Abstract
The combination of high temperature (1050°C -1150°C) testing and in situ high energy X-Ray diffraction measurements using synchrotron Three Crystal Diffractometry may give various insights into the mechanical behaviour of superalloys: measurement of the lattice mismatch, order within the ' phase, elastic constants, and dynamic response to changes in the experimental conditions. Several examples are given on the rafted AM1 superalloy, resulting from experiments at the ID15A (ESRF) and BW5 (DESY) high energy beamlines.
Highlights
During the second stage of their high temperature tensile creep curve ([001] tensile axis), rafted single crystalline nickel-based superalloys may be seen as very simple two-phased materials: they are formed of alternate, semi coherent, layers perpendicular to the tensile axis of a L12 (γ’) phase and of a disordered fcc γ phase (γ corridors)
Experimental data on the elastic constants (Young modulus Eγ and Eγ') are scarce, as their measurement with classical methods at a given temperature would require growth of single phase, single crystalline specimens with the exact equilibrium composition of the γ and γ' phases at that temperature
If the lattice mismatch is partly relaxed by the dislocation array left at the γ/γ' interfaces by dislocation which moved within the γ corridors and were not transmitted into the rafts, we have no reason to suppose they are cancelled at equilibrium, or that they remain constant while the corridor width increases with time, or when the external stress is changed
Summary
During the second stage of their high temperature tensile creep curve ([001] tensile axis), rafted single crystalline nickel-based superalloys may be seen as very simple two-phased materials: they are formed of alternate, semi coherent, layers perpendicular to the tensile axis of a L12 (γ’) phase (so called rafts) and of a disordered fcc γ phase (γ corridors). Experimental data on the elastic constants (Young modulus Eγ and Eγ') are scarce, as their measurement with classical methods at a given temperature would require growth of single phase, single crystalline specimens with the exact equilibrium composition of the γ and γ' phases at that temperature. While these parameters remain constant during a test, we may expect dislocation densities, the level of internal stress, and even the fraction f of γ' phase to vary on timescales of one hour or less. A second silicon crystal, termed analyzer, selects one of these beams, and sends it to an energy selective Ge detector
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
