High strain rate deformation of Alloy 718

Licentiate thesis, 2013

Alloy 718 is a high temperature alloy, used where high temperature strength or oxidation resistance is required. As the alloy is precipitate heat treatable it is possible to have a large variety of strength depending on microstructure. The different microstructures used in this study are relevant for industry and used at various stages in production and service. Mechanical properties of Alloy 718 with different microstructures have been studied at high strain rates ranging from 0.001 to 3000 s-1, and at room temperature up to 800°C. The adapted Johnson-Cook material model shows a good agreement with the experimental data. The deformed microstructures are studied and the deformation patterns of the different microstructures show some differences, for small grain size the deformation appear to be on primary and secondary glide systems and change direction at grain boundaries and for large grain size the deformation seem to occur primarily on primary glide systems and the glide systems does not seem to change direction so much at grain boundaries. For aged condition the hardening precipitates seem to give most of the strength, as the aged condition show superior strength up to 600°C, and at 800°C the different microstructures show similar strength and the effect of the hardening precipitates have vanished.