In this paper, an attempt is made to investigate the performance of Al-SI/40 polyester abradable coating under the sliding condition. The abradable coating is produced by using a High Velocity Oxygen Fuel (HVOF) thermal spray process. The specimen preparation and the experimentation are carried out according to the ASTM G99 standards. Wear tests are performed using a pin-on-disc type wear tester within the load range 20-70 N, sliding speed range 0.2-2 m/s and sliding distance 1000-5000m. Splat tips on the contact surface are responsible for high wear rates at low speeds and high loads. Wear rates of the coating decreased with increasing sliding speed and increased with increasing load. The optimum combination of parameters and their levels for obtaining minimum wear rate are also found using Design of Experiment (DOE) technique. The obtained results are shown in the form of graphs describing how the wear rate of the coating occurs. Further, in order to analyze the percentage contribution of different wears parameters, ANOVA is used. The results show that the sliding speed has the highest influence, i.e., 70.92%, and the load has 28.45% of contribution on the wear behavior.

The gap between the rotating blades and the casing should be small in order to increase the efficiency and reduce the fuel consumption of an aircraft turbine engine (Demasi, 1994). The thermal sprayed abradable seal coating has been used because it is a simple process, the components are easy to repair, and has good sealing effectiveness (Novinski, 1991). In application, it is required that the rotor blades scrape the coating to form a minimum gap. So the coating should be not only soft enough to be easily scraped without damaging the blades but also hard enough to resist against the erosion by the high speed solid particles in the gas (Maozhong et al., 1999). To reduce the gap between the rotating blades and the casing, the air can be transferred to the compressor as efficiently as possible to provide thrust and reduce fuel consumption (Ghasripoor et al., 1997). The coating is mostly composed of metal phase and self-lubricating nonmetal phase with high porosity (Oka, 1990). Coddet et al. (2000) found that the clearance reduction between blades and seals can result in 2.5% improvement in thrust-specific fuel consumption. Brandt (1995) showed that the High Velocity Oxygen Fuel (HVOF) process with porosity levels of less than 1% behaves like a homogeneous material with improved ductility. The thermal spray coating process is one of the most successful of all the advanced coating techniques because of the wide range of coating materials and substrates to which it can be applied. Thermally sprayed coatings are used to protect components from different types of wear and corrosion (Mareceau et al., 1995). In this paper, the sliding wear behavior of Al-Si/40 polyester thermal spray coatings deposited on Al alloy substrates using a HVOF spraying process is investigated at different operating parameters.

Mechanical Engineering Journal, Thermal spray process, HVOF, Sliding wear, Abradability.