Mark Gilbert Benz

Superalloys made by conventional vacuum melting and a novel spray forming process

Abstract Wrought Ni-base superalloys used in modern gas turbine engines are typically produced by vacuum induction melting (VIM) plus consumable remelting (ESR and/or VAR). For the more advanced alloys, these processes have certain limitations; namely, the ability to produce sound ingots of a reasonable size, free of harmful segregation related defects, which can readily be converted into wrought product. Powder metallurgy processes have been developed to overcome these problems but substitute another problem: high cost. To address these concerns, a clean, ceramicless spray forming process has been developed which uniquely combines electroslag remelting (ESR), bottom pouring through a cold induction guide (CIG) and spray forming (Osprey Metals Ltd). This paper discusses some of the issues encountered in current superalloy manufacturing processes and describes the clean metal spray forming (CMSF) plant which has been constructed to address them.

Melt-formed superconducting joints for Nb 3 Sn tape

Several new persistent-current superconducting magnet applications become possible for Nb3Sn when joints can be fabricated that are superconducting over the full range of temperatures and fields accessible with Nb3Sn. Melt forming has been found to be an effective way to form such a joint. Both tungsten inert gas welding and laser welding have been used successfully for this purpose. Methods for fabrication, microstructures, and performance of melt-formed Nb3Sn superconducting joints are discussed in detail.

Interface Structure, Grain Morphology, and Kinetics of Growth of the Superconducting Intermetallic Compound Nb 3 Sn Doped with ZrO 2 and Copper

One method for the fabrication of the superconducting compound Nb 3 Sn involves interdiffusion of a surface coating of Sn alloyed with Cu on Nb containing Zr and O. In this study, the kinetics and microstructure associated with this reaction have been studied in detail. The results show that small Nb3Sn grains nucleate at the Nb 3 Sn/Nb interface, and that the Nb 3 Sn grains experience grain growth immediately after they are formed. ZrO 2 precipitates are observed in the Nb 3 Sn at the Nb 3 Sn/Nb interface and throughout the Nb 3 Sn. The ZrO 2 precipitates occur in the form of small partially-coherent spheres in the Nb 3 Sn. No ZrO 2 precipitates are observed by TEM in the unreacted Nb. The grain boundaries in the Nb 3 Sn region are coated with a Sn-Nb-Cu alloy which would have been liquid at the diffusion/reaction temperature. The thickness of the Nb 3 Sn reaction layer formed during the isothermal diffusion anneal is proportional to time to the first power, indicating “reaction”-controlled rather than “diffusion”-controlled kinetics. The absence of diffusion-controlled kinetics can be explained by the presence of the liquid coating on the Nb 3 Sn grains. Diffusion of Sn in this liquid layer is apparently fast enough to not be the limiting kinetic step.