ANISOTROPIC ELASTIC DISTORTIONS OF A BURIED DISSOCIATED HEXAGONAL NETWORK OF DISLOCATIONS IN A NICKEL BASED SUPER ALLOYS

摘要

Nickel based super alloys are promising materials for high temperature structural applications because of their low density. The single grain γ/(111)γ' super alloys are extremely creep resistant at high temperature, due to the fraction of Ni_3Al based γ' precipitates coherent with a Ni based γ matrix [1,3]. The cuboids group together and form semi-coherent interfaces after a long annealing at high temperature. The γ' precipitate growths in nickel base super alloys often favor the parallelism of (111) planes between cubic dissimilar crystals [4]. In consequences, a hexagonal network of dislocations, that covers the γ/(111)γ' hetero-interphase, is arranged by accommodation of the angular misfit between two semi coherent crystals (b=1/2<110>). In this work, the magnitude of the distortions is simulated as arising from a trigonal network of subsurface misfit dislocations partly dissociated in Shockley dislocations limiting intrinsic and/or extrinsic stacking faults. The results derived from a previous explicit formulation using double Fourier series [5]. Each harmonic term of the series depends on the anisotropic elastic constants and the thickness of each phase. The program built is in a double precision Fortran language and it shows the magnitude and the aspect of the distortions of the free surfaces when the dissociation change in the hetero-interphase. Also, the program has the advantage to fully apply to hetero-epitaxial systems, whatever is the thickness of the free surfaces.