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.

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

Profile

Molybdenum
fiber composites
metal matrix composites
molybdenum
creep strength
Creep
Creep resistance
Metals
microstructure
Microstructure
Fibers
Composite materials
matrices
tensile creep
fiber volume fraction
fiber-matrix interfaces
Debonding
Loads (forces)
Volume fraction
Carbon

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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N2 - 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.

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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