Method of coating metallic surfaces with layers of nickel-chromium and aluminum

Claim 1

A PROCESS FOR APPLYING A COATING ON AT LEAST A PORTION OF A METALLIC SURFACE, SAID METALLIC SURFACE BEING SUFFICIENTLY RESISTANT TO CORROSION THAT SUBSTANTIALLY NO OXIDE WILL FORM THEREON DURING THE PERIOD REQUIRED TO RAPIDLY HEAT SAID SURFACE IN AIR TO A TEMPERATURE IN THE RANGE OF ABOUT 1300 TO ABOUT 1800*F., COMPRISING THE STEPS OF PREHEATING SAID SURFACE IN AIR TO A TEMPERATURE IN THE RANGE OF ABOUT 1300 TO ABOUT 1800*F., METAL SPRAYING AT LEAST A PORTION OF THE METALLURGICALLY CLEAN PREHEATED SURFACE WITH AN ALLOY CONTAINING AT LEAST 90 WEIGHT PERCENT OF THE ELEMENTS NICKEL AND CHROMIUM, SAID NICKEL CONTENT RANGING FROM ABOUT 97 TO ABOUT 70 WEIGHT PERCENT, SAID CHROMIUM CONTENT RANGING FROM ABOUT 3 TO ABOUT 30 WEIGHT PERCENT, HEATING SAID COATED SURFACE TO A TEMPERATURE IN THE RANGE OF ABOUT 1800 TO ABOUT 2250*F. FOR A PERIOD OF TIME SUFFICIENT TO INTERDIFFUSE AND ALLOY SAID COATING WITH SAID METALLIC SURFACE THEREBY TENACIOUSLY BONDING SAID COATING TO SAID SURFACE, APPLYING A COATING COMPRISED PREDOMINANTLY OF ALUMINUM OVER SAID BONDED NICKEL CHROMIUM ALLOY COATING, HEATING SAID COATED SURFACE TO A TEMPERATURE IN THE RANGE OF ABOUT 1500 TO ABOUT 2100*F. FOR A PERIOD OF FROM A FEW SECONDS TO ABOUT FIVE MINUTES AND FORMING THEREBY A HARD, INTERDIFFUSED ALLOY LAYER COMPRISED PREDOMINANTLY OF ALUMINUM, NICKEL AND CHROMIUM.