Alloys and Alloying Elements

In general, additions of large amounts of an alloying element reduce the corrosion resistance of pure titanium. Small amounts of palladium, platinum, and rhodium, however, increase the resistance to corrosion, including corrosion in moderate concentrations of hydrochloric and sulfuric acids. Additions of approximately 30% molybdenum improve the resistance to hydrochloric acid.

Other typical alloying elements used in titanium alloys include aluminum, chromium, iron, manganese, molybdenum, tin, vanadium, and zirconium. Aluminum additions above 6% causes a significant degradation in the SCC resistance, while titanium aluminide intermetallics may have increased resistance to oxidation and oxygen embrittlement. Additions of approximately 2% nickel improves crevice corrosion resistance in hot brine environments, but reduces the resistance to hydrogen embrittlement and also degrades the formability of titanium. Table 38 shows the resistance or various titanium alloys to SCC in a hot-salt environment.