The effect of molybdenum on the microstructure and creep behavior of Ti-24Al-17Nb-xMo alloys and Ti-24Al-17Nb-xMo SiC-fiber composites

J. P. Quast, C. J. Boehlert

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    Abstract

    The effect of molybdenum (Mo) on the microstructure and creep behavior of nominally Ti-24Al-17Nb (at.%) alloys and their continuously reinforced SiC-fiber composites (fiber volume fraction = 0.35) was investigated. Constant-load, tensile-creep experiments were performed in the stress range of 10-275 MPa at 650 °C in air. A Ti-24Al-17Nb-2.3Mo (at.%) alloy exhibited significantly greater creep resistance than a Ti-24Al-17Nb-0.66Mo (at.%) alloy, and correspondingly a 90°-oriented Ultra SCS-6/Ti-24Al-17Nb-2.3Mo metal matrix composite (MMC) exhibited significantly greater creep resistance than an Ultra SCS-6/Ti-24Al-17Nb-0.66Mo MMC. Thus, the addition of 2.3 at.% Mo significantly improved the creep resistance of both the alloy and the MMC. An Ultra SCS-6 Ti-25Al-17Nb-1.1Mo (at.%) MMC exhibited creep resistance similar to that of the Ultra SCS-6/Ti-25Al-17Nb-2.3Mo (at.%). Using a modified Crossman model, the MMC secondary creep rates were predicted from the monolithic matrix alloys' secondary creep rates. For identical creep temperatures and applied stresses, the 90°-oriented MMCs exhibited greater creep rates than their monolithic matrix alloy counterparts. This was explained to be a result of the low interfacial bond strength between the matrix and the fiber, measured using a cruciform test methodology, and was in agreement with the modified Crossman model. Scanning electron microscopy observations indicated that debonding occurred within the carbon layers of the fiber-matrix interface.

    Original languageEnglish (US)
    Pages (from-to)4411-4422
    Number of pages12
    JournalJournal of Materials Science
    Volume43
    Issue number13
    DOIs
    StatePublished - Jul 2008

    Profile

    Enzyme Reactivators
    Creep
    Composite materials
    metal matrix composites
    creep strength
    Abnormal Erythrocytes
    Fibers
    Metals
    Temporal Lobe Epilepsy
    Creep resistance
    molybdenum
    matrices
    Molybdenum
    fiber composites
    microstructure
    Anthralin
    Addison Disease
    Microstructure
    tensile creep
    fiber volume fraction

    ASJC Scopus subject areas

    • Materials Science(all)
    • Electronic, Optical and Magnetic Materials
    • Condensed Matter Physics

    Cite this

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    title = "The effect of molybdenum on the microstructure and creep behavior of Ti-24Al-17Nb-xMo alloys and Ti-24Al-17Nb-xMo SiC-fiber composites",
    abstract = "The effect of molybdenum (Mo) on the microstructure and creep behavior of nominally Ti-24Al-17Nb (at.%) alloys and their continuously reinforced SiC-fiber composites (fiber volume fraction = 0.35) was investigated. Constant-load, tensile-creep experiments were performed in the stress range of 10-275 MPa at 650 °C in air. A Ti-24Al-17Nb-2.3Mo (at.%) alloy exhibited significantly greater creep resistance than a Ti-24Al-17Nb-0.66Mo (at.%) alloy, and correspondingly a 90°-oriented Ultra SCS-6/Ti-24Al-17Nb-2.3Mo metal matrix composite (MMC) exhibited significantly greater creep resistance than an Ultra SCS-6/Ti-24Al-17Nb-0.66Mo MMC. Thus, the addition of 2.3 at.% Mo significantly improved the creep resistance of both the alloy and the MMC. An Ultra SCS-6 Ti-25Al-17Nb-1.1Mo (at.%) MMC exhibited creep resistance similar to that of the Ultra SCS-6/Ti-25Al-17Nb-2.3Mo (at.%). Using a modified Crossman model, the MMC secondary creep rates were predicted from the monolithic matrix alloys' secondary creep rates. For identical creep temperatures and applied stresses, the 90°-oriented MMCs exhibited greater creep rates than their monolithic matrix alloy counterparts. This was explained to be a result of the low interfacial bond strength between the matrix and the fiber, measured using a cruciform test methodology, and was in agreement with the modified Crossman model. Scanning electron microscopy observations indicated that debonding occurred within the carbon layers of the fiber-matrix interface.",
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    AB - The effect of molybdenum (Mo) on the microstructure and creep behavior of nominally Ti-24Al-17Nb (at.%) alloys and their continuously reinforced SiC-fiber composites (fiber volume fraction = 0.35) was investigated. Constant-load, tensile-creep experiments were performed in the stress range of 10-275 MPa at 650 °C in air. A Ti-24Al-17Nb-2.3Mo (at.%) alloy exhibited significantly greater creep resistance than a Ti-24Al-17Nb-0.66Mo (at.%) alloy, and correspondingly a 90°-oriented Ultra SCS-6/Ti-24Al-17Nb-2.3Mo metal matrix composite (MMC) exhibited significantly greater creep resistance than an Ultra SCS-6/Ti-24Al-17Nb-0.66Mo MMC. Thus, the addition of 2.3 at.% Mo significantly improved the creep resistance of both the alloy and the MMC. An Ultra SCS-6 Ti-25Al-17Nb-1.1Mo (at.%) MMC exhibited creep resistance similar to that of the Ultra SCS-6/Ti-25Al-17Nb-2.3Mo (at.%). Using a modified Crossman model, the MMC secondary creep rates were predicted from the monolithic matrix alloys' secondary creep rates. For identical creep temperatures and applied stresses, the 90°-oriented MMCs exhibited greater creep rates than their monolithic matrix alloy counterparts. This was explained to be a result of the low interfacial bond strength between the matrix and the fiber, measured using a cruciform test methodology, and was in agreement with the modified Crossman model. Scanning electron microscopy observations indicated that debonding occurred within the carbon layers of the fiber-matrix interface.

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