NEW SILICIDES FOR NEW NIOBIUM PROTECTIVE COATINGS

Efforts to improve at high temperature the oxidation resistance of pur e niobium or commercial niobium alloys have led to the development of a pack cementation process for the co-deposition of Si, Ti. Cr and Fe. Owing to the knowledge of the quaternary Nb(Ti)-T-Cr-Si phase diagram s (T=Fe or Co or Ni) and of the crystallographic features of phases pr esent in the silicide coatings, new protective coatings have been appl ied on pure niobium and Cb752 alloy. The results of the crystallograph ic study of three new silicides isostructural with Nb3Fe3CrSi6, in whi ch Nb is substituted by Ti and Fe by Co or Ni are reported. The oxidat ion performances of two new coatings mainly consisting of such a silic ide are also outlined. (C) 1998 Elsevier Science S.A.