Microstructural characterization of novel in-situ Al-Be composites

The microstructure of cast and extruded in-situ Al-Be alloys, of compositio ns of Be-37Al-3Ni (wt pet) and Be-34Al-2Ni-2Ag-2Si (wt pet), was investigat ed using optical microscopy, scanning electron microscopy (SEM), and transm ission electron microscopy (TEM). The study indicates that both the Be and Al phases are continuous. The Be phase has a coarse dendritic structure in the as-cast material. Fractographic analysis of failed tensile specimens te sted at room temperature revealed basal-plane cleavage failure of the Be ph ase and ductile failure of the Al phase. A significant number of deformatio n twins were observed in the Be phase when the tensile loading axis was par allel to the Be dendrite growth axis. An additional fracture mode was obser ved in the samples tested at elevated temperatures. At elevated temperature s, decohesion of the A-Be interface was observed on the fracture surface. T his phenomena was observed to increase as the test temperature increased fr om 150 degreesC to 315 degreesC. A high density of dislocations with a tang led morphology were observed in the Al phase after the tensile test. These were determined to be associated with easy slip of 1/2[101]-type dislocatio ns. The limited ductility of the Be phase was attributed to the predominant basal slip of (a)-type dislocations, b = 1/3[1120], and the lack of disloc ations with (c) components. However, a significant number of dislocations w ith (c) components were found in localized areas of the Be phase after extr usion.