Micro Spark Coating (MSC) has been developed as a new functional coating process for Ni-based superalloys used in advanced gas turbines. In this study, some metallurgical and mechanical properties of a MSC layer made of a Co-based wear resisting alloy (X40), and its influence on the high temperature fatigue properties of Ni-based superalloy, Alloy718, were investigated. Prior evaluation of the metallurgical and mechanical properties of the MSC layer that the cavity fraction of MSC layer significantly decreased during the thermal exposure period at 650°C associating with the generation of an oxide phase, progressive sintering and the subsequent increase in hardness and elastic modulus of MSC layer. However, at 480°C these changes were not significant even after 1000hrs exposure. It was found from the high temperature fatigue tests at 480°C and 650°C that the fatigue life of the specimen with MSC layer was almost comparable to that of bare Alloy718 specimen at 480°C, while at 650°C the life of the former was slightly longer than that of the latter. These results suggested that the MSC would have a potential to add a new function to Ni-based superalloy without a reduction in fatigue properties at elevated temperature.

An aircraft may suffer from foreign object damage (FOD) during flight operations, and a bird strike is a potentially serious and damaging FOD event. For simulated bird strike experiments, gelatin has been traditionally used as the projectile material. However, it has not been sufficiently determined how the material properties of the projectile affect the simulated bird strike results, especially for deformable targets. In this work, using gelatin as the conventional simulated bird material, silicone resin is used to investigate the effects of the projectile material properties. Two types of impact tests are conducted. One uses a solid target with a flat face, and the pressure change due to the impact is investigated. The other uses a cantilever target made from aluminum alloy or carbon fiber/epoxy composite laminate to investigate the plastic deformation or damage, respectively. From these experiments, the effects of the projectile material type and properties are evaluated.

The high temperature strength and the microstructural change of strongly cold worked austenitic stainless steel SUS305 were investigated. 60% cold rolled specimens suggested strong decrease of fatigue strength, creep rupture strength and Vickers hardness (hereafter; hardness) after aging, corresponding to the increase of recrystallized grains. On the other hand, 30% cold rolled specimens suggested less decrease of strength and hardness, and revealed no recrystallization. In this study, the microstructure and hardness of strongly deep drawn SUS305 at high temperature were also investigated. On this specimen, similar to 60% cold rolled SUS305, decrease of hardness corresponded to the increase of recrystallized grains. But, since M 23 C 6 precipitations were fine and closely spaced in the material, the recrystallization was delayed. On the other hand, the both materials suggested same relativeness between the softening tendency and recrystallization. Therefore, fatigue strength and creep rupture strength of deep drawn SUS305 should decrease with the recrystallization at high temperature.

No abstract