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Notch Effect on Stress Rupture Behavior of Ti-24Al-llNb at 650°C

Published online by Cambridge University Press:  01 January 1992

Jin Liang  and
R. M. Pelloux
Jin Liang
Affiliation:
Department of Materials Science and Engineering, Massachusetts Institute of Technology Cambridge, MA 02139, USA.
R. M. Pelloux
Affiliation:
Department of Materials Science and Engineering, Massachusetts Institute of Technology Cambridge, MA 02139, USA.
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Abstract

Notch stress rupture behavior of a titanium aluminide Ti3Al alloy, Ti-24A1-11Nb, was investigated. Three axisymetric test bar geometries were used: smooth bar (kt =1), circular notch (U-notch, kt = 1.6) and British standard notch (V-notch, kt = 4.2). Tests were performed at 650 °C, with a real-time DC potential drop (DCPD) automated data acquisition system continuously monitoring local creep deformation and damage accumulation in the notched specimens. Two microstructures were investigated, an equiaxed grain structure produced by an α2+β heat treatment and a transformed β microstructure produced by a β heat treatment. It was found that the effects of notches on the stress rupture lives are dependent on microstructure, notch geometry, and applied stress level. For the α2+β treated Ti-24A1-11Nb alloy, a U-notch has a notch strengthening effect in the high stress or short life region and a notch weakening effect in the low stress, long life region; a V-notch always has a notch weakening effect. The β treated Ti-24A1-1 INb alloy shows notch weakening effects both for U-notch and V-notch, with V-notch and high stress levels being the most deleterious. The theoretical DCPD response corresponding to a FEM-calculated creep deformation at a given time t was estimated and compared with the real time recorded DCPD changes. This combined DCPD-FEM analysis method provided quantitative information about the relative contributions of creep deformation and damage mechanisms (cavitation, micro- and macro-cracking) to the experimental DCPD curve in a notch stress rupture test.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 288: Symposium L – High-Temperature Ordered Intermetallic Alloys V , 1992 , 769
Copyright
Copyright © Materials Research Society 1995

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