The structure and mechanical properties of Al and Al-Al(2)O(3) microlaminate films synthesized by ion beam-assisted deposition.

The effects of the constituent Al and Al$\sb2$O$\sb3$ layer properties, as modified by ion beam assisted deposition (IBAD), on the fracture behavior of Al-Al$\sb2$O$\sb3$ microlaminate films were analyzed. Residual stress in monolithic Al and Al$\sb2$O$\sb3$ films could be tailored by proper control of the R-ratio (ion to atom arrival rate ratio) and E$\sb{\rm n}$ (ion energy deposited per atom, eV/atom). Residual stress in microlaminate films could be controlled by adjusting the deposition parameters of the individual layers because the stress followed a rule of mixtures. Al$\sb2$O$\sb3$ films exhibited a transition from tensile to compressive stress with increasing E$\sb{\rm n}$. Al films exhibited a tensile residual stress over the entire range of E$\sb{\rm n}$ from 0 to 50 eV/atom. Fracture behaviors of Al$\sb2$O$\sb3$ films and Al-Al$\sb2$O$\sb3$ microlaminate films were assessed by deformation of films deposited on ductile substrates. The true fracture strain of both PVD and IBAD (R = 0.1), 5-bilayer microlaminate films increased with decreasing magnitude of residual stress as the volume fraction of Al was increased from 0.20 to 0.55. Critical strain energy release rates, calculated from the experiments, for two IBAD R = 0.02 Al$\sb2$O$\sb3$ films indicated that differences in the strain energy release rates by a factor of 2 are not significant. The role of the Al layer on microlaminate fracture was analyzed in trilayer films with near zero residual film stress. Critical strain energy release rates for all trilayer films were similar (6-14 J/m$\sp2$); there was no effect of the Al layer processing or mixing at the interfaces. However, the effects of IBAD on the structure and mechanical properties of 500 nm thick Al films were significant. Mean grain size of IBAD Al was 120 nm compared with a mean grain size of 260 nm for IBAD Al. 0.2% offset yield strengths of both films were similar ($\sim$180 GPa). IBAD Al exhibited a region of increased work-hardening compared to PVD Al, albeit a decreased mean elongation to fracture. PVD Al failed by necking to a point, while the IBAD Al exhibited intergranular fracture. Differences in grain boundary character between PVD and IBAD may be responsible for both the reduced ductility and the intergranular fracture in IBAD Al.Ph.D.Applied SciencesMaterials scienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130270/2/9722009.pd