Search Results (9)

This study employs computational fluid dynamics (CFD) to analyze the in-flight dynamics of particles in an Ar–H₂ atmospheric plasma spray (APS) torch with a modified diverging-type nozzle. The focus is on optimizing injection parameters—plasma gas flow rates, input power, and carrier gas flow rates—to enhance coating microstructure and deposition efficiency by achieving superheated molten metal droplets. Using a discrete phase model, the heat and momentum transfer of Ni/Al/C (2 wt.% diamond) composite powders (30–110 µm) within the plasma jet were simulated. Results show that particle characteristics, such as temperature and oxidation, can be controlled by adjusting plasma jet temperature (T∞) and velocity (U∞). Smaller particles heat faster, reaching higher temperatures with increased evaporation and oxidation rates. The modified nozzle enables Ni-based alloy particles to reach ~2500 °C, reducing oxygen inclusion in the plasma jet core. This setup allows for the control of the onset of carbon and oxygen reactions, wherein carbon serves as a sacrificial element, protecting the base alloy elements (such as aluminum) from excessive oxidation. Full article

The study explored the possibility of producing thick coatings of fully metallic composite phase change materials with suitable microstructure for thermal energy storage or thermal energy management purposes. The composite materials are based on Al-Si-based alloys with Sn additions, potentially obtainable from scraps. This leads to an Sn-rich low-melting phase which is able to store/release heat when it melts/solidifies. The material can thus be considered as a composite phase change material (C-PCM). A thick coating was deposited on an Al alloy substrate by plasma spray, mixing AlSi10Mg and Sn powders in a 60:40% mass ratio. Optical scanning microscopy and X-ray diffraction revealed a microstructure suitable for a C-PCM, presenting Sn basins interrupted by a matrix made up of primary Al and Al–Si eutectic. Preliminary investigation into the reliability of the coating was conducted by performing up to 10 heat cycles across the melting temperature of the low-melting phase, simulating service in TES/TEM devices. No significant changes in its coating microstructure were observed. Minor surface leakage of molten Sn occurred, mainly during the first heat cycle. No detachment of the coating or cracks formed within the coating were observed, which could have been expected due to the mismatch in the coefficients of thermal expansion of the main phases and to the expansion/shrinkage due to Sn melting/solidification. Full article

The descaling roller is a significant component in steel rolling production. Under harsh service conditions, the descaling roller is subjected to the dynamic impact caused by high-pressure water erosion and a high-temperature billet descaling process for a long time. Under the harsh conditions of high temperature, strong wear, multi-cycle heat, force, flow, and multi-field strong coupling, the roller surface is prone to wear and corrosion failure, which affects the production cost and efficiency. Through plasma surfacing technology, a high-performance coating can be applied on the conventional metal surface to effectively improve its surface properties. It is important to carry out experimental research on the surface plasma surfacing of the descaling roller to prolong product life, improve product quality, and save cost. At present, the research on the 42CrMo scaler matrix plasma surfacing of nickel-based alloys with different WC contents is still lacking. In this paper, 70%NiCrBSi+30%WC powder and 40%NiCrBSi+60%WC powder were used as surfacing materials; plasma surfacing experiments were carried out on the 42CrMo matrix; and SEM, XRD, microhardness, friction and wear, and corrosion tests were carried out on the surfacing layer to evaluate the feasibility of preparing an ultra-high-hardness WC-particle-reinforced nickel-based alloy plasma surfacing layer on the descaling roller surface and to explore the WC hard phase dissolution behavior and complex secondary phase formation mechanism. The results show that γ(Fe/Ni), Fe-Ni, FeSi, Fe₃C, and M₇C₃ are the main phases in the Ni/WC plasma surfacing layer. The diffusion and precipitation of elements occur in the molten pool, and complex secondary phases are formed in the surfacing layer. Compared with the 70%NiCrBSi+30%WC surfacing layer, the WC deposition phenomenon of the 40%NiCrBSi+60%WC surfacing layer has been significantly improved and has better hardness, wear resistance, and corrosion resistance. Based on the welding test, the correlation law between powder formulation, welding structure, and surfacing layer properties was revealed in this study, which lays a theoretical foundation for the preparation of high-performance coating on the descaling roller surface and has significant engineering application value and practical significance. Full article

Magnetic abrasive finishing (MAF) is an efficient finishing process method using magnetic abrasive particles (MAPs) as finishing tools. In this study, two iron-based alumina magnetic abrasives with different particle size ranges were synthesized by the plasma molten metal powder and powder jetting method. Characterization of the magnetic abrasives in terms of microscopic morphology, phase composition, magnetic permeability, particle size distribution, and abrasive ability shows that the magnetic abrasives are spherical in shape, that the hard abrasives are combined in the surface layer of the iron matrix and remain sharp, and that the hard abrasives combined in the surface layer of the magnetic abrasives with smaller particle sizes are sparser than those of the magnetic abrasives with larger particle sizes. The magnetic abrasives are composed of α-Fe and Al₂O₃; the magnetic permeability of the magnetic abrasives having smaller particle sizes is slightly higher than that of the magnetic abrasives having larger particle sizes; the two magnetic abrasives are distributed in a range of different particle sizes; the magnetic abrasives have different magnetic permeabilities, which are higher than those of the larger ones; both magnetic abrasives are distributed in the range of smaller particle sizes; and AZ31B alloy can obtain smaller surface roughness of the workpiece after the grinding process of the magnetic abrasives with a small particle size. Full article

The internal wall of cardiovascular stent tubing produced by a drawing process has defects such as pits and bumps, making the surface rough and unusable. In this research, the challenge of finishing the inner wall of a super-slim cardiovascular stent tube was solved by magnetic abrasive finishing. Firstly, a spherical CBN magnetic abrasive was prepared by a new method, plasma molten metal powders bonding with hard abrasives; then, a magnetic abrasive finishing device was developed to remove the defect layer from the inner wall of ultrafine long cardiovascular stent tubing; finally, response surface tests were performed and parameters were optimized. The results show that the prepared spherical CBN magnetic abrasive has a perfect spherical appearance; the sharp cutting edges cover the surface layer of the iron matrix; the developed magnetic abrasive finishing device for a ultrafine long cardiovascular stent tube meets the processing requirements; the process parameters are optimized by the established regression model; and the inner wall roughness (Ra) of the nickel–titanium alloy cardiovascular stents tube is reduced from 0.356 μm to 0.083 μm, with an error of 4.3% from the predicted value. Magnetic abrasive finishing effectively removed the inner wall defect layer and reduced the roughness, and this solution provides a reference for polishing the inner wall of ultrafine long tubes. Full article

In this investigation, spherical Al₂O₃ magnetic abrasive particles (MAPs) were used to polish the inner surface of ultra-fine long cobalt–chromium alloy cardiovascular stent tubes. The magnetic abrasives were prepared by combining plasma molten metal powder and hard abrasives, and the magnetic abrasives prepared by this new method are characterized by high sphericity, narrow particle size distribution range, long life, and good economic value. Firstly, the spherical Al₂O₃ magnetic abrasives were prepared by the new method; secondly, the polishing machine for the inner surface of the ultra-fine long cardiovascular stent tubes was developed; finally, the influence laws of spindle speed, magnetic pole speed, MAP filling quantities, the magnetic pole gap on the surface roughness (Ra), and the removal thickness (RT) of tubes were investigated. The results showed that the prepared Al₂O₃ magnetic abrasives were spherical in shape, and their superficial layer was tightly bound with Al₂O₃ hard abrasives with sharp cutting; the use of spherical Al₂O₃ magnetic abrasives could achieve the polishing of the inner surface of ultra-fine cobalt–chromium alloy cardiovascular bracket tubes, and after processing, the inner surface roughness (Ra) of the tubes decreased from 0.337 µm to 0.09 µm and had an RT of 5.106 µm. Full article

In order to solve the problem of difficult sintering and high brittleness of B₄C-based ceramics, B₄C@ZrB₂-TiB₂ composite powder was synthesized by molten salt method, and B₄C–(Zr, Ti)B₂ composite ceramics were successfully prepared by spark plasma sintering. The effects of different raw material ratios on the composition, microstructure, and mechanical properties of the prepared composite ceramics were characterized by XRD, XPS, SEM, and TEM. The results show that ZrB₂ and TiB₂ were grown on the surface of B₄C by template mechanism to form a dense nanocrystalline coating, and the original surface of B₄C was exposed gradually with the decrease of the ratio of metal powder. When the composite powders were sintered at 1700 °C, ZrB₂ and TiB₂ formed a solid solution, which can refine grains and improve strength. When the raw material ratio is n(B₄C): n(Zr): n(Ti) = 12:1:1, the composite ceramics have excellent comprehensive properties, the Vickers hardness reaches 41.2 GPa. Full article

High-performance iron-based Al₂O₃ magnetic abrasive powder (MAP) prepared by combining plasma molten metal powder with sprayed abrasive powder is used for magnetic abrasive finishing (MAF) of AZ31B magnesium alloy to remove surface defects such as creases, cracks, scratches, and pits generated during the manufacturing process of the workpiece, and to reduce surface roughness and improve its wear and corrosion resistance. In order to solve the problem of magnetic abrasive powder splash in the MAF process, the force analysis of the MAP in the processing area is conducted, and a composite magnetic pole processing device was designed and simulated to compare the effects of both devices on MAF, confirming the feasibility of composite magnetic pole grinding. Then, experiments have been designed using Response Surface Methodology (RSM) to investigate the effect of four factors-magnetic pole rotation speed, grinding gap, magnetic pole feed rate, magnetic abrasive filling quantity-on surface roughness and the interactions between them. The minimum surface roughness value that can be obtained is used as the index for parameter optimization, and the optimized parameters are used for experiments, and the results show that the established surface roughness model has good predictive ability. Full article

Thermal spraying of aluminum nitride (AlN) is a challenging issue because it decomposes at a high temperature. In this work, the use of suspension plasma spray (SPS) technology is proposed for the in situ synthesis and deposition of cubic-structured AlN coatings on metallic substrates. The effects of the nitriding agent, the suspension liquid carrier, the substrate materials and the standoff distance during deposition by SPS were investigated. The plasma-synthesized coatings were analyzed by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The results show higher AlN content in the coatings deposited on a carbon steel substrate (~82%) when compared to titanium substrate (~30%) or molybdenum (~15%). Melamine mixed with pure aluminum powder produced AlN-richer coatings of up to 82% when compared to urea mixed with the Al (~25% AlN). Hexadecane was a relatively better liquid carrier than the oxygen-rich liquid carriers such as ethanol or ethylene glycol. When the materials were exposed to a molten aluminum–magnesium alloy at 850 °C for 2 h, the corrosion resistance of the AlN-coated carbon steel substrate showed improved performance in comparison to the uncoated substrate. Full article