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Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

Effect of Prior Creep Strain on High Cycle Fatigue Life of TI 834

[+] Author and Article Information
Xijia Wu, Dongyi Seo

National Research Council Canada,
Ottawa, ON K1A 0R6, Canada

Marc Head, Stephen Chan

Siemens Canada Ltd.,
Dorval, QC H9P 1A5, Canada

Contributed by the Manufacturing Materials and Metallurgy Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 20, 2018; final manuscript received October 25, 2018; published online November 22, 2018. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(5), 052101 (Nov 22, 2018) (6 pages) Paper No: GTP-18-1510; doi: 10.1115/1.4041872 History: Received July 20, 2018; Revised October 25, 2018

Room-temperature fatigue tests were conducted on Ti 834 with prior creep strains accumulated under constant load at 550 °C and 600 °C, respectively. Microstructural and fractographic examinations on specimens with prior creep strain > 3% revealed the failure process consisting of multiple surface crack nucleation and internal void generation by creep, followed by fatigue crack propagation in coalescence with the internally distributed damage, leading to the final fracture. The amount of prior creep damage increased with creep strain. The fatigue life of Ti 834 was significantly reduced by prior creep straining. The behavior is rationalized with the integrated creep-fatigue theory.

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References

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Figures

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Fig. 1

Electron backscatter diffraction microstructure of Ti 834 in as-received condition

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Fig. 2

Creep curves under various stresses at: (a) 550 °C and (b) 600 °C

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Fig. 3

Longitudinal section of specimen P1 with 5% strain at 550 °C: (a) multiple surface cracks and (b) internal cracks/voids at grain boundaries

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Fig. 4

Transverse section of specimen P1 with 5% strain at 550 °C: (a) multiple surface cracks and (b) internal cracks/voids at grain boundaries

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Fig. 5

Longitudinal section of specimen N3 with 3% strain at 550 °C: (a) multiple surface cracks and (b) internal cracks/voids at grain boundaries

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Fig. 6

Transverse section of specimen N3 with 3% strain at 550 °C: (a) multiple surface cracks and (b) internal cracks/voids at grain boundaries

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Fig. 7

Surface crack size distribution in both P1 (5% prior creep strain) and N3 (3% prior creep strain) specimens

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Fig. 8

Normalized fatigue life as function of nonrecoverable prior creep strain. The solid lines represent Eq. (2) for the trend. The dash line represents the ductility exhaustion theory, Eq. (1).

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Fig. 9

Fracture mode of specimen B1: (a) mostly transgranular fatigue and (b) area of intergranular fracture

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Fig. 10

Cracks in (a) longitudinal section of B1, (b) transverse section of B1, (c) longitudinal, and (d) transverse sections of D2

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Fig. 11

(a) Surface cracks and (b) internal voids along the grain boundary in the longitudinal section of F1, (c) longitudinal and (d) transverse sections of F2. Arrows indicate internal cracks/voids.

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