In this study, 1-1.5 μm chromium carbide particles are used to prepare CrC-NiCr and CrC-Ni-Cr powders by spray drying and vacuum sintering with the aim of optimizing the properties while minimizing the cost of HVOF-sprayed NiCr-CrC coatings. The powders are characterized by means of SEM and XRD analysis and the coatings are evaluated based on microstructure, microhardness, bonding strength, and erosion resistance.

Agglomerated and sintered Cr 3 C 2 -25%NiCr powders possess excellent flow ability and appearance that have been extensively applied to resist abrase and erosion in high temperature applications such as power boiler and turbine blade. Microstructure of Cr 3 C 2 -25%NiCr coatings were observed through scanning electronic microscope (SEM), and bond strength and microhardness of coatings were measured by tensile shearing test and Vickers hardness test. It is indicated that ultrafine Cr 3 C 2 -25%NiCr coatings have some outstanding properties to traditional Cr 3 C 2 - 25%NiCr coatings by plasma sprayed.

Plasma sprayed chromium oxides coatings have been widely applied in anilox rolls and pump seal for many years. This paper is researching the effect of nanostructured Cr 2 O 3 5SiO 2 3TiO 2 composite powder preparation when adding nano-size SiO 2 and TiO 2 powder in Cr 2 O 3 powder, to prepare for through spray drying, high temperature sintering and flame density. The microstructure of powder and plasma sprayed coating are analyzed by SEM and XRD, compared with pure Cr 2 O 3 powder and METCO 136F powder. The Microhardness of the coatings are measured by 402MVA TM Vickers hardness tester. Fracture test is used to analysis the ductility of coatings, and the fracture appearance is analyzed by SEM. The result indicates that the mechanical behaviors of nanostructured Cr 2 O 3 5SiO 2 3TiO 2 coating has better performance in the nature of hardness and ductility.

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.

Chromium oxide coatings are used in gas turbine engines in anti-wear applications. Ultrafine YPSZ and WC/Co feedstock powders have already been widely used to prepare the ultrafine structured YPSZ and WC/Co coatings, which exhibited improved mechanical properties when compared to those of conventional coatings. Ultrafine chromium oxide powders, prepared by the method of solution precipitation, can not be directly used as plasma spray feedstock powder, because of its low mass of individual ultrafine particle and not good flowability. In this paper, spray drying and heat treatment are used to reprocess the ultrafine chromium oxide powder. The chromium oxide coating is prepared by plasma spraying. X-ray diffraction (XRD) is used to analyze the phase constituents of the feedstock powder and coatings. Scanning electron microscopy (SEM) is used to observe the morphology and particle size of ultrafine powder feedstock powder as well as to examine the microstructure of the chromium oxide coating. In addition, loose density and flowability of the feedstock powder and hardness and bond strength of the ultrafine chromium oxide coating are measured. Experimental results show that the large agglomerated ultrafine chromium oxide feedstock powder after being reprocessed are spherical, have good flowability and high loose density, which are suitable for plasma spraying. The wear properties and microstructure of the ultrafine chromium oxide coatings are improved when compared to the ones of the conventional coatings.

In this study, cored wires and high velocity arc spraying technique (HVAS) were applied to produce Zn-Al and Zn-Al-Mg alloy coatings on low carbon steel substrates. The microstructures and mechanical properties were studied by SEM, EDS, XRD, and Vickers micro-indentor. The electrochemical corrosion behaviors of Zn-Al and Zn- Al-Mg coatings were investigated comparing with Zn and Al coatings in 5%NaCl. The results show that, Zn-Al and Zn-Al-Mg coatings have good quality of uniform microstructure and low porosity. The corrosion resistance of Al coating deteriorated rapidly after nearly 16h immersion, and then kept at a relative stable value. In the contrast, the corrosion potential of the coatings containing Zn decreased a little and then increased towards the noble potential. The potentiodynamic polarization tests show that the icorr value of Zn-Al coating changed greatly at different steps, and it trended to increase continuously which may imply that the coating is easy to be corroded. Comparatively, no obvious change had been found in the Zn-Al-Mg coating which may indicate that the corrosion resistance enhanced with the addition of Mg, and the role of Mg appears to be associated with the self sealing process. Abstract only; no full-text paper available.

Cold gas dynamic spraying is a promising technology and successfully applied to a wide range of materials. In this paper, orthogonal experimental method was introduced to seek out the optimal parameters for cold spraying copper coating. According to the results, standoff distance influenced the coating’s quality the most significantly as well as the carrier gas temperature had a remarkable impact either, but the carrier gas pressure and controlling voltage which influenced feeding speed subsequently had little influence on the coating’s quality. The coating’s porosity, bonding strength, microhardness and the coating’s conductivity were determined respectively. More over, optical and scanning electron microscopies were introduced to study the coating’s surface morphology and its internal structure. Also the effect of subsequent heat treatment on coating’s microhardness was investigated.