosphere. Furthermore, the pressure of oxygen atmosphere gives an obvious enhancement in the critical diameter of Fe76Si9B10P5 glassy alloy. A dependence of GFA on casting atmosphere species (argon, nitrogen, air, and oxygen) is also observed for this glassy alloy, and its critical diameter is 1, 1.5, 2.5, and 3 mm, respectively. In addition, the Fe-based glassy alloy exhibits excellent soft magnetic properties regardless of the applied casting atmosphere. The mechanism for such an unusual oxygen effect on the GFA of Fe76Si9B10P5 glassy alloy is attributed to the reduced nucleation rate caused by the enhancement of surface tension of the alloy melt.
With the aim of investigating fundamental properties and nano-imprintabilities of glassy alloy in the film form, Zr49Al11Ni8Cu32, Pd39Cu29Ni13P19 and Cu38Zr47Al9Ag6 alloy thin films were fabricated on Si substrate by a magnetron sputtering method. These thin films exhibit distinct glass-tradition phenomenon and large supercooled liquid region of about 80 K, confirming as a glassy structure and have very smooth surface and sufficient hardness to maintain imprinted shape, which are suitable for nano-imprint processing. Moreover, thermal nano-imprintabilies of these obtained films are demonstrated by using a dot array mold with a dot diameter of 90 nm and a pitch of 180 nm. Surface observations revealed that periodic nano-hole arrays were successfully imprinted on the surface of these films and precisely corresponded to the periodic dot pattern of the mold. Particularly, Pd-based glassy alloy thin film indicated more precise pattern imprintability, namely, more flat residual surface plane and sharper hole edge. These results suggest that these glassy alloy thin films, especially Pd-based glassy alloy thin film have high potential for application to the nano-imprinting materials.
A non-equilibrium Cu-Zr-Ag alloy was designed for the development of an alternative electric connector to Cu-Be alloys. This work aims at producing a Cu-Zr-Ag sheet using a hot-powder-rolling (HPR) process. The sheets were produced by a sequential process of HPR, pre-annealing, and cold rolling, using Cu93.5Zr5.5Ag1 (at.%) alloy powder produced by an argon gas atomization method. The Cu93.5Zr5.5Ag1 alloy sheet has a tensile strength of 1188 MPa and a conductivity of 33.2% IACS, which are similar values to those of Cu-Be alloys. In this paper, we optimize the conditions of the HPR process and reveal the correlation between the microstructure and properties of the Cu-Zr-Ag sheet produced by the HPR process. In addition, we discuss the alloy’s applicability for use as a connecter material.
The surface of Ti-based bulk metallic glass (BMG) was irradiated by the femto-second laser and microgrooves were formed on the surface. The titanate nanomesh layers were fabricated on the micro-grooved BMG surface by hydrothermal-electrochemical (H-E) treatment changing the conditions of the concentration of electrolyte solution (0 and 5 M) and applying current density (0-200 mA/cm2). The bone-inducing capacity of the samples with different H-E treatment was confirmed by soaking them in a simulated body fluid for 12 days. The H-E treatment in higher concentration 5 M NaOH aq. and applying higher current density above 0.5 mA/cm2 exhibited excellent bioactivity inducing large hydroxyapatite crystallites.
Present progress in developments of glassy alloy composites for bit-patterned-media and non-equilibrium Cu-based alloys for conductive materials of electrical connectors are reviewed. It is proven that the imprinting of the Pd-based glassy alloy thin film is favorable for the formation of nano-structured devices. Detailed imprinted morphologies formed by different imprinting conditions were examined. In addition, technology of large area imprinting up to 2.5 inches area has been successfully developed and it is now available for production. These technological developments will be utilized for next generation bit-patterned-media with high data density. A newly developed non-equilibrium Cu-Zr-Ag alloy was prepared into sheet form by the combination of casting, cold rolling and annealing. The alloy sheet exhibited high tensile strength of exceeding 1500 MPa and good electrical conductivity of 30% IACS. However, bending ductility should be improved for the actual production of connector. Through the several examinations, remaining issues that should be solved are discussed in the framework of industrialization and commercialization. These obtained results suggest that the glassy alloy composite or non-equilibrium alloy designed by the glass-forming rules have a great potential to develop innovative products in the near future.
Zr65Al7.5Ni10Cu12.5Nb5 glass was found to exhibit a large plastic compressive strain of over 10% and the property was suggested to be due to deformation-induced nanocrystallization. A transmission electron microscopic observation, however, only revealed obscure ordered clusters with a size of ˜2 nm in the fracture surface of a deformed sample, instead of well-identified crystals as previously reported for the Zr–Al–Ni–Cu–Pd system. This phenomenon is suggested to correlate with the higher viscosity of supercooled liquid and the slower grain growth of icosahedral phase during primary crystallization in the Zr65Al7.5Ni10Cu12.5Nb5 compared to those in the Zr65Al7.5Ni10Cu12.5Pd5 alloy. The role of the deformation-induced nanoclusters on the enhanced compressive plasticity was discussed.
Precipitation of ZrCu with the B2 structure in Zr50Cu50–xAlx (x = 0, 4, 6) metallic glasses by rapidly heating and cooling was investigated. By rapidly heating and cooling, the ZrCu B2 phase precipitates the most in Zr50Cu46Al4 metallic glass plates prepared by tilt-casting without using a silica nozzle. The amount of the ZrCu B2 phase precipitated in Zr50Cu46Al4 metallic glass ribbons prepared by using a silica nozzle decreases by Si diffused from the silica nozzle during the preparation. This work is discussed from the viewpoint of crystallization behavior and why larger Zr-based bulk metallic glasses can be formed by suction, tilt, and cap casting without using a silica nozzle.
New Cu-based bulk glassy alloys (BGAs) with high glass-forming ability (GFA) were synthesized in a Cu-Zr-Al-Ag system. As the compositions of Cu-Zr-Al-Ag alloys with lower Ag and Al content shifted to the Cu-rich range, the supercooled liquid region, reduced glass transition temperature, and γ value increased, leading to the improvement of GFA. The best GFA is located around Cu47Zr45Al5Ag3, which is close to eutectic. Fully glassy samples with diameters up to 15 mm were fabricated by copper mold casting. These Cu-based BGAs exhibit excellent mechanical properties under compression. A large Young's modulus of 104–111 GPa, high fracture strength of 1905–1942 MPa, and distinct plastic strain of 0.002–0.011 were obtained. Additionally, the BGAs also show good corrosion resistance in 1 N H2SO4 solution.
A Cu- and Ni-free Zr-based metallic glass with high glass-forming ability was found in the Zr-Al-Co ternary system. The eutectic Zr56Al16Co28 alloy could be cast into glassy cylindrical rods with diameters up to 18 mm. The glassy alloy exhibited high tensile fracture strength of 1830 MPa and low Young's modulus of 83 GPa in conjunction with better corrosion resistance compared with the glassy Zr57Nb5Al10Ni12.6Cu15.4 in a simulated body fluid. Hydrothermal-electrochemical treatment in the aqueous 5M-NaOH solution resulted in the formation of amorphous sodium cobaltate layer on the surface of glassy Zr56Al16Co28 alloy. Hydroxyapatite was spontaneously formed on the surface of the alloy, indicating bioactivity after surface modification. The discovery of a Cu- and Ni-free Zr-based metallic glass with a critical diameter larger than 1 cm in conjunction with excellent mechanical properties, superior corrosion resistance, and good bioactivity may open up the application field as biomaterials.
The crystallization behavior of melt-spun ribbons and bulk samples of the Cu36Zr48Al8Ag8 glassy alloy on heating is presented here. The crystallization kinetics and structural changes in the Cu36Zr48Al8Ag8 glassy alloy were studied using x-ray diffraction, transmission electron microscopy, differential scanning, and isothermal calorimetry methods. A clear comparison is made of the differences in the crystallization kinetics of the melt-spun ribbons and the copper-mold-cast bulk rod samples. It was suggested that the kinetics of crystallization in the rod sample, at any given temperature, are somewhat different than in the ribbon samples, probably because of size and free volume effects. Differences in the crystallization behavior of this alloy with other Cu-Zr-Al-Ag alloys have also been discussed.
The effect of Ag substituting Cu on the structural features of the Cu55Zr45, Cu45Zr45Ag10, and Cu35Zr45Ag20 glassy alloys was studied using the real-space pair distribution and radial distribution functions. The experimental x-ray diffraction data obtained in a synchrotron beam were used to derive pair and radial distribution functions through Fourier transformation processing. These results suggest that a certain degree of medium-range order in this alloy is maintained up to about 2.5 nm distance. It is suggested that the addition of Ag causes formation of a more homogeneous local atomic structure compared with that of a binary Cu–Zr alloy, which could be considered as a reason for the improved glass-forming ability of this alloy.
In this work, we study the cooling behavior of several typical bulk glassy alloys on casing and present the relationship between the thermal conductivity of a glassy alloy and the cooling rate upon mold casting. The cooling rates obtained for Ti-, Zr-, Pd-, and Cu-based bulk glass forming alloys are found to scale with the thermal conductivities of the studied glassy alloys.
The coexistence of high Fe content and high glass-forming ability (GFA) has been earnestly desired from academia to industry. We report a novel Fe76Si9B10P5 bulk metallic glass with an unusual combination of high magnetization of 1.51 T due to high Fe content as well as high GFA leading to a glassy rod with a diameter of 2.5 mm despite not containing any glass-forming metal elements. This alloy composed of familiar and low-priced elements, also exhibiting very excellent magnetic softness, has a great advantage for engineering and industry, and thus should make a contribution to energy saving and conservation of earth’s resources and environment.
The melting behavior, thermal stability, and glass-forming ability (GFA) of Cu84−xZrxAg8Al8 (x = 42 to 50) glassy alloys were investigated. The alloy with x = 46 exhibits the highest reduced glass transition temperature (Trg). However, the best GFA was obtained for alloy with x = 48 corresponding to the largest supercooled liquid region (ΔTx) and a deep eutectic composition. At the best GFA composition, full glassy samples with diameters of over 20 mm could be fabricated by injection copper mold casting and water quenching without flux. The underlying mechanism of the unusual GFA of the alloy is discussed.
The influence of the cooling rate on the structure, microhardness, relaxation, and devitrification behavior of Cu44Ag15Zr36Ti5 glassy alloy on heating is studied in the present work. According to transmission electron microscopy investigations, the structures of Cu44Ag15Zr36Ti5 glassy ribbon and bulk samples are somewhat different. The structure of the ribbon samples is amorphous while, the nanoscale clusters of the crystalline phase (highly ordered regions) are formed in the bulk samples. It is reflected in the shift of the x-ray diffraction peak, in the magnitude of the heat of structure relaxation and crystallization, as well as in the change in the Vickers microhardness. An analysis of the cooling curve is also performed.
Since 1988, it has been demonstrated that metallic glasses can be made in bulk form with diameters larger than several millimeters. At present, several alloy systems with maximum diameters for glass formation exceeding 1 cm are known. As a result, Zr-, Ti-, Fe-, Co-, Ni-, and Cu-based bulk metallic glasses (BMGs) are already in use for magnetic-sensing, chemical, and structural applications. In this article, recently developed BMGs with critical diameters of more than 1 cm are summarized, and some of their industrial applications are reviewed.
If a metal contracts upon solidification, the specific volume of a metallic liquid phase must not be smaller than that of the corresponding crystal. As molten metals have higher thermal expansion coefficients compared with those of the corresponding crystals, the intersection point of two specific-volume–temperature plots of the liquid and the corresponding solid crystalline phase by analogy with Kauzmann’s paradox for entropy could be treated as an ideal glass-transition temperature. This paper describes this phenomenon observed for a number of pure metals and gives a semiempirical criterion for the achievement of a good glass-forming ability.
A new Ti-based bulk-metallic glassy (BMG) alloy without Ni was developed in various forms such as melt-spun ribbon and cylindrical rods. Ti metal and Ti-based alloys are well known as biomaterials because Ti has good biocompatibility with the human body. We examined mechanical and chemical properties of a newly developed Ti-based BMG alloy in comparison with pure Ti metal and Ti–6Al–4V alloy, which are used for biomaterials. The new Ti-based BMG (Ti45Zr10Pd10Cu31Sn4) alloy does not contain Ni, Al, and Be elements, which are known to be toxic. The Ti45Zr10Pd10Cu31Sn4 BMG alloy rod with a diameter of 3 mm, which is produced by copper mold casting, exhibits a compressive strength of 1970 MPa and a Young’s modulus of 95 GPa. In addition, the Ti45Zr10Pd10Cu31Sn4 BMG alloy shows a supercooled liquid region of 56 K and a reduced glass-transition temperature, Trg(=Tg/Tl), of 0.56. The high thermal stability of supercooled liquid has enabled the fabrication of a cylindrical rod specimen with a diameter of 4 mm. This alloy exhibits precipitation of a primary nanoscale icosahedral phase upon devitrification followed by the formation of a metastable unidentified phase. Ti2Cu and Ti3Sn are stable phases formed in this alloy. The Ti45Zr10Pd10Cu31Sn4 BMG alloy has a high corrosion resistance and is passivated at a lower passive current density of approximately 10−2 A/m2 compared to those of pure titanium and the Ti–6Al–4V alloy in 1 mass% lactic acid and phosphate-buffered saline solutions at 310 K.