In the present study, Mg nanocomposites with a high volume fraction (10 vol %) of SiC particles were fabricated by two approaches: mechanical milling and mixing, followed by the powder consolidation steps, including isostatic cold pressing, sintering, and extrusion. A uniform distribution of the high content SiC particles in a fully dense Mg matrix with ultrafine microstructure was successfully achieved in the mechanically milled composites. The effect of nano- and submicron-sized SiC particles on the microstructure and mechanical properties of the nanocomposites was evaluated. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), and X-ray diffractometry (XRD) were used to characterize microstructures of the milled and mixed composites. Mechanical behavior of the Mg composites was studied under nanoindentation and compressive loading to understand the effects the microstructural modification on the strength and ductility of the Mg/SiC composites. The mechanical properties of the composites showed a significant difference regarding the size and distribution of SiC particles in the Mg matrix. The enhanced strength and superior ductility achieved in the mechanically milled Mg composites are mainly ascribed to the effective load transfer between matrix and SiC particles, grain refinement of the matrix, and strengthening effects of the nano- and submicron-sized SiC particles.

Metal-ceramic nanocomposites are promising candidates for applications necessitating light weight and excellent fatigue resistance. We produced Mg-SiC nanocomposites from mechanically milled powders, yielding a homogeneous nanocrystalline structure and excellent quasistatic strength values. Little is known, however, about the fatigue behavior of such composites. Here, we used load increase tests on the macroscale to yield estimation values of the fatigue endurance limit. Fatigue strength increased significantly for the materials processed by the powder metallurgical route. We further investigated the cyclic deformation behavior under stress-controlled conditions on the macroscale and nanoscale. Cyclic nanoindentation showed that indentation depth and cyclic plastic deformation decreased with increasing reinforcement content, hinting to a higher cyclic strength and corroborating the results from the macroscopic load increase tests. Our results therefore show that cyclic nanoindentation reliably determines the plastic deformation behavior of Mg nanocomposites offering the possibility of fast material analysis.

Porous magnesium has a great potential to be used as degradable bone scaffolds. In this study, porous magnesium with 35% percolating porosity has been successfully fabricated through powder metallurgy route utilizing space holders. The intrinsic mechanical properties of the porous magnesium were measured by nanoindentation testing and analyzed with the Oliver–Pharr method. Afterward, a ceramic coating on the surface of the porous magnesium was performed by plasma electrolytic oxidation (PEO) treatment in a silicate‐based solution. The morphology and composition results of the PEO coatings indicated that it is possible to apply a homogenous and adhesive ceramic coating layer on all free surface of the porous magnesium through PEO method. The protective performance of the PEO coatings was evaluated using by potentiodynamic polarization and electrochemical impedance spectroscopy tests in simulated body fluid. The results revealed the PEO coating significantly improves biocorrosion resistance of the porous magnesium. Therefore, it can be used as an effective method to control the degradation rate of porous magnesium implants in the human body.

The production of fully dense nanocomposites with a homogeneous distribution of nanoparticles through powder metallurgy (PM) techniques is challenging. Additionally to mechanical milling, pressing and sintering, a final consolidation process is needed to fully densify the nanocomposite. Hot isostatic pressing (HIP) is a promising alternative method to other hot forming processes to eliminate porosity in these PM parts. In contrast to hot extrusion, for instance, isotropic properties are achieved, and textures, as they are usually observed in Mg after uniaxial deformation, are avoided. Here, we evaluate the effect of HIP on the densification, microstructure and (nano)hardness of Mg–SiC nanocomposites. Even though density increased indeed, we observed no increase in the mechanical properties, due to significant heterogeneity in the microstructure. SiC-free regions with a higher grain size developed. Local nanohardness measurements of the HIPed Mg nanocomposite revealed that these regions had a significantly lower nanohardness than the SiC-containing regions. Under consideration of mechanisms reported to be active in Mg in the pressure and temperature regime we used, we conclude that grain growth is the most likely mechanism leading to the microstructure observed after HIP. This is driven by the thermodynamic pressure to decrease the grain boundary energy and facilitated by a slightly inhomogeneous distribution of SiC nanoparticles in the sintered nanocomposite.

Due to the rapidly increasing price of tungsten carbide and the significant health risks associated with the wear products of WC-Co (Co3O4 and Wo3), an alternative is required. Niobium carbide (NbC) is well suited as a cutting tool due to its high melting point and low solubility in iron. Compared to pure NbC, a complete substitution of WC to NbC-Co resulted in an increased toughness and strength. As alternative binders, nickel and iron-based binders were subsequently investigated. Although iron-based cermets would be an economical, low-cost alternative to NbC-Ni cermets, they showed a higher coefficient of friction and wear rate. So far, NbC-Ni cermets best met the requirements of high hardness and toughness. Various secondary carbides such as VC, Mo2C, TiC, but also WC were added to further improve the hardness. Elemental analyses of NbC-Ni-MeC cermets (Me = metal) showed that the binder is a face-centered cubic solid solution, while the NbC phase is a solid solution of the type (Nb, Me)C.