The effect of single and two-stage Si modified aluminide coatings on thermal fatigue behaviour of nickel based superalloy Inconel 713LC was examined. Specimens were loaded under test condition of heating to 11008C followed by cooling to258C. The experimental results showed that the coatings increased thermal fatigue resistance in both crack initiation and propagation stages. The comparison of the crack growth rates indicated that both coatings imparted resistance to the crack lengthening. However, the effect of single stage coating on the fatigue resistance was superior compared with that of two-stage coating. Through scanning electron microscopy observation, it was found that the width of c9 denuded zone was the main reason in the control of crack growth in all specimens.

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The thermal fatigue behavior of superalloy Inconel 713LC was investigated at peak temperatures of 900, 1 000 and 1 100 °C. Thermal fatigue tests were performed on self-constraint single-edge V-type notch specimens. The effect of the maximum temperature, Tmax in the thermal cycles on the crack characteristics was studied. Under identical test conditions a comparable crack propagation rate was observed for all three peak temperatures. The results showed that cycle numbers for crack initiation decreased while crack propagation rate increased with the increase in peak temperature. Therefore, it was concluded that in the current experimental conditions, thermal fatigue resistance reduced dramatically with the rise of upper temperature. Through optical microscopy and scanning electron microscopy observation, it was found that the primary cracks generally propagated along a preferential direction. Microstructure changes after thermal fatigue are also discussed on the basis of scanning electron microscopy observation.