A detailed study was made of the formation and protective nature of surface alloy diffusion coatings for columbium. Vacuum vapor deposited, diffusion alloy coatings combining chromium, titanium and silicon were found to protect D-31 alloy f-48 alloy an unalloyed colu bium from surface oxidation or internal contamination for considerable lengths of time in air in the range of 2000 to 2600 F and for shorter periods up to 2800 F. Tests on the coating-base metal systems included cyclic oxidation, thermal shock and high velocity-hot gas erosion in a plasma flame.