Corrosion Fatigue Cracking Response of Beta Annealed Ti-6Al-4V Alloy in 3.5% NaCl Solution. Volume 5

摘要

A systematic investigation has been conducted to examine the effect of frequency on fatigue crack growth in a beta-annealed Ti-6Al-4V alloy in 3.5% NaCl solution at room temperature. Fractographic and metallographic examinations were also made to help identify the probable mechanism for crack growth enhancement (or embrittlement) and to evaluate the frequency effect. Fatigue crack growth tests covered a range of frequencies from 0.03 to 15 Hz and a range of K sub max levels from about 16 to 61 MPA-m1/2. The results show that fatigue crack growth rates increased with decreasing frequency, and then decreased with further decreases in frequency. The frequency at which the crack growth rates reached a maximum depended on the K level, and is inversely proportional to delta K cubed. The fracture surface morphology also depended strongly on frequency and K level, and suggested that the enhancement of crack growth resulted from the formation and rupture of a hydride phase. Based on the experimental observations, crack growth response is interpreted in terms of control by hydrogen diffusion and of a critical strain rate required for hydride formation in the crack tip region. (Author)