MICROSTRUCTURES OF CUBIC AL2O3 PRECIPITATES IN OXYGEN-IMPLANTED ALUMINUM

The microstructure of Al ion-implanted at room temperature with 17 at.% O has been characterized with TEM. The alloy has extremely small (1.5-3.5 nm) oxide precipitates whose crystal structure is interpreted to be a disordered version of gamma-Al2O3 having a fcc lattice of O2- ions with Al3+ ions in random interstitial sites. The small sizes can account for the exceptionally high strength of as-implanted alloys: 2500-3300 MPa. Larger precipitates are found when the alloy is annealed 1/2 h at 550-degrees-C, which is consistent with its somewhat lower strength: 800-1600 MPa.