Changes in the Coating Composition Due to APS Process Conditions for Al₂O₃-Cr₂O₃-TiO₂ Ternary Powder Blends.

Area of Science:

• Materials Science
• Surface Engineering
• Ceramic Coatings

Background:

• Thermally sprayed coatings from Al2O3-Cr2O3-TiO2 systems offer multifunctional properties.
• Ternary compositions are key for enhancing coating performance.
• Compositional stability during spraying is crucial for blended feedstock powders.

Purpose of the Study:

• To investigate compositional changes in a ternary Al2O3-Cr2O3-TiO2 powder blend during atmospheric plasma spraying (APS).
• To understand the influence of varying argon flow rates on coating composition, microstructure, and properties.
• To analyze the role of oxide properties like melting difficulty and thermal diffusivity in compositional stability.

Main Methods:

• Atmospheric plasma spraying (APS) of a ternary blend of Al2O3, Cr2O3, and TiO2 powders.
• Variation of argon flow rate while maintaining a constant hydrogen flow rate.
• Analysis of coating composition (EDS), microstructure (optical microscopy, SEM), phase (XRD), hardness, and electrical impedance.

Main Results:

• Increasing argon flow rate significantly altered coating composition, reducing Al2O3 content to 8 wt.% while Cr2O3 remained stable.
• Stoichiometric TiO2 was formed due to TiO2 oxidation, influenced by the Ar/H2 ratio.
• Limited interactions between large oxide particles were observed, with titanium found in Cr2O3 splats.

Conclusions:

• The chemical composition stability of ternary oxide powder blends during APS is highly sensitive to process conditions, particularly argon flow rate.
• Differences in the difficulty of melting factor and thermal diffusivity of the oxides drive compositional changes.
• Optimizing APS parameters is essential for achieving desired coating compositions and properties from blended feedstocks.