IMPACT OF 2ND GENERATION SINGLE-CRYSTAL SUPERALLOYS ON FOUNDRY TECHNOLOGY

Superalloys developed after the Second World War to meet the demands o f the jet engine reached the limit of known alloying in the late 1960s . The continuing requirement for materials with higher temperature cap abilities was met by developments in solidification and processing tec hnologies leading to directional solidification and single crystals. B y the mid 1980s it was apparent that further improvements in material temperature capability could be achieved by alloying with such exotic elements as rhenium and yttrium. The success of these alloys is due to the retarding of diffusion rates and greatly increased oxidation resi stance at high temperatures. Superalloys containing these elements are generally known as second generation materials and are by virtue of t heir unique advantages very difficult to process. In particular the sl ow diffusion rates give significant difficulties with hear treatment a nd the retention of yttrium presents a foundry challenge of the highes t order. This paper will review the advantages of second generation ma terial and address the process problems associated with their successf ul introduction into service.