Synergistic effect of Zr addition and grain refinement on corrosion resistance and pitting corrosion behavior of single α-phase Ti-Zr-based alloys

The synergistic effect of Zr addition and grain refinement on the corrosion resistance and pitting corrosion behavior of single α-phase Ti-Zr-based alloys was evaluated. The corrosion mechanisms of as-cast and hot-rolled Ti-xZr-4Al-0.005B alloys (x = 0, 10, 20, 30, 40 wt%) in 5 M aqueous hydrochloric acid solution are investigated by analyzing their electrochemical and immersion corrosion behavior using scanning electron microscopy, electrochemical analyses, and X-ray photoelectron spectroscopy. Both Zr alloying and grain refinement improve the corrosion resistance; while grain refinement improves the stability of the passivation film, Zr addition increases the pitting sensitivity. Zr alloying and grain refinement greatly affects the pitting corrosion behavior in the alloy. In Ti or Ti-Zr alloys with low Zr content, grain refinement inhibits the appearance of corrosion pits inside the grains. For Ti-Zr alloys with higher Zr content, grain refinement induces small corrosion pits in the alloy. Grain refinement increases the frequency of corrosion pits in the Ti-Zr alloys with higher Zr content but inhibits the growth of the pits by improving the corrosion resistance and stability of the passivation film through the formation of more high-valence oxides and a thicker passivation film.