β-phase forms a continuous pathway, as it does for Ti-5111, the mechanism of hydrogen embrittlement changes significantly. The β-phase has a higher solubility of hydrogen than does the α-phase, and hydrogen will diffuse more rapidly into the β-phase. Thus when the sample is tested in a sodium chloride solution under conditions where hydrogen is generated, the atomic hydrogen will quickly diffuse into the material through this phase and be primarily concentrated there. This high concentration then leads to embrittlement. This result is again similar to that reported by Nelson and Williams for Ti-6Al-4V that had been heat treated to have a continuous β-phase [7,8]. They found cracking along the α/β interfaces and that the fracture mode was a brittle cleavage along the α/β interface. CONCLUSIONS This paper has presented results for hydrogen embrittlement in three titaniumbase materials. Two were commercial purity titanium in which only the α-phase was present. The third was an α/β alloy. The results showed in the commercial purity titanium that the embrittlement occurred through the formation of hydrides. However, the fracture was completely ductile and the hydrides acted as sights for void nucleation and growth. These voids were then connected up through a fracture process that led to crack advance. Thus, precipitation of hydrides in front of the crack tip is a critical feature of this model. In the α/β material, the fracture was brittle. As shown in reference 5, the crack propagated through the β-phase, which has a higher solubility for hydrogen and also provides a faster diffusion path. Thus by a change in the microstructure of the material, the fracture mode changes significantly. ACKNOWLEDGMENTS This research was supported by the United States Office of Naval Research under Grant No. N00014-96-0272. The authors would also like to thank Dr. Jenny Been, TIMET, for providing the Ti-5111 material and for many helpful discussion. REFERENCES 1. Nelson, H.G. (1984). In: Embrittlement of Engineering Alloys, pp. 275-359, C.L. Briant and S.K. Banerji, (Eds.) Academic Press, New York. 2. Liu, C.T., Lee, E.H., and McKamey, C.G. (1989) Scripta Metall., 23, 875. 3. Wang, Z.F., Briant, C.L., and Kumar, K.S. (1999) Corrosion, 55, 128. 4. Wang, Z.F., Briant, C.L., and Kumar, K.S. (1998) Corrosion, 54, 553. 5. Wang Z.F., Chollocoop, N., Briant, C.L., and Kumar, K.S. (2001) Metall. Trans. to be published 6. Wang, Z.F., Briant, C.L., and Kumar, K.S. (2001) Corrosion 2001, Paper 01239, NACE, Houston, Texas. 7. Nelson, H.G., Williams, D.P., and Stein, J.E. (1972), Metall. Trans. 3, 469. 8. Nelson, H.G (1973) Metall. Trans. 4, 364.
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