Oxydation et protection des alliages base niobium

Abstract
The ceaseless demand for higher temperatures in aerospace systems explains the research programs about both the intermetallic compounds and the refractory metals. Concerning refractory metals, niobium has received the greatest attention, because of its good physical and mechanical properties (melting point, density, ductile-brittle transition temperature, strength above 1000 °C). Nevertheless, the bad oxidation behaviour of niobium or niobium alloys has excluded their use whithout protective coatings, as important research from 1955 to 1975 has clearly proved it. Despite this severe handicap, an intensive research is again conducted since some years, on niobium alloys, bare or coated. These recent investigations profit by new techniques in domains of alloys elaboration or coatings deposition. This paper also will treat our niobium program, which is focused in two main directions : developments of new niobium alloys structures, copied from [MATH] superalloys structure, and protective coatings elaborated by pack cementation.