Improving oxidation resistance of Ti3Al and TiAl intermetallic compounds with electro-spark deposit coatings

Aluminide coatings were directly applied onto Ti3Al and TiAl intermetallic compounds using a simple but effective method-electro-spark deposition (ESD). The coating has a typical thickness of 15-20 mum, with gradient composition and metallurgical bonding to the substrate. Isothermal oxidation tests in air at 800 and 900 degreesC for the time period up to 300 h showed that all coated specimens had much lower oxidation rates than uncoated samples. Furthermore, all coated samples exhibited excellent oxide scale spallation resistance. SEM and XRD analysis indicated that on the coated specimens the oxide scales consisted mainly of dense alumina or alumina with rutile, while on the uncoated samples rutile is the main oxidation product. It was clear that the changes in the oxide nature and microstructure played a critical role in decreasing the oxidation rate and improving the scale spallation resistance. (C) 2002 Elsevier Science B.V. All rights reserved.