Phase composition and microstructure of hydroxyapatite (HA) significantly affects the biological and mechanical properties of final hydroxyapatite (HA) coating. In the present study, HA coatings were deposited on Ti-6Al-4V by micro-plasma spraying (MPS) using different spray parameters. The influence of spray parameters on the composition and microstructure of the coatings were investigated. To understand the formation mechanism of HA coatings, the in-flight particles and splats were examined as well. The morphologies of coatings surface, cross-sections, initial powder, in-flight particles and splats were characterized by scanning electron microscopy (SEM). Xray diffraction (XRD) was employed to analyze the phase composition. Three typical HA coatings were fabricated. The results indicated that the coating composition and microstructure were tightly related to the melting state of inflight particles. And this was influenced by the spraying parameters. The formation mechanisms of these coatings were discussed.

To manufacture a protective coating with low thermal conductivity and good frictional wear performance, a Fe 59 Cr 12 Nb 5 B 20 Si 4 coating was designed and produced by high velocity oxygen fuel (HVOF) spraying; the properties and performance of this coating where then compared with those of a commercially available AISI 316L stainless steel coating. In the as-deposited state, both coatings exhibit dense layered structures with porosity below 1% and slight oxidation. The microstructure of the Fe-based coating has an amorphous matrix and some precipitated nanocrystals. The result is that the designed Fe-based coating has a thermal conductivity (2.66 W/m·K) that is significantly lower than that of the 316L stainless steel coating (5.87 W/m·K). Based on its advantageous structure, the Fe-based coating exhibits higher microhardness, reaching 1258±92 HV. The friction coefficient and wear rate of the Fe-based coating show an increase at 200°C followed by a decrease at 400°C, due to the evolution of the wear mechanism at different temperatures. The dominant wear mechanism of the Fe-based coating at room temperature is fatigue wear accompanied by oxidative wear. At 200°C, due to the existence of “third body” abrasive wear, the wear process was accelerated. The large-area oxide layer is likely responsible for the decrease of friction of the coating at 400°C.

In this work, micro-plasma spraying is used to produce hydroxyapatite coatings on Ti-6Al-4V substrates. To understand coating formation mechanisms, in-flight particle velocity and surface temperature were monitored under different spraying conditions. XRD measurements show that the resulting coatings have a high degree of crystallinity with little amorphous or metastable phases. Some of the coatings were also found to have a uniformly distributed columnar structure, corresponding to a strong (002) texture and excellent stability in Hanks’ salt solution even after 14 days of immersion.

In this study, Fe-Cr-Al and Fe-Cr-Al-B cored wires were produced and deposited on steel substrates by wire arc spraying. The microstructure, hardness, and high-temperature corrosion behavior of the cored-wire deposits were evaluated in comparison to Fe-Cr and commercial Fe-Cr-Al solid-wire coatings. All coating samples exhibited lamellar microstructures with oxide inclusions, the fewest being in the Fe-Cr-Al-B deposits. Microhardness was measured along coating cross-sections at various distances from the coating-substrate interface. The Fe-Cr coatings were the hardest, followed by the Fe-Cr-Al-B deposits. Thermogravimetric analysis was used to evaluate high-temperature corrosion behavior in a molten salt environment under cyclic conditions, with the Fe-Cr-Al-B cored-wire deposits performing the best.

A Fe48Cr15Mo14C15B6Y2 alloy with high glass forming ability (GFA) was selected to prepare amorphous metallic coatings by atmospheric plasma spraying (APS) process. The as-deposited coatings present a dense layered structure and low porosity. Microstructural studies show that some nanocrystals and a fraction of yttrium oxides formed during spraying process, which induced the amorphous fraction of the coatings decreasing to 69% compared with fully amorphous alloy ribbons of the same component. High thermal stability employs the amorphous coatings to work below 910K temperature without crystallization. Corrosion behavior of the amorphous coating was investigated by electrochemical measurement. The results show that the coatings exhibit extremely wide passive region and low passive current density in 3.5% NaCl and 1mol/L HCl solutions, which illustrate their superior ability to resist localized corrosion. Moreover, the corrosion behavior of the amorphous coatings in 1mol/L H 2 SO 4 solution is similar to their performance in chlorine ions contained conditions, which manifests their flexible and extensive ability to withstand aggressive environments.

A ceramic composite coating of a FeB alloy reinforced with cobalt-coated tungsten carbide (WC-12Co) particles and nickel-coated tungsten carbide (WC-12Ni) particles was deposited on a mild steel substrate by arc spraying cored wire, respectively. The microstructure and the worn surfaces of the coatings were analyzed by X-ray diffraction (XRD), Scanning electron microscope (SEM). And wear mechanisms of the coatings have been discussed on the basis of the observation. The results showed that adding WC powders can obviously increase the hardness and abrasive wear resistance property of the coating. The average microhardness of the coatings is about 900~1000 HV 0.1 . In the experimental conditions, the coatings have the excellent abrasive wear resistance which is 7~10 times higher than that of the Q235 mild steel. Plastic microcutting and brittle peeling play the predominant role in abrasion wear of the coating.

Yttria-stabilized zirconia coatings were deposited onto a Ti-6Al-4V substrate through a microplasma spray technique and incubated in simulated body fluid (SBF) for different periods of time (3, 7, 14, 28 days). The formation of apatite on the surface was investigated to evaluate the bioactivity of the coatings. Surface morphologies and structural changes in the coatings before and after immersion were analyzed by optical microscopy, scanning electron microscopy, and x-ray diffractometry. The calcium (Ca 2+ ) concentration in the solutions was measured directly after the samples were removed, using an inductively coupled plasma atomic emission spectrometer (ICP). The results showed that yttria-stabilized zirconia coatings can be produced by microplasma spraying and, even though the coatings contain few small unmelted particles, apatite can be formed on the coatings that are soaked in SBF solution. These results indicate that the yttria-stabilized zirconia coatings exhibited definite bioactivity.