Kenichiro Sasamori

Ultrahigh strength Al-based amorphous alloys containing Sc

Amorphous metallic alloys possess high strength characteristics, which are superior to crystalline materials. Here we report an influence of Sc addition on glass-forming ability, glass-transition behavior, supercooled liquid region, and mechanical properties of an Al 8 4 Y 9 Ni 5 Co 2 glassy alloy. This paper also aims to present a promising (Al 0 . 8 4 Y 0 . 0 9Ni 0 . 0 5 Co 0 . 0 2 ) 9 5 Sc 5 amorphous alloy. This alloy has an ultrahigh tensile fracture strength exceeding 1500 MPa, which surpasses those for all the other Al-based fully crystalline and amorphous alloys reported to date, in addition to high Youngs modulus of 78 GPa. The fracture surface of this new alloy exhibited vein pattern typical for amorphous alloys with good ductility, and multiple shear bands were observed on the lateral surface. The ultrahigh tensile strength of the (Al 0 . 8 4 Y 0 . 0 9 Ni 0 . 0 5 Co 0 . 0 2 ) 9 5 Sc 5 amorphous alloy results from an increase in the interatomic constraint force by the addition of Sc, an element having highly negative enthalpy of mixing with Al, Ni, and Co and the highest chemical affinity with Al among the alloying elements.

Formation, microstructure and mechanical properties of Al-Fe base quasicrystalline alloys

An icosahedral (I) phase in coexistence with Al-phase was formed in the size fraction range up to 125 μm of atomized Al 93 Fe 3 Cr 2 Ti 2 powder. The decomposition temperature of the I-phase is about 790 K. As per energy dispersive X-ray spectroscopy analysis, the constituent composition of the I-phase is Al 84.2 Fe 7.0 Cr 6.3 Ti 2.5 . It is found that the Al 84.2 Fe 7.0 Cr 6.3 Ti 2.5 alloy forms a mostly single I-phase in the melt-spun state. Bulk I-alloys in a rod form were produced by extrusion of the atomized powders at 673 K and an extrusion ratio of 10. The extruded Al 93 Fe 3 Cr 2 Ti 2 alloys have good mechanical properties, i.e., σ 0.2 of 550 MPa, σ UTS of 660 MPa and e p of 4.5% at room temperature and σ 0.2 of 330 MPa, σ UTS of 350 MPa and e p of 1.5% at 573 K. The I-based Al 93 Fe 3 Cr 2 Ti 2 alloy is expected to be useful as a new type of high-elevated temperature strength material.

Structure and mechanical strength of Al-V-Fe melt-spun ribbons containing high volume fraction of nanoscale amorphous particles

A new nonequilibrium structure consisting of nanoscale amorphous particles surrounded by fcc-Al phase was found to form in an Al94V4Fe2 alloy rapidly solidified at the condition of circumferential velocity of 40 m/s and ejection temperature of molten alloy between 1273 and 1423 K. Deviations of the alloy component and solidification condition cause the formation of the nanoscale mixed structure of Al+icosahedral(I) phases or Al+I+amorphous phases. The sizes of the amorphous and Al phase regions are about 10 and 7 nm, respectively, and the volume fraction of the amorphous phase region is about 60%. The formation of the nanoscale amorphous particles in coexistence with Al phase is presumably due to the suppression of the transition from super-cooled liquid to I-phase resulting from the retardation of the diffusivity of the solute elements. The tensile strength is as high as 1400 MPa for the mixed amorphous+Al phases and decreases significantly by the transition to I+Al phases. The first success in fabricating a nano-amorphous structure is particularly important for the subsequent development of nanophase materials.

Al–Fe-based bulk quasicrystalline alloys with high elevated temperature strength

An icosahedral (I) phase in coexistence with Al phase was found to precipitate in atomized Al93Fe3Cr2Ti2 and Al93Fe3Cr2V2 powders. The mixed structure was formed in the size fraction range up to 125 μm for the Al–Fe–Cr–V alloy, while the increase of the particle size to 125 μm for the Al–Fe–Cr–Ti powder led to the precipitation of Al23Ti9. The replacement of Cr by Mn for the Al93Fe3Cr2Ti2 powder caused a mixed structure of Al+I+Al23Ti9 +Al6Mn even for the ?26 mm powder. The formation tendency of the I-phase increased in the order of Al–Fe–Cr–V > Al–Fe–Cr–Ti > Al–Fe–Mn–Ti system. The decomposition temperature of the I-phase was about 790 K. The I particles were analyzed to have approximate compositions of Al84.2Fe7.0Cr6.3Ti2.5 and Al82.9Fe9.0Mn6.4Ti1.7, and the use of the analytical compositions enabled the formation of a mostly single I phase with an average grain size of 90 to 130 nm in the melt-spun state. Bulk I alloys in a cylindrical rod form were produced by extrusion of the atomized powders at 673 K and an extrusion ratio of 10. The extruded Al93Fe3Cr2Ti2 alloys exhibited good mechanical properties; i.e., σ 0.2 of 550 MPa, σ UTS of 660 MPa, and e P of 4.5% at room temperature, and σ 0.2 of 330 MPa, σ UTS of 350 MPa, and e P of 1.5% at 573 K. The high σ UTS exceeding 350 MPa at 573 K was superior to the final target of the United States Air Force and hence the I-based Al93Fe3Cr2Fe2 alloy is expected to be extended as a new type of high elevated temperature strength material.

Synthesis and high mechanical strength of Al-based alloys consisting mainly of nanogranular amorphous particles

Abstract A new nonequilibrium structure consisting of nanogranular amorphous and fcc-Al phases was found to form in the rapidly solidified Al 94 V 4 M 2 (M = Fe or Co) alloys. The deviation from the Al-V-M components causes the formation of the nanoscale mixed structure of Al plus icosahedral (I) phases. The sizes of the amorphous and Al phase regions are about 10 nm and 7 nm, respectively, for the Al-V-Fe alloy and about 25 nm and 20 nm, respectively, for the Al-V-Co alloy. The formation of the nanogranular amorphous phase in coexistence with the Al phase is presumably owing to the suppression of the transition from the supercooled liquid to the I phase. The tensile fracture strength (σ f ) reaches as high as 1390 MPa for the Al 94 V 4 Fe 2 alloy and 1250 MPa for the Al 94 V 4 Co 2 alloy and decreases significantly by the transition of I + Al phases. The high σ f is presumed to result from the formation of the nanoscale mixed structure consisting of amorphous + Al phases. The first success of fabricating the nanogranular amorphous phase is particularly important for the future development of nanophase materials.

Consolidation mechanism of aluminum-based amorphous alloy powders during warm extrusion

Abstract Al 85 Ni 10 Mm 5 (M ≡ mischmetal) amorphous compacts with full density were produced by warm extrusion of an ordinary billet. The extrusion conditions for the ordinary billet were found to be appropriate in the case of reduction ratios of 55%–60% for the cross-sectional area, extrusion temperatures of 383–443 K and extrusion speeds (ram speeds) of 1.0–2.5 mm s −1 . The effects of these extrusion conditions on the density, powder particle bonding and structure of the extruded compacts have been discussed in terms of the pressure, shear deformation, stretch deformation, heat generation and the ratio of pressure to the flow stress of the alloy.

Hydrogen absorption of nanoscale Pd particles embedded in ZrO 2 matrix prepared from Zr-Pd amorphous alloys

Nanocomposite materials consisting of ZrO 2 and Pd phases were prepared by heating the amorphous Zr 6 5 Pd 3 5 alloy for 24 h at 553 K in air. The maximum hydrogen absorption amount is about 2.4 mass% (H 2 /Pd) at 323 K and2.2 mass% (H 2 /Pd) at 423 K at hydrogen pressure of I MPa. The absorption amount of Pd nanoparticles in the nanocomposite is a few times larger than those for the bulk and powder Pd metals. The remarkable increase in the hydrogen absorption/desorption amounts seems to result from the isolated dispersion state of Pd nanoparticles in the ZrO 2 phase containing a tremendously large interface area in the nanocomposite.

Formation of nanogranular amorphous phase in rapidly solidified Al-Ti-M (M = V, Fe, Co or Ni) alloys and their mechanical strength

Abstract A nanogranular mixed structure consisting of amorphous andfcc-Al phases was formed in melt-spun Al-Ti-M (M=V, Fe, Co or Ni) alloys containing more than 92 at% Al. The composition range of the nanogranular structure is the widest for M=Fe and Co, followed by Ni and then V. The highest Al concentration for formation of the nanogranular amorphous phase reaches 94% Al for the Fe- and Co containing alloys. The amorphous and Al phases are homogeneously coexistent. The grain sizes of the amorphous and Al phases are about 11 and 10 nm, respectively, for Al93Ti4Fe3 and increase in the order of Fe Ni > Co > V. This order does not completely agree with that for the grain sizes of the amorphous and Al phases because of the difference in their volume fractions. The high mechanical strength of the nanogranular alloys is due to the refinement effect of the amorphous and Al grains and the disordering-induced strengthening effect of the amorphous phase. The highformation tendency of the amorphous phase is presumably due to the increase in the stability of the supercooled liquid against crystallizaion caused by the difficulty of atomic diffusivity resulting from the strong attractive interaction among the constituent elements. The synthesis of the nanogranular amorphous and Al phases with high mechanical strength in the Al-rich alloys is important for future development of a new type of high specific strength material.

High mechanical strengths of rapidly solidified Al93Mn5Ce1M1 (M ≡ transition metal) alloys containing nanoscale quasi-crystalline phase as a main component

Abstract The microstructure and mechanical properties of rapidly solidified Al 93 Mn 5 Ce 1 M 1 (M ≡ Cr, Mn, Fe, Co, Ni, Pd or Cu) alloys were examined with the aim of obtaining a high specific strength alloy by structural control in a mixed structure consisting of nanoscale icosahedral particles surrounded by Al phase. The as-quenched structure consists of spherical icosahedral particles and equiaxed Al grains with icosahedral precipitates along the grain boundary for the Al 93 Mn 5 Ce 1 M 1 (M ≡ Ni, Co or Fe) alloys and the highest value of σ f is 1160 MPa for the Ni-containing alloy. The reasons for the formation of the novel mixed structure and the achievement of high σ f and good ductility have also been investigated on the basis of the present results and the previous data reported by the present authors.

High-strength Al94(V, Ti)4Fe2 alloys consisting of nanogranular amorphous and fcc-Al phases

Abstract Nanogranular amorphous (Am) phase with a grain size of 7 nm was formed in coexistence with fcc-Al phase in melt-spun Al94V4-xTixFe2 (x=0 to 3 at%) alloys. The formation of the Am phase is due to the solidification process of liquid(L) → primary Am + remaining L → Am + Al resulting from the suppression of the precipitation from liquid to icosahedral (I) phase. The Am + Al alloys exhibit high tensile strength (σf) of 1400 MPa. The nanogranular Am phase is important for the development of high strength materials through the formation of nonequilibrium phases.