The rheological properties of synovial fluid (SF) are essential for the friction behavior and wear performance of total joint replacements. Standardized in vitro wear tests for endoprosthesis recommend diluted calf serum, which exhibits substantial different rheological properties compared to SF. Therefore, the in vitro test conditions do not mimic the in vivo conditions. SF samples from osteoarthritis knee patients and patients undergoing knee endoprosthesis revision surgery were compared biochemically and rheologically. The flow properties of SF samples were compared to synthetic fluid constituents, such as bovine serum albumin (BSA) and hyaluronic acid (HA). Interestingly, HA was identified as a significant contributor to shear-thinning. Using the acquired data and mathematical modelling, the flow behavior of human SF was modelled reliably by an adapted adjustment of biorelevant fluid components. Friction tests in a hard/soft bearing (ceramic/UHMWPE) demonstrated that, in contrast to serum, the synthetic model fluids generate a more realistic friction condition. The developed model for an SF mimicking lubricant is recommended for in vitro wear tests of endoprostheses. Furthermore, the results highlight that simulator tests should be performed with a modified lubricant considering an addition of HA for clinically relevant lubrication conditions.

Mo-Ti-Si, Mo-Zr-B, and Mo-Hf-B are promising alloy systems for high-temperature applications as they show higher toughness and higher creep resistance than other Mo-based alloys. Regarding ductility and toughness, the chemical composition of the Mo solid-solution phase is the main parameter with which to tweak these properties of multiphase Mo-based alloys. Besides the common solid-solution hardening, one goal is to minimize embrittlement by decreasing the detrimental effects of interstitials like oxygen atoms in Mo alloys, which might be present in the bulk material due to trapping. For a better understanding of the trapping mechanisms and behavior of Mo solid solutions, the bonding situation and interaction of Mo atoms with the atoms of the alloying partners, as well as oxygen atoms, is worthwhile to investigate. For this, an in-depth analysis of the chemical bonding situation with calculations based on density functional theory in selected Mo-TM(-O) (TM = Ti, Zr, Hf) solid solutions is conducted in this work. It is shown that Ti atoms in a Mo solid solution are strong traps for oxygen atoms, while Hf and, even more clearly, Zr atoms are not. It is pointed out that the ionic and covalent interactions are the primary influence on the trapping behavior, as the change in ionic and covalent interactions between trapping and nontrapping models follows the trend Mo-1Ti > Mo-1Hf > Mo-1Zr, which resembles the trend of the trapping energy.

Complex‐concentrated alloys based on the combination of the 3d transition elements and aluminum are promising candidates for future lightweight high‐temperature applications. However, the thermodynamically driven phase composition of these alloys has not been clearly understood, leading to conflicting results. In this work, investigations on the alloy are carried out with an emphasis on identifying the crystal structure(s). The microstructure and crystal structures are studied using a combination of scanning electron microscopy and X‐Ray diffraction. The alloy possesses a two‐phase microstructure with a Fe‐rich matrix and Cu‐rich precipitates after aging heat treatment. The matrix is found to possess the crystal structure in combination with precipitates, having a characteristic A2 structure. The phase fractions, precipitate size, and morphology are studied using quantitative microscopy. The thermodynamic origin of the phase composition is explained by using the results from binary and ternary subsystems and the Miedema's model for binary interactions. Finally, an overaging phenomenon in the studied alloy system is correlated in terms of microhardness measurements.

Despite the development of three‐dimensional imaging techniques in materials science, most of the microstructural data is taken from two‐dimensional sections. It includes images produced by optical, scanning, and transmission electron microscopy. Due to the stochastic indefinite characteristics of such sections, it is a challenge to reproduce three‐dimensional microstructure characteristics quantitatively. Several analytical techniques were developed in stereology to overcome such limitations. Nevertheless, available analytical techniques are restricted to limiting cases of entirely random or fully coaxial orientation of microstructural features. On the other hand, achieving ideal coaxiality of such inclusions in actual technological conditions is not achievable. In this work, the Monte‐Carlo‐based optimization algorithm is constructed to overcome the limitations of existing stereometric models. This algorithm considers information from longitudinal and transverse sets of images. Orientations, as well as size distributions, are taken into account. The model operates under the assumption of log‐normal distribution of 3d size characteristics and von Mises distributions of angles. Then, a derivation‐free optimization algorithm is used to match histograms of simulated and observed sections. The method for estimating the initial values of optimized variables is proposed, based on the existing analytic solutions. The reconstruction algorithm is then applied to estimate three‐dimensional angle and size distributions of inclusion of phase in near‐eutectic alloy, produced by directional solidification technique. Finally, the algorithm's convergence is discussed, as well as its limitations and future developments.