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The values of mixing enthalpy (¦Hmix) and Delta parameter (¤) were calculated with 73 elements from Miedema’s model for multicomponent equi-atomic alloys to investigate the possibilities of the alloys to be formed into high-entropy (H-E) alloys or high-entropy bulk metallic glasses (HE-BMGs). The equi-atomic alloys from about 15 million (73C5) quinary to 621 billion (73C10) decimal systems were evaluated by referring to a ¦Hmix­¤ diagram for zones S and B’s for H-E alloys with disordered solid solutions and BMGs, respectively, reported by Zhang et al. The results revealed that the number of quinary equi-atomic alloys plotted in zone S is 28405 (30.19% in 73C5), whereas those in zones B1 and B2 for conventional and Cuand Mg-based BMGs, respectively, were 1036385 and 21518 (36.90 and 30.14%), respectively. This kind of statistical approach using ¦Hmix­¤ diagram will lead to finding out unprecedented H-E alloys and HE-BMGs. [doi:10.2320/matertrans.M2013352]

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]

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.

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.

Novel long-period hexagonal structures with six and fourteen layered atomic configurations were formed in melt-spun Mg97Ln2Zn1 (Ln=Y, Gd and Sm) ternary alloys annealed at 573 K for 1.2-3.6 ks and in an as-spun Mg97Y2Zn1 alloy, respectively. The Mg-based alloys containing La or Ce as the Ln element have a mixed structure of hcp Mg and compound phases and no long-period hexagonal structure is formed in the as-spun and annealed states. There is a clear formation tendency of the novel long-period structure to increase with a decrease in the precipitation tendency of the intermetallic compound, an increase in the atomic size ratio of Ln/Mg and an enhancement of the formation tendency of Mg-based reinforced solid solution. The formation of the novel long-period structure is interpreted to result from the necessity of relaxation of strains caused by the reinforced solid solution of Ln and Zn elements into the Mg phase. In addition, the enrichment of Y and Zn elements was observed at the misfit sites of the atomic array in the fourteen layered hexagonal structure of the as-spun Mg97Y2Zn1 alloy. The atomic level segregation of Y and Zn elements is also thought to be the origin for the high stability of the long-period structure. The two types of long-period hexagonal structures found in the Mg-Ln-Zn alloys are important as a new mechanism for future development of high-strength Mgbased alloy.

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.

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.