Optimization of Process Parameters for the Manufacturing of High Temperature Vacuum Brazed WC-NiCrBSi Coatings

Process parameters play a crucial role in the final characteristics and properties of every product. The current work focuses mainly on improving the vacuum furnace brazing process for tungsten carbide reinforced Ni-based alloy (NiCrBSi) metallic composite coatings, by establishing the best set of parameters adapted to this specific chemical composition. In order to determine the optimum parameters, a fine adjustment of a typical vacuum brazing process was performed. The melting interval of the filler metal was identified by means of Differential Thermal Analysis. Morphology, microstructure and metallurgical bond of the cladding to the substrate material were investigated by Scanning Electron Microscopy and Light Microscopy combined with a Porosity Analysis Software. The process optimization resolved the initial problem of fractures and crack initiation, making possible to achieve high quality hardfacing coatings with a low degree of porosity (approximately 1 %).</jats:p

A Comparison between Hardness, Corrosion and Wear Performance of APS Sprayed WC-CoMo and WC-Co Coatings

In order to be competitive, it is demanded to have thin, tough and long lasting coatings. An important aspect is to use stable deposition technologies. As Cr assures wear, corrosion and high temperature resistance, the most employed coatings in industry generally contain Cr. Nevertheless, Cr is a hazardous element for the humans’ health, therefore, sustainable alternatives are needed to be implemented. The aim of this work is to investigate the microstructure, hardness, corrosion resistance and wear behavior of the novel WC-CoMo compared to conventional WC-Co coatings. So far, WC-CoMo coatings are not part of state of the art regarding the Atmospheric Plasma Sprayed (APS) coatings. WC-Co powder in plain form and mechanically mixed with Mo was deposited using the APS method on standardized Type A Almen Strips (C67 steel). The size of the powder grains varies between 5 µm and 30 µm. The obtained samples were investigated by means of Scanning Electron Microscopy, Energy Dispersive X-Ray Spectroscopy, X-Ray Diffraction, and hardness, wear and corrosion behavior were also evaluated. Results revealed formation of different intermetallic phases around the WC particles, which have a benefic influence on the coating characteristics and microstructure.</jats:p

Synthesis and characterisation of platinum–cobalt–manganese ternary alloy catalysts supported on carbon nanofibers: An alternative catalyst for hydrogen evolution reaction

A systematic method for obtaining a novel electrode structure based on PtCoMn ternary alloy catalyst supported on graphitic carbon nanofibers (CNF) for hydrogen evolution reaction (HER) in acidic media is proposed. Ternary alloy nanoparticles (Co0.6Mn0.4 Pt), with a mean crystallite diameter under 10 nm, were electrodeposited onto a graphitic support material using a two-step pulsed deposition technique. Initially, a surface functionalisation of the carbon nanofibers is performed with the aid of oxygen plasma. Subsequently, a short galvanostatic pulse electrodeposition technique is applied. It has been demonstrated that, if pulsing current is employed, compositionally controlled PtCoMn catalysts can be achieved. Variations of metal concentration ratios in the electrolyte and main deposition parameters, such as current density and pulse shape, led to electrodes with relevant catalytic activity towards HER. The samples were further characterised using several physico-chemical methods to reveal their morphology, structure, chemical and electrochemical properties. X-ray diffraction confirms the PtCoMn alloy formation on the graphitic support and energy dispersive X-ray spectroscopy highlights the presence of the three metallic components from the alloy structure. The preliminary tests regarding the electrocatalytic activity of the developed electrodes display promising results compared to commercial Pt/C catalysts. The PtCoMn/CNF electrode exhibits a decrease in hydrogen evolution overpotential of about 250 mV at 40 mA cm−2 in acidic solution (0.5 M H2SO4) when compared to similar platinum based electrodes (Pt/CNF) and a Tafel slope of around 120 mV dec−1, indicating that HER takes place under the Volmer-Heyrovsky mechanism

Synthesis and characterisation of platinum–cobalt–manganese ternary alloy catalysts supported on carbon nanofibers: An alternative catalyst for hydrogen evolution reaction

A systematic method for obtaining a novel electrode structure based on PtCoMn ternary alloy catalyst supported on graphitic carbon nanofibers (CNF) for hydrogen evolution reaction (HER) in acidic media is proposed. Ternary alloy nanoparticles (Co0.6Mn0.4 Pt), with a mean crystallite diameter under 10 nm, were electrodeposited onto a graphitic support material using a two-step pulsed deposition technique. Initially, a surface functionalisation of the carbon nanofibers is performed with the aid of oxygen plasma. Subsequently, a short galvanostatic pulse electrodeposition technique is applied. It has been demonstrated that, if pulsing current is employed, compositionally controlled PtCoMn catalysts can be achieved. Variations of metal concentration ratios in the electrolyte and main deposition parameters, such as current density and pulse shape, led to electrodes with relevant catalytic activity towards HER. The samples were further characterised using several physico-chemical methods to reveal their morphology, structure, chemical and electrochemical properties. X-ray diffraction confirms the PtCoMn alloy formation on the graphitic support and energy dispersive X-ray spectroscopy highlights the presence of the three metallic components from the alloy structure. The preliminary tests regarding the electrocatalytic activity of the developed electrodes display promising results compared to commercial Pt/C catalysts. The PtCoMn/CNF electrode exhibits a decrease in hydrogen evolution overpotential of about 250 mV at 40 mA cm−2 in acidic solution (0.5 M H2SO4) when compared to similar platinum based electrodes (Pt/CNF) and a Tafel slope of around 120 mV dec−1, indicating that HER takes place under the Volmer-Heyrovsky mechanism