Preparation and Performance of an Abradable NiCrFeAlBN-YSZ-NiCrAl Layered Seal Coating for Aircraft Engines
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Preparation and Performance of an Abradable NiCrFeAlBNYSZ-NiCrAl Layered Seal Coating for Aircraft Engines Xuying Cheng1,2 • Yueguang Yu1,2 • Deming Zhang2 • Tong Liu2 • Jianming Liu1,2 Jie Shen2
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Submitted: 18 January 2020 / in revised form: 11 July 2020 Ó ASM International 2020
Abstract Ti2AlNb alloys are often used to fabricate highpressure compressor blades and casings in aircraft engines with high thrust/weight ratios. In this study, a three-layered seal coating, NiCrFeAlBN-YSZ-NiCrAl, was prepared by thermal spraying on a titanium alloy (Ti2AlNb) substrate. The microstructure, surface hardness, and bond strength of coatings as well as their thermal cycling performance and abradability under simulated working conditions were investigated. The coating surface hardness was 61 HR15Y and the bond strength was 7.13 MPa. The coating maintained a good bonding to the substrate with no cracks after 40 cycles of water-cooling from 750 °C to room temperature. The abradability of the as-sprayed coating and the coating heat-treated at 750 °C for 200 h was tested against a Ti2AlNb blade at 750 °C, with a tip line speed of 300 m/ s, and feed rates of 5, 50 and 480 m/s. The coating wear mechanisms involved micro-ruptures. The Cr2O3 phase formation and a decrease in the number of micropores in the heat-treated coating decreased its abradability. Keywords aircraft engine abradable coating abradability layered coating seal coating Ti2AlNb
& Xuying Cheng [email protected] 1
Northeastern University, Shenyang 110819, China
2
Beijing General Research Institute of Mining and Metallurgy, Beijing 100160, China
Introduction The performance of the most recent generation of aircraft engines has been improved by increasing their thrust and reducing their weight, i.e., increasing the thrust/weight ratio. The materials used for compressor parts are typically high-temperature-resistant titanium alloys, particularly Ti2AlNb, an intermetallic alloy that maintains good oxidation resistance at 700 °C (Ref 1, 2). This lightweight titanium alloy shows the same high-temperature resistance as many of the heat-resistant steels and super-alloys currently in use; however, its wear resistance is worse due to the lower hardness of Ti2AlNb (HV290-400) (Ref 3). Therefore, new Ti2AlNb casings and blades require the development of new coatings. The coating applied to the rubbing surface of stationary parts of a compressor should act as a sacrificial layer to reduce the blade-tip clearance by allowing the Ti2AlNb blade to scratch the coating. This will improve the dynamic sealing between rotating and stationary components, and will thus improve engine efficiency and reduce fuel consumption (Ref 4-7). The coating should prevent the blade tip from damage when the rotating blade tip rubs against the stationary casing (i.e., good abradability), while withstanding erosion by high-speed gas flow and solid particles in hot gases above 700 °C (i.e., good erosion resistance) (Ref 5, 8). As shown in the technical reports of Oerliko
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