The aim of the investigations was to compare the microstructure, mechanical, and wear properties of Cr 3 C 2 -NiCr+Ni and Cr 3 C 2 -NiCr coatings deposited by HVOF technique (the high-velocity oxygen fuel spray process) on ductile cast iron. The effect of nickel particles added to the chromium carbide coating on mechanical and wear behavior in the system of Cr 3 C 2 -NiCr+Ni/ductile cast iron was analyzed in order to improve the lifetime of coated materials. The structure with particular emphasis of characteristic of the interface in the system of composite coating (Cr 3 C 2 -NiCr+Ni)/ductile cast iron was studied using the optical, scanning, and transmission electron microscopes, as well as the analysis of chemical and phase composition in microareas. Experimental results show that HVOF-sprayed Cr 3 C 2 -NiCr+Ni composite coating exhibits low porosity, high hardness, dense structure with large, partially molten Ni particles and very fine Cr 3 C 2 and Cr 7 C 3 particles embedded in NiCr alloy matrix, coming to the size of nanocrystalline. The results were discussed in reference to examination of bending strength considering cracking and delamination in the system of composite coating (Cr 3 C 2 -NiCr+Ni)/ductile cast iron as well as hardness and wear resistance of the coating. The composite structure of the coating provides the relatively good plasticity of the coating, which in turn has a positive effect on the adhesion of coating to the substrate and cohesion of the composite coating (Cr 3 C 2 -NiCr+Ni) in wear conditions.

In the present work Cr3C2-NiCr powder containing Al particles was deposited on ductile cast iron with high-velocity oxy-fuel (HVOF) thermal spray coating technique. An investigation was conducted to determine the role of Al particles in the Cr3C2-NiCr coating produced with HVOF technique on microstructure, mechanical and wear properties in a system Cr2C3-NiCr coating/ductile cast iron. The microstructure of the HVOF-sprayed Cr3C2-NiCr+Al coating was characterized by light microscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS). Microstructure analysis reveals the formation of coating with low porosity, good adhesion to the substrate and dense structure with irregularly shaped particles of Al arranged in strips and finely fragmented Cr3C2 particles embedded in a nanocrystalline Ni-Cr alloy matrix. In addition, the results were discussed in reference to examination of bending strength considering cracking and delamination in the system of (Cr3C2-NiCr+Al)/ductile cast iron as well as microhardness and wear resistance of the coating. It was found that the addition of Al particles significantly increased resistance to cracking and wear behaviour in the studied system.

Silicon-boron alloys have been recently pointed out as novel ultra-high temperature phase change materials for applications in Latent Heat Thermal Energy Storage (LHTES) and conversion systems. One of the emerging challenges related to the development of such devices is a selection of refractories applicable to build a vessel for storing molten Si-B alloys at high temperatures and under consecutive melting/solidification conditions. Previously, it has been documented that hexagonal boron nitride (h-BN) is the only one ceramic showing a non-wettability and limited reactivity with Si-B alloys at temperatures up to 1750 • C, what makes it a good candidate of the first selection for the predicted application. Nevertheless, pure h-BN shows a rather low mechanical strength that could affect a durability of the LHTES vessel. Therefore, the main purpose of this work was to examine high temperature behavior of commercial high strength h-BN composite having a nominal composition of h-BN-24ZrO 2 -6SiC (vol.%) in contact with a solid/liquid eutectic Si-3.2B alloy. Two types of sessile drop experiments were carried out: a step-contact heating up to 1750 • C, and a thermocycling at 1300 − 1450 • C composed of 15 cycles of the alloy melting/solidification. The obtained results showed a lack of wettability in the examined system at temperatures up to 1750 • C. The Si-3.2B alloy presented good repeatability of melting/solidification temperatures in consecutive thermal cycles, which was not affected by the interaction with the h-BN composite. However, due to reactions taking place between the composite's components leading to structural degradation, it is not recommended to increase operational temperature of this material above 1450 • C. Keywords Silicon-boron alloys • Hexagonal boron nitride • Sessile drop method • Latent heat thermal energy storage • AMADEUS project Electronic supplementary material The online version of this article (

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