Micro-Yield Behavior and Mechanism of Powder Metallurgical Beryllium-Aluminum Alloys

Micro-yield behavior of powder metallurgical beryllium-aluminum alloys was researched. The dislocation changes of the two phases at different stains in the process of micro-yield of the alloys were studied by TEM, and the fracture character was observed by SEM. The results show that the Be-Al alloy exhibits a lower micro-yield strength; the dislocations are difficult to discover before micro-yield to reaching 2x10(-6) stains in Be phase; when the stain reaches 79 x 10(-6), the dislocations appear both in the grain and along the grain boundaries; the dislocations move and connect to lines after 121 x 10(-6) stains; the dislocations tangle at 500 x 10(-6) stains, which are straightened in the grain and decrease in the vicinity of grain boundary. Different from Be phase, a few dislocations of Al phase have appeared before micro-yield; when the stain reaches 2x10(-6), large plastic strain occurs in Al phase; driven by the external load and thermal residual stress, the dislocations in Al phase gather at the interface and cause them cut into Be phase, reducing its deformation resistance. The failure mode of beryllium-aluminum alloys is brittle cleavage failure of beryllium regions combined with ductile dimple failure of aluminum regions.