A new vacuum-assisted low-pressure investment casting process for K446 alloy

Non-metallic inclusions and zyglo indications frequently occur in the superalloy castings produced through the traditional vacuum gravity investment casting process, particularly in components with thin-walled and complex structural features. The vacuum-assisted low-pressure casting (VLC), a type of counter-gravity casting (CGC) method, has been developed to minimize non-metallic inclusions and zyglo indications in superalloy castings. Rectifying frames for gas turbines made from K446 alloy were produced semi-continuously using the VLC process and subsequently evaluated through tensile testing, chemical composition analysis, X-ray diffraction, and zyglo penetrant inspection. The results indicate a roughly 10% improvement in tensile strength at 800 °C compared to gravity casting. Moreover, no significant changes are observed in the chemical composition of the alloys from the beginning to the end of a casting campaign, indicating that the developed VLC process is viable for the engineering-scale production of superalloy castings. Compared to traditional vacuum gravity casting (GC) method, the application of VLC can reduce the numbers of non-metallic inclusions and Zyglo indications in the castings by over 80%. At the same time, it significantly shortens the production time by 3 to 5 days.