Corrosion Resistant Nb Coatings Grown by Combined Steered Arc/Unbalanced Magnetron Deposition

Abstract

SummaryNiobium is well known for its chemical stability and excellent corrosion resistance which is based on the formation of a stable oxide layer of Nb205 in aqueous media It therefore finds wide application in areas where chemical stability is important, such as in chemical engineering equipment. Disadvantages of Nb are its high material costs and the fact that it is not possible to deposit Nb by the rather economic technique of aqueous electrodeposition. However, other deposition techniques such as physical vapour deposition may be used to produce niobium coatings. Due to its high melting point, sputtering is the preferred PV D deposition technology.Improved corrosion resistance approaching that of bulk Nb was found for lμm thick Nb coatings on 304 stainless steel substrates The corrosion performance very much depends on the method of ion etching prior to deposition. Microstructure, texture and microhardness as well are strongly influenced by the type of ion etching pre-treatment and by the temperature during deposition. Nb-ion etching of the 304 stainless steel substrate and-consequent Nb deposition with unbalanced magnetron sputtering at a temperature as low as 250°C, utilising an ion to neutral ratio of 4, leads to dense films. These films exhibit passivation over the whole range of the applied polarisation measurements in a 3% NaCl solution.