Impact of Second Generation Single Crystal Superalloys on Foundry Technology

Superalloys developed after the Second World War to meet the demands of the jet engine reached the limit of known alloying in the late 1960s. The continuing requirement for materials with higher temperature capabilities was met by developments in solidification and processing technologies leading to directional solidification and single crystals.

By 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 resistance at high temperatures.

Superalloys containing these elements are generally known as second generation materials and are by virtue of their unique advantages very difficult to process. In particular the slow diffusion rates give significant difficulties with heat treatment and the retention of yttrium presents a foundry challenge of the highest order.

This paper will review the advantages of second generation material and address the process problems associated with their successful introduction into service.