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. (Author).

A comparative evaluation was made of 18 coatingbase metal systems, six different coatings applied to 3 Nb base materials (D-31 alloy, F-48 alloy and unalloyed Nb). The 18 coating-base metal systems were tested under the same conditions in cyclic oxidation (2300 and 2500 F), thermal shock (2 00 to 250 F), bend-oxidation (2500 F) nd stress-oxidation (2500 F) plus tensile tests. The tests produced directly comparable data between the coating-base metal systems relating to the protective nature of each coating and the effect of the coating and the coating treatment on the mechanical properties of the substrate.

The properties of materials depend on the characteristics of the bulk and on those of the surf ace. Any change in surface characteristics affects a wide variety of material properties. During the last few years the role of surface phenomena in metallurgy has been the subject of many studies. Surface energy, surface tension, the activity of surfaces, and related problems are under discussion in the western world * as well as in the eastern world. t The relation between volume and surface properties in metals and alloys has been investigated and is still under investigation. Materials are frequently exposed to environments which change their physical and chemical characteristics on account of a reaction going on between the material surface and the environment. The science and technology of surface preparation ro improve material properties have gained importance during the last decade in many parts of the world. Main efforts have been concentrated especially on the coating of material surfaces in connection with the exposure of these materials to space en vironment.