Coatings for turbine blades

A process for coating an external and an internal surface of a turbine blade or vane with aluminium and chromium, respectively, at substantially the same time comprising the following steps (i) and (ii) in either order:

• (i) applying to the external surface an aluminising compound comprising aluminium, a moderator, an energiser and a diluent by immersing the blade or vane in the aluminising compound, where the aluminising compound comprises 3-20 wt % aluminium, 10-50 wt % moderator, 0.1-2 wt % energiser and at least 20 wt % diluent, and the weight ratio of aluminium to moderator is from 1:2 to 1:5;
• (ii) applying to the internal surface a chromising compound comprising chromium, an energiser and a diluent, wherein the chromising compound comprises 15-65 wt % chromium, 0.1-5 wt % energizer and at least 20 wt % diluent, and the weight ratio of aluminium to moderator is from 1:2 to 1:5;
• followed by:
• (iii) heating the turbine blade or vane to form an aluminium layer on the external surface and a chromium layer on the internal surface.