Formation and evolution of phosphorus-containing species during high-temperature oxidation of TiAl dipped in a low-concentrated phosphoric acid solution

✍ Scribed by S.Y. Brou; G. Bonnet; J.L. Grosseau-Poussard

• Book ID: 104094446
• Publisher: Elsevier Science
• Year: 2009
• Tongue: English
• Weight: 899 KB
• Volume: 203
• Category: Article
• ISSN: 0257-8972
• DOI: 10.1016/j.surfcoat.2008.10.009

✦ Synopsis

TiAl samples were dipped in a low-concentrated phosphoric acid solution, air dried, then heated to 800 °C under argon gas before oxidation under reconstituted air at this temperature. At the end of the heating ramp, sample surfaces were covered by a titanium pyrophosphate (TiP 2 O 7 ) layer, well adhered to the substrate. This pyrophosphate was shown to be detectable from 400 °C. Chemical reactions have been proposed for the formation of this compound. TiP 2 O 7 coating strongly increased the oxidation resistance of TiAl at 800 °C for 100 h. After 100 h, a transition period occurred leading to the change of TiP 2 O 7 into TiO 2 , which was achieved after 230 h, total mass gain always remaining below that of raw substrate. This evolution was demonstrated not resulting from a thermal decomposition of pyrophosphate compound.