Ni-base superalloys are traditionally melted and cast under high vacuum for most investment casting applications. In this study, Haynes 230, a Ni-base superalloy, was melted and cast in an inert atmosphere using the Counter-gravity Low-pressure Inert-atmosphere (CLI) process. Two approaches were used to melt and cast the Haynes 230 alloy. In the first approach, a relatively high vacuum was first created in the melting chamber. High purity argon was then introduced into the chamber and the alloy was melted under argon atmosphere. In the second approach, a partial vacuum was first created in the furnace chamber. The furnace chamber was then flooded with argon and the alloy melted under argon. Several molds consisting of test bar blanks and test coupons were then cast from alloys melted using these two approaches. Test coupons were analyzed for chemical composition and the test bar blanks machined and tested for tensile and stress rupture properties. Fracture surfaces and microstructure of the test bars was evaluated using optical and scanning electron microscopy techniques.

Chemical composition of the alloy was found to be relatively stable and within the specification limits for both the alloy melting approaches. Grain size ranging from 0.010” to 0.060” was observed and both the tensile and stress rupture properties exceeded the customer requirements. No notable defects were identified by non-destructive X-ray and fluorescent penetrant inspections (FPI), or by fractographic and microstructure evaluations.

The CLI casting process is an investment casting process developed by Metal Casting Technology, Inc., and patented by Hitchiner Manufacturing Co., Inc. Several components are currently in production using the CLI process in other Ni-base superalloys such as IN718, IN713LC and Nimonic 90. Some of these applications and the specific advantages of CLI casting for these applications will be reviewed.