Corrosion Fatigue Crack Growth Behavior of Titanium Alloys in Aqueous Solutions

The corrosion fatigue crack growth (FCG) behavior, the effect of applied potential on corrosion FCG rates, and the fracture surfaces of VT20 (near-a) and TS6 (near-b) titanium alloys were studied. Environments were aqueous solutions of sodium chloride (NaCl), sodium hydroxide (NaOH), potassium hydroxide (KOH), ferric chloride (FeCl₃), and chromic acid (H₂CrO₄) with and without NaCl. Depending upon solution composition, corrosion FCG rates were found to be higher or lower than those in air. Cathodic polarization retarded the corrosion FCG, while anodic polarization accelerated insignificantly or almost did not influence it in most of the solutions investigated. However, cathodic polarization accelerated corrosion FCG in 0.6 M FeCl₃ and 0.5 M to 2 M H₂CrO₄ + 0.01 M to 0.1 M NaCl solutions by a dozen times when the maximum stress intensity (K_max) exceeded certain critical values. When K_max was lower than the critical values, the same cathodic polarization (with all other conditions being equal) retarded corrosion FCG. Results suggested the accelerated crack growth at cathodic potentials resulted from hydrogen-induced cracking (HIC). Therefore, critical values of K_max, as well as the stress intensity range (ΔK) were regarded as corresponding to the beginning of corrosion FCG according to a HIC mechanism and designated as K_HIC and ΔK_HIC.