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Effects of specimen thickness and orientation on creep and stress-rupture properties of two advanced single crystal alloys were investigated. The alloys were CMSX-3, a derivative of Mar-M247, and a new single crystal alloy, designated as Alloy X, which is based on modification of IN-792 composition. Section thickness effects were ascertained utilizing four different specimen geometries, including 0.250 in. diameter bars and 0.020 in. thick specimens. The stress-rupture lives of both materials degraded with section thickness at stress levels less than 40,000 lb/in.2. The life degradation was approximately 3X at 20,000 lb/in.2. Investigations into the effects of orientation on stress-rupture properties indicated that for Alloy X the <110> oriented specimens suffered a loss of approximately 3X in stress-rupture lives compared to <001> oriented specimens.

Evaluation of Carborundum (CBO) injection-molded sintered alpha-silicon carbide (Sic) AGT 100 gasifier turbine rotors by spin testing established a baseline for material strength characteristics. Spin test results of a subsequent group of rotors demonstrated a reduction in average failure speed. Post-test fracture analysis identified surface and near-surface flaws in the back face region to be the typical failure origins. Corrective actions were initiated to address the elimination of the strength-controlling flaws. Initial evaluation of rotors fabricated to these process modifications indicates improvements in overall surface quality and average burst speed.