TY - JOUR

T1 - Modeling thermomechanical fatigue life of high-temperature titanium alloy IMI 834

AU - Maier, H. J.

AU - Teteruk, R. G.

AU - Christ, H. J.

N1 - Funding Information: Financial support of this study by Deutsche Forschungs-gemeinschaft is gratefully acknowledged. The authors thank S. Hardt and P. Pototzky for help in the experimental work.

PY - 2000

Y1 - 2000

N2 - A microcrack propagation model was developed to predict thermomechanical fatigue (TMF) life of high-temperature titanium alloy IMI 834 from isothermal data. Pure fatigue damage, which is assumed to evolve independent of time, is correlated using the cyclic J integral. For test temperatures exceeding about 600 °C, oxygen-induced embrittlement of the material ahead of the advancing crack tip is the dominating environmental effect. To model the contribution of this damage mechanism to fatigue crack growth, extensive use of metallographic measurements was made. Comparisons between stress-free annealed samples and fatigued specimens revealed that oxygen uptake is strongly enhanced by cyclic plastic straining. In fatigue tests with a temperature below about 500 °C, the contribution of oxidation was found to be negligible, and the detrimental environmental effect was attributed to the reaction of water vapor with freshly exposed material at the crack tip. Both environmental degradation mechanisms contributed to damage evolution only in out-of-phase TMF tests, and thus, this loading mode is most detrimental. Electron microscopy revealed that cyclic stress-strain response and crack initiation mechanisms are affected by the change from planar dislocation slip to a more wavy type as test temperature is increased. The predictive capabilities of the model are shown to result from the close correlation with the microstructural observations.

AB - A microcrack propagation model was developed to predict thermomechanical fatigue (TMF) life of high-temperature titanium alloy IMI 834 from isothermal data. Pure fatigue damage, which is assumed to evolve independent of time, is correlated using the cyclic J integral. For test temperatures exceeding about 600 °C, oxygen-induced embrittlement of the material ahead of the advancing crack tip is the dominating environmental effect. To model the contribution of this damage mechanism to fatigue crack growth, extensive use of metallographic measurements was made. Comparisons between stress-free annealed samples and fatigued specimens revealed that oxygen uptake is strongly enhanced by cyclic plastic straining. In fatigue tests with a temperature below about 500 °C, the contribution of oxidation was found to be negligible, and the detrimental environmental effect was attributed to the reaction of water vapor with freshly exposed material at the crack tip. Both environmental degradation mechanisms contributed to damage evolution only in out-of-phase TMF tests, and thus, this loading mode is most detrimental. Electron microscopy revealed that cyclic stress-strain response and crack initiation mechanisms are affected by the change from planar dislocation slip to a more wavy type as test temperature is increased. The predictive capabilities of the model are shown to result from the close correlation with the microstructural observations.

UR - http://www.scopus.com/inward/record.url?scp=0033880106&partnerID=8YFLogxK

U2 - 10.1007/s11661-000-0280-2

DO - 10.1007/s11661-000-0280-2

M3 - Article

AN - SCOPUS:0033880106

VL - 31

SP - 431

EP - 444

JO - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

JF - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

SN - 1073-5623

IS - 2

ER -