The oxidation damage of Ni-based superalloy, RR1000, with different surface modifications and the role of oxidation in fatigue crack initiation

Cruchley, Sam (2015). The oxidation damage of Ni-based superalloy, RR1000, with different surface modifications and the role of oxidation in fatigue crack initiation. University of Birmingham. Ph.D.

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Abstract

The oxidation behaviour of RR1000 with different surface modifications has been well studied using detailed metallographic and mass gain measurements. The oxide comprises of an external chromia scale with isolated grains of TiO\(_2\) on the outer surface. Sub-surface internal alumina is present, beneath which the presence of TiN occurs (at higher temperatures >800\(^o\)C), all contained within a ɣ' denuded zone. The chromia external scale growth rate is significantly greater than pure chromia on chromium and the enhancement is attributed to the increased ionic transport caused by doping of the chromia layer with Ti. This effect is still seen regardless of surface condition prior to oxidation.

Oxides, especially internal intergranular oxides have been shown to crack under room temperature fatigue conditions, causing a significant fatigue life deficit at a maximum applied stress of 800 MPa and 1000 MPa. At 825 MPa, it is suggested that plastic yielding of the ɣ' denuded zone initiated leading to a substantial increase in fatigue life, through either blunting the crack by deforming to accommodate the stress concentration at the crack tip or by preventing cracking of the oxides.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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