Process for producing a protective chromium layer

Abstract

Process for producing a gastight and crack-free protective chromium layer for substrates composed of iron- and nickel- and titanium-based alloys by means of plasma spraying, where the chromium content in the finished layer is at least 70% by weight and a spray powder composed of three components, namely a first component composed of finely particulate chromium powder, a second composed of finely particulate powder of a nickel-based alloy and a third composed of coarsely particulate cristobalite or quartz powder as support for the first and second component, is selected.

1 . A process for producing a gas-tight and crack-free protective chromium layer for substrates of alloys based on iron and nickel and titanium by plasma spraying, wherein a spray powder is selected from three components, a first component of fine-grained chromium powder, a second component for improvement of the mechanical characteristics of the protective layer of fine-grained powder of a nickel-base alloy and a third component for improvement of the coefficients of thermal expansion of the protective layer of coarse-grained cristobalite or quartz powder as carrier for the first and second components, and wherein the chromium content in the formed protective layer is at least 70 wt %, the content of the nickel-base alloy is 7-25 wt % and the cristobalite content is 1-5 wt %. 
     
     
         2 . (canceled) 
     
     
         3 . (canceled) 
     
     
         4 . A process according to  claim 1 , characterized by a subsequent heat treatment of the protective layer in air at temperatures higher than 900° C. 
     
     
         5 . A process according to  claim 1 , wherein the thickness of the protective layer is selected up to 1 mm. 
     
     
         6 . The use of a plasma-sprayed protective layer according to  claim 1  on substrates threatened by corrosion from components of internal combustion engines, gas turbines, steam turbines, propulsion-unit compressors or heat exchangers.