Coating for refractory alloy part

A process comprising:

• coating a part by chemical vapor diffusion;
• placing a powder mixture in a chamber,
• the powder mixture comprising at least one first component, at least one second component and an inert component;
• the powder mixture including a mass proportion comprised between 6 and 8% of the first component and between 8 and 12% of the second component;
• the first component comprising at least one halide species selected from NH4Cl, NH4F, AlCl3, CrCl2;
• the second component comprising at least one species selected from silicon, aluminum, iron, copper, cobalt, nickel, lanthanum, germanium, zirconium, chromium, titanium, hafnium, rhenium and a mixture thereof;
• immersing the part at least partially in the powder mixture,
• the part comprising a metal refractory alloy,
• the metal refractory alloy comprising molybdenum;
• and
• heat treating the part, the first component and the second component forming a gaseous compound during the heat treating step so as to allow deposition of the second component on the part;
• the second component forming a solid diffusion alloy by solid diffusion with at least one metal species of the metal refractory alloy so as to generate a coating;
• the solid diffusion alloy generating a passivating oxide layer when subjected to oxidizing conditions;
• wherein the process produces a coating on the part, the coating comprising a plurality of superimposed layers;
• the superimposed layers comprising:
• a first layer having a thickness comprised between 0.1 μm and 30 μm, a molar fraction of the second component in the first layer being comprised between 0 and 50%,
• a second layer covering the first layer and having a thickness comprised between 1 μm and 50 μm, the second layer having a molar fraction of the second component less than 2%;
• a third layer covering the second layer and having a thickness comprised between 0.5 μm and 50 μm, the third layer having a molar fraction of the second component comprised between 60 and 70%.