Abstract
Corrosion on turbine blades in calcium magnesium alumino-silicate (CMAS) environment is a crucial failure for turbine engines and its components. In this study, oxide-oxide (O-O) ceramic matrix composites (CMCs) (AS-N610), the potential materials for gas turbine components are examined for its corrosion behaviour at high temperature at various intervals of time in presence of CMAS. The corrosion studies indicated that dip coated CMAS revealed a weight gain of ∼3% owing to formation of α-Al2O3 at 1400 °C. The SE images indicated cracks at the interface due to thermal mismatch between CMAS and O-O substrate. With increase in corrosion time, cracks at the interface propagated onto the matrix and fibres of O-O CMCs. This crack propagation is attributed to the diffusion of calcium aluminosilicate (CAS) with small traces of Mg which wicks the columns of O-O CMCs. Indentation fracture toughness of O-O CMCs degraded by ∼22% for 1400 °C in presence of CMAS compared to un-corroded sample.
| Original language | English |
|---|---|
| Pages (from-to) | 1214-1219 |
| Number of pages | 6 |
| Journal | Ceramics International |
| Volume | 50 |
| Issue number | 1 |
| Early online date | 23 Oct 2023 |
| DOIs | |
| Publication status | Published - 1 Jan 2024 |
Bibliographical note
© 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).Funder
The microstructural observation of the CMAS coated O-O CMCs is illustrated in Fig. 3. From Fig. 3, it could be observed that CMAS attained its transitional glassy temperature state at ∼800 °C which led to melting of CMAS onto the porous structures as well as phase changes at 1200 °C and 1400 °C at 10 h with small amount of CMAS layer deposition on the surfaces of the O-O CMCs. This could have been due to the adherence between the substrates and CMAS during the heat treatment. On the other hand, in Fig. 4(b) cracks were observed on the intermediate region between CMCs and CMAS surfaces which could have been due to the thermal mismatch between the two different materials which led to continuous crack propagation throughout the surface of CMAS [32]. The EDS on the spots A and B marked in Fig (4) supported the evidence of CMAS on the surfaces with elemental compositions corresponding towards calcium (26.43 wt%), aluminium (16.24 wt%), silicon (8.16 wt%) and oxygen (39.24 wt%).Further, microstructural evaluation on the CMAS coatings indicated delamination layers at 1200 °C/5 h propagating inwards towards the matrices as illustrated in Fig. 4(a). This crack propagation on the surface of coatings could be due to release of the in-plane stain energy [33]. Further, crack propagation could also be caused due to thermal mismatch between the CMAS (∼10.25 × 10-6 K-1) and O-O CMC (8 × 10-6 K-1) substrate as illustrated in Fig. 4(b). Fig. 4(c) represents the crack propagation from CMAS onto the matrices and fibres of substrate at 1400 °C/10 h. This could have been the reason at high temperature when the CMAS melts which may lead to wicks in the matrices of the columns of the porous CMCs leading to failure. The crack on the surfaces of matrices propagates to fibers of the O-O CMCs which may be due to stress transfer mechanism between the matrix and reinforcements [34]. The elemental distribution of the CMAS corroded oxide CMCs are reported in Table 3 which showcases presence of CMAS on the surface of oxide CMC substrate in both spots A and spot B. With increase in the holding duration, CMAS melted and penetrated the O-O substrate with presence of calcium aluminosilicate (CAS) with small quantity of Mg on the surfaces. The presence of CAS supports the damage/degradation which may take place on the O-O CMCs. However, black pigmentation of the CAS with small Mg quantity was not noticed on the surfaces of the O-O CMCs as reported in previous research works [21,25].Authors Karthikeyan Ramachandran would like to acknowledge Kingston University, United Kingdom for support towards his PhD research. Authors would also acknowledge the thank Senior Technicians in Kingston University, Mr. Dean Wells and Mr. Simon Crust for their support in experimental and characterisation proceduresKeywords
- CMAS
- Corrosion behaviour
- Dip coatings
- Fracture Toughness
- Oxide-oxide CMCs
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Materials Chemistry
- Surfaces, Coatings and Films
- Process Chemistry and Technology