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Metallic glass (MG) has unique mechanical properties, combining high strength and low Young's modulus. By using MG to fabricate fasteningbolts, high resistance against bolt loosening is expected. However, MG components are considered brittle because MG exhibits poor ductility when subjected to uniaxial loading at room temperature. We have developed hexagonal cap bolts made of zirconium-based MG by cold thread rolling. The MG bolts showed a 1.6% plastic strain with a tensile strength of more than 1550 MPa. In addition, the load–strain curve was similar to that of a strain hardening material, although MG itself is free of strain hardening. In this study, we attempted to clarify the reasons for these characteristics, which are advantageous for bolts in terms of toughness and reliability. Various experiments and numerical analysis indicated that residual stress plays an important role in the behavior.

Fatigue tests were carried out on ultra-high strength Co- and Fe-based bulk metallic glasses (BMGs), and the fatigue results were investigated together with the ones which had already been obtained from the fatigue tests on the super-high strength Ni-based BMG and the high strength Ti- and Cu-based BMGs. The test alloy rods with a diameter of 2 mm were prepared in [(Co 0.6 Fe 0.4 ) 0.75 B 0.2 Si 0.05 ] 96 Nb 4 , (Fe 0.5 Co 0.5 ) 72 B 20 Si 4 Nb 4 , Ti 41.5 Zr 2.5 Hf 5 Cu 42.5 Ni 7.5 Si 1 , Ni 60 Zr 20 Nb 15 Al 5 and Cu 60 Zr 30 Ti 10 at% systems by the copper mold casting method. The test specimens were machined to hourglass shape type with a minimum diameter of 0.9 mm. The specimens were tested at a stress ratio of 0.1 and a frequency of 10 Hz. The fatigue limits in the Co- and Fe-based BMGs exceeded 2 GPa, and those in the Ni- and Ti-based BMG surpassed about 1.5 GPa. Fatigue ratios in all BMGs were found to be about 0.5. Exceptionally, only the Ti-based BMG showed the high ratio, which may indicate the possibility that the BMG does not cause the fatigue phenomenon. In front of the fatigue crack initiation sites, fracture surfaces showed a radial ridges and valleys morphology as well as a striation like pattern. Unstable fracture surfaces consisted of facets with vein patterns. As the facet and vein pattern sizes increase, the strength and fatigue limit decreased, whereas the fracture toughness increased. Fracture surfaces in front of the fatigue cracks in strong BMGs showed the clear elastic wave traces.

The influence of the substrate temperature on the structure, the pore distribution, and the adhesion strength of Fe-10Cr-based amorphous coating films has been examined. The amorphous coating films have been produced by a thermal spraying technique using our developed cylindrical nozzle on SS400 substrates. The splat morphology of the sprayed particles changed drastically from an irregular splash shape to a disk shape at a transition temperature of about 325°C. When the substrate temperature increased to the transition temperature region, between 325 and 350°C, the porosity in the boundary regions between the sprayed coating films and the substrates drastically decreased to about 6%, which may be due to the drastic increase in the wettability of the sprayed particles accompanied with the change of morphology from the splashed shape to the disk shape. When the substrate temperature increased from the transition temperature of 325°C up to 400°C, the porosity decreased gradually, and the volume fraction of the amorphous phase increased with increasing substrate temperature, resulting in an increase in the adhesion strength up to about 15MPa. [doi:10.2320/matertrans.M2011261]

Bolts are commonly employed machine elements used for joining and fastening, and their performance and reliability influence the overall performance of machines. In this study, we have plastically worked and formed bolts using metallic glass (MG) that exhibits unique mechanical properties such as high tensile strength, low Young’s modulus, and large elastic limit. The large elastic limit increases the permissible elongation range of the bolt and helps avoid bolt loosening, while the low Young’s modulus effectively resists screwed-in bolt loosening by increasing the frictional forces on both bolt-nut contact area and bearing surface. We employed a zirconium-based MG Zr55Al10Cu30Ni5 for our experimental investigations. A pre-form of a hexagon socket head cap screw (bolt) was fabricated by squeeze casting. Cold and warm thread rolling were performed to form a metric screw thread M3� 0:5 (class 6g (ISO)) below the glass transition temperature (Tg) using a flat rolling machine. Despite the extremely poor ductility of MG at room temperature, thread rolling was successfully performed. Straining behavior analysis by a three-dimensional finite element method demonstrated that these remarkable results are due to the compressive stress distribution induced during the thread rolling process. In addition, thread rolling is fundamentally an incremental process, and it enhances the deformability of MG by gradually improving ductility in the deformed region. The tensile strength of the thread-rolled bolt was approximately 1600 MPa, which is considerably higher than that of conventional heat-treated high strength steel bolts. MG was thus successfully employed to manufacture improved bolts. [doi:10.2320/matertrans.M2010292]

In this paper, ion-implantation technique was applied to improve corrosion resistance of a newly developed La-based bulk metallic glass with poor corrosion resistance. It is found that the alloys after ion implantation with doses ranging 6 × 1016–1 × 1017 Nb/cm2 have a remarkable enhancement of corrosion resistance in chloride containing environments and acid solution with respect to the alloy without the surface treatment while the implanted alloys still have high glass forming ability. The improvement of corrosion resistance for the implanted alloys is attributed to the high passivating ability of the Nb-containing surface layer. These results obtained here clearly demonstrate that the ion-implantation technique could be a useful method to improve the corrosion resistance of bulk metallic glasses without losing glass forming ability of alloys.

The possibility of applying metallic glass parts in industrial products is investigated. Ti-based glassy tubes have been applied to a Coriolis mass flowmeter, and the prototype of the flowmeter exhibits 28.5 times higher sensitivity than that of the conventional one made of SUS630. Zr55Al10Ni5Cu30 glassy diaphragms are applied in pressure sensors. The prototype of pressure sensor with a Zr-based glassy diaphragm exhibits 3.8 times higher sensitivity than that of the sensor with the conventional SUS630 diaphragm. The obtained results suggest that innovative products can be produced by using of metallic glass parts, and metallic glass is promising as an industrial material with outstandingly high performance for the near future.

Nanoscale structural change in (Fe0.5Co0.5)72B20Si4Nb4 bulk glassy alloy on annealing has been investigated using transmission electron microscopy. On annealing at temperatures above 773K, electron diffraction intensity analysis showed a clear structure change for a Cr23C6-type local atomic ordering. The local structure formation of Cr23C6-type nanophase was confirmed by nanobeam electron diffraction. A development process of dense precipitates of the Cr23C6-type nanophase was further studied by high-resolution electron microscopy. It was found that the formation of the highly-dense nanoprecipitates provides an increase in Vickers hardness.

A glassy Fe-base alloy plate with a composition of Fe 36 Co 36 B 20 Si 4 Nb 4 (at.%) was prepared by a twin-roller continuous casting method. The alloy plate had a width of 70 mm, a thickness of 0.5 mm and a length of 150 mm. The cast plate contained small crystalline grains in the glassy matrix. These crystalline grains were identified as an α-Fe ( cI 2) phase. Thermal characteristics of the plate are almost consistent with those of the melt-spun ribbon, while the exothermic heat of crystallization for the cast plate is about 5% smaller than that for the ribbon. The coercive force ( H c ) and maximum permeability ( μ m ) of the Fe-base alloy in a ring form of 10 mm in outer diameter, 5 mm in inner diameter and 0.6 mm in thickness made by mechanical machining from the cast plate are 2.1 A/m and 40,000, respectively, for the as-cast one, and 1.6 A/m and 170,000, respectively, for the annealed one at 723 K for 1800 s under rotation magnetic field of 80 kA/m. It can be thus said that the cast plate has good soft magnetic properties. The possibility of forming a glassy alloy plate by twin-roller continuous casting is confirmed and the Fe-base glassy alloy plate produced by the developed continuous process will be applicable for magnetic parts.

The glass-forming ability and mechanical properties of (Fe,Co)-(Cr,Mo)-(C,B)-Tm glassy alloys have been investigated. The (Fe,Co) 48 Cr 15 Mo 14 C 15 B 6 Tm 2 glassy alloys were prepared in a cylindrical form with a diameter of 10mm. These alloys have high glass forming ability (GFA) enough to produce a single glassy rods with a diameter above 10 mm. The largest supercooled liquid region before crystallization in (Fe 1-x Co x ) 48 Cr 15 Mo 14 C 15 B 6 Tm 2 alloys is 90K for Co 48 Cr 15 Mo 14 C 15 B 6 Tm 2 . These glassy alloys have high fracture strength of over 4100MPa for the entire composition range and the strength level is almost independent of Co content. The high GFA is attributed to the retardation of precipitation of the crystallized phases caused by the formation of the stabilized glassy local structure in which short-range ordered trigonal prisms are connected through glue effect of Tm element. The combination of high strength and high glass-forming ability indicates high possibility of applying the (Fe,Co)-(Cr,Mo)-(C,B)-Tm glassy alloys to various industrial materials.

Mg-8Zn-4Al-xY base alloys containing an icosahedral quasicrystal phase (i-phase) as a main strengthening phase were prepared by casting into a copper mould at moderate cooling rates. The Y addition was effective for decreasing the size of i-phase and the more homogeneousness of its dispersed state. The mechanical properties at room temperature were much superior to those of AZ91 alloy. The creep tests indicated a promising high temperature creep resistance of the quasicrystal-reinforced Mg-Zn-Al-Y cast alloy. The dislocation characteristic in crept specimens which containing i-phase and no i-phase was analyzed and strengthening mechanism was discussed.

A new type of Mg–Zn–Cu–Gd-based alloy strengthened by quasicrystal and Laves phase was developed. This alloy exhibits much better creep properties compared to AE42(Mg–4 wt% Al–2 wt% rare-earth) alloy, which is the benchmark creep-resistant magnesium die-casting alloy under the compressive creep condition of 180 °C and80 MPa. The new alloy also exhibits high room-temperature mechanical properties close to that of AZ91 alloy. The good mechanical properties are attributed to the special microstructure; the thermally stable icosahedral quasicrystals phase (i-phase) and Laves phase distributed along the grain boundary as a hard skeleton, and some fine β′1 precipitates distributed homogenously on the matrix. The dislocation morphology after the creep test was studied, and the strengthening mechanism was proposed.

The structural relaxation and glass-forming ability (GFA) of Mg–Cu–Gd-based glassy alloys and the effect of Ni addition on the glass-forming ability, structural relaxation and mechanical properties were studied by thermal analysis, X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The medium-range order (MRO) zones of about 1–2 nm size were observed in the Mg 65 Cu 25 Gd 10 glassy alloy after structural relaxation caused by annealing for 180 s at 305 K. The structural relaxation resistance increased with decreasing Cu content, although the GFA also decreased in Mg–Cu–Gd-based alloys. Appropriate substitution of Cu by Ni in Mg 75 Cu 15 Gd 10 -based alloy not only improved the glass-forming ability and mechanical properties, but also increased the stability against structural relaxation.

It is known that the cooling rate from the liquid state is an important factor in the production of bulk metallic glasses. However, the effects of other factors such as electric and magnetic fields have not been thoroughly investigated. Here, we present a new method for producing bulk metallic glasses by using electromagnetic vibrations with simultaneous imposition of an alternating electric current and a magnetic field. This method was found to be effective in enhancing apparent glass-forming ability in Mg65-Cu25-Y10 (atomic percent) alloys. Indeed, larger bulk metallic glasses could be obtained by the electromagnetic vibration process under the same cooling conditions. We presume that disappearance or decrement of clusters by the electromagnetic vibrations applied to the liquid state cause suppression of crystal nucleation. This electromagnetic vibration process should be effective in other bulk metallic glass systems if the clusters in the liquid state cause the crystal nucleation.

The structure and mechanical properties of Mg–Zn–Al–Y base cast alloys containing an icosahedral quasicrystal phase (i-phase) as a main strengthening phase were investigated. Mg–8Zn–4Al–xY base bulk alloys containing the i-phase were prepared by casting into a copper mold at moderate cooling rates. The Y addition was effective for decreasing the size of the i-phase and the increasing the homogeneity of its dispersed state. The mechanical properties examined by compression tests at room temperature were much superior to those of a conventional AZ91 Mg alloy. The creep tests at elevated temperatures indicated a promising high temperature creep resistance of the quasicrystal-reinforced Mg–Zn–Al–Y cast alloy. The strengthening mechanism was also discussed.

By use of excellent properties of bulk metallic glasses, some industrial products were practically prepared and their performances were investigated. Ni-based BMG microgear prepared by injection casting exhibits nano-imprintability against the surface roughness of mold. Linear actuator constructed by a set of Fe-based BMG yokes generates relatively large driving force due to the Lorentz force. The newly developed alloy with a nominal atomic composition of Ti52Cu23Ni11Mo7Fe7 exhibits high yield strength of 1250 MPa, high fracture strength of 2740 MPa and large plastic elongation of over 20%. These results for the industrial products made of BMGs are promising for future developments as industrial materials with high performance.

The glass-forming ability and mechanical properties of Fe-B-Si-Nb glassy alloys have been investigated. The Fe72B20Si4Nb4 glassy alloy was prepared in a cylindrical form with a diameter of 2 mm. Young’s modulus, compressive fracture strength and plastic elongation of the bulk metallic glass were 200 GPa, 4200 MPa and 1.9%, respectively. Many shear bands were observed along the shear plane, which was declined by about 43 degrees to the direction of applied load, and the fracture occurred along the shear plane. The local-ordered regions were recognized in the high-resolution TEM image of the Fe72B20Si4Nb4 bulk metallic glass with a diameter of 2 mm. The good mechanical properties are attributed to the suppression effect of the local-ordered regions on the propagation of shear bands.

The fillability and imprintability of a Ni-based bulk metallic glass (BMG) prepared by the precision die-casting was investigated. A three-dimensional microgear made of Ni-based BMG is successfully prepared by the precision die-casting technique. The cast Ni-based BMG has excellent fillability against a microindentation formed by Vickers indentation, and the filling area obtained using a confocal scanning microscope reaches 99%. In addition, the cast Ni-based BMG exhibits excellent imprintability of the die surface even on a nanometer scale. It is therefore concluded that the Ni-based BMG is suitable as a material for micromachines due to its superior fillability and imprintability.

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.

Calcium-based bulk glassy alloys in Ca-Mg-Ag and Ca-Mg-Ag-Cu systems were produced by a metallic mold casting method. The maximum rod diameter (d max ) for the formation of a glassy phase was 4 mm for Ca 60 Mg 20 Ag 20 and 7 mm for Ca 60 Mg 20 Ag 10 Cu 10 . The glass transition temperature (Tg), crystallization temperature (Tx), temperature interval of supercooled liquid region (ΔT x = T x - T g ) and melting temperature (T m ) were 401 K, 435 K, 35 K and 654 K, respectively, for the former alloy and 398 K, 428 K, 30 K and 624 K, respectively, for the latter alloy. The simultaneous addition of Ag and Cu in the Ca-Mg-(Ag, Cu) system causes a steep decrease in T m and an increase in the reduced glass transition temperature (T g /T m ), leading to an increase in the glass-forming ability.

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.

The application of a melt extraction method to Ti- and Al-based alloys with highly reactive molten states was found to cause the formation of continuous amorphous alloy wires with good bending ductility. The wire diameter is in the range of 40 to 150 μm for Ti 40 Zr 10 Cu 50 and 40 to 100 μm for Al 85 Ni 10 Ce 5 and the difference reflects the difference in the glass-forming ability between both alloys. The glass transition temperature, crystallization temperature and heat of crystallization are 629 K, 691 K and 1.71 kJ/mol, respectively, for the Ti-based wire with the diameter of 100 μm and 530 K, 546 K and 0.37 kJ/mol for the Al-based wire with the diameter of 50 μm. The tensile strength is 2000 MPa for the former wire and 930 MPa for the latter wire. The thermal stability and mechanical strength are nearly the same as those for the melt-spun amorphous ribbons with the thickness of 15 μm. No appreciable concave resulting from the use of the copper wheel with a steep edge is seen in the cross section and the solidification is completed during the flight after extraction. The cooling rate of the Al-based wire with the diameter of 70 μm is estimated to be of the order 6 x 10 4 K/s. Thus, the formation of the amorphous alloy wires with a circular cross section is due to the rapid solidification of the fine supercooled liquid stream in the suppression of heterogeneous nucleation during the high-velocity flight in the argon atmosphere. The combination of the solidification process with high cooling rate and the good formability into the wire shape allows us to expect that the present process develops as an alternative method to produce amorphous alloy wires in various kinds of alloy systems including reactive elements as main components.

Amorphous (Fe, Co)-Si-B ternary and quaternary wires were found to be produced over a wire diameter range of 20 to 80 μm by a melt extraction method using a copper wheel with an edge angle of 60 degrees. The wires without any concaves in the transverse cross section were prepared in the extraction condition where the circumferential velocity of the wheel and the rising velocity of the molten alloy are in the range of 20 to 40 m/s and 0.1 to 4.0 mm/s, respectively. The resulting amorphous wires have good bending ductility in the wire diameter range below 80 μm for the Fe 75 Si 10 B 15 alloy and below 60 μm for the Co 72.5 Si 12.5 B 15 alloy. The thermal stability and mechanical properties except tensile fracture strength (σ f ) for the amorphous wires are nearly the same as those for the melt-spun amorphous ribbons. The σ f is 3800 MPa for the Fe 75 Si 10 B 15 wire and 3600 MPa for the Co 72.5 Si 12.5 B 15 wire, being about 10% higher than those for the corresponding ribbon samples because of the low degree of stress concentration resulting from the good smoothness on the outer surface. The magnetic properties of saturation magnetization, coercivity and effective permeability at 1 kHz for the wires are nearly the same as those for the ribbons. The squareness of the hysteresis B-H loop for the Fe-Si-B amorphous wire is better than that for the same Fe-based ribbon and the sharp output voltage due to the reversion of magnetic flux is also observed for the present Fe 78 Si 10 B 12 amorphous wire. The combined properties of good mechanical properties and unique magnetic properties leading to the generation of the sharp output voltage seem to be promising for the subsequent development of the present fine amorphous wires.

Ti-based alloy powders produced by the high pressure gas atomization technique were found to consist of an amorphous single phase in the particle size range below 32 μm for Ti 50 Zr 10 Cu 40 and below 25 μm for Ti 50 Zr 10 Ni 20 Cu 20 , though the cooling rate of their molten alloys for gas atomization is considerably lower than that for melt spinning. In addition, the TiZrCu amorphous powders exhibit a rather wide supercooled liquid region before crystallization. This is believed to be the first evidence for the appearance of the supercooled liquid region for atomized Ti-based amorphous powders. The significant increase in the glass-forming ability and the wide temperature range of the supercooled liquid region for the TiZrCu ternary alloys are presumably due to the simultaneous satisfaction of the two criteria of the significantly different atomic size ratios among the constituent elements and the difficulty of long-range redistribution of the constituent elements for the growth of crystalline phases.

TiCuNiCo quaternary amorphous alloys produced by melt spinning were found to have a wide supercooled liquid region before crystallization, though no glass transition was observed in TiCu binary amorphous alloys. The largest temperature interval of the supercooled liquid region ( ΔT x ) is as large as 90 K for Ti 50 Cu 25 Ni 20 Co 5 . There is a tendency for ΔT x to increase with an increase in storage modulus and with a decrease in loss modulus. It is therefore presumed that the increase in ΔT x for the multicomponent amorphous alloy is due to the suppression of crystallization for the supercooled liquid resulting from the increase in viscosity.

Cylindrical glassy alloys with diameters up to 12 mm were prepared for-a Mg 65 Y 10 Cu 15 Ag 5 Pd 5 with a high reduced glass transition temperature (T g /T m ) of 0.62 by water quenching the molten alloy in the iron tube. Neither cavities nor voids are seen over the whole inner region and no contrast revealing a crystalline phase is seen over the transverse cross section. The glass transition temperature (T g ), crystallization temperature (T x ), the temperature interval of the supercooled liquid region (ΔT x = T x - T g ) and the melting temperature (T m ) are measured to be 436, 468, 32 and 706 K, respectively, for the Mg 65 Y 10 Cu 15 Ag 5 Pd 5 alloy with a diameter of 12 mm. The simultaneous addition of Ag and Pd to Mg-Y-Cu system causes an increase in the T g /T m , leading to an increase in the glass forming ability. It is thus concluded that the application of the water quenching process with the iron tube to the Mg-based glassy alloys is useful for the formation of the bulk glassy alloys.

Magnesium-based bulk amorphous alloys with a diameter of 7 mm for Mg 65 Y 10 Cu 15 Ag 5 Pd 5 were produced by a metallic mold casting method. The glass transition temperature (T g ), crystallization temperature (T x ), the temperature interval of the supercooled liquid region (ΔT x = T x - Tg) and the melting temperature (T m ) are measured to be 437, 472, 35 and 707 K, respectively, for the Mg 65 Y 10 Cu 15 Ag 5 Pd 5 alloy. The simultaneous addition of Ag and Pd to Mg-Y-Cu system causes a steep decrease in T m and an increase in the reduced glass transition temperature (T g /T m ), leading to an increase in the glass-forming ability. The Mg-Y-Cu-(Ag, Pd) bulk amorphous alloys have a high compressive fracture strength of 770 MPa. The simultaneous addition of Ag and Pd is useful for the improvements of glass-forming ability and fracture strength.

Completely glassy thin films of Zr-Al-Cu-Ni exhibiting a large super-cooled liquid region (deltaTx = 95 K), very smooth surface (Ra = 0.65 nm), and an extremely high value of Vicker's hardness (Hv = 940), as compared to bulk Zr-Al-Cu-Ni metallic glass, were deposited by radiofrequency magnetron sputtering. Nanoscale patterning ability of Zr-Al-Cu-Ni metallic glass thin films was demonstrated by a focused ion beam etching. The capability to write nanometer-scale patterns (line width approximately 12 nm) opens up a variety of possibilities for fabricating nanomolds for imprint lithography, and a wide range of two- or three-dimensional components for future nanoelectromechanical systems.

Ti-based amorphous powders were produced through the finding of compositions with large glass-forming ability and the modification of the high-pressure gas atomization technique. The amorphous single phase was obtained for the powders with a particle size fraction below 63 μ in Ti-Zr-Cu system. The thermal properties including the glass transition for the powders with a size below 25 μ are nearly the same as those for the melt-spun amorphous ribbon. The appearance of the glass transition for the amorphous Ti-Zr-Cu powders is attractive because of the expectation that bulk amorphous Ti-based alloys are obtained by extrusion of the amorphous powders in the vicinity of T g .

The glass-forming ability and magnetic properties of (Fe, Co)–B–Si–Nb glassy alloys have been investigated. The maximum diameter for the formation of a glassy alloy rod was 2.0mm for Fe72B20Si4Nb4 and 4.0mm for (Fe0.5Co0.5)72B20Si4Nb4. A number of local-ordered regions are recognized in Fe72B20Si4Nb4 bulk glassy alloy by high-resolution transmission electron microscopy. However, no local-ordered regions are observed in (Fe0.5Co0.5)72B20Si4Nb4 bulk glassy alloy. Saturation magnetization, coercive force, and maximum permeability were 1.14T, 1.5A∕m, and 32 000, respectively, for the (Fe0.6Co0.4)72B20Si4Nb4 bulk glassy alloy.

In this letter, we propose an in situ detection method for obtaining permeability of soft magnetic Fe-based amorphous alloys. The temperature dependence of ac resistance was measured at different frequencies during heat treatment of Fe84Nb7B9 amorphous alloys. A significant increase in the ac (∼1000kHz) resistance appears at around 920 K during the heating process, which arises from the skin effect caused by a marked increase in sample permeability. This skin effect diminishes when the sample is heated to approximately 1100 K, which corresponds to the decrease in its permeability. Consequently, we note that the ac resistance measurement is useful for quick in situ assessment to achieve the soft magnetic property of an Fe-based amorphous alloy.