Effect of solution heat treatments on superalloys Part 1 – alloy 718

Abstract

The hot ductility as measured by Gleeble testing of Alloy 718 at four different solution heat treatments (954°C/15 h, 954°C/1 h, 982°C/1 h and 1050°C/3 h+954°C/1 h) has been investigated. It is concluded that constitutional liquation of NbC assisted by δ phase takes place and deteriorates the ductility. Parameters established by analysing the ductility dependence on temperature indicate a reduced weldability of the material in the coarse grain size state (ASTM 3) while indicating an increased weldability when containing a large amount of δ phase due to a grain boundary pinning effect. The accumulation of trace elements during grain growth at the highest temperature is believed to be the cause for the observed reduced on-cooling ductility.

Keywords:

• Alloy 718
• Hot ductility
• Gleeble testing
• Weldability

At the Department of Mechanical and Industrial Engineering at the University of Manitoba we sincerely acknowledge Dr O. A. Ojo for all fruitful comments and advice, Dr Krutika Vishwakarma and Mr Mike Boskwick for all help with the Gleeble testing and Christopher Knee at the Department of inorganic chemistry at Göteborg University for performing the DSC measurements.