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  • 1
    Electronic Resource
    Electronic Resource
    Metastable phase formation in mechanically alloyed and ball milled Ti–Si (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2478-2487 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Ti–Si system is chosen as a model system to study the mechanical alloying of elemental powder blends in which one of the components is brittle. In addition, the stability of intermetallic compounds upon milling is investigated, in order to interpret the metastable phase formation during the milling process. Detailed x-ray investigations show that during mechanical alloying, a solution of Si in Ti preceeds the formation of amorphous or intermetallic phases. The selection of phases formed, as well as the final state, are influenced by the overall composition of the powder blends, and by the milling procedure applied. However, predictions can be made by considering the free energy curves of the stable and metastable phases in the Ti–Si system, which have been calculated by the CALPHAD method. Milling of the intermetallic compounds generally leads to the same final state as the mechanical alloying of elemental powder blends with corresponding compositions. These results demonstrate that the intermetallic compounds are energetically destabilized upon milling, allowing for phase transformations into metastable phases, such as amorphous or metastable crystalline alloys. The energetic destabilization of intermetallic compounds mainly originates from the chemical disorder caused by the milling process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351594
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  • 2
    Electronic Resource
    Electronic Resource
    Mechanical properties of submicron-grained TiAl alloys prepared by mechanical alloying (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 941-943 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ti-48 at. % Al powders of the metastable hexagonal-closed-packed solid solution with a grain size of 15 nm were prepared by mechanical alloying. The powders were consolidated to a density of greater than 99.5% by hot isostatic pressing (HIP) at 800 °C. After HIP the material exhibits a globular microstructure of the equilibrium phases α2 and γ with a mean grain size of 150 nm. Microhardness measurements show a Hall–Petch type [E. O. Hall, Proc. Phys. Soc. B 64, 747 (1951); N. J. Petch, J. Iron Steel Inst. 174, 25 (1953)] dependence on grain size. Room temperature compression tests reveal low ductility, but high fracture strengths ≥1800 MPa. On increasing the test temperature the yield strength drops sharply in the temperature range 600–800 °C to very low values. The results indicate that submicron-grained TiAl alloys can be deformed at much lower temperatures than coarse-grained material, making them suitable as precursors for net shaping, in particular if high deformation ratios are required. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113604
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  • 3
    Electronic Resource
    Electronic Resource
    Inverse melting of a metastable Nb45Cr55 solid solution (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 318-320 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An Nb45Cr55 solid solution was prepared by mechanical alloying in a planetary ball mill and investigated by x-ray diffraction and calorimetry. It was found that the structure evolution upon heating exhibited three distinct stages, the first resulting in complete amorphization, whereas the second and third are related to the subsequent crystallization of the amorphous phase. These results are in agreement with the free-energy functions calculated from the thermochemical data of the system. They show that for a composition of Nb45Cr55 a second melting point (often termed "inverse melting point'') exists at about 900 °C, below which the undercooled liquid has a lower free energy than the crystalline body-centered-cubic phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112358
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  • 4
    Electronic Resource
    Electronic Resource
    Processing and Deformation Behavior of Gamma TiAl Alloys with Fine-Grained Equiaxed Microstructures (1999)
    Springer
    Advanced performance materials 6 (1999), S. 107-116 
    Details
    ISSN: 1572-8765
    Keywords: binary alloys ; dynamic recrystallization ; fine-grained microstructure ; gamma titanium aluminide ; hot forging ; multicomponent alloys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper describes how a submicrocrystalline structure can be produced by isothermal deformation of cast and powder metallurgy γ-TiAl-based alloys at temperatures 1000°C and below using relatively inexpensive nickel-based superalloy die tooling. A detailed analysis of the effects of initial microstructure, chemical compositions, conditions of heat treatment and hot working on the formation of a homogeneous fine-grained microstructure in γ-TiAl-based alloys is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008718724229
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