Effects of Contact Load on the Fretting Fatigue Behavior of IN-100 at Elevated Temperature
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH GRADUATE SCHOOL OF ENGINEERING AND MANAGEMENT
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This thesis studied the effects of contact load of 8006 N on the fretting fatigue behavior of IN-100 at an elevated temperature of 600 deg C. First, S-N curves were created for a range of applied axial stresses at an identical stress ratio of 0.03 at 8006 N. A condition of partial slip condition necessary to fretting fatigue was verified by generating hysteresis loops, plotting shear force against axial stress. The half-contact width and the crack initiation location were determined for all of the fretting specimens using optical and scanning electron microscopes. The contact widths were consistent with expected analytical values and the crack initiation location was at the trailing edge of contact for all fretting specimens at a mean angle of 45 deg. This study compared the fretting results at higher contact load 8006 N to similar results from previous studies of IN-100 at lower contact load 4003 N with an identical microstructure at an elevated temperature of 600 deg C as well as to previous room temperature testing. It was found that fretting fatigue at higher contact load drastically reduces the cycles to failure compared to fretting fatigue at elevated temperature with a lesser contact load. While the higher temperature environment allowed a longer initiation and crack propagation time, this was quickly negated by the increase in the contact load. The development of glaze oxide films and temperature induced softening or plasticity were both found to act as crack closure mechanisms in another nickel-based superalloy, IN-718, when fatigued in the high temperature environment. This glaze oxide reduces the coefficient of friction between contact surfaces, an important factor in fretting fatigue, and is also observed to be present in high temperature studies of IN-100.
- Properties of Metals and Alloys