Hydrogen permeation resistant glass-ceramic coatings for gamma-titanium aluminide

Hydrogen embrittlement is no doubt a limiting factor in the high performance applications of many intermetallics. This is mainly because of the inward diffusion of hydrogen atoms and formation of brittle hydride phases during hydrogen exposure of the intermetallic components that resulted in lowering the component's ductility and fracture toughness. gamma-TiAl intermetallic is not an exception in this regard. The present study dealt with the method of providing oxide based glass-ceramic coatings on the surface of gamma-TiAl by vitreous enameling technique to protect the substrate from the detrimental effect of hydrogen at high temperatures like 800 degrees C at 0.1 MPa gas pressure for up to 75 It. Results showed that although the uncoated gamma-TiAl alloy was severely affected by the hydrogen exposure test, the coated samples were remained mostly unaffected after the test with minimum changes in their microstructure. While the gain in weight of the uncoated alloy after 75 h of H-2 permeation test was similar to 1.05 mg/cm(2), the weight gain of the two coated samples were only similar to 0.12 mg/cm(2) for BaO-SiO2-MgO and similar to 0.15 mg/cm(2) for MgO-SiO2-TiO2 glass-ceramic coated substrates. As revealed from the XRD phase analysis, after the high temperature exposure of the coated samples in flowing H-2 for up to 75 h, the coated layers were only enriched with their major crystalline phases with little or no trace of the detrimental hydride phases, whereas, in the uncoated alloy, presence of aluminum hydride and titanium hydrides were observed. (C) 2009 Elsevier B.V. All rights reserved.