Hydroxyapatite substrates are common biomaterials, yet samples of natural teeth do not meet the demands for well-defined, highly reproducible properties. Pellets of hydroxyapatite were produced via the field assisted sintering technology (FAST) as well as via pressureless sintering (PLS). The applied synthesis routes provide samples of very high density (95%-99% of the crystallographic density) and of very low surface roughness (lower than 1 nm when averaged per 1 μm). The chemical composition of the raw material (commercial HAP powder) as well as the crystalline structure is maintained by the sintering processes. These specimens can therefore be considered as promising model surfaces for studies on the interactions of biomaterial with surfaces of biological relevance, as demonstrated for the adsorption of BSA proteins.

Magnetic-field-dependent small-angle neutron scattering (SANS) has been utilized to study the magnetic microstructure of bulk metallic glasses (BMGs). In particular, the magnetic scattering from soft magnetic Fe 70 Mo 5 Ni 5 P 12.5 B 2.5 C 5 and hard magnetic (Nd 60 Fe 30 Al 10 ) 92 Ni 8 alloys in the as-prepared, aged, and mechanically deformed state is compared. While the soft magnetic BMGs exhibit a large field-dependent SANS response with perturbations originating predominantly from spatially varying magnetic anisotropy fields, the SANS cross sections of the hard magnetic BMGs are only weakly dependent on the field, and their angular anisotropy indicates the presence of scattering contributions due to spatially dependent saturation magnetization. Moreover, we observe an unusual increase in the magnetization of the rare-earth-based alloy after deformation. Analysis of the SANS cross sections in terms of the correlation function of the spin misalignment reveals the existence of field-dependent anisotropic long-wavelength magnetization fluctuations on a scale of a few tens of nanometers. We also give a detailed account of how the SANS technique relates to unraveling displacement fields on a mesoscopic length scale in disordered magnetic materials.

We utilized synchrotron-based in-situ diffraction and dominant shear deformation to identify, dissect, and quantify the relevant deformation mechanisms in nanocrystalline Pd 90 Au 10 in the limiting case of grain sizes at or below 10 nm. We could identify lattice and grain boundary elasticity, shear shuffling operating in the core region of grain boundaries, stress driven grain boundary migration, and dislocation shear along lattice planes to contribute, however, with significantly different and nontrivial stress-dependent shares to overall deformation. Regarding lattice elasticity, we find that Hookean linear elasticity prevailed up to the maximal stress value of ≈ 1.6 GPa. Shear shuffling that propagates strain at/along grain boundaries increases progressively with increasing load to carry about two thirds of the overall strain in the regime of macroplasticity. Stress driven grain boundary migration requires overcoming a threshold stress slightly below the yield stress of ≈ 1.4 GPa and contributes a share of ≈ 10 % to overall strain. Appreciable dislocation activity begins at a stress value of ≈ 0.9 GPa to then increase and eventually propagate a maximal share of ≈ 15 % to overall strain. In the stress regime below 0.9 GPa, which is characterized by a markedly decreasing tangent modulus, shear shuffling and lattice-and grain boundary elasticity operate exclusively. The material response in this regime seems indicative of nonlinear viscous behavior rather than being correlated with work-or strain hardening as observed in conventional fcc metals.

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Preparation history and processing have a crucial influence on which configurational state material systems assume. Glasses and nanocrystalline materials usually reside in nonequilibrium states at room temperature, and as a consequence, their thermodynamic, dynamical, and physical properties change with time—even years after manufacture. Such changes, entitled aging or structural relaxation, are all manifestations of paths taken in the underlying potential energy landscape. Since it is highly multidimensional, there is a need to reduce complexity. Here, we demonstrate how to construct a one-dimensional pathway across the energy landscape using strain/volume as an order parameter. On its way to equilibrium, we map the system’s release of energy by calorimetry and the spectrum of barrier heights by dilatometry. The potential energy of the system is reduced by approximately kBT during relaxation, whereas the crossing of saddle points requires activation energies in the order of 1eV/atom relative to the energy minima. As a consequence, the system behaves as a bad global minimum finder. We also discovered that aging is accompanied by a decrease in the non-ergodicity parameter, suggesting a decline in density fluctuations during aging.