Vacuum Continuously Cast Superalloys: A World's First

摘要

Ni and Co based superalloys have long been used for demanding applications in aerospace and industrial gas turbines, turbochargers and biomedical prosthetic implant components. Of these, Ni based superalloys have seen rapid developments to meet the strength and operating temperature capabilities demanded principally by aerospace gas turbine manufacturers for hot sections of engines. Ni based superalloys now routinely contain reactive elements such as Al, Ti, Hf, Zr and Y often with treatments of La, Ce and Mg. In the main, the manufacture of alloys for investment casting with such alloying additions has been achieved through the use of vacuum induction melting (VIM) and pouring under vacuum into ingot moulds. In the steel industry continuous casting through a semi-open tundish system has been widely adopted as the method of casting, almost entirely replacing conventional ingot casting. Similarly, the continuous casting of Co based alloys has been developed, utilising their short freezing ranges and relatively good castability. Ni based superalloys on the other hand having more complex freezing ranges, inferior castability and the need to protect from oxidation any reactive element additions, have not been continuously cast successfully on a commercial basis. This paper describes the development of continuous casting of vacuum melted Ni based superalloys at Ross and Catherall and the benefits of the continuously cast product to the investment caster.