Localised Corrosion Properties of Lanthanum Containing Free-machining Titanium Alloys

F. Depentori, J. Laukart, S. Benfer, C. Siemers, W. Fürbeth

Proceedings of the 12th World Conference on Titanium (Ti-2011), Beijing, China, June 19th - 25th 2011, Science Press Beijing, 2012, Vol. 3, pp. 1915 - 1919


Titanium alloys combine outstanding specific mechanical properties with corrosion resistance and biocompatibility. Addition of lanthanum to (α+β)-titanium alloys like Ti6Al4V leads to improved machinability due to formation of short breaking chips and thus, the possibility of automated manufacturing. These alloys consist of a titanium matrix and metallic lanthanum particles located on the grain boundaries. Free-machining alloys based on Ti6Al4V have been developed by replacing vanadium with an iron-molybdenum pre-alloy to lower the material costs, by adding lanthanum to improve machinability and copper and silicon to improve particle distribution. Two alloys, Ti6Al2Fe1Mo0.9La0.5Cu and Ti6Al2Fe1Mo0.9La0.5Cu0.3Si, have been investigated. Both alloys contain precipitates of lanthanum as well as Cu4La intermetallic phase besides the (α-β)-matrix. The focus of this work lies on the characterisation of the local corrosion properties by atomic force microscopic methods, like Scanning Kelvin Probe Force Microscopy (SKPFM) and in-situ Atomic Force Microscopy (EC-AFM) in a fluid cell to understand the underlying corrosion mechanisms. Integral testing methods like potentiodynamic polarization and electrical impedance spectroscopy (EIS) are also conducted. The alloys have been exposed to different corrosive media. The results show that the precipitates undergo selective dissolution in time intervals of a few minutes up to several hours depending on the electrolyte.

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