Synthesis of bulk nanostructured aluminum containing in situ crystallized amorphous particles

5083 Al containing in situ crystallized Al85Ni10La 5 amorphous particles (10% and 20% in volume fraction) was synthesized through a powder metallurgy route consisting of cold isostatic pressing, degassing and hot extrusion. The nanostructured 5083 Al powders (grain size ∼28 nm) were produced through mechanical milling in liquid nitrogen. The Al 85Ni10La5 powders were produced via gas atomization using helium gas and the fraction in the size range of <500 mesh (<25 mum), which appeared to be fully amorphous on the basis of X-ray diffraction studies, was isolated for further investigation.; The amorphous Al85Ni10La5 alloy exhibited a glass transition at ∼259°C (at a heating rate of 40°C/min) and nanoscale crystallites (< 100 nm) with an equiaxed morphology formed during the subsequent crystallization reactions. At temperatures higher than 283°C, only the equilibrium phases Al, Al3Ni and Al11La 3 were formed. An unusually high nucleation density (1021-22 /m3) was recorded in the crystallization process. The copious nucleation sites were rationalized from the presence of quenched-in Al nuclei, which were evidenced by isothermal calorimetric tracing (235°C) and a direct HRTEM observation of the amorphous Al85Ni10La 5 powders. The feasibility of preparation of nanocrystalline/amorphous particles via melt spinning followed by ball milling was also studied.; In the as-extruded composites, the amorphous Al85Ni10 La5 particles underwent complete crystallization resulting in a grain size of 100 ∼ 200 nm; the 5083 Al matrix had a grain size around 200 nm in the fine-grained region interspersed by coarse-grained region with a grain size of 600 ∼ 1500 nm. A metallurgical bond formed between the 5083 Al matrix and Al85Ni10La5 particles showing a grain-boundary-like interface. The compressive fracture strength of the as-extruded 10% and 20% Al85Ni10La5 composites were determined to be 1025 MPa and 837 MPa, respectively. The influence of secondary processing, i.e., swaging, following extrusion on the mechanical behavior was also studied. The coarse grain formation in cryomilled 5083 Al during the thermomechanical process was discussed and it was evident that grain rotation and coalescence played an important role in the overall mechanism.