The Effect of Small Amount of Alloying Elements on the Crevice Corrosion Resistance of Titanium in High Temperature NaCl Solutions.

Abstract

The effect of single alloying additon (Pd, Ni, Co, Mo, W, V, Nb, Si) and double alloying addition (Ni-(Mo, W, V, Ta, Zr, Nb, Si), Co-(Mo, W, V) or Pd-(Co, Ni, Mo, W, V)) on crevice corrosion resistance of titanium were investigated by autoclave test up to 473 K. Weight loss measurements of those materials in boiling HCl solutions were also conducted. It was found that small amount of Pd addition greater than 0.05% was remarkably effective and prevent from the crevice corrosion occurrence as same as ASTM Grade 7 (0.15 Pd). Ni and Co additions also improved the crevice corrosion resistance but their effect was not complete. In double alloying, synergistic improvement of crevice corrosion resistance was observed in the case of Pd-Co. Simultaneous Ni, W and Co addition with Pd also improved acid corrosion resistance. It was considered that the effect of Co addition was to reduce anodic current density in passive state, and reduce hydrogen overpotential to stabilize the passivity more than the material added Pd alone.