| 摘要 |
<p>Coating molybdenum (or its alloys) with a "thick" (normally over 5 mils) coating of a nickel-silicon-boron alloy powder of minus 200 mesh by flame spraying and heat treating the coated article. The base metal is cleaned by electro-polishing and grit blasted to a dull matte finish. The final hardness is desirably not greater than 40 Rockwell C. Preferably the spraying is done with a reducing flame. The heat treatment (preferably in a reducing atmosphere such as dry hydrogen) normally has three stages:-preheat below the fusing temperature of the sprayed coating (e.g. at 1500 DEG -1900 DEG F.) during which partial sintering occurs; fusing at a temperature no cooler than the fusing temperature of the alloy used (about 2100 DEG F.); and cooling off. An irregularly shaped object is rotated during heat treatment. The process is applicable to flat sheets or irregularly shaped objects (e.g. gas turbine buckets). In addition to nickel the coating alloy contains 2.5-4 per cent silicon, 1.5-2.2 per cent boron and 0.05-0.1 per cent carbon.</p> |
