The results of structure observations of Ni base superalloy subjected to long-term influence of high pressure hydrogen atmosphere at 750K and 850K are presented. The structure investigation were carried out using conventional light-, scanning- (SEM) and transmission electron microscopy (TEM). The results presented here are supplementary to the mechanical studies given in part I of this investigations. The results of study concerning mechanical properties degradation and structure observations show that the differences in mechanical properties of alloy subjected different temperature are caused by more advanced processes of structure degradation during long-term aging at 850K, compare to that at 750K. Higher service temperature leads to formation of large precipitates of δ phase. The nucleation and growth of needle- and/or plate-like, relative large delta precipitates proceed probably at expense strengthening γʺ phases. Moreover, it can’t be excluded that the least stable γʺ phase is replaced with more stable γʹ precipitates. TEM observations have disclosed differences in dislocation structure of alloy aged at 750K and 850K. The dislocation observed in alloy subjected to 750K are were seldom observed only, while in that serviced at high stress and 850K dislocation array and dislocation cell structure was typical.
 Chester, T.S., Norman, S.S., William C.H. (1976). Superalloys II, Eds.John Willey & Sons, Inc., New York,
 Xishan Xie, Jianxin Dong, Gailian Wang, Wei You. (2005) The Effect of Nb, Ti Al on Precipitation and Strengthening Behavior of 718 Type Superalloys, Superalloys 718, 625, 706 and Derivatives, Ed. Loria TMS. 287-299.
 El-Bagoury, N. & Ramadan, M. (2012). Heat Treatment Effect on Microstructure and Mechanical Properties of Re- Containing Inconel 718 Alloy, J. of Minerals and Materials Charact. & Eng., 11. 924-930.
 ASM Handbook: vol. 9: Fractography, Nine Edition. ASM INternational. Metals Park, Ohio.
 Thomas, G. (1979). Transmission Electron Microscopy. New York, Chichester, Brisbane, Toronto, Singapore. Eds. John Wiley & Sons
 Hirsh, P.B., Howie, A., Nicholson, R.B., Pashley, D.W., Whelan, M.J. (1965). Electron Microscopy of Thin Crystals. Londor. Butterworths.
 Whelan, M.J. Chapter 1 (1969). Dynamical Theory of Electron Diffraction. In S. Amelinx, R. Gevers, R. Remaut, and J. Van Landuyt. Modern Diffraction and Imaging Technique in Materials Science. 35-99.
 Gray, R.H. (1972). Hydrogen Environment Embrittlement. In Standardization of Test Methods for Hydrogen Embrittlement, Los Angeles, California, June 26.
 Zhang, J.X., Wang, J.C., Harada, H., Koizumi, Y. (2005). The effect of lattice misfit on the dislocation motion in superalloys during high-temperature low-stress creep. Acta Materialia, 53, 4623-4633.
 Liu, L., Tanaka, K., Hirose, A. & Kobayashi, K.F. (2002). Effects of precipitation phases on hydrogen embrittlement sensitivity of Inconel 718. Science and Technology of Advanced Materials. 3, 335-344.