Method of forming a protective coating on molybdenum

Claim 1

A PROCESS FOR FORMING A DUCTILE, HIGH TEMPERATURE OXIDATION-RESISTANT COATING ON A MOLYBDENUM BASE METAL ARTICLE WHICH COMPRISES CLEANING SURFACE OF A MOLYBDENUM BASE METAL ARTICLE, ELECTROPLATING A RELATIVELY SOFT, CRACK-FREE LAYER OF CHROMIUM ON SAID ARTICLE TO A DEPT OF ABOUT 0.5 MIL TO 4 MILS, FLAME SPRAYING A POROUS OVERLAY OF A METAL POWDER ON SAID CHROMIUM PLATE IN AN AMOUNT EQUAL TO APPROXIMATELY 0.1 TO 0.15 GRAM PER SQUARE CENTIMETER, SAID POWDERED METAL COMPRISING ABOUT 15% TO 50% CHROMIUM AND THE BALANCE SUBSTANTIALLY ALL NICKEL, SINTERING SAID OVERLAY IN A SUBSTANTIALLY DRY HYDROGEN ATMOSPHERE AT A TEMPERATURE OF ABOUT 1700*F. TO 3000*F., FLAME SPRAYING A POWDERED ALLOY COMPRISING APPROXIMATELY 10% TO 20% CHROMIUM, 0.5% TO 6% BORON AND THE BALANCE PRINCIPALLY NICKEL ON SAID OVERLAY IN AN AMOUNT EQUAL TO ABOUT 0.1 TO 0.15 GRAM PER SQUARE CENTIMETER, AND THEREAFTER HEATING SAID ARTICLE IN SAID ATMOSPHERE AT A TEMPERATURE OF APPROXIMATELY 1800* F. TO 2250* F. TO MELT THE NICKEL-CHROMIUM-BORON ALLOY AND CAUSE IT TO PENETRATE INTO THE PORES OF SAID OVERLAY, AND CONTINUING TO HEAT SAID ARTICLE TO REDUCE LOCAL BORON CONCENTRATION GRADIENTS IN THE RESULTANT COATING BY SOLID STATE DIFFUSION.