EFFECTS OF HEAT TREATMENT ON DYNAMIC DEFORMATION AND FAILURE OF NICKEL BASED SUPERALLOYS

摘要

Engine fan-blade containment systems, required in many aviation applications, are frequently manufactured from high-temperature alloys, such as Inconel 718. As in many other applications, there is an incessant desire to maximize mechanical properties of the containment component while minimizing the weight. However, a thorough understanding of the impact behavior of various heat treatments of these alloys in blade containment applications does not currently exist. Due to this incomplete state of knowledge, a combined experimental-analytical investigation is currently underway at NASA GRC and CWRU. As a part of this investigation thin plates of Inconel 718, in both annealed and precipitation hardened conditions, were subjected to semi-quantitative high speed penetration tests. Dynamic compression tests and top hat shear localization tests using a split-Hopkinson pressure bar facility were also conducted as part of a more fundamental assessment of this material. Material parameters generated from the split Hopkinson bar compression tests were used to construct a material model which adequately describes the dynamic behavior of IN-718 in both annealed and precipitation hardened states, and at strain rates in the range from 0.1 /s to 5000 /s. The results from these tests show that the annealed material demonstrated superior penetration resistance when compared with the hardened material. The annealed IN-718 absorbed more energy through multiple deformation modes and did not show any susceptibility to localization, which was in contrast to the precipitation hardened material. Samples of the hardened material demonstrated high flow stresses and showed minimal strain hardening at high strain rates, which would enhance the propensity of this material to localize. These results therefore suggest a precipitation hardened condition may not be optimal for applications such as fan-blade containment.