The elevated-temperature creep behavior of boron-modified Ti-6A1-4V alloys

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    Abstract

    This work investigated the effect of nominal boron (B) additions of 0.1 mass% and 1 mass% on the elevated-temperature (673-728 K) tensile-creep deformation behavior of a Ti-6Al-4V(mass%) alloy for applied stresses between 400-600 MPa. The alloys were evaluated in the as-cast and cast-then-extruded conditions. Boron additions resulted in a dramatic refinement of the as-cast grain size and TiB whisker volume percents of approximately 0.6 and 6.0 for the Ti-6A1-4V-0.1B and Ti-6A1-4V-1B alloys, respectively. The extrusions were performed in the β-phase field and resulted in the TiB-phase whiskers aligning in the extrusion direction. The creep resistance of the as-cast alloys significantly improved with increased B concentration, where around an order of magnitude decrease in the secondary creep rate was observed between the Ti-6A1-4V-1B and Ti-6A1-4V as-cast alloys. Grain refinement due to the B addition did not deleteriously affect the creep resistance in the temperature and stress ranges considered, where dislocation creep was suggested to be the dominant secondary-creep mechanism. The enhanced creep resistance was attributed to load sharing by the TiB whiskers. For the same nominal B contents, the cast-then-extruded alloys exhibited significantly greater creep resistance and tensile strength than the as-cast alloys. This was explained to be an effect of the α-phase texture and the decreased lath spacing in the cast-then-extruded alloys compared with the as-cast alloys. The cast-then-extruded alloys exhibited four times lower lath widths than the as-cast alloys, and the α-phase was strongly textured such that the basal plane was predominately oriented perpendicular to the extrusion axis. Comparing the cast-then-extruded alloys, the Ti-6A1-4V alloy exhibited the greatest creep resistance. Overall the α-phase consisted of approximately 80% of the microstructure, and the α-phase texture appeared to be more dominant to the creep resistance and tensile strength than the small volume percent of TiB-phase in the microstructure. Although B is not necessary to optimize the elevated-temperature creep performance of the Ti-6A1-4V alloy, when boron was present, greater boron additions increased the creep resistance. In-situ creep observations of the surface indicated that the TiB whisker cracking occurred prior to slip and void formation in the α + β phases. This was followed by α/β interface cracking and ductile failure of the α + β microstructure.

    Original languageEnglish (US)
    Pages (from-to)1690-1703
    Number of pages14
    JournalMaterials Transactions
    Volume50
    Issue number7
    DOIs
    StatePublished - Jul 2009

    Profile

    creep strength
    casts
    cast alloys
    Creep resistance
    Creep
    Temporal Lobe Epilepsy
    boron
    temperature
    microstructure
    Boron
    Temperature
    Acetanilides
    tensile strength
    textures
    Extrusion
    Microstructure
    Dextrothyroxine
    Tensile strength
    Textures
    Preganglionic Autonomic Fibers

    Keywords

    • Boron
    • Casting
    • Creep
    • Extrusion
    • Microstructure
    • Titanium

    ASJC Scopus subject areas

    • Materials Science(all)
    • Condensed Matter Physics
    • Mechanical Engineering
    • Mechanics of Materials

    Cite this

    The elevated-temperature creep behavior of boron-modified Ti-6A1-4V alloys. / Boehlert, C. J.; Chen, W.

    In: Materials Transactions, Vol. 50, No. 7, 07.2009, p. 1690-1703.

    Research output: Contribution to journalArticle

    Boehlert, C. J.; Chen, W. / The elevated-temperature creep behavior of boron-modified Ti-6A1-4V alloys.

    In: Materials Transactions, Vol. 50, No. 7, 07.2009, p. 1690-1703.

    Research output: Contribution to journalArticle

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    abstract = "This work investigated the effect of nominal boron (B) additions of 0.1 mass% and 1 mass% on the elevated-temperature (673-728 K) tensile-creep deformation behavior of a Ti-6Al-4V(mass%) alloy for applied stresses between 400-600 MPa. The alloys were evaluated in the as-cast and cast-then-extruded conditions. Boron additions resulted in a dramatic refinement of the as-cast grain size and TiB whisker volume percents of approximately 0.6 and 6.0 for the Ti-6A1-4V-0.1B and Ti-6A1-4V-1B alloys, respectively. The extrusions were performed in the β-phase field and resulted in the TiB-phase whiskers aligning in the extrusion direction. The creep resistance of the as-cast alloys significantly improved with increased B concentration, where around an order of magnitude decrease in the secondary creep rate was observed between the Ti-6A1-4V-1B and Ti-6A1-4V as-cast alloys. Grain refinement due to the B addition did not deleteriously affect the creep resistance in the temperature and stress ranges considered, where dislocation creep was suggested to be the dominant secondary-creep mechanism. The enhanced creep resistance was attributed to load sharing by the TiB whiskers. For the same nominal B contents, the cast-then-extruded alloys exhibited significantly greater creep resistance and tensile strength than the as-cast alloys. This was explained to be an effect of the α-phase texture and the decreased lath spacing in the cast-then-extruded alloys compared with the as-cast alloys. The cast-then-extruded alloys exhibited four times lower lath widths than the as-cast alloys, and the α-phase was strongly textured such that the basal plane was predominately oriented perpendicular to the extrusion axis. Comparing the cast-then-extruded alloys, the Ti-6A1-4V alloy exhibited the greatest creep resistance. Overall the α-phase consisted of approximately 80% of the microstructure, and the α-phase texture appeared to be more dominant to the creep resistance and tensile strength than the small volume percent of TiB-phase in the microstructure. Although B is not necessary to optimize the elevated-temperature creep performance of the Ti-6A1-4V alloy, when boron was present, greater boron additions increased the creep resistance. In-situ creep observations of the surface indicated that the TiB whisker cracking occurred prior to slip and void formation in the α + β phases. This was followed by α/β interface cracking and ductile failure of the α + β microstructure.",
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    AB - This work investigated the effect of nominal boron (B) additions of 0.1 mass% and 1 mass% on the elevated-temperature (673-728 K) tensile-creep deformation behavior of a Ti-6Al-4V(mass%) alloy for applied stresses between 400-600 MPa. The alloys were evaluated in the as-cast and cast-then-extruded conditions. Boron additions resulted in a dramatic refinement of the as-cast grain size and TiB whisker volume percents of approximately 0.6 and 6.0 for the Ti-6A1-4V-0.1B and Ti-6A1-4V-1B alloys, respectively. The extrusions were performed in the β-phase field and resulted in the TiB-phase whiskers aligning in the extrusion direction. The creep resistance of the as-cast alloys significantly improved with increased B concentration, where around an order of magnitude decrease in the secondary creep rate was observed between the Ti-6A1-4V-1B and Ti-6A1-4V as-cast alloys. Grain refinement due to the B addition did not deleteriously affect the creep resistance in the temperature and stress ranges considered, where dislocation creep was suggested to be the dominant secondary-creep mechanism. The enhanced creep resistance was attributed to load sharing by the TiB whiskers. For the same nominal B contents, the cast-then-extruded alloys exhibited significantly greater creep resistance and tensile strength than the as-cast alloys. This was explained to be an effect of the α-phase texture and the decreased lath spacing in the cast-then-extruded alloys compared with the as-cast alloys. The cast-then-extruded alloys exhibited four times lower lath widths than the as-cast alloys, and the α-phase was strongly textured such that the basal plane was predominately oriented perpendicular to the extrusion axis. Comparing the cast-then-extruded alloys, the Ti-6A1-4V alloy exhibited the greatest creep resistance. Overall the α-phase consisted of approximately 80% of the microstructure, and the α-phase texture appeared to be more dominant to the creep resistance and tensile strength than the small volume percent of TiB-phase in the microstructure. Although B is not necessary to optimize the elevated-temperature creep performance of the Ti-6A1-4V alloy, when boron was present, greater boron additions increased the creep resistance. In-situ creep observations of the surface indicated that the TiB whisker cracking occurred prior to slip and void formation in the α + β phases. This was followed by α/β interface cracking and ductile failure of the α + β microstructure.

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    KW - Microstructure

    KW - Titanium

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