Kazuhiko Kita

New Amorphous Mg-Ce-Ni Alloys with High Strength and Good Ductility

New Mg-based amorphous alloys with high strength and good ductility were produced in the Mg-Ce-Ni system by melt spinning. The tensile fracture strength ( σf) and Vickers hardness reach 750 MPa and 199 DPN for Mg80Ce10Ni10. The specific strength defined by the ratio of σf to density is as high as 27, being considerably higher than the highest value (≃20) for conventional Al-based alloys. The high-strength Mg-base amorphous alloys are expected to attract much attention as a new type of high-strength material with low density.

New Amorphous Alloys with Good Ductility in Al-Ce-M (M=Nb, Fe, Co, Ni or Cu) Systems

New Al-based amorphous alloys were formed in Al-Ce-M (M=Nb, V, Cr, Mn, Fe, Co, Ni or Cu) ternary systems by melt spinning. The compositional range is the widest for Al-Ce-Ni alloys and extends from 2 to 15 at% Ce and below 30%Ni. The Al-Ce-M (M=Nb, Fe, Co, Ni or Cu) alloys containing over 80%Al have good bending ductility. The crystallization temperature (Tx) and hardness (Hv) of the ductile alloys increase to 625 K and 400 DPN with increasing M and Ce content and the highest tensile strength reaches 935 MPa. The effect of M elements on Tx and Hv is interpreted by taking the bonding nature of Ce and M atoms into consideration.

Nanostructured Al–Fe alloys produced by e-beam deposition: static and dynamic tensile properties

Three different aluminum–iron alloys were produced by electron-beam deposition with the iron content in the range 1.15–1.71 at.%. These alloys did not contain any identifiable iron-bearing particles, and exhibited full density with high-angle grain boundaries in the micrometer range, and a sub-grain size typically smaller than 100 nm. The tensile deformation characteristics of the alloys were examined at a dynamic strain rate of 1.1×103 s−1 and a quasi-static strain rate of 1×10−3 s−1 at room temperature. The alloy containing 1.7% Fe exhibited an abnormally high tensile strength of about 950 MPa with a ductility of up to 6%. Detailed atomic resolution imaging of the structure of the alloys has been performed along with an examination of their fracture surface features. The fracture surfaces of the alloys showed ductile dimples which typically spanned five to 10 times the sub-grain diameter. It is postulated that the nano-scale sub-grains of the alloy impart high strength, while the structure associated with high-angle boundaries provides reasonable ductility. Possible mechanisms responsible for the high strength in the present Al–Fe alloys are explored. The present results are also examined in conjunction with a comprehensive survey of available results on the strain-rate sensitivity of tensile yield strength and ductility in microcrystalline, sub-microcrystalline and nanocrystalline metals and alloys, and on the solid-solution strengthening of aluminum alloys.

Crystallization behavior of Al100 − xSmx (x = 8–14 at%) amorphous alloys

Abstract Crystallization processes of Al 100 − x Sm x ( x = 8–14 at %) amorphous alloys were investigated. The alloys were rapidly solidified into ribbons by a single roller method. The rapidly solidified ribbons are composed of mainly amorphous phase and a little crystal phase. Subsequent decomposition behavior of the melt spun ribbons was examined by XRD, TEM and DSC. Three kinds of new phases which are defined as M1, M2 and S3 were found to appear in the decomposition process of the amorphous ribbons. M1, M2 and S3 are a metastable hexagonal phase with lattice parameters a = 0.4597 nm and c = 0.6358 nm , a metastable cubic phase with lattice parameter a = 1.9154 nm and an orthorhombic phase with lattice parameters a = 1.3781 nm , b = 1.1019 nm and c = 0.7303 nm , respectively.

Mechanical properties, microstructure and crystal structures of Al98-3xCu2xFexCe1Zr1 (x = 1 − 3 at.%) alloys extruded from their atomized powders

Abstract The mechanical properties, microstructures and crystal structures of Al 98−3 x Cu 2 x Fe x Ce 1 Zr 1 ( x = 1–3 at.%) alloys extruded from their atomized powders were investigated. The extruded alloys have high tensile strength, large elongation and good heat-resistant properties. The tensile strength and elongation of the alloys range from 880 to 580 MPa and from 1.5% to 19.2% respectively. The Al 98−3 x Cu 2 x Fe x Ce 1 Zr 1 ( x = 2–3 at.%) alloys have a high temperature tensile strength of 264–295 MPa at 573 K. The thermal stability of the as-extruded Al 98−3 x Cu 2 x Fe x Ce 1 Zr 1 ( x = 1–3 at.%) alloys was evaluated by differential scanning calorimetry. The microstructures and crystal structures of these alloys were analysed by X-ray diffractometry and transmission electron microscopy. The as-extruded Al 98−3 x Cu 2 x Fe x Ce 1 Zr 1 ( x = 1–3 at.%) alloys are composed of α-Al and a cubic phase with lattice parameter a = 0.8420 nm. The excellent mechanical properties originate from the existence of the cubic phase.

New metastable phases in rapidly solidified AlZr and AlTi alloys with high solute contents

Abstract Al 100- M Zr M (M = 5, 10, 15 at.%) and Al 100- X Ti X ( X = 2–25 at.%) alloys were rapidly solidified into a ribbon form by a single roller melt spinning method. All the rapidly solidified AlZr alloys were composed of α-Al and L1 2 -Al 3 Zr phases, while the phase of rapidly solidified AlTi alloys is closely related to the Ti content. With increasing Ti content, a metastable phase appears. The decomposition processes of these metastable phases were also investigated. When the rapidly solidified AlZr alloys are heated in the temperature range 573–773 K, the L1 2 -Al 3 Zr phase changes into a new metastable tetragonal structure. As the temperature rises to about 873 K, the new metastable phase decomposes and transfers into the equilibrium DO23-Al 3 Zr phase.

Mechanical properties of Al based alloys containing quasi-crystalline phase as a main component

Abstract The application of high-pressure Ar atomization to Al-Mn-TM and Al-Cr-TM (TM = Co, Ni) ternary alloys caused the formation of a coexistent Al + quasi-crystalline (Q) structure where the Q phase is included as a main constituent phase. Subsequently, a bulk alloy consisting of Q and Al was produced by extrusion of the atomized powder. The particle size and inter-particle spacing of the Q particles are 150 and 140 nm, respectively and the volume fraction is about 60%. The mixed phase alloy exhibit high tensile strength and elongation of 720 MPa and 6.4%, respectively for Al 93 Mn 5 Co 2 alloy. The Youngs modulus is also as high as 92 GPa. The Al-based alloy exhibits a small coefficient of thermal expansion of 20 × 10 −6 K −1 between 373–473 K which is about 20% smaller than those for conventional Al alloys. These superior mechanical properties are presumably due to the fine dispersion and high volume fraction of Q particles and the high rigidness of the Q phase.

High mechanical strength and strengthening mechanism of aluminium alloys with an ultrafine grain structure

Abstract The Al alloys extruded from rapidly solidified powders in AlNiX (X≡Zr, Ti or Mm; Mm is mischmetal) systems have very fine structures consisting of the Al phase and a large volume fraction of intermetallic compounds. The specific strengths are 266 MPa Mg−1 m−3 for Al89.5Ni8Zr2.5 alloy and 279 MPa Mg−1 m−3 for Al88.5Ni8Ti3.5 alloy. The specific Youngs moduli are 31.3 GPa Mg−1 m−3 for Al89.5Ni8Zr2.5 alloy and 34.1 GPa Mg−1 m−3 for Al88.5Ni8Ti3.5 alloy. The high specific strength is due to the effect of refinement of the Al grain size and dispersion strengthening by intermetallic compounds. The high specific Youngs modulus is related to a high volume fraction of intermetallic compounds. Furthermore, the specific strength of Al89.5Ni8Zr1.75Mm0.75 alloy is as high as 316 MPa Mg−1 m−3.

Effect of Mass Fraction of Dolomite on the Foaming Behavior of AlSiCu Alloy Foam by Powder Metallurgy Route

AbstarctMetallic foams are commonly produced using hydride foaming agents. Carbonates are safer to handle than hydrides; furthermore, a fine and homogenous cell structure can be obtained by carbonates in the powder metallurgy route. In this study, the principle of foaming by dolomite, which is a carbonate, for AlSiCu alloy was investigated by observing foaming with a high-temperature transmission X-ray system and identifying the foaming gas with a gas chromatography–mass spectrometry technique. During foaming by dolomite, two stages of expansion were observed. The first stage of expansion was induced by the water vapor absorbed onto the AlSiCu powder surface, and the second stage of expansion was induced by the decomposition of dolomite. The coarse cells of the first stage of expansion were filled with H2, and the fine cells of the second stage of expansion were filled with CO. A fine and homogenous cell structure was achieved by controlling the mass fraction of dolomite with the fraction of adsorbed water, which induced cell coarsening.

Crystallization behavior of amorphous Al90Y10 and Al88Y12 alloys

Abstract Al90Y10 and Al88Y12 alloys were rapidly solidified into amorphous ribbons with a thickness of about 25 μm by a single roller method. As annealing temperature increases, α-Al phase first precipitates from the rapidly solidified Al90Y10 and Al88Y12 amorphous alloys at 473 and 503 K, respectively. As soon as the α-Al phase appears, a new tetragonal structure phase with lattice parameters a = 0.4203 nm and c = 0.9677 nm forms from the α-Al phase at the same temperature. As annealing temperature rises, the amorphous phase gradually changes into α-Al and the new phase. At 544 K for the Al90Y10 and 549 K for the Al88Al12 alloy, all the amorphous phase has decomposed into these phases. Further at 554 K for Al90Y10 and at 600 K for Al88Y12, the new tetragonal phase disappears and the α-Al3Y hexagonal structure phase with lattice parameters a = 0.6195 nm and c = 2.1137 nm forms. At last, the α-Al3Y phase disappears and the β-Al3Y hexagonal structure phase with lattice parameters a = 0.6276 nm and c = 0.4582 nm forms at 673 K.