Effect of Vacuum Annealing on Microstructure and Hot-Salt Corrosion Behavior of CoNiCrAlY/YSZ/LaMgAl11O19 Double-Ceramic Coating

Abstract

This study investigated the potential effect of vacuum annealing on the microstructure and hot salt corrosion behavior of CoNiCrAlY/YSZ/LaMgAl11O19 (LMA) double-ceramic coatings. A hot-salt corrosion test revealed that sprayed coatings exhibited an unsatisfactory anti-corrosion performance, and the LMA layer underwent severe fracture and corrosion degradation. Vacuum annealing induced a prominent recrystallization of the amorphous phase in LMA layer, triggering severe volume shrinkage and microcrack initiation. The recrystallization and volume shrinkage of the LMA layer were aggravated by an increase in the annealing temperature. The annealed coating with a higher fraction of the LaMA phase showed superior resistance to hot-salt corrosion. However, the salt mixture diffused simultaneously along the microcracks and eventually eroded into the YSZ layer. These results confirmed that vacuum annealing significantly enhanced the hot-salt corrosion resistance of the LMA layer. However, it deteriorated the barrier effect of the salt mixture through microcrack formation.

Enhanced structural stability of yttria‐stabilized zirconia–LaMgAl11O19 dual ceramic coating by an α‐Al2O3 layer

“…Figure 5 shows the XRD characterization results of all coatings after the oxidation tests at 1000°C. As displayed in Figure 5A, according to the standard cards of 26‐0873 and 43‐0923, sample Y1 is mainly composed of LaMA phases, but the intensities of LaMA phases gradually increase with the increase of oxidation time, indicating an accelerated crystallization reaction 18 . Meanwhile, a small amount of LaAlO 3 phase appears in the XRD pattern, which likely originates from high temperature decomposition of LaMA phase.…”

“…The mass gain value of sample Y2 is .530 mg/cm 2 , which was much lower Figure 5 shows the XRD characterization results of all coatings after the oxidation tests at 1000 • C. As displayed in Figure 5A, according to the standard cards of 26-0873 and 43-0923, sample Y1 is mainly composed of LaMA phases, but the intensities of LaMA phases gradually increase with the increase of oxidation time, indicating an accelerated crystallization reaction. 18 Meanwhile, a small amount of LaAlO 3 phase appears in the XRD pattern, which likely originates from high temperature decomposition of LaMA phase. As shown in Figure 5B, LaMA and LaAlO 3 phases are also identified in sample Y2, but a large amount of α-Al 2 O 3 phase (PDF46-1212) is detected in this XRD pattern, confirming that an in situ α-Al 2 O 3 reaction film forms on the top LaMA layer.…”

Understanding the Enhanced Protective Mechanism of CoCrNiAlY–YSZ–LaMgAl11O19 Double-Ceramic Coating with Aluminum Plating

“…We found in previous research that the CoCrNiAlY-YSZ-LaMgAl 11 O 19 double ceramic coating provides a significant improvement in the thermal corrosion resistance of the coating at a high temperature of 1200 • C, but the volume shrinkage of the coating leads to the initiation of a large number of microcracks. These microcracks act as oxidation diffusion channels, leading to the deterioration of the barrier effect of the coating [14]. To improve the oxidation resistance of the CoCrNiAlY-YSZ-LaMgAl 11 O 19 coating, we developed a new type of arc aluminum plating process.…”