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.

LanguageEnglish (US)
Pages1690-1703
Number of pages14
JournalMaterials Transactions
Volume50
Issue number7
DOIs
StatePublished - Jul 2009

Profile

Boron
creep strength
Creep
boron
casts
cast alloys
Creep resistance
Temperature
temperature
tensile strength
microstructure
textures
boron alloys
Extrusion
tensile creep
Microstructure
Tensile strength
Textures
voids
slip

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

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