S. Shendye, B. King, Metal Casting Technology, Inc., Milford, NH; P. McQuay, Hitchiner Manufacturing Company, Inc., Milford, NH

Summary:

Three molds consisting of 36 test bar blanks each and test coupons were cast in IN718, a Ni-base alloy, using the Counter-gravity Low-pressure Inert-atmosphere (CLI) investment casting process. Test coupons were analyzed for chemical composition and the test bar blanks machined and tested for tensile and stress rupture properties. Larsen-Miller parameter was calculated from the stress rupture test data. Stress levels ranged from 75 to 130 ksi and the temperature ranged from 1000 F to 1300 F for the stress rupture test. 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. A slightly higher oxygen and nitrogen content was observed as compared with the vacuum induction melted and gravity-cast IN718. This however, did not adversely affect the stress rupture properties. The experimentally determined Larsen-Miller parameter was found to be comparable to that published in the literature. Grain size ranging from 0.010” to 0.060” was observed. No notable defects were identified by non-destructive X-ray and fluorescent penetrant inspections (FPI), or by microstructure and fractographic 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 IN713C, Haynes 230 and Nimonic 90. Some of these applications and the specific advantages of CLI casting for these applications will be reviewed.