Microstructure, creep, and tensile behavior of a Ti-12Al-38Nb (at.%) beta+orthorhombic alloy

Research output: Research - peer-reviewArticle

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Abstract

The microstructural evolution, creep, and tensile deformation behavior of a Ti-12Al-38Nb (at.%) alloy were studied. Monolithic sheet materials were produced through conventional thermomechanical processing techniques comprising nonisothermal forging and pack rolling. TEM studies showed that depending on the heat-treatment schedule, this alloy contains two constituent phases including: β (disordered body-centered cubic) and O (ordered orthorhombic based on Ti2AlNb). Heat treatments at all temperatures above 800°C, followed by water quenching, resulted in fully-β microstructures. Below 800°C, fine Widmanstatten O-phase needles precipitated within the β grains. Fully-β microstructures exhibited room-temperature (RT) elongations of more than 27%. The second-phase O precipitates provided strengthening at the expense of elongation. However, RT elongations of more than 12% were recorded for aged microstructures containing 30 vol.% O-phase. Metallographic observations revealed that slip was compatible between the two phases. Tensile creep tests were conducted in the temperature range 650-705°C and stress range 50-172 MPa. The deformation observations and measured creep exponents and activation energies suggested that the creep mechanisms were dependent on stress. For applied stresses less than 123 MPa, the creep exponents were between 1.6 and 2.0 and low dislocation densities were observed. For higher stresses, the stress exponents were between 3.5 and 7.2 and higher dislocation densities were observed. The calculated activation energies for the low-stress regime were approximately half those calculated for the high stress regime. These data suggest that Coble creep operates at low stress levels and dislocation climb is active at high stresses. Microstructural effects on the tensile properties and creep behavior are discussed in the light of existing models.

LanguageEnglish (US)
Pages82-98
Number of pages17
JournalMaterials Science and Engineering A
Volume267
Issue number1
StatePublished - Jul 15 1999
Externally publishedYes

Profile

Creep
Microstructure
microstructure
Temperature
Elongation
elongation
exponents
Activation energy
Heat treatment
tensile creep
heat treatment
activation energy
room temperature
temperature
Microstructural evolution
Forging
Tensile properties
Needles
Precipitates
Quenching

Keywords

  • Body-centered-cubic
  • Creep
  • Microstructure
  • Orthorhombic
  • Tension
  • Titanium

ASJC Scopus subject areas

  • Materials Science(all)

Cite this

Microstructure, creep, and tensile behavior of a Ti-12Al-38Nb (at.%) beta+orthorhombic alloy. / Boehlert, C. J.

In: Materials Science and Engineering A, Vol. 267, No. 1, 15.07.1999, p. 82-98.

Research output: Research - peer-reviewArticle

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