Early work on rapidly solidified uranium

The microstructure of rapidly solidified U droplets impinged on solid Cu is examined. The 1/2 in. thick Cu collector was cooled with helium precooled by liquid nitrogen. This collector rotated at 1750 rev/min in a direction to move the deposit away from the melting region of the rotating unalloyed U electrodes. Removal and recovery of individual U splats was undertaken to insure that succeeding droplets would impinge on a bare Cu surface rather than build up on a preceding splat. Optical metallography of splats showed them to have a mixture of very fine grains ( < 10 mu m) and an acicular structure. Test samples were heated in a hot stage microscope for 1 h at either 550 or 600 deg C. At either temp. the acicular structure was transformed. Extremely fine grains were retained at 550 deg C but that treatment coarsened the grains to dia. of approx 20 mu m.--J.R.D.