Papers by Keyword: Slip Markings

Abstract: Cylindrical specimens of cast polycrystalline nickel base superalloy Inconel 738LC were cyclically strained under total strain control at 23 and 800 °C to fracture. Cyclic hardening/softening curves, cyclic stress-strain curves, and fatigue life curves were obtained at both temperatures. Surface relief was studied in specimens fatigued to failure using scanning electron microscopy. Cyclic hardening/softening behaviour depends both on temperature and strain amplitude. Low amplitude straining was characterized by saturation of the stress amplitude. In high amplitude straining a pronounced hardening was found which was followed by saturation at room temperature and by cyclic softening at 800 °C. The cyclic stress-strain curves can be fitted by power law. They are shifted to lower stresses with increasing temperature. Fatigue life curves can be approximated by the Manson- Coffin and Basquin laws. The Manson-Coffin and Basquin curves are shifted to lower lives with increasing temperature. Slip markings were detected on specimen surface at all test temperatures. When temperature grows the density of slip markings is reduced.

Abstract: Cyclic strain control tests have been performed on cylindrical specimens of cast polycrystalline Inconel 792-5A superalloy at 23, 500, 700 and 800 °C in laboratory atmosphere to study the effect of temperature on the fatigue behavior. Cyclic hardening-softening curves and fatigue life curves were measured. Scanning electron microscopy was used to investigate the surface relief. Low amplitude straining was characterized by saturation of the stress amplitude. In room temperature high amplitude straining cyclic hardening was followed by marked saturation. Pronounced continuous hardening until failure was observed at 500 °C. Initial cyclic hardening was followed by softening at 800 °C. A systematic shift of the Manson-Coffin and of the Basquin curves to lower fatigue lives was found when temperature was increased. Fatigue cracks were observed to initiate from surface slip markings at all temperatures.