Query: Calcium–Magnesium–Alumina–Silicate

title: Hot corrosion behavior and wettability of calcium magnesium alumina silicate (CMAS) on LaTi2Al9O19 ceramic
abstract: The development of thermal barrier coating (TBC) has been limited by the calcium magnesium alumina silicate (CMAS) corrosion. In this work, a promising CMAS resisted LaTi2Al9O19 (LTA) rich in Ti and Al is proposed. CMAS corrosion behavior of LTA ceramics is investigated at a temperature range of 1200 degC 1300 degC. By combining the experimental results and thermodynamics analysis, Ca and Si are arrested effectively by formation of CaAl2Si2O8 layer and (Ca,La0.7)(Ti,Al)O3 to prevent CMAS from moving downward. Meanwhile, the contact angle of CMAS on LTA is larger than that of YSZ, contributing to the CMAS resistance.

title: Thermal properties and Calcium Magnesium Alumina Silicate (CMAS) resistance of LuPO4 as environmental barrier coatings
abstract: LuPO4 ceramics have been synthesized by chemical precipitation and calcination approaches. The phase stability and the thermal properties of the ceramics as well as the thermochemical reactions between LuPO4 pellet and calcium magnesium alumina silicate at 1300 have been investigated. The results indicated that LuPO4 has a relatively lower thermal conductivity (1.86 W m 1 K 1 at 1200 and a well matched coefficient of thermal expansion (5.92 x 10 6 K 1) with SiC based ceramic matrix composites. No phase transformation occurs in single phase LuPO4 during the heating from room temperature to 1300 Corrosion tests showed that CMAS can dissolve LuPO4 and cause precipitation of crystalline phases such as Lu2Si2O7, CaAl2Si2O8, CaMgSi2O6, Ca2Lu8 (SiO4)6O2 and Ca8MgLu (PO4)7. Extending the corrosion duration results in the formation of Ca2Lu8 (SiO4)6O2 apatite and other crystalline phases with a dendritic like structure in the CMAS layer. CMAS corrosion resistance of LuPO4 is significantly greater than Lu2Si2O7 since less LuPO4 need to be dissolved to form a protective apatite barrier layer. Ca8MgLu (PO4)7 tends to form a continuous reaction layer at the CMAS/LuPO4 interface. This dense and continuous layer can effectively inhibit molten CMAS penetration into LuPO4.

title: Calcium magnesium alumina silicate (CMAS) resistance characteristics of LnPO4 (Ln Nd, Sm, Gd) thermal barrier oxides
abstract: Calcium magnesium alumina silicate (CMAS) attack has been considered as a significant failure mechanism for thermal barrier coatings (TBCs) As a promising series of TBC candidates, rare earth phosphates have attracted increasing attention. This work evaluated the resistance characteristics of LnPO4 (Ln Nd, Sm, Gd) compounds to CMAS attack at 1250 degC. Due to the chemical reaction between molten CMAS and LnPO4, a dense, crack free reaction layer, mainly composed of Ca3Ln7(PO4)(SiO4)5O2 apatite, CaAl2Si2O8 and MgAl2O4, was formed on the surface of compounds, which had positive effect on suppressing CMAS infiltration. The depth of CMAS penetration in LnPO4 (Ln Nd, Sm, Gd) decreased in the sequence of NdPO4, SmPO4 and GdPO4. GdPO4 had the best resistance characteristics to CMAS attack among the three compounds. The related mechanism was discussed based on the formation ability of apatite phase caused by the reaction between molten CMAS and LnPO4.

title: Hot corrosion behavior of Y4Al2O9 ceramics for thermal barrier coatings exposed to calcium magnesium alumina silicate at 1250 degC
abstract: The degradation of thermal barrier coatings (TBCs) by calcium magnesium alumina silicate (CMAS) attack has become increasingly dramatic. Y4Al2O9 ceramic, a new potential TBC candidate, has received an increasing attention. In this study, porous Y4Al2O9 ceramic pellets, instead of actual TBCs, are used to investigate the CMAS corrosion resistance at 1250 degC. Results indicate that Y4Al2O9 reacts with CMAS melt to form an impervious sealing layer mainly containing Ca Y Si apatite, which could mitigate CMAS further penetration. Once the sealing layer formed, further reaction would occur above the layer accompanying by the recession of sealing layer. This process is probably related to a solid state diffusion.

title: Corrosion resistant plasma sprayed (Y0.8Gd0.2)3Al5O12/YSZ thermal barrier coatings towards molten calcium magnesium alumina silicate
abstract: Chemical reaction between (Y0.8Gd0.2)3Al5O12 (GYAG) and calcium magnesium alumina silicate (CMAS) with four different compositions was investigated. The GYAG revealed excellent chemical stability with molten CMAS even after 24 h heat treatment at 1250 degC. A GYAG layer was sprayed onto an yttria stabilized zirconia (YSZ) thermal barrier coating (TBC) by plasma spray and the thermal cycling behavior and resistance to CMAS corrosion of the coating system were researched. The GYAG/YSZ TBC system exhibited a lifetime of more than 1500 h during thermal cycling testing at 1100 degC. Also, the GYAG/YSZ TBC has shown good resistance to CMAS corrosion at 1250 degC, mainly due to the chemical stability of GYAG to CMAS and dense lamellar structure of the GYAG layer. In addition, the infiltration of CMAS was further prohibited by the Ca4Y6(SiO4)6O and CaAl2Si2O8 phases generated from the reaction of (Y,Gd)AlO3 phase in the coating with the molten CMAS.

title: Corrosion resistance and thermal mechanical properties of ceramic pellets to molten calcium magnesium alumina silicate (CMAS)
abstract: Because gas turbine engines must operate under increasingly harsh conditions, the degradation of thermal barrier coatings (TBCs) by calcium magnesium alumina silicate (CMAS) is becoming an urgent issue. Mullite (3Al2O3*2SiO2) is considered a potential material for CMAS resistance; however, the performance of mullite in the presence of CMAS is still unclear. In this study, mullite and Al2O3 SiO2 were premixed with yttria stabilized zirconia (YSZ) in different proportions, respectively. Porous ceramic pellets were used to conduct CMAS hot corrosion tests, and the penetration of molten CMAS and its mechanism were investigated. The thermal and mechanical properties of the samples were also characterized. It was found that the introduction of mullite and Al2O3 SiO2 mitigated the penetration of molten CMAS into the pellets owing to the formation of anorthite, especially at 45 wt% mullite/55 wt% YSZ. Compared with Al2O3 SiO2, mullite possesses a higher chemical activity and undergoes a faster reaction with CMAS, thus forming a sealing layer in a short time. Additionally, the thermal expansion coefficient, thermal conductivity, and fracture toughness of different samples were considered to guide the architectural design. Considering the CMAS corrosion resistance, thermal and mechanical performance of TBCs systematically, a TBC system with a multilayer architecture is proposed to provide a theoretical and practical basis for the design and optimization of the TBC microstructure.

title: Preparation of nanostructured Gd2Zr2O7 LaPO4 thermal barrier coatings and their calcium magnesium alumina silicate (CMAS) resistance
abstract: 30 mol% LaPO 4 doped Gd 2 Zr 2 O 7 (Gd 2 Zr 2 O 7 LaPO 4 thermal barrier coatings (TBCs) were produced by air plasma spraying (APS) The coatings consist of Gd 2 Zr 2 O 7 and LaPO 4 phases, with desirable chemical composition and obvious nanozones embedded in the coating microstructure. Calcium magnesium alumina silicate (CMAS) corrosion tests were carried out at 1250 degC for 1 8 h to study the corrosion resistance of the coatings. Results indicated that the nanostructured Gd 2 Zr 2 O 7 LaPO 4 TBCs reveals high resistance to penetration by the CMAS melt. During corrosion tests, an impervious crystalline reaction layer consisting of Gd La P apatite, anorthite, spinel and tetragonal ZrO 2 phases forms on the coating surfaces. The layer is stable at high temperatures and has significant effect on preventing further infiltration of the molten CMAS into the coatings. Furthermore, the porous nanozones could gather the penetrated molten CMAS like as an absorbent, which benefits the CMAS resistance of the coatings.

title: Self crystallization characteristics of calcium magnesium alumina silicate (CMAS) glass under simulated conditions for thermal barrier coating applications
abstract: Understanding self crystallization characteristics of calcium magnesium alumina silicate (CMAS) glass is of great significance for seeking for solution to its corrosion to thermal barrier coatings (TBCs) Here, we design a series of experiments to investigate the relationship between CMAS self crystallization behavior and cooling/heating rates and dwell temperature, and emphasize the potential influence of self crystallization on CMAS corrosion behavior to TBCs. With the cooling rate decreasing, crystalline phases formed in a sequence of diopside, wollastonite and anorthite, and the thickness of the crystalline layer increased. During the heating process, diopside and melilite phases formed when the temperature was lower than 1050 degC; while at higher temperatures, melilite transformed to anorthite and wollastonite, independent on the heating rate. Although self crystallization can slow molten CMAS penetration, the function on protecting TBCs from damage is limited, and other strategies alleviating CMAS corrosion are necessitated to be developed.

title: Improved resistance of lanthanum zirconate coatings to calcium magnesium alumina silicate corrosion through composition tailoring
abstract: Calcium magnesium alumina silicate (CMAS) corrosion resistance is an important issue on the design of next generation thermal battier coatings. As one of the promising thermal battier coatings, the lanthanum zirconate coating has attracted continuous attention. In this work, three lanthanum zirconate coatings with different La/Zr composition, i.e. La1.8Zr2.2O7.1, La2Zr2O7, and La2.5Zr1.5O6.75, are fabricated by laser enhanced chemical vapour deposition, and their resistance to CMAS corrosion at 1250 degC is investigated. Among them, La2.5Zr1.5O6.75 shows the best CMAS corrosion resistance because increased La content is beneficial to the formation of a dense and continuous apatite Ca2La8(SiO4)6O2 layer, which effectively slows down the subsequent molten CMAS penetration. This study clarifies the significant role of rare earth on CMAS corrosion resistance and is expected to guide the future design of rare earth based thermal battier coatings through composition tailoring.

title: Calcium magnesium alumina silicate (CMAS) resistant Ba2REAlO5 (RE Yb, Er, Dy) ceramics for thermal barrier coatings
abstract: Calcium magnesium alumina silicate (CMAS) attack has been a great challenge for the application of thermal barrier coatings (TBCs) in modern turbine engines. In this study, a series of prospective TBC candidate materials, Ba2REAlO5 (RE Yb, Er, Dy) are found to have high resistance to CMAS attack. The rapid formation of a continuous crystalline layer on sample surface contributes to this desirable attribute. At 1250 degC, Ba2REAlO5 dissolve in the molten CMAS, accumulating Ba, RE and Al in the melt, which could trigger the crystallization of celsian, apatite and wollastonite crystals. Especially, the formation of the crystalline layer in the Ba2DyAlO5 sample is the fastest. This study also reveals that Ba is a useful element for altering CMAS composition to precipitate celsian. Thus, doping Ba2+ in yttria partially stabilized zirconia or other novel TBCs might be an attractive way of mitigating CMAS attack.