Dmitri V. Louzguine

Nanocrystalline composites with high strength obtained in Zr–Ti–Ni–Cu–Al bulk amorphous alloys

Nanocrystalline composites with the grain size less than 10 nm were produced by annealing of Cu-mold cast Zr70−x−yTixNi10Cu20Aly (X=5–7.5 and Y=10–15 at %) bulk amorphous alloys. The nanostructured alloys show increased tensile strength at the volume fraction of nanoparticles less than 30%. The microstructure of the amorphous alloys was found to contain medium range order (MRO) domains, which uniformly distributed in the amorphous matrix. We suggest that MRO domains provide nucleation sites for precipitation of the primary crystals and lead to the formation of nanocrystalline composites.

Crystallization behaviour of Al-based metallic glasses below and above the glass-transition temperature

Abstract The present paper aims to report an effect of a supercooled liquid region on crystallization behaviour of the Al85Y8−xNdxNi5Co2 metallic glasses produced by rapid solidification of the melt. The paper describes the crystallization process at different regimes of heat treatment. It is found that crystallization behaviour of the above-mentioned Al-based metallic glasses above the glass-transition temperature and below it follows different transformation mechanisms. Formation of the primary nanoscale α-Al particles was observed during continuous heating or after isothermal annealing above the glass-transition temperature. During isothermal annealing below the glass-transition temperature an unknown metastable phase is formed conjointly with α-Al. The metastable phase formed in the Nd-free alloy varies from that in the Nd-bearing alloys. Al85Nd8Ni5Co2 amorphous alloy exhibiting no glass transition crystallizes equally during isothermal calorimetry at different temperatures and during continuous heating.

Electronegativity of the constituent rare-earth metals as a factor stabilizing the supercooled liquid region in Al-based metallic glasses

The letter describes influence of the electronegativity of the constituent rare-earth metals on the supercooled liquid region in the Al–(Gd, Dy or Er)–Ni–Co metallic glasses. The samples were studied by x-ray diffractometry and differential scanning calorimetry. Calorimetry data for the La and Sm—bearing glasses studied earlier were also taken in consideration for comparison. It is found that supercooled liquid range in the Al85RE8Ni5Co2 alloys strongly depends upon electronegativity of the RE metal.

Synthesis and magnetic properties of Fe¿Pt¿B nanocomposite permanent magnets with low Pt concentrations

Microstructure and magnetic properties of melt-spun Fe80−xPtxB20 (x=20,22,24) alloy ribbons have been investigated. A homogeneous nanoscale mixed structure with amorphous and fcc γ-FePt phases was formed in the melt-spun ribbons. The average sizes of the amorphous and fcc γ-FePt phases are about 5nm, and the enrichment phenomenon of B is recognized in the coexistent amorphous phase. The melt-spun ribbons exhibit soft magnetic properties. The nanocomposite structure consisting of fct γ1-FePt, fcc γ-FePt, and Fe2B phases was obtained in the melt-spun ribbons annealed at 798K for 900s, and their average grain sizes are about 20nm. The remanence (Br), reduced remanence (Mr∕Ms), coercivity (Hci), and maximum energy product (BH)max of the nanocomposite alloys are in the range of 0.93–1.05T, 0.79–0.82, 375–487kA∕m, and 118–127kJ∕m3, respectively. The good hard magnetic properties are interpreted as resulting from exchange magnetic coupling between nanoscale hard fct γ1-FePt and soft magnetic fcc γ-FePt or Fe2B p...

Nanoparticles with icosahedral symmetry in Cu-based bulk glass former induced by Pd addition

Abstract Formation of the nanoicosahedral particles having a size ranged from 3 to 10 nm is observed in Cu 55 Zr 30 Ti 10 Pd 5 glassy alloy in the initial stage of the devitrification process. The structure changes on heating were studied by X-ray diffraction, transmission electron microscopy differential scanning and isothermal calorimetry.

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.

Comparison of the long-term thermal stability of various metallic glasses under continuous heating

Abstract Continuous heating transformation diagrams for different metallic glasses were constructed using the differential scanning calorimetry data by applying the corollary of the Kissinger analysis method. The diagrams allow to perform comparison of the stabilities of metallic glasses on the long-term scale.

Evaluation of the thermal stability of a Cu60Hf25Ti15 metallic glass

The present letter shows how a continuous heating transformation diagram for a Cu60Hf25Ti15 metallic glass can be obtained by applying an extension of the Kissinger analysis. According to the calculation this glass is completely stable in the Earth’s climate for its lifetime. This extension of the Kissinger analysis method can be applied to any other metallic glass.

High-strength hypereutectic Ti–Fe–Co bulk alloy with good ductility

The structure of an arc-melted ingot of Ti70Fe15Co15 alloy has been studied by X-ray diffractometry and scanning electron microscopy. Its microstructure consists of a primary Pm m Ti(Fe, Co) phase and a binary Ti(Fe, Co) + Im m β-Ti solid solution eutectic. The mechanical properties were tested by an Instron-type machine. A sample cut from the central part of the ingot exhibits excellent mechanical properties.

Structural and thermal investigations of a high-strength Cu-Zr-Ti-Co bulk metallic glass

Cu 55 Zr 30 Ti 10 Co 5 bulk metallic glass exhibits a high compressive fracture strength of 2.31 GPa and Youngs modulus of 130 GPa, values that are higher than those of other Cu- and Zr-based metallic glasses. The addition of Co to the ternary Cu-Zr-Ti alloy stabilizes the supercooled liquid. On heating, the Cu 55 Zr 30 Ti 10 Co 5 metallic glass devitrified and formed an intermediate intermetallic compound prior to reaching equilibrium by diffusion-controlled growth at constant nucleation rate. In the fully annealed state the structure consists of the equilibrium Cu 10 Zr 7 phase with the slightly reduced lattice parameters a = 0.933 nm, b = 0.928 nm and c = 1.254 nm and a small fraction of an unidentified phase.