Time-dependent crack growth in a coarse-grained Ni-based superalloy RR1000

Sun, Jifeng (2013). Time-dependent crack growth in a coarse-grained Ni-based superalloy RR1000. University of Birmingham. Ph.D.

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Abstract

The dwell fatigue crack growth behaviour of coarse grained RR1000 has been studied using advanced mechanical testing and characterization techniques. Crack growth under sustained loading has also been considered.
Environmentally enhanced crack growth at high temperatures in air follows a stress assisted grain boundary oxidation (SAGBO) mechanism, with a 100-300 nm long Al2O3 intrusion ahead of the crack tip. When its thickness of reaches a critical value, this intrusion fails and crack advance ensues. The crack growth process is discontinuous and highly uneven. The dwell fatigue/sustained loading crack growth rates are affected by the stress relaxation ability of the materials, which is related to the size and distribution of tertiary γ' precipitates, testing temperature and stress state.
Oxidation damage is deduced to be a dominant factor affecting crack growth over a range of temperature from 600 to 700 °C. At 700 °C oxidation damage begins to have an effect on fatigue crack growth at a dwell time of 30 s. Creep damage is suggested to make the dominant contribution to crack growth at 750 and 775 °C both in air and in vacuum.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):