Aluminum-chromium diffusion coating
A process includes applying a slurry to a surface of a metallic article to produce a slurry film on the surface. The slurry is composed of a liquid carrier, chromium and aluminum, and an agent that is reactive with the chromium and aluminum to form intermediary compounds. The article and slurry film are then thermally treated at an activation temperature at which the agent reacts with the chromium and aluminum to form the intermediary compounds. The intermediary compounds deposit the chromium and aluminum on the surface. The thermal treating also diffuses the chromium and aluminum into a sub-surface region of the article such that the sub-surface region becomes enriched with chromium and aluminum.
1. A slurry for use in a process to coat an article, the slurry comprising:
a liquid carrier;
chromium-aluminum alloy particles that have a composition, by weight, of 5% to 10% aluminum and 95% to 90% chromium; and
an agent that is reactive at an activation temperature with the chromium and aluminum to form intermediary compounds.
2. The slurry as recited in claim 1 , wherein the agent is a halide.
3. The slurry as recited in claim 2 , wherein the halide is selected from the group consisting of ammonium chloride, chromium chloride, ammonium fluoride, and combinations thereof.
4. The slurry as recited in claim 3 , further comprising an additive that has yttrium.
5. The slurry as recited in claim 3 , further comprising an additive that has hafnium.
6. The slurry as recited in claim 3 , further comprising an additive selected from the group consisting of yttrium, hafnium, silica, mullite, alumina, and mixtures thereof.