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Abstract: The WC–9Ni–2Cr cemented carbides were prepared by ball milling method and low pressure sintering. The microstructure and properties of the cemented carbides were then investigated using scanning electron microscopy, mechanical property tester and immersion corrosion tests. The results showed that the adding method of Cr significantly influenced the microstructure and properties of the WC–9Ni–2Cr cemented carbides. Cemented carbides with Cr added in the form of chromium carbide (Cr3C2) were characterized by carburizing and showed a relative lower density, while the addition of metallic chromium and nichrome (Ni–18Cr) resulted in the formation of (W,Cr)C phase and a decrease in the bending strength. However, no defects were found in the microstructure of the cemented carbides in which Cr was added via Cr–Cr3C2 composite powder. Furthermore, cemented carbides prepared with nichrome powder and metallic Cr powder exhibited a higher immersion corrosion resistance in neutral tap water after soaking six times according to BS:6920:2000. [Copyright &y& Elsevier]

In this work, the Metal-rich phase Chromium Aluminum (CrAl)/Ceramic phase Chromium Aluminum Nitride (CrAlN) multi-layer coatings were prepared by Arc Ion Plating (AIP). The micro-structure and phase composition of CrAl/CrAlN multi-layer coatings were characterized, and the microstructure, mechanical properties, residual stress and fracture toughness of the coating were emphatically analyzed. It has been found out that the residual stress of the multi-layer coating was only −0.932 ± 0.065 GPa, which was significantly lower than that of the mono-layer coating for −1.569 ± 0.093 GPa. At the same time, it was also found that the preferred growth orientation of the coating changed from a mono-layer (111) to a multi-layer (200) crystal plane. The hardness of the multi-layer (22.74 ± 0.57 GPa) is slightly lower than that of the mono-layer (24.92 ± 0.5 GPa), and the adhesion strength (46.2 ± 3.8 N) is obviously higher than that of the mono-layer (37.4 ± 2.4 N), and the fracture toughness is also higher (8.7 ± 0.8 MPa m1/2). In addition, the mechanism of crack initiation and propagation in stress-induced coatings was studied in detail on the basis of the structure of micro-nano CrAl/CrAlN multi-layer coatings. [ABSTRACT FROM AUTHOR]

Very low-pressure plasma spray is a promising technique for preparing dense metal/ceramic coatings due to the high-speed plasma jet. However, at the same time, the low-pressure environment weakens the ability of the plasma jet to heat sprayed materials. In order to improve this shortcoming, a novel bi-cathode plasma torch was firstly designed in this study, which could enhance the plasma power from 40 kW to 81 kW and realize the axial powder feeding. By using this torch under 6 mbar, a dense and uniform yttria-stabilized zirconia coating with a porosity of 2.7% was fabricated, which had a hybrid microstructure that deposited with the form of unmelted particles, melted droplets, and vapor clusters. Meanwhile, 40% of the zirconia phase changed from the monoclinic type to the tetragonal type, indicating that the yttria-stabilized zirconia powder was melted well. The microhardness and elastic modulus of the coating was high compared with those prepared with other plasma spraying processes, which was 11.7 ± 0.6 GPa and 167.8 ± 4 GPa, respectively. The high density and mechanical property of the YSZ coating demonstrated that using the bi-cathode plasma torch at low pressure has the potential for the preparation of SOFC electrolytes. [ABSTRACT FROM AUTHOR]