Vera Maria Marx

Fragmentation testing for ductile thin films on polymer substrates

Fragmentation testing of thin films on substrates has in the past been mostly performed in situ using optical and scanning electron microscopy. While these techniques work well for brittle materials, they cannot always discern the difference between through-thickness cracks (TTCs) and localized plastic deformation of ductile films. Here, we describe fragmentation testing with atomic force microscopy and present criterion to distinguish TTCs and localized deformation for ductile films.

Adhesion measurement of a buried Cr interlayer on polyimide

A fundamental knowledge and understanding of the adhesion behaviour of metal–polymer systems is important as interface failure leads to a complete breakdown of flexible devices. A combination of in situ atomic force microscopy for studying topological changes and in situ synchrotron based stress measurements both during film tensile testing were used to estimate the adhesion energy of a thin bilayer film. The film systems consisted of 50–200 nm Cu with a 10 nm Cr adhesion layer on 50 μm thick polyimide. If the Cu film thickness is decreased to 50 nm the Cr interlayer starts dominating the system behaviour. An apparent transition from plastic to predominantly brittle deformation behaviour of the Cu can be observed. Then, compressive stresses in the transverse direction are high enough to cause delamination and buckling of the Cr interlayer from the substrate. This opens a new route to induce buckling of a brittle interlayer between a ductile film and a compliant substrate which is used to determine the interfacial adhesion energy.

Oxidation of Fe-Al Alloys (5-40 at.% Al) at 700 and 900 °C

Fe-Al alloys with Al contents between 5 and 40 at.% Al were oxidised for 1000 h in synthetic air at 700 and 900 °C to determine their oxidation behaviour. The minimum Al content which is necessary for the formation of protective Al2O3 scales decreases with increasing temperature from about 17 at.% Al at 700 °C to about 12 at.% Al at 900 °C. Established parabolic rate constants for the steady state growth of Al2O3 indicate formation of γ-Al2O3 at 700 °C while at 900 °C α-Al2O3 + Θ-Al2O3 scales form. At lower Al contents scales are predominantly formed by Fe2O3 as revealed by GI-XRD. It is also found that the oxidation behaviour is independent of the crystallographic order of the alloys, i.e. whether they are disordered A2 or ordered B2.