Advanced, model-driven forming of direct-sliced, medium grain high RRR niobium

RRR-grade niobium sheet is one of the many cost drivers concerning superconducting RF accelerators such as the EIC and ILC. Direct-sliced, medium grain niobium holds promise to reduce these costs since it omits the cross-rolling and vacuum annealing required to generate fine grain material. Furthermore, the possibility of sheet contamination is lower for direct-sliced niobium. Although less expensive, direct-sliced medium grain niobium is challenging to form. In this project, material-related deficiencies in formability will be compensated with sophisticated simulations and advanced processing equipment. We will develop a calibrated plasticity model of medium grain niobium in ABAQUS with the objective of virtually prototyping the tooling and double-action deep drawing using a servopress. By optimizing the process sequence between electron beam melting and deep drawing, this project aims to lower the per unit costs SRF cavities via reduced cost material and higher forming yields. In Phase I, the properties of ATI medium grain Nb will be characterized at Ohio State University using a series of forming-specific material tests and state-of-the-art analysis equipment. The work will be guided by Prof. Yannis Korkolis, a recognized leader in model-driven forming optimization. Coupon level metallography, finishing (BCP, EP, abrasive), vacuum annealing and EBW studies will also be performed at RadiaBeam, while RRR measurements will be performed at JLab. The final deliverable of Phase I will be a 3.9 GHz medium grain half-cell formed on a double action servopress. In Phase II, a single cell 1.3GHz TESLA style cavity will be fabricated by RadiaBeam and tested a JLab. A comparison between hydraulic forming of fine grained and servopress forming of medium grain niobium will be provided. Reducing the costs of SRF cavities will further the development of future large scale accelerator facilities. The forming simulations developed in this project can also be adapted to other difficult SRF sheet metal geometries. Furthermore, the engineering expertise developed concerning refractory sheet metal processing (simulation, forming, surface treatment, advanced welding) can be applied to other high value applications including nuclear, aerospace and space.