Microstructure, creep, and tensile behaviour of a Ti-15Al-33Nb (at.%) beta+orthorhombic alloy

C. J. Cowen, C. J. Boehlert

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Abstract

The microstructural evolution, creep and tensile deformation behaviour of a Ti-15Al-33Nb (at.%) alloy was studied. Monolithic sheet material was produced through conventional thermomechanical processing techniques comprising non-isothermal forging and pack rolling. Electron microscopy studies showed that depending on the heat-treatment schedule, this alloy may contain three constituent phases including:β(disordered body-centred cubic), 2 (ordered hexagonal close-packed based on Ti3Al) and O (ordered orthorhombic based on Ti2AlNb). Heat treatments at all temperatures above 990°C, followed by water quenching, resulted in fully-β microstructures. Below 990°C, Widmanstätten O-phase or 2-phase precipitated within theβgrains. The fine-grained as-processed microstructure, which exhibited 90vol.% β-phase, exhibited excellent strength (UTS=916MPa) and ductility (f>12%). After heat treatment, greater volume fractions of the orthorhombic phase precipitated and resulted in lower f values with UTS values ranging between 836-920MPa. However, RT elongations of more than 2% were recorded for microstructures containing up to 63vol.% O-phase. Specimens subjected to 650°C tensile experiments tended to exhibit lower strength values while maintaining higher elongation-to-failure. Tensile creep tests were conducted in the temperature range 650-710°C and stress range 49-275MPa. The measured creep exponents and activation energies suggested that grain boundary sliding operates at intermediate stress levels and dislocation climb is active at high stresses. Microstructural effects on the tensile properties and creep behaviour are discussed in comparison to a Ti-12Al-38Nb O+β alloy.

LanguageEnglish (US)
Pages99-124
Number of pages26
JournalPhilosophical Magazine
Volume86
Issue number1
DOIs
StatePublished - Jan 1 2006

Profile

tensile creep
heat treatment
microstructure
elongation
creep tests
tensile deformation
forging
tensile properties
schedules
ductility
sliding
electron microscopy
grain boundaries
quenching
exponents
activation energy
temperature
water
Microstructure
Creep

ASJC Scopus subject areas

  • Philosophy

Cite this

Microstructure, creep, and tensile behaviour of a Ti-15Al-33Nb (at.%) beta+orthorhombic alloy. / Cowen, C. J.; Boehlert, C. J.

In: Philosophical Magazine, Vol. 86, No. 1, 01.01.2006, p. 99-124.

Research output: Contribution to journalArticle

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