N18, POWDER-METALLURGY SUPERALLOY FOR DISKS - DEVELOPMENT AND APPLICATIONS

The preliminary industrial development of a powder metallurgy (PM) sup eralloy, designated N18, for disk applications has been completed. Thi s alloy exhibits good overall mechanical properties after appropriate processing of the material. These properties have been measured on bot h isothermally forged and extruded billets, as well as on specimens cu t from actual parts. The temperature capability of the alloy is about 700-degrees-C for long-term applications and approximately 750-degrees -C for short-term use because of microstructural instability. Further improvements in creep and crack propagation properties, without signif icant reduction in tensile strength, are possible through appropriate thermomechanical processing, which results in a large controlled grain size. Spin pit tests on subscale disks have confirmed that the N18 al loy has a higher resistance than PM Astroloy and is therefore an excel lent alloy for modern turbine disk applications.