Katsumasa Ohtera

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.

Aluminum-Based Amorphous Alloys with Tensile Strength above 980 MPa (100 kg/mm2)

New Al-based amorphous alloys with high strength and good ductility were produced in an Al-Y-Ni system by liquid quenching. The tensile fracture strength ( σf) and Vickers hardness reach 1140 MPa and 300 DPN for Al87Y8Ni5. The specific strength defined by the ratio of σf to density is as high as 38, being much higher than that for conventional alloy steels. The high-strength Al-base amorphous alloys are expected to attract strong attention as a new type of high-strength material with low density.

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

New aluminum-based amorphous alloys were found to be formed in Al-Y-M and Al-La-M (M=Fe, Co, Ni or Cu) ternary systems by melt spinning. Their compositional ranges are 3 to 33 at%M and 3 to 22 at%Y or 2 to 18 at%La. The alloys containing more than about 80 at%Al have good bend ductility. The crystallization temperature Tx increases from 414 to 831 K with an increase of M and yttrium or lanthanum contents. The effect of the solute elements on Tx is interpreted to be dominated by the attractive interaction between aluminum and M, yttrium or lanthanum atoms.

New Amorphous Al-Y, Al-La and Al-Ce Alloys Prepared by Melt Spinning

New amorphous alloys in Al-M (M=Y, La or Ce) binary systems have been formed in the compositional ranges of 9 to 13 at% Y and 7 to 10 at% La or Ce by liquid quenching. Crystallization temperature, Vickers hardness and electrical resistivity at 293 K of the binary amorphous alloys increase with an increase of Y, La or Ce content from 437 to 516 K, 116 to 216 DPN and 54 to 93 µΩcm, respectively. The first amorphization for the Al-M binary alloys is important for subsequent development of Al-based amorphous alloys with high specific strength.

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.

Glass Transition Behavior of Al-Y-Ni and Al-Ce-Ni Amorphous Alloys

Ductile Al-Y-Ni and Al-Ce-Ni amorphous alloys were found to exhibit a glass transition at temperatures just below crystallization temperature. The glass transition temperature increases from 490 to 582 K with increasing solute concentration. The difference in specific heat between amorphous solid (AS) and supercooled liquid (SL) reaches 9.2 J/mol-K and the temperature coefficient of expansion and viscosity of the supercooled liquid are 100×10-5 K-1 and 3×1013 poise. By the transition of AS to SL, the Youngs modulus and tensile strength also decrease steeply by about 63 and 66%, accompanied with an increase of elongation by about 320%.

New Amorphous Al-Ln (Ln=Pr, Nd, Sm or Gd) Alloys Prepared by Melt Spinning

New amorphous alloys in Al-Ln (Ln=Pr, Nd, Sm or Gd) binary systems have been formed in the vicinity of 10 at% Pr and in the ranges of 8 to 12%Nd or Gd and 8 to 16%Sm by rapid solidification. Crystallization temperature, hardness, tensile strength and electrical resistivity at 293 K of the binary amorphous alloys increase with an increase of solute content from 453 to 511 K, 150 to 325 DPN, 495 to 960 MPa and 96 to 170 µΩcm, respectively. The compositional dependences are interpreted on the basis of the presumption that the attractive bonding nature between Al and Ln metals is a dominant factor.

High mechanical strength of aluminum-based crystalline alloys produced by warm consolidation of amorphous powder

Abstract Aluminum alloys have been widely used as industrial materials. Recently many studies on rapidly solidified aluminum-based alloy powders have been done. This paper deals with the microstructure and mechanical properties of AlYNi bulks produced by extrusion of amorphous powders. The extruded bulks at temperatures above 613 K have high tensile strength, good wear resistance and a low coefficient of thermal expansion, and good forgeability. These aluminum alloys are expected to be a new type of high strength structural material with light weight.

Glass transition behavior of Al- and Mg-based amorphous alloys

Abstract AlNi(Y, La or Ce) and MgNi(La or Ce) amorphous alloys were found to exhibit a glass transition prior to their crystallization. The T g increases from 440 to 582 K with increasing solute concentration. The difference in C p between amorphous solid (AS) and supercooled liquid (SL) reaches 10 to 18 J/mol-K and the viscosities of these supercooled liquids are of the order 10 14 N.s./m 2 . By the transition of AS to SL, the Youngs modulus and tensile strength decrease steeply by 80 to 99 %, accompanied with an increase of elongation by 5 to 36 times.

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.