Relationships between Microstructural and Mechanical Properties of Plasma Sprayed AlSi-Polyester Composite Coatings: Application to Abradable Materials

Abstract

Abradable coatings are widely used within aeroengines. These materials are applied onto the inner surface of compressor and turbine shroud sections using thermal spray processes, coating the periphery of the blade rotation path. The functionality of an abradable seal is to wear preferentially when rotating blades come into contact with it, while minimizing the over-tip clearance, and improving the overall efficiency of the engine. This study is concerned with the relationships between the microstructure and mechanical properties of atmospheric plasma sprayed AlSi-Polyester composite coatings.

Application of FEM to Estimate Thermo-Mechanical Properties of Plasma Sprayed Composite Coatings

“…The reader is thus informed that the mechanical properties shown in Table 4 represent an upper limit. However, the experimental result reported in [22] (i.e., 7 GPa measured with a bending test) is only slightly below the calculated value of E x (7.6 GPa as shown in Table 4), so the data may be considered as consistent. The strategy applied in future works will implement a two-magnification level method for this type of application (i.e., the case of composite coatings).…”

“…The material selected as a "test case" in this work was an AlSi/polyester composite coating [10,21,22]. This material is widely used as an abradable seal in aeroengines, in the low temperature range (<325 • C, i.e., compressor section only).…”

“…The case of EKONOL polyester (not so different from XYDAR, another polyester used in abradable coatings) is a little trickier so that the considered references are provided. [23] 59 [24] 1440 [24] * From NHT measurements performed on coatings [22]. Figure 1 presents a view of the coating microstructure (M601 powder) at low magnification level (i.e., about 3 µm/pixel) [10,21].…”

“…As shown is Table 3, no lowering factor was applied to the mechanical properties of the coating phases (as suggested for example in the works of Faraoun [8]), meaning that the white pixels on Figure 2 have similar properties in comparison with dense AlSi and that grey pixels have the mechanical properties of dense polyester in the coating (Young's modulus measured at 3.5 GPa from NHT measurements [22]). In reality, this assumption is not fully valid, especially for the AlSi phase due to the presence of a small-scale pore network observable at higher magnification level only (i.e., by SEM for example).…”

An Inverse Analysis Method for Determining Abradable Constitutive Properties

“…The obtained material values were then assigned to the 2D geometry, and a tensile test conducted to find the homogenised Young's Modulus and Poisson's ratio. Similarly, Duramou et al [12] used a finite element (FE) model to determine a relationship between the microstructure of atmospheric plasma sprayed AlSi-PES and its mechanical properties. Nano-Hardness Tests (NHT) were conducted to determine the Young's Modulus for both the AlSi and PES phases.…”