Search

hydroxyapatite (HA) powder has been used widely not only in the bioceramics for hard tissue replacement but also in bioactive coatings of orthopaedic and dental implants. In this communication, we introduce a new hollow spherical HA powder with a thin shell structure (TS-HSHA powder) for the high-performance plasma-sprayed HA coating on the metallic implant. The TS-HSHA powder was prepared by the plasma process with a heat preservation zone around the flight particle. Scanning electron micrographs of the TS-HSHA powder showed that it exhibited a highly spherical morphology and a hollow structure with a shell enclosing a large central cavity. The mean size of the TS-HSHA powder is about 105.75 μm, and the mean shell thickness is only 3.11 μm. Furthermore, not only the formation mechanism of the TS-HSHA powder but also its comparison with the powder obtained by the plasma process without a heat preservation zone were also discussed.

A carbon&ndash, aluminum composite layer was prepared on the surface of pure titanium by double glow plasma carburizing, magnetron sputtering aluminizing, and vacuum-diffusional annealing treatment. The microstructure, phase composition, and properties of the composite layer obtained at different annealing temperatures were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and the ball-on-disc wear method. Results showed that the layer contained a mixture of TiAl3, Ti2Al5, and TiC phases at 650 &deg, C for 6 h, which can significantly enhance the hardness and wear resistance of pure titanium. The layer exhibited a higher hardness of around 1231 HV0.1, a lower friction coefficient of 0.33, and lower wear volumes of 0.018 mm3 than those of the titanium substrate.

Based on the limitations of traditional viewpoint that the carbide types in chromium wear-resistant alloys were determined by the Cr/C value, the aim of this study was to reveal the mechanism of recombination-reconstruction between different atoms and the influence of various elements on the formation of carbide types during the mutual transformation of M3C, M7C3 and M23C6 carbides by analyzing the difference of carbide types in different Fe-Cr-C alloys and the transformation characteristics of carbide types before and after carburization and decarbonization of 3Cr13 stainless steel. The viewpoints were put forward as follows: the transformation between M3C and M7C3 carbides are predominantly controlled by the chromium content, and the main controlling factor of transformation between M7C3 and M23C6 carbides is the carbon content. In the different stages of carbide transformation, the chromium and carbon play the main controlling role respectively

The correlations of microstructure, hardness and fracture toughness of high chromium cast iron with the addition of alloys (titanium, vanadium, niobium and molybdenum) were investigated. The results indicated that the as-cast microstructure changed from hypereutectic, eutectic to hypoeutectic with the increase of alloy contents. Mo dissolved in austenite and increased the hardness by solid solution strengthening. TiC and NbC mainly existed in austenite and impeded the austenite dendrite development. V existed in multicomponent systems in forms of V alloy compounds (VCrFe8 and VCr2C2). With the increase of alloy additions, carbides size changed gradually from refinement to coarseness, hardness and impact toughness were increased and then decreased. Compared with the fracture toughness (6 J/cm2) and hardness (50·8HRC) without any alloy addition, the toughness and hardness at 0·60 V–0·60Ti–0·60Nb–0·35Mo (wt%) additions were improved and achieved to 11 J/cm2 and 58·9HRC, respectively. The synergistic roles of Ti, Nb, V and Mo influenced the solidification behaviour of alloy. The refinement of microstructure and improvement of carbides morphologies, size and distribution improved the impact toughness.

Combining the intermetallic compound with the ductile metal at the eutectic composition is one promising method to improve the ductility of the intermetallic compound. This paper reports the microstructure and the micro-hardness of the Ni–Ni 3 Si eutectic in situ composites prepared by electron beam floating zone melting technique. Ni–Ni 3 Si eutectic in situ composites display regular lamellar eutectic structure at the solidification rate R =0.3–4.0 mm/min. The lamellar spacing is decreased with the increase of the solidification rate. The phase composition of the Ni–Ni 3 Si eutectic in situ composites is also determined by X-ray diffraction. Ni–Ni 3 Si eutectic in situ composites present lower micro-hardness than pure Ni 3 Si, although a small quantity of metastable Ni 31 Si 12 phase is formed during the directional solidification process.

Diffusion alloying processing is an emerging, environmentally friendly, surface engineering technique. In this study, we have utilized diffusion alloying processing to alloy aluminum and zinc mixed powder on pure magnesium for erosion wear protection. A stirring device was used for erosion testing. The treated and untreated samples were immersed in oil slurry and water slurry with quartz sand in suspension and rotated at a given speed. Scanning electron microscopy and X-ray diffraction were used to study the surface morphology and chemical composition of the coatings before and after erosion testing.

Ni–Ni 3 Si composites are prepared by the Bridgman directional solidification technology under different growth conditions, aiming to improve the ductility of the Ni 3 Si compound and investigate the relationship between solidification microstructure and the properties. Microstructure of the Ni–Ni 3 Si hypoeutectic in situ composites transforms from regular lamellar eutectic to cellular structure then to dendritic crystal with the increase of the solidification rate. Ni–Ni 3 Si eutectic composites display regular lamellar eutectic structure at the solidification rate R =6.0–40.0 μm/s and the lamellar spacing is decreased with the increase of the solidification rate. Moreover, the Ni–Ni 3 Si hypoeutectic composites present lower micro-hardness than pure Ni 3 Si, which indicate Ni–Ni 3 Si hypoeutectic composites have higher ductility, whereas the ductility of the Ni–Ni 3 Si eutectic composites has scarcely been improved. This is caused by the formation of the metastable Ni 31 Si 12 phase in the Ni–Ni 3 Si eutectic composites.

SiC reinforced Mn13 matrix composite was synthesised by vacuum evaporation pattern casting infiltration process. The interface reaction between SiC particles and matrix was investigated. Hardness test, optical metallography observation and X-ray diffraction analysis indicated SiC decomposition. Some decomposition products C and Si were solid solute in steel matrix to increase matrix hardness, while others reacted with Fe and formed primary carbides and Fe3Si respectively. Some C atoms coming from SiC decomposition precipitated in the form of graphite. The reaction zone might act as a diffusion barrier preventing further SiC decomposition. The added alloy elements Cr and Mn obstructed Fe in rapidly diffusing to SiC particulate and retarded SiC decomposition rate. The strong attraction between C and Cr avoided the presence of abundant graphite in composite microstructure.

During the formation flight time, the Unmanned Aerial vehicles (UAVs) have to transform their flight formation in many cases, such as environmental change, the modification of the task and some UAV's leaving of the formation. During the time to change the formation, the most important thing is to avoid UAVs crash into each other, then, they should finish the transformation process in certain time. This paper firstly focuses on the UAV formation keeping by using Proportion Integration Differentiation (PID) control method. Secondly, several control strategy are designed for formation transformation. Then, use the above methods to complete the formation transformation. Finally, the effectiveness of UAVs formation transformation is taken into account by simulated verification and comparative analysis.