Transformation superplasticity of super {alpha}{sub 2} titanium aluminide

Journal Article · Fri Oct 09 04:00:00 EDT 1998 · Acta Materialia

DOI:https://doi.org/10.1016/S1359-6454(98)00252-3· OSTI ID:289517

Schuh, C; Dunand, D C ^[1]

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1. Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science and Engineering

Transformation superplasticity of an intermetallic Ti{sub 3}Al-based alloy (Super {alpha}{sub 2}) is demonstrated by thermal cycling about the {alpha}{sub 2}/{beta} transformation temperature range under a uniaxial tensile biasing stress. Failure strains up to 610% were recorded at a stress of 3 MPa, compared with 110% for deformation by isothermal creep at the same stress. The strain increment produced during each half-cycle is determined as a function of applied biasing stress, thermal cycle amplitude, and cycling frequency. Since internal stresses are generated both by transformation mismatch and by thermal expansion mismatch between the two coexisting phases, an effective volume mismatch is defined to account for both contributions. Introduction of this parameter into existing continuum-mechanics models results in good agreement with experimental data in both the low-stress regime, where cycling strain rate and stress are proportional, and the high-stress regime where the stress sensitivity is increasing. Cycling strain increments at various temperature amplitudes and cycling frequencies are considered in terms of the equilibrium thermodynamics and transformation kinetics of Super {alpha}{sub 2}. Finally, thermal cycling produces ratcheting, where texture and crystallographic orientation of the {beta}/{alpha}{sub 2} transformation front affect the direction of ratcheting strains.

• OSTI ID: 289517
• Journal Information: Acta Materialia, Journal Name: Acta Materialia Journal Issue: 16 Vol. 46; ISSN 1359-6454; ISSN ACMAFD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
CRYSTAL-PHASE TRANSFORMATIONS
INTERMETALLIC COMPOUNDS
PLASTICITY
STRAINS
STRESSES
THERMAL CYCLING
TITANIUM ALLOYS