INVESTMENT CASTING OF ALLVAC ® 718PLUS™ ALLOY

Many jet engine structural components are fabricated using investment castings, generally a lower-cost material alternative to built-up structures. Waspaloy is a nickel-base, age-hardenable superalloy with excellent high-temperature strength and good oxidation resistance, utilized in rotating aero engine components up to 704°C and higher temperatures for static components in modern jet engines. Typical applications include casings, frames and rings. Waspaloy has improved temperature capability, but suffers from producibility issues such as poor weldability and hot tear resistance. Additionally, the raw materials for Waspaloy are significantly more expensive than those for other casting alloys. Allvac ® 718Plus™ alloy was developed as a castwrought material with elevated temperature mechanical properties roughly equivalent to those for alloys such as Waspaloy at a significantly lower cost. Cast/wrought 718Plus also has formability and weldability characteristics that are very comparable to alloy 718. Previous ATI Allvac evaluation of 718Plus alloy cast-to-size test bars provided tensile strengths of approximately 690 MPa at 704°C. An evaluation of the producibility of investment cast alloy 718Plus components is necessary to determine suitability for Waspaloy replacement in high performance aero engines. The objective of this work is to evaluate and compare the castability of model components of 718Plus alloy to Waspaloy. Generic molds to compare the fill, hot tearing and weldability of the two materials were investment cast and processed. Samples were excised from the castings and tested mechanically and compared to program goals.