A process for coating a part by chemical vapor diffusion is provided and includes placing a powder mixture in a chamber, immersing the part partially in the powder mixture, and applying a heat treatment to the part. The powder mixture includes a first component and a second component forming a gaseous compound during the heat treatment so as to allow deposition of the second component on the part. The part includes a metal refractory allow and the second component forms a solid diffusion alloy by solid diffusion with a metal species of the refractory metal alloy to generate a coating. The solid diffusion allow generates a passivating oxide layer when subjected to oxidizing conditions.