Investigation of the Oxidation of Plasma Sprayed Silicon Coating

The quality of plasma sprayed silicon coating determined by density and spreading condition of lamella greatly influences its performance. The oxidation of silicon coating deteriorates its performance. However, the investigators mostly focus on the oxidation and mechanism of amorphous silicon, porous silicon and specific crystal planes on single crystal. The factors which influence the quality and oxidation of silicon coating has never be studied. The helium secondary gas flow has more influence on the quality of silicon coating than other spraying parameters. So, we prepare the silicon coating by plasma spraying technology with different secondary gas flow. The relationship between silicon coating’s quality and secondary gas flow is investigated. Furthermore, the oxidation of plasma sprayed silicon coating is discussed. We find that the secondary gas has an adverse effect on quality and oxidation degree of silicon coating. With the decrease of secondary gas flow, both quality and oxygen content of coatings increase. Besides, the oxygen atoms heterogeneously concentrate at the outermost layer of silicon lamellas. Components of oxygen enrichment area (OEA) from outside to inside are Si + SiOx+SiO2→Si + Si2O + SiO2→Si + SiOx→Si (1 < x < 1.5). The width of OEA in lamellas at top layer of silicon coating is about 180nm, obviously thicker than that in inner lamellas. The results obtained from research can provide support to better understand the behavior of silicon coating in the service process.

Characterization of Tribological and Mechanical Properties of the Si3N4 Coating Fabricated by Duplex Surface Treatment of Pack Siliconizing and Plasma Nitriding on AISI D2 Tool Steel

Silicon nitride (Si3N4) coating was deposited on AISI D2 tool steel through employing duplex surface treatments—pack siliconizing followed by plasma nitriding. Pack cementation was performed at 650 °C, 800 °C, and 950 °C for 2 and 3 hours by using various mixtures to realize the silicon coating. X-ray diffraction analyses and scanning electron microscopy observations were employed for demonstrating the optimal process conditions leading to high coating adhesion, uniform thickness, and composition. The optimized conditions belonging to siliconizing were employed to produce samples to be further processed via plasma nitriding. This treatment was performed with a gas mixture of 75 pct H2-25 pct N2, at the temperature of 550 °C for 7 hours. The results showed that different nitride phases such as Si3N4-β, Si3N4-γ, Fe4N, and Fe3N can be recognized as coatings reinforcements. It was demonstrated that the described composite coating procedure allowed to obtain a remarkable increase in hardness (80 pct higher with respect to the substrate) and wear resistance (30 pct decrease of weight loss) of the tool steel.

Understanding why poly(acrylic acid) works: decarbonylation and cross-linking provide an ionically conductive passivation layer in silicon anodes

PAA undergoes decarbonylation during electrode curing to form polyethers that provide a silicon coating that assists Li-ion desolvation and conduction.

Resistance spot welding with variable electrode force—development and benefit of a force profile to extend the weldability of 22MnB5+AS150

Compared with conventional steels, press-hardened steels with an aluminium-silicon coating have a smaller welding range, which is resulting in reduced process stability. For this reason, an analytical methodology is required, which can optimise the welding parameters and extend the welding range significantly. Consequently, most publications focus on the variation of welding time and welding current at a constant electrode force. This paper deals with the design of a force profile to improve weldability and joint quality. The basis for this investigation is the identification of significant characteristic values by the recorded process signals.

Development of a Disposable Single-Nozzle Printhead for 3D Bioprinting of Continuous Multi-Material Constructs

Fabricating multi-cell constructs in complex geometries is essential in the field of tissue engineering, and three-dimensional (3D) bioprinting is widely used for this purpose. To enhance the biological and mechanical integrity of the printed constructs, continuous single-nozzle printing is required. In this paper, a novel single-nozzle printhead for 3D bioprinting of multi-material constructs was developed and characterized. The single-nozzle multi-material bioprinting was achieved via a disposable, inexpensive, multi-fuse IV extension set; the printhead can print up to four different biomaterials. The transition distance of the developed printhead was characterized over a range of pressures and needle inner diameters. Finally, the transition distance was decreased by applying a silicon coating to the inner channels of the printhead.