Fatigue crack growth threshold behaviour of nickel-based superalloy RR1000 for gas turbine disc rotors

Airey, Joe Christian (2021). Fatigue crack growth threshold behaviour of nickel-based superalloy RR1000 for gas turbine disc rotors. University of Birmingham. Ph.D.

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Abstract

Fatigue crack growth threshold behaviour has been investigated in coarse and fine grain RR1000 variants, across a range of frequencies, dwell times, R-ratios, test procedures and environments. Threshold tests were conducted on corner-crack specimens under uniaxial load at elevated temperature. Cyclic-dependent fatigue and time-dependent oxygen embrittlement failure mechanisms, characterized by transgranular and intergranular fracture morphology respectively, are encountered in this work. With the introduction and extension of dwell time, threshold values and crack growth rates at higher ∆K increased, along with the amount of intergranular crack growth. Threshold values can be nearly doubled, with considerable time spent at high temperature under stress prior to threshold. Lower bound threshold values for fully intergranular crack growth, have been identified for a coarse and a fine grain RR1000, where time spent prior to threshold was minimal. A substantially high threshold value has been observed for a coarse grain RR1000. Fatigue is driven by ∆K\(_{open}\) and oxygen embrittlement by K\(_{max}\). Critical time required for fully intergranular crack growth, has been identified for any given K\(_{max}\) for a fine grain RR1000. Possible crack-tip shielding and damaging mechanisms are discussed. Unfamiliar damaging mechanisms are exposed from novel high frequency tests in compression, and vacuum.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):