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Thermal Cycle Testing of Bare Bond Coats

Time:2022-04-03 21:14:39  From:  Author:

René N5 substrates coated on one face with as-sprayed MCrAlX bond coats were also tested, to compare their relative scale adhesion behavior. Although there were no major differences in the cyclic oxidation behavior of the VPS MCrAlX bond coats (Fig. 1), there were subtle differences in the transient oxidation rates, the time to scale spallation, and the apparent rate of scale spallation. The VPS NiCoCrAlYHfSi displayed the lowest initial oxidation rate and maximum weight gain, as compared to VPS NiCrAl-1Y and NiCrAl-0.25Y.

Fig. 1 Comparison of the weight changes during cyclic oxidation test ing (1 h cycles at 1150 °C) of a René N5 substrate and various APS or VPS MCrAlX bond coats (with no YSZ top coat) on René N5 substrates. One specimen of each type was tested. Specimen weight losses are due to alumina scale spallation. Note that only one face of the substrates was coated with MCrAlX.

The points at which the weights of the VPS coatings (Fig. 1) begin to decrease can be considered the initiation of significant scale spallation. Significant scale spallation initiated at approximately 150 1 h cycles for bare René N5, 120 cycles for APS NiCrAl-1Y, 96 cycles for VPS NiCrAl-0.25Y, 72 cycles for VPS NiCrAl-1Y, and 60 cycles for VPS NiCoCrAlYHfSi. Furthermore, from comparison of the slopes of the curves after scale spallation initiated, René N5 displayed the most gradual rate of scale spallation (which appears to be only partially due to the lower surface area of the René N5), followed by VPS NiCrAl-1Y, VPS NiCoCrAlYHfSi, and then VPS NiCrAl-0.25Y. These comparisons suggest that Al2O3 scale adhesion to the René N5 surfaces during thermal cycling was superior to scale adhesion to the plasma sprayed MCrAlX bond coats. This result agrees with the relative oxidation behavior previously reported for cast NiCrAl and René N5.


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