Ni-base alloys are traditionally melted and cast under vacuum for most investment casting applications. In this study, IN713LC, a Ni-base superalloy, was melted and cast in an inert atmosphere using the Counter-Gravity Low-Pressure Inert-Atmosphere (CLI) process, an investment casting process developed by Metal Casting Technology, Inc., and patented by Hitchiner Manufacturing Co., Inc. The CLI process has several advantages over the conventional gravity casting processes including lower alloy and shell materials usage, ability to tailor-make alloys, reduction in defects such as porosity and inclusions, improved mechanical properties, ability to fill thin-wall sections, increased throughput, and reduced overall cost.

A total of 19 molds consisting of test bar blanks and chemistry test coupons were cast in alloy IN713LC in approximately 3 hours spread over 2 days. The test coupons were analyzed for chemical composition and the test bar blanks machined and tested for tensile and stress rupture properties. In addition, microstructure of the test bars was evaluated using optical and scanning electron microscopy techniques.

No significant change was observed in the chemical composition of the alloy from the beginning to the end of the melting and casting campaign. Both tensile and the stress rupture properties exceeded the AMS 5377E requirements. A fine grain size ranging from 0.010” to 0.080” was observed in the ½” diameter section of the test bars. Furthermore, no defects were found in the microstructure evaluation.

Casting trials on other Ni-base superalloys such as IN718, Haynes 230 and Nimonic 90 were extremely encouraging and several components are currently in production using the CLI process. Some of these applications and the specific advantages of CLI casting for these applications will be reviewed.