The nature of non-crystalline materials causes the local potential energy of a cluster of atoms or molecules to vary significantly in space. Different configurations of an ensemble of atoms in a metallic glass lead therefore to a distribution of elastic constants which also changes in space. This is totally different to their crystalline counterparts, where a long-range order exists in space and therefore a much more unified elastic modulus is expected. Using atomic force acoustic microscopy, we present data which show that the local so-called indentation modulus M indeed exhibits a wide distribution on a scale below 10 nm in amorphous PdCuSi, with ΔM/M≈30%. About 10(4) atoms are probed in an individual measurement. Crystallized PdCuSi shows a variation that is 10-30 times smaller and which is determined by the resolution of the microscope and by the polycrystalline structure of the material.

No abstract

In this work, tailored copolymers of tert‐butyl acrylate and acrylic acid (AA) with an ABA type structure were systematically analyzed via dynamic‐mechanical analysis with regard to their relaxations, in which the main focus was put on a chemical confinement (cc) mode caused by hydrogen bonds. Four different relaxation modes were detected, whereupon two modes seem to depend on the length of the inner B‐block and one on the length of the outer A‐blocks. One mode below room temperature could be identified as a secondary relaxation which belongs to the B‐block and is most likely induced by a cc. A softening of the polymer corresponding to the glass transition is found near to room temperature and surprisingly shifts to lower temperatures with increasing chain length of the B‐block. A second softening of the ABA type copolymers is caused by the AA containing A‐blocks and was found at higher temperatures.magnified image

Abstract. In this work we analyzed the mechanical damping behavior of amorphous Pd 77.5Cu6.0Si16.5 below the glass transition temperature (T g ) with creep/recovery measurements. Here a correlation between temperature stimulation and external stress is found in an exponential, multiplicative way. This demonstrates that not only is the yield stress of the material influenced by temperature variation (mechanical melting) but also the secondary relaxation is modified under stress and temperature.

No abstract