(Ti,Zr)C synthesized and aged in the immiscibility temperature range was investigated to improve understanding of the mechanism of phase separation, particularly the nucleation and early growth stages. The phase separation was observed to occur through discontinuous precipitation at grain boundaries. The nuclei were found enriched in titanium and associated with dislocations intersecting grain boundaries. During growth, zirconium enriched regions form subsequently and the semi-coherent interfaces of the Ti- and Zr-rich phases contain misfit dislocations. These observations suggest that dislocations play an important role for the nucleation and growth during discontinuous precipitation in the (Ti,Zr)C high misfit miscibility gap system.

The mixed carbide Ti-Zr-C has been synthesized through carbothermal reduction of TiZrO4 at 2200 °C, 2300 °C, and 2400 °C. As-synthesized carbide was subsequently aged at 1400 °C to study phase separation. Microstructural investigations and nano-indentation measurements were performed. It was found that the synthesis temperature was important for the homogeneity and porosity of the as-synthesized powder, which strongly influenced the subsequent phase separation upon aging. The phase separation occurred via discontinuous precipitation, and high-angle boundaries were preferred. Furthermore, the characteristics of discontinuous precipitation in the present Ti-Zr-C system with a miscibility gap were compared to those of classical discontinuous precipitation. Finally, fully decomposed particles were found to be slightly harder than the unaged carbide particles.

(Ti,Zr)C powder was sintered with WC-Co following an industrial process, including an isotherm at 1410 °C. A series of interrupted sintering trials was performed with the aim of studying the sintering behavior and the microstructural evolution during both solid-state and liquid-state sintering. Reference samples, using the same elemental compositions but with the starting components TiC and ZrC instead of (Ti,Zr)C, were also sintered. The microstructure was investigated using scanning electron microscopy and energy dispersive X-ray spectroscopy. It is found that the (Ti,Zr)C phase decomposes into Ti-rich and Zr-rich nano-scale lamellae before the liquid-state of the sintering initiates. The final microstructure consists of the binder and WC as well as two different γ phases, rich in either Ti (γ₁) or Zr (γ₂). The γ₂ phase grains have a core-shell structure with a (Ti,Zr)C core following the full sintering cycle. The major differences observed in (Ti,Zr)C with respect to the reference samples after the full sintering cycle were the referred core-shell structure and the carbide grain sizes; additionally, the microstructural evolution during sintering differs. The grain size of carbides (WC, γ₁, and γ₂) is about 10% smaller in WC-(Ti,Zr)C-Co than WC-TiC-ZrC-Co. The shrinkage behavior and hardness of both composites are reported and discussed.

(Ti,Zr)C powder was synthesized by carbothermal reduction and subsequently aged at 1150–2000 °C. The phase composition and microstructure was investigated using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and electron backscatter diffraction. It was found that the as-synthesized (Ti,Zr)C particles have a concentration gradient with a higher concentration of Ti at the surface of the particles. Furthermore, during aging the (Ti,Zr)C decomposes into Ti-rich and Zr-rich lamellae. During aging at 1400 and 1800 °C for 10 h, most Zr-rich and Ti-rich domains precipitate at grain boundaries, inheriting the crystal orientation of the parent grain behind the growth front. When the precipitate grows into another (Ti,Zr)C grain, that grain adopts the same crystal orientation as the parent grain. The crystallographic misorientation between adjacent lamellae is 0–5°. Based on these microstructural observations it is hypothesized that the mechanism of decomposition is discontinuous precipitation.

A nanoindentation and first-principles calculation study of a self-organizing nanostructured lamellar (Ti,Zr)C powder has been performed. The nanoindentation measurements reveal that the hardness of the carbide is comparable to the hardest transition metal carbides that have been reported previously. The origin of the super-high hardness is postulated to be due to the inherent bond strength and the large coherency strains that are generated when the carbide demixes within the miscibility gap. The high hardness is maintained at a high level even after 500 h aging treatment at 1300°C. Therefore, it is believed that the new superhard mixed carbide has a high potential in various engineering applications such as in bulk cemented carbide and cermet cutting tools, and in surface coatings.

Antibiotic incorporation into hydroxyapatite (HA) coatings by co-precipitation and the impact of bone relevant doping elements on the adsorption kinetics are investigated from both theoretical and experimental points of view. Tobramycin interactions with bioactive TiO2 and HA surfaces are analyzed using density functional theory. According to the calculations, the drug molecule has larger adsorption energy than the Ca+ ion on both surfaces under study in Phosphate Buffered Saline (PBS). The results support the experimental observations that HA nucleation and growth are strongly limited on TiO2 surfaces in the presence of clinically relevant antibiotic concentrations in PBS. The drug molecule is more likely to adopt parallel arrangement onto the HA surface, as the adsorption energy of such arrangement is higher compared to a perpendicular one. Strontium substitution of the HA surface is found to results in a weaker drug-surface interaction, and leads also to a decrease in coating thickness. However, the presence of strontium gives rise to a coating morphology with enhanced drug incorporation capacity and slower antibiotic release compared to non-substituted, co-precipitated counterparts. Our theoretical calculation results were found to be in excellent agreement with experimental data and provide a powerful tool to understand the interaction mechanism between drug and different surface chemistries necessary for development of future versatile orthopedic and dental implant surfaces.