Microstructural characterization and mechanical behaviour of novel in-situ Be-Al composites

The deformation behavior of as-cast in-situ Be-Al alloys of compositions of Be-37Al-3Ni and Be-34Al-2Ni-2Ag-2Si (wt.%) has been investigated. The microstructure of the as-cast materials consisted of globular particles of Be dispersed discretely within a continuous distribution of the minor Al phase. The occurrence of this microstructure has been discussed in the context of a submerged metastable monotectic reaction in Be-Al alloys. Fractography of specimens fractured in tension revealed a cleavage mode of brittle and ductile failure in the Be and Al phases, respectively. A high density of dislocations were observed in the Al phase, which has been determined to be associated with easy slip of 1/2 < 101 > type of dislocations. It was found that the primary deformation mechanism in the Be phase involved motion of dislocations with Burgers vector, b, given by b=1/3 < 11 (2) over bar 0 > on the basal plane. Straight screw segments of these types of dislocation and much shorter segments with edge character have been observed.