FABRICATION OF BERYLLIUM SHEET BY GAS-PRESSURE BONDING.

Abstract : Beryllium sheet with a high third-dimensional ductility has been produced by a process combining gas-pressure bonding of beryllium powder and limited cross rolling of the resulting compact. QMV beryllium after pressure bonding at 1450 F is characterized by a high strength and low ductility. As-bonded strengths were improved by outgassing the pack at 1000 F prior to bonding. As a result of cross rolling with light reductions at 1450 F, a fine structure was developed in the material, which exhibited an apparent grain size of approximately 3 microns. The development of this structure in QMV beryllium was observed to parallel an increase in third-dimensional ductility. After rolling to a total reduction of 8:1, bend specimens of this material could not be tested to failure in the present four-point-loading bend-test apparatus. An estimate of approximately 3 percent third-dimensional strain was, however, determined from a curved sample edge compressed to fracture. The effect of cross rolling on the yield and tensile strengths of the material was to first decrease these strengths from the as-bonded level followed by an increase to 55,000 and 77,000 psi, respectively, at an 8:1 reduction. Over this range of rolling reductions, tensile elongations to 11 percent were obtained. Reproducibility of the tensile and bend properties for QMV beryllium were demonstrated in the fabrication of larger sheet sizes cross rolled with light reductions. CR beryllium sheet produced in the same manner also exhibited a high third-dimensional ductility with high tensile strengths. Yield strengths for the CR beryllium were lower, and the tensile elongations were found to be directional.