High temperature fatigue of nickel-base superalloys - A review with special emphasis on deformation modes and oxidation

Failure of metals II: Fatigue

Effects of microstructure on high temperature dwell fatigue crack growth in a coarse grain PM nickel based superalloy

Crack growth micro-mechanisms in the IN718 alloy under the combined influence of fatigue, creep and oxidation

Oxidation ahead of a crack tip in an advanced Ni-based superalloy

This paper is concerned with the intergranular crack tip oxidation mechanism in alloy 718 at elevated temperatures. The basic concept is based on the ability of the oxygen partial pressure to control the preferential formation of oxide layers at the crack tip. The time required to complete the build-up of the protective oxide type at the metal-oxide interface is considered a measure of the limits of the oxidation process. Identification by transmission electron microscopy of oxide scale formed along fracture surfaces during a low frequency fatigue crack process in alloy 718 at 650°C supports the proposed model concepts. An experimental program was carried out to investigate the role of passivation time in controlling the progressive process of crack tip oxidation. This was achieved by testing the influence of oxide buil-up during hold time at minimum load, as well as the effect of a minor high frequency cycle imposed on the hold time period. It was established that an increase in fatigue crack growth rate accompanies the increase in passivation time period. These results were interpreted on the basis of the oxidation formation concepts.

Intergranular crack tip oxidation mechanism in a nickel-based superalloy

This paper describes the evolution of precipitation at a selected aging temperature of 593 °C in a new silicon-bearing near-α titanium alloy designated Ti-1100. This particular aging temperature was chosen to simulate the aging process occurring during service in a gas turbine engine. Over-aging results in the formation of silicide precipitates along the α platelet boundaries and the formation of Ti 3 Al distributed homogeneously throughout the matrix. The overall hardness response with aging exhibits two peaks: a minor peak at 800 min and a major peak at 10 000 min. Transmission electron microscopy evidence suggests that the silicide forms prior to the Ti 3 Al and that the minor peak is associated with silicide formation. The major peak is related to the silicide and/or Ti 3 Al. Metallurgical stability is only achieved after 60 000 min aging time. Since precipitation occurs over both short and long time periods (800–60 000 min), aging effects should be considered when characterizing high temperature mechanical behavior in this and similar near-α titanium alloys.

E. Andrieu

Papers

Intergranular crack tip oxidation mechanism in a nickel-based superalloy

Microstructural changes during aging of a near-α titanium alloy