Furnace thermal cycle testing of TBC specimens with René N5 substrates and identical APS YSZ top coats revealed significant differences in TBC lifetimes depending on the MCrAlX bond coat composition and deposition method. Figure1 compares the average lifetimes of the TBCs in this study. The TBCs with VPS NiCrAl-1Y bond coats were the most durable and exhibited a 20% improvement in lifetime as compared to TBCs with APS NiCrAl-1Y bond coats. The lifetimes of TBCs with VPS NiCoCrAlYHfSi bond coats were ∼50% lower than TBC lifetimes on VPS NiCrAl-1Y and ∼37% lower than those on APS NiCrAl-1Y. The range of values in Fig. 1 indicates relatively good consistency in coating lifetimes (within the constraints of the specimen amounts).
Fig.1 Comparisons of the average lifetimes of plasma-sprayed TBCs with various bond coats on René N5 substrates, as determined by 1 h thermal cycles to 1150 °C. The mean TBC life and standard deviation are shown for each specimen type.
Representative weight change curves during thermal cycle testing of the various TBC specimens on René N5 substrates are compared to bare René N5 in Fig. 2. There was little internal oxidation of the VPS bond coats or René N5 (as determined by SEM analysis of metallographic cross sections), so the weight changes of these specimens can be attributed to their relative oxidation behavior at the metal surfaces. Specimens with APS NiCrAl-1Y bond coats experienced oxidation along internal porosity, which is reflected by their higher weight gains (Fig. 2). Since these specimens were coated on only one face, the weight gains of the coated specimens actually indicate the composite oxidation behavior of the plasma-sprayed MCrAlX surfaces and the René N5 surfaces. The coating weight gain values were not corrected for the actual MCrAlX surface areas (which were unknown because of the surface roughness) and, thus, are only valid for comparison purposes within this study (with these comparisons being limited by variations in bond coat surface roughness from specimen to specimen). The magnitude and rate of weight gain were greater for the TBC specimens than René N5, due to their greater surface area and inhibition of Al2O3 scale spallation from the MCrAlX-coated face by the APS YSZ. The cyclic oxidation rates of TBCs with VPS NiCrAl-1Y and NiCrAl0.25Y bond coats were nearly identical, whereas TBCs with VPS NiCoCrAlYHfSi bond coats displayed a slightly higher rate after 100 cycles (Fig. 2).
Fig. 2 Representative weight change curves from cyclic oxidation testing (at 1150 °C) of bare René N5 substrates and the four types of TBC specimens with various MCrAlX bond coats (coated with YSZ) on René N5 substrates. Note that only one face of the TBC specimens was coated.
本文由桑尧热喷涂网收集整理。本站文章未经允许不得转载；如欲转载请注明出处，北京桑尧科技开发有限公司网址：http://www.sunspraying.com/
|
