Tuning the Corrosion Behavior of Rapidly Solidified and Thermally-annealed Fe-Ti-Pd Alloys

The corrosion behavior of rapidly solidified Fe(91-x)Ti9Pdx (x=0, 1, 3 5) alloys (wt. %), both in the as-cast and thermally annealed (i.e., slowly cooled) states, has been investigated by means of electrochemical potentiodynamic polarization and immersion tests. Addition of Pd shifts the corrosion potential towards more anodic values than in the Fe91Ti9 alloy, both in the as-cast and annealed samples. In turn, the processing route (rapid cooling vs. thermal annealing) has a strong influence in the resulting microstructure, thus inducing drastic changes in the corrosion resistance. The values of corrosion potential in the as-cast samples increase with the Pd content since the cooling rate during casting is fast enough to allow Pd entering the Fe-Ti solid solution, hence making the alloy overall nobler. Conversely, the resistance against corrosion becomes lower in the heat-treated samples, presumably due to the precipitation of noble Pd-rich phases, which promote formation of micro-galvanic pairs.