High temperature abradable sealing coating for SiCf/SiC ceramic matrix composites

Isothermal Oxidation and Thermal Shock Resistance of Thick and Porous LaMgAl11O19 Abradable Topcoat

“…The macroscopic photographs of coated samples after heat treatment at 1200 • C (LMA-0) and isothermal oxidation at 1300 • C (LMA-10, LMA-100, and LMA-200) are shown in Figure 4. No obvious cracking phenomena were observed on the front surfaces of any of the coated samples, but a few horizontal cracks appeared at the chamfered edges, which was caused by stress concentration [26]. Due to the purpose of over-spray in the APS process, one side surface of the coated sample was also slightly covered by the loose coating, which is clearly visible from the side view of the LMA-0 sample, while the other side surface was not covered due to the presence of the fixture used to hold the sample in place during spraying (not shown).…”

“…On the one hand, cracks tend to propagate along the path of the least resistance (porosity); on the other hand, this is related to the excellent mechanical properties of YbMS itself, which has higher stress tolerance [42,43]. This crack deflection acts as a toughening mechanism to reduce the risk of damage to the interlayer from thick topcoats with higher stress levels [26,44]. Compared with heat treatment at 1200 • C, the microstructure of the porous LMA topcoat remained almost unchanged after isothermal oxidation at 1300 • C, as shown in Figure 9a -c .…”

“…After the prolonged isothermal oxidation, there was no significant increase in the opening displacement or propagation of the mud cracks in the YbMS layer, and the cracks terminated within the YbMS layer and did not propagate further into the Si + YbDS layer. This is mainly attributed to the relatively good thermal expansion matching between the underlayers [26]. In addition, due to the lower CTE of Si than that of SiC/SiC substrate, the compression in the Si regions can prevent the cracks from extending downward.…”

“…However, a crucial aspect that should not be overlooked is the thermal shock resistance and chemical compatibility of the ceramic abradables with the corresponding seal substrates applied to the turbine stage at the service temperature, as this may cause the premature failure of the ceramic abradables [20][21][22][23][24]. Additionally, leveraging the concept of thermal environmental barrier coatings (TEBCs) and incorporating a fugitive phase (polyester) makes the TBC topcoat porous, which is expected to not only enhance thermal insulation but also improve abradability [25,26].…”

Evolution of the Microstructure and Mechanical Performance of As-Sprayed and Annealed Silicon Coating on Melt-Infiltrated Silicon Carbide Composites

“…A Yb 2 SiO 5 /mullite/Si tri-layer EBC was coated on CMC substrates via APS by Yang et al [ 16 ], and the bond strength between the Si layer and CMC was 12.28 MPa. Huang et al [ 17 ] reported a bond strength of about 5.0 MPa because of the failure of CMC substrates. Niu et al [ 18 ] obtained a higher Si bonding of 20.6 MPa using vacuum plasma spraying technology, but a Ti-6Al4V alloy was adopted as the substrate in the study.…”