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

    Research output: Research - peer-reviewArticle

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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.

    LanguageEnglish (US)
    Pages4411-4422
    Number of pages12
    JournalJournal of Materials Science
    Volume43
    Issue number13
    DOIs
    StatePublished - Jul 2008

    Profile

    Molybdenum
    Creep
    Microstructure
    Fibers
    Composite materials
    fiber composites
    molybdenum
    microstructure
    Metals
    metal matrix composites
    Creep resistance
    creep strength
    matrices
    Debonding
    Loads (forces)
    Volume fraction
    Carbon
    Scanning electron microscopy
    Air
    Experiments

    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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