Micro- and nanomechanical study on aluminum bulk material and micromachined surfaces

To enable future applications of micromilling for production of small-scale components with sufficient precision and repeatability fundamental understanding of the process and changes in material behavior is necessary. For this purpose, microstructure and mechanical properties of aluminum-based materials subject to strain hardening were investigated. In the present thesis, crystal anisotropy (aluminum single crystals in (100), (110) and (111) orientations), plastic flow under uniaxial compression (recrystallized high purity aluminum) and the effect of micromilling on strain hardening of the AA6082 surface (micromilled with monocrystalline diamond (radius 17 nm) and solid carbide (radius 671 nm) tools) were studied in detail. Nanoindentation was used to investigate mechanical properties with high precision. It could be determined that crystal orientation influences the indentation modulus by~1.3~\%. The combined effect of crystal symmetry and indenter geometry (Vickers indenter) was found to affect hardness and modulus by up to~1.8~\%. Deformation behavior of aluminum under uniaxial load was found to be significantly influenced by the initial orientation of the respective grains and their slip-system in respect to the load direction. This led to highly anisotropic plastic flow for degrees of deformation over 40~\% as resulting in an intermittent grain softening. This effect is attributed to dynamic discontinuous recovery. The milling experiments showed that the surface roughness is largely influenced by the cutting edge radius and roughness along the cutting edge. Depth and hardness of the deformation zone introduced due to the ploughing-effect was demonstrated to depend mostly on the cutting edge radius. The influence of cutter material on surface roughness and the ploughing effect is not considered to be significant. The monocrystalline diamond tool showed superior performance by producing very smooth and nearly undeformed surfaces. Based on our studies we conclude, that the it should be the tool of choice for high-precision micromanufacturing