Primary and Anelastic Creep of a Near α-Ti Alloy and Their Dependencies on Stress and Temperature
Tóm tắt
The primary creep behaviour of a high temperature near α-Ti alloy Ti6242Si has been investigated in the temperature range from 500 to 625°C, and the stress range from 80 to 450 MPa. The results are analysed in terms of the dependencies of stress on strain (strain hardening) and on strain rate (strain rate sensitivity). Furthermore, full unloading experiments were conducted in order to gain additional information as to the nature of primary creep. It is shown that primary creep can be described by an athermal component, strain hardening, with a mean strain hardening coefficient of 0.37, and a thermally activated component, strain rate sensitivity, with a strain rate sensitivity coefficient suggesting a mechanism based on climb controlled recovery. This is confirmed by the activation energy of 259 kJ/mol determined at different stresses, which is similar to the activation energy of Ti self diffusion in α-Ti. The anelastic strain obtained on full unloading was analysed in its fast stage in a similar way. The kinetics of anelastic creep and its activation energy are in many aspects very similar to those of primary creep. It is thought that, in the stress and temperature range investigated, primary creep is to a relatively high extent anelastic in nature, and is controlled by the climb controlled bow out of pinned dislocation segments, particularly dislocations pinned at lath boundaries.
Tài liệu tham khảo
Ahmadieh, A. and Mukherjee, A.K., ‘Stress-temperature-time correlation for high temperature creep curves’, Mater. Sci. Engrg. 21, 1975, 115–124.
Beere, W. and Grossland, I.G., ‘Primary and recoverable creep in 20/25 stainless steel’, Acta Metall. 30, 1982, 1891–1899.
Conrad, H., ‘Experimental evaluation of creep and stress rupture’, in Mechanical Behaviour at Elevated Temperature, J. E. Dorn (ed.), McGraw-Hill, New York, 1961, 149–217.
Delos-Reyes, M.A., Kassner, M.E., Thiehsen, K.E., Hiatt, R.D. and Bristow, B.M., ‘The Effect of Nickel, Chromium, and Primary Aplha on the Creep Behavior of Ti 6242Si’, in Microstructure/ Property Relationships of Titanium Alloys, S. Ankem and J.A. Hall (eds.), Metals & Materials Society, Warrendale, PE, 1994, 47–54.
Derby, B. and Ashby, M.F., ‘A microstructural model for primary creep’, Acta Metall. 35, 1987, 1349–1353.
Es-Souni, M., ‘Primary and anelastic creep in a high Temperature near α-Ti alloy: Effects of microstructure and stress’, in Proceedings of the 5th European Conference on Advanced Materials and Processes and Applications, Vol. 1, L.A.J.L. Sarton and H.B. Zeedijk (eds.), Netherland Society for Materials Science, Zwijndrecht, 1997, 233–236.
Es-Souni, M., ‘Primary and anelastic creep in a high temperature near γ-Ti alloy: Effects of microstructure and stress’, High Temperature and Materials Science, 1998 (in press).
Es-Souni, M., Bartel, A. and Wagner, R., ‘Creep behaviour of a fully transformed near-TiAl alloy Ti-48Al-2Cr’, Acta Metall. Mater. 43, 1995, 153–161.
Gibeling, J. C. and Nix, W., ‘Observation of anelastic backflow following stress reductions during creep of pure metals’, Acta Metall. Mater. 29, 1981, 1769–1784.
Kuhlmann-Wilsdorf, D., ‘Theory of work hardening 1934–1984’, Metall. Trans. 16A, 1985, 2091–2107.
Li, J.C.M., ‘A dislocation mechanism of transient creep’, Acta Metall. 11, 1963, 1269–1270.
Lloyd, G.J. and McElroy, R.J., ‘On the anelastic contribution to creep’, Acta Metall. 22, 1974, 339–348.
Lubahn, D.J., ‘Deformation phenomena’, in Mechanical Behaviour at Elevated Temperature, J.E. Dorn (ed.), McGraw-Hill, New York, 1961, 319–392.
Lupinc, V. and Gabrielli, F., ‘Effect of grain size, particle size and α′ volume fraction on strain relaxation in Ni-Cr base alloys’, Mater. Sci. Engrg. 37, 1979, 143–149.
Malakondaiah, G. and Rama Rao, P. ‘Creep of alpha-Titanium at low stresses’, Acta Metall. A192/193, 1995, 756–762.
Mishra, R.S., Banerjee, D. and Mukherjee, A.K., ‘Primary creep in a Ti-25Al-11Nb alloy’, Mater. Sci. Engrg. 21, 1975, 115–124.
Nabarro, F.R.N., The Physics of Creep, Taylor & Francis, London, 1995, 15–78.
Nakayama, G.S. and Gibeling, J.C., ‘Constant structure creep of aluminium following stress reductions’, Acta Metall. 38, 1990, 2023–2030.
Weertmann, J. and Weertmann, J.R., ‘Mechanical properties, strongly temperature-dependent’, in Physical Metallurgy, R.W. Cahn and P. Haasen (eds.), Elsevier Sciences Publishers, Amsterdam, 1983, 181–193.
Yaney, D.L. Gibeling, J.C. and Nix, W.D., ‘A new strain rate change technique for distinguishing between pure metal and alloy type creep behaviour’, Acta Metall. 35, 1987, 1391–1400.