Friction and Wear Properties of Al2O3-GdAlO3 (GAP) Amorphous Ceramic Coatings under High Load Capacity

doi:10.15541/jim20250016

Abstract

Abstract:

Key components of aerospace power systems operating under extreme conditions, such as high loads, elevated temperatures, oxygen-rich environments, and wide-temperature-range alternating thermal shocks, impose stringent requirements on material mechanical properties, thermal stability, and oxidation resistance. Conventional thermally sprayed Al₂O₃ coatings, characterized by high hardness, excellent wear resistance, superior oxidation resistance, and good thermal stability, have been widely applied to aerospace, energy, and mechanical engineering fields. However, these coatings primarily consist of metastable γ-Al₂O₃ as the dominant crystalline phase, which exhibits inferior mechanical and thermal conductivity properties compared to α-Al₂O₃. This limitation hinders their effectiveness under extremely high-load conditions. To address this issue and enhance the overall coating performance, atmospheric plasma spraying (APS) was employed to fabricate Al₂O₃-GdAlO₃ (GAP) amorphous coating with a thickness of approximately 350 µm. The friction and wear behavior, along with the mechanical properties of the coating, were systematically investigated through a designed wear test under a load of 2000 N, a rotational speed of 500 r/min, and a duration of 1 h. Experimental results indicate that due to the high proportion of the amorphous phase and the optimized microstructure, the Al₂O₃-GAP coating exhibits excellent wear resistance and superior crack propagation resistance under high-speed and heavy-load friction conditions, significantly outperforming conventional polycrystalline Al₂O₃ coatings. Furthermore, the Al₂O₃-GAP coating demonstrates a lower and more stable friction coefficient, effectively reducing frictional surface temperature. This mitigates high-temperature oxidation and thermal damage while alleviating stress concentration effects. In summary, the Al₂O₃-GAP amorphous coating demonstrates remarkable advantages under high-load, high-speed friction conditions, providing a high-performance and reliable coating solution for the protection of critical aerospace power system components.

Key words: atmospheric plasma spraying, Al₂O₃-GdAlO₃(GAP), amorphous ceramic coating, high-load wear resistance

CLC Number:

TQ174

AI Yizhaotong, REN Jiulong, QIANG Linya, ZHANG Xiaozhen, YANG Kai, GAO Yanfeng. Friction and Wear Properties of Al₂O₃-GdAlO₃ (GAP) Amorphous Ceramic Coatings under High Load Capacity[J]. Journal of Inorganic Materials, 2025, 40(10): 1111-1118.

Figures/Tables 11

Table 1 Spray coating parameters for NiCr bondcoat and Al2O3-GAP ceramic topcoat

Sample	Arc current/A	Primary plasma gas (Ar)/slpm	Secondary plasma gas (Ar)/slpm	Power/ kW	Carrier gas (Ar)/slpm	Powder feed rate/(g·min^-1)	Spray distance/cm
NiCr bondcoat	590-610	55-60	7.5-8.0	40-50	3.5	10	120
Al₂O₃-GAP topcoat	640-660	45-50	8.5-9.0	45-50	4.0	30	110

Fig. 1 Schematic diagram of the principle of the friction and wear test

Fig. 2 Morphologies of different powder samples (a, b) SEM images of Al2O3 spray powder prepared by the melting and crushing method; (c, d) TEM images of mixed powder composed of nanoscale or submicron Al2O3 and Gd2O3 raw materials; (e, f) SEM images of sprayed Al2O3/Gd2O3 powder after heat treatment at 900 ℃

Fig. 3 XRD patterns of the feedstock and as-sprayed Al2O3-GAP amorphous coating

Fig. 4 Morphology and EDS analysis of as-sprayed Al2O3-GAP amorphous coating (a, b) Surface morphology of the coating; (c, d) Cross-sectional morphology of the coating; (e, f) EDS elemental analysis of the coating

Fig. 5 Coefficients of friction (a) and wear surface temperatures (b) of sprayed Al2O3 coating and Al2O3-GAP amorphous coating under conditions of 2000 N@500 r/min

Table 2 Coefficients of friction and wear surface temperatures of Al2O3 and Al2O3-GAP coatings

Coating system	Coefficient of friction			Wear surface temperature/℃
Coating system	Average	Maximum	Minimum	Average	Maximum
Al₂O₃	0.236	0.305	0.127	513.14	553.80
Al₂O₃-GAP	0.146	0.213	0.067	438.54	464.20

Fig. 6 Wear surface morphology and EDS analysis of Al2O3 coating under conditions of 2000 N@500 r/min (a) SEM image of the overall worn surface of coating wear ring; (b) Magnified view of a worn region in (a); (c, d) EDS elemental analysis

Fig. 7 Wear surface morphology of Al2O3-GAP amorphous coating under conditions of 2000 N@500 r/min (a) A typical wear scar region of the coating; (b) Magnified view of an abrasive wear characteristic region selected from (a); (c) Magnified view of a typical dark ‘scratch’ region selected from (b); (d) Further magnified view of the region in (c)

Fig. 8 Morphology and EDS analysis of wear debris from Al2O3-GAP/graphite under conditions of 2000 N@500 r/min (a-c) SEM images of wear debris with different sizes and shapes; (d) EDS elemental analysis of the wear debris in (c)

Fig. 9 3D stress maps of Al2O3 coating and Al2O3-GAP coating before and after wear under conditions of 2000 N@500 r/min

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Friction and Wear Properties of Al₂O₃-GdAlO₃ (GAP) Amorphous Ceramic Coatings under High Load Capacity

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