Mechanical behavior of nanocrystalline aluminum-zirconium

An investigation of the room-temperature mechanical properties and deformation behavior of nanocrystalline aluminum-zirconium has been conducted 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-grained aluminum. The hardness, strength and ductility of the samples, however, were found to be strongly impacted by grain size, which is reduced at higher zirconium levels. Extremely high hardnesses were obtained for the materials (up to ~ 3 GPa), while the tensile strengths were less impressive. Some ductility in tension was exhibited by specimens with relatively large grain sizes (≥ 100 nm), although the elongation to failure dropped to less than 1% when the grains were stabilized to ~ 10 nm by zirconium additions. This behavior appears to be linked to the increasingly high stresses 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, diffusional-based deformation mechanism takes over at the smallest grain sizes.