A Study upon the Corrosion Behavior of MoC-Co-Nb Alloys in the Bromide Media

It’s known that hard metals are sintered composites of metal-ceramic powders. In this case, the mixtures of one or more finely divided hard carbides particles, such as tungsten, molybdenum,titanium, tantalum, and vanadium, embedded in a matrix of soft and ductile binding materials such as cobalt, iron, or nickel. These metals are hard and have very good wear resistance, and this make them suitable alloys in several industrial applications, such as cutting tools or sealrings, linings, valves, jet nozzles, saw blades, fluid mixers, and conveyor belt scrapers. A series of MoC-Co-Nb alloys was evaluated in different bromide containing media to investigate their corrosion resistance. Standard electrochemical corrosion tests, chronoamperometricmeasurements, and surface analyses with Raman spectroscopy were conducted. An increasing amount of Nb improves the corrosion resistance of all the alloys. The effect is not as dramatic as that observed with stainless steels containing Nb in corrosive media. In both corrosive media Nbdecreased the cathodic Tafel constant and has a retarding influence on the cathodic part of the corrosion reaction. Raman analyses indicated the presence of molybdenum oxide, hydrated molybdenum oxide compounds, and CoO and Co3O4 formed on the alloy surfaces during the corrosion process

Keywords:

corrosion , electrochemical , alloy , SEM