Inconel 718 probes are widely used in aerospace engine combustion chambers, but at 1200°C, their performance degrades without proper coating—alumina (Al??O??) coatings emerge as a critical solution to extend service life and maintain accuracy.Gas Pressure Scanwelcome to click on the website to learn more!
Alumina coatings, applied via plasma spraying, act as a thermal barrier, reducing heat transfer to the Inconel substrate by 40-50%. A thickness of 100-150μm balances insulation and adhesion; thinner coatings (50μm) fail after 200 hours due to thermal fatigue, while thicker ones (200μm) crack from differential expansion. In a combustion chamber test, an uncoated Inconel probe showed oxidation damage after 300 hours at 1200°C, while a 120μm Al??O??-coated probe remained intact for 800+ hours.
Coating porosity is another key parameter. A porosity of 5-8% allows for thermal expansion without cracking, whereas <3% porosity leads to delamination. A scanning electron microscopy (SEM) analysis of failed coatings found that 2% porosity samples had 3x more cracks than 6% porosity ones.
Surface preparation before coating is vital. Sandblasting the Inconel surface to a roughness of Ra 2.0-3.0μm ensures mechanical bonding between the coating and substrate. A smooth surface (Ra < 1.0μm) resulted in coating detachment in 150 hours, highlighting the need for proper pre-treatment.
Post-coating, a sealant (e.g., silicon carbide) fills micro-pores to prevent hot gas ingress. In a turbine test, sealed coatings reduced oxidation under the coating by 70% compared to unsealed ones, further extending probe life. For 1200°C environments, this combination of optimized thickness, porosity, and sealing makes Al??O??-coated Inconel 718 probes the most reliable choice.