An Advanced Cast/Wrought Technology for GH720Li Alloy Disk from Fine Grain Ingot

Abstract

The cast & wrought (C&W) route is one of the earliest production techniques and still commonly used in the overall production of turbine components due to its low cost and processing benefits. However, the C&W route can not be applied to some modern disk alloys that contain high volume fraction of γ′ phase and refractory alloying elements. Therefore, the latest Ni-base disk alloys such as RR1000, Rene 95 and ME3 are produced by powder metallurgy processing routes. However, the requirement of clean powder and subsequent thermo-mechanical processing steps economically limit its applications in some cases. Recent development in fine grain ingot casting technology is demonstrated in this investigation.The experimental results indicate that it is possible to convert highly alloyed GH720Li alloy directly from fine grain ingot to billet without powder process. The experimental fine grain ingot is sound and crack-free, typically with an uniform grain size ASTM 1~3. Hot ductility of the fine grain ingot has been systematically studied by hot compression testing, optical microscopy and scanning electron microscopy. Based on these results, a hot die forged pancake was produced with an ASTM 7 fine grain structure, which demonstrates the potential of GH720Li alloy disk to meet the component technical requirement.

Microstructure Evolution and Processing Map of Superalloy GH720Li during Isothermal Compression

“…Problems such as short working temperature range and low thermal conductivity may cause cracks or non-uniform structures during hot working. Previous research indicated that hot ductility has intimately relationship with deformation parameters [2], it is necessary to investigate the effects of parameters on deformation rules.…”