Process for protecting alloys which are resistant when hot, especially nickel-based

摘要

The process for deposition of a protective coating on a substrate made of alloy which is resistant when hot comprises a first stage of chromium enrichment of the surface region of the substrate by gas phase diffusion without contact of the solid-solid type and a second stage of gas phase aluminising at low activity also without solid-solid contact. The operating conditions, additionally comprising temperatures between 1000 DEG C and 1200 DEG C and times of between 1 and 5 hours, permit the formation of an internal layer of aluminide of nickel alloyed with chromium and with other elements of the substrate by diffusion of aluminium into the nickel and an outer layer of pure and homogeneous nickel aluminide by extraction of the nickel towards the aluminium. These conditions avoid, at all stages, the formation of alpha phase in the chromium-enriched layer and then in the inner layer during the diffusion of the aluminium and also during the extraction of the nickel from this layer.