MECHANICAL-BEHAVIOR OF NANOCRYSTALLINE ALUMINUM-ZIRCONIUM

An investigation of the room-temperature mechanical properties and def ormation behavior of nanocrystalline aluminum-zirconium has been condu cted via microhardness, nanoindentation and novel tensile experiments. Nanocrystalline specimens were produced by the inert-gas condensation process with electron beam evaporation. The modulus of elasticity of nanocrystalline Al-Zr was determined to be similar to that of coarse-g rained aluminum. The hardness, strength and ductility of the samples, however, were found to be strongly impacted by grain size, which is re duced at higher zirconium levels. Extremely high hardnesses were obtai ned for the materials (up to similar to 3 GPa), while the tensile stre ngths were less impressive. Some ductility in tension was exhibited by specimens with relatively large grain sizes(greater than or equal to 100 nm), although the elongation to failure dropped to less than 1% wh en the grains were stabilized to similar to 10 nm by zirconium additio ns. This behavior appears to be linked to the increasingly high stress es required to generate dislocations to prevent crack propagation and cause yielding as the grain size is reduced into the nanometer regime. At room temperature and at the strain rate employed in this study (10 (-4) s(-1)), no evidence was found to suggest that an alternative, dif fusional-based deformation mechanism takes over at the smallest grain sizes. (C) 1997 Elsevier Science S.A.