Effects of corrosive environments on near-threshold fatigue crack growth behavior of T1-6A1-4V

Abstract

The near-threshold fatigue crack growth behavior of Ti-6A1-4V alloy has been investigated in low O 2 steam (< 1 ppm), high O 2 steam (40ppm), and boiling water with various concentrations of Nad and/or Na 22SO 4. At load ratio ( R) of 0.5, high O 2 steam increased the crack propagation rates in the threshold region, relative to low O 2 steam. However, at R = 0.8, the near-threshold crack growth rates in low and high O 2 steam were comparable. Values of threshold stress intensity range, ΔK th , slightly increased with an increase in the concentration of NaCl in the solution. Varying solution pH from 5.0 to 10.0 in a 0.1 g NaCl plus 0.1 g Na 2SO 4 per 100ml H 2O solution had no effect on the rates of near-threshold crack propagation. Increasing the hydrazine level from 30 to 10 7 ppb in the same salt solution also did not change the resistance to crack growth. Comparing the present results with the previous data on 403 stainless steel, the near-threshold crack propagation rate performance in Ti-6Al-4V alloy is superior to that in 403 steel in both the steam and salt solution environments.