Production of fine-grained beryllium-6 WT% copper for fusion ignition capsules by arc melting and equal channel angular extrusion

Beryllium doped with 6 weight % copper is the material of choice for fabrication of target capsules for the National Ignition Facility because of its combination of attractive neutronic, electronic, physical, and mechanical properties. The target capsules are 2 mm in diameter and thin-walled (150 microns) and must meet demanding dimensional specifications. The material must be fine-grained and of low inclusion content. Arc-melted Be-Cu is being produced to eliminate the oxide content that is inevitably present in conventional powder-metallurgy materials. Equal channel angular extrusion (ECAE) is being used to refine the as-cast grain structure. Be-Cu rods produced by the arc-melting process (5 mm in diameter by 30 mm in length) are enclosed in nickel cans with electron-beam welded plugs. The Be-in-Ni billets (9.5 mm in diameter by 45 mm in length) have been processed by ECAE at temperatures from 500 to 750degreesC in tooling with a 120degrees angle. Selected samples have been annealed for 1 hour at temperatures from 700 to 775degreesC The ECAE processing creates a heavily deformed and finely subdivided structure, and the annealing can produce an equiaxed microstructure with a grain size of approximately 20 mum.