Creep Behavior and Deformation Mechanisms of Spark Plasma Sintered Oxide Ceramics for Aerospace Systems at 1300 deg C-1400 deg C
[Technical Report, Doctoral Thesis]
AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH
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The mechanical behavior of YAG and LuAG was investigated at elevated temperatures. The specific materials investigated in this work include high-purity, polycrystalline YAG, high-purity, polycrystalline LuAG, and two doped variants of YAG 2at Yb-doped, polycrystalline YAG and 2at Er-doped, polycrystalline YAG. Several billets of each material were prepared and processed by means of spark plasma sintering SPS. Many different sintering parameters were utilized in order to obtain materials with various physical properties and to identify the effects of sintering parameters on the average grain size of the resulting materials. The compressive creep behavior of these materials was investigated at 1300C and 1400C in air and in steam. Several billets of each material variant were tested in order to determine the effects of grain size on the creep behavior. The steady-state creep strain rates were determined from the results of each creep test, which enabled the identification of the stress exponent, grain size exponent, and the activation energy for the steady-state creep of both YAG and LuAG.