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Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 alloys were investigated for their possibility to be formed into a high-entropy alloy (HEA) with a quasicrystalline (QC) structure that contains an icosahedral- (I-) phase. The melt-spun alloys quenched at a circumference speed of 39 m/s were formed into an amorphous single phase. The amorphous alloys annealed up to a temperature between the first and second crystallization temperatures exhibited mixed phases of I- and remaining amorphous phases. Observation of the Zr30Hf30Ni15Cu10Ti15 amorphous alloy heated up to 745 K with transmission electron microscope revealed the presence of precipitates with diameters ranging 10–20 nm. Nano-beam diffraction demonstrated that the precipitates were identified to be the I-phase with the five-, three- and two-fold symmetries. The Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 alloys were not formed into a single quasicrystalline phase as HEAs, but the discussions of the current and early experimental data led to provide the way to approach high-entropy quasicrystalline alloys (HE-QCs).

The phase stability of high entropy alloy (HEA), Al 0.5 TiZrPdCuNi, under fast electron irradiation was studied by in-situ high voltage electron microscopy (HVEM). The initial phase of this alloy quenched from the melt was dependent on cooling rate. At high cooling rates an amorphous phase was obtained, whereas a body-centered cubic ( b.c.c. ) phase were obtained at low cooling rates. By thermal crystallization of the amorphous phase b.c.c. phase nano-crystals were formed. Upon fast electron irradiation solid state amorphization (SSA) was observed in b.c.c. phase regardless of the initial microstructure (i.e., “coarse crystalline structure” or “nano-crystalline structure with grain boundaries as a sink for point defects”). SSA behavior in the Al 0.5 TiZrPdCuNi HEAs was investigated by in-situ transmission electron microscopy observations. Because the amorphization is very rarely achieved in a solid solution phase under fast electron irradiation in common metallic materials, this result suggests that the Al 0.5 TiZrPdCuNi HEA from other common alloys and the other HEAs. The differences in phase stability against the irradiation between the Al 0.5 TiZrPdCuNi HEA and the other HEAs were discussed. This is the first experimental evidence of SSA in HEAs stimulated by fast electron irradiation.

High-entropy alloys (HEAs) with an atomic arrangement of a hexagonal close-packed (hcp) structure were found in YGdTbDyLu and GdTbDyTmLu alloys as a nearly single hcp phase. The equi-atomic alloy design for HEAs assisted by binary phase diagrams started with selecting constituent elements with the hcp structure at room temperature by permitting allotropic transformation at a high temperature. The binary phase diagrams comprising the elements thus selected were carefully examined for the characteristics of miscibility in both liquid and solid phases as well as in both solids due to allotropic transformation. The miscibility in interest was considerably narrow enough to prevent segregation from taking place during casting around the equi-atomic composition. The alloy design eventually gave candidates of quinary equi-atomic alloys comprising heavy lanthanides principally. The XRD analysis revealed that YGdTbDyLu and GdTbDyTmLu alloys thus designed are formed into the hcp structure in a nearly single phase. It was found that these YGdTbDyLu and GdTbDyTmLu HEAs with an hcp structure have delta parameter (δ) values of 1.4 and 1.6, respectively, and mixing enthalpy (ΔH mix) = 0 kJ/mol for both alloys. These alloys were consistently plotted in zone S for disordered HEAs in a δ-ΔH mix diagram reported by Zhang et al. (Adv Eng Mater 10:534, 2008). The value of valence electron concentration of the alloys was evaluated to be 3 as the first report for HEAs with an hcp structure. The finding of HEAs with the hcp structure is significant in that HEAs have been extended to covering all three simple metallic crystalline structures ultimately followed by the body- and face-centered cubic (bcc and fcc) phases and to all four simple solid solutions that contain the glassy phase from high-entropy bulk metallic glasses.

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]

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.

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]

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.

An in situ formed (Cu 0.6 Hf 0.25 Ti 0.15 )9oNbio (number indicate at.%) bulk metallic glass (BMG) composite was prepared by copper mold casting. The ductile Nb-rich crystalline phase with a dendritic structure disperses homogeneously in the glassy matrix. The (Cu 0.6 Hf 0.25 Ti 0.15 )9oNbio composite alloy exhibits much higher corrosion resistance in IN HCl and 3 mass% NaCl solutions than the Nb-free alloy. The addition of Nb is favorable for the alloys to form a Hf-, Ti- and Nb-enriched highly protective surface film with higher chemical stability in HCl and NaCl solutions. Young's modulus, compressive fracture strength and compressive plastic strain of the (Cu 0.6 Hf 0.25 Ti 0.15 )9oNbio BMG composite are 106 GPa, 2625 MPa and 12.5%, respectively. The increase in compressive strain-to-failure is due to the ductile dendrites restricting shear band propagation, promoting the generation of multiple shear bands.

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.

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.

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.

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.

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.