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Register a new userInfluence of KCl and HCl on a Laser Clad FeCrAl Alloy: In-Situ SEM and Controlled Environment High Temperature Corrosion
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Increasing pressure on the power industry to reduce carbon emissions has led to increased research into the use of biomass feedstocks. This work investigates the effects of HCl and KCl, key species influencing biomass boiler corrosion, on a laser clad coating of the FeCrAl alloy Kanthal APMT. In-Situ SEM exposure of the coating at 450 oC for 1 h was performed to investigate the initial effects of KCl on the corrosion process. The same coatings were exposed to 250 h exposures in both an air environment and a HCl rich environment. The influence of KCl was investigated in both. Evidence of a slow growing aluminium oxide was observed. It was found that HCl allowed chlorine based corrosion to occur suggesting it can interact from the gas phase. It was also observed that the presence of both HCl and KCl reduced the mass gain compared to KCl in an air environment.
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Magnesium alloys have been considered to be favorable biodegradable metallic materials used in orthopedic and cardiovascular applications. We introduce NH+2 to the AZ31 Mg alloy surface by ion implantation at the energy of 50 KeV with doses ranging from 1e16 ions/cm2 to 1e17 ions/cm2 to improve its corrosion resistance and biocompatibility. Surface morphology, mechanical properties, corrosion behavior and biocompatibility are studied in the experiments. The analysis confirms that the modified surface with smoothness and hydrophobicity significantly improves the corrosion resistance and biocompatibility while maintaining the mechanical property of the alloy.
With important application prospects, eutectic high entropy alloys have received extensive attention for their excellent strength and ductility in a large temperature range. The excellent casting characteristics of eutectic high entropy alloys make it possible to achieve well manufacturability of selective laser melting. For the first time, we have achieved crack-free eutectic high entropy alloy fabricated by selective laser melting, which has excellent mechanical properties in a wide temperature range of -196 degrees Celsius~760 degrees Celsius due to ultra-fine eutectic lamellar spacing of 150 ~ 200nm and lamellar colony of 2 ~ 6 {mu}m. Specifically, the room temperature tensile strength exceeds 1400MPa and the elongation is more than 20%, significantly improved compared with those manufactured by other techniques with lower cooling rate.
FeCrAl alloys are proposed and being intensively investigated as alternative accident tolerant fuel (ATF) cladding for nuclear fission application. Herein, the influence of major alloy elements (Cr and Al), reactive element effect and heating schedules on the oxidation behavior of FeCrAl alloys in steam up to 1500{deg}C was examined. In case of transient ramp tests, catastrophic oxidation, i.e. rapid and complete consumption of the alloy, occurred during temperature ramp up to above 1200{deg}C for specific alloys. The maximum compatible temperature of FeCrAl alloys in steam increases with raising Cr and Al content, decreasing heating rates during ramp period and doping of yttrium. Isothermal oxidation resulted in catastrophic oxidation at 1400{deg}C for all examined alloys. However, formation of a protective alumina scale at 1500{deg}C was ascertained despite partial melting. The occurrence of catastrophic oxidation seems to be controlled by dynamic competitive mechanisms between mass transfer of Al from the substrate and transport of oxidizing gas through the scale both toward the metal/oxide scale interface.
Polyynes are finite chains formed by sp-hybridized carbon atoms with alternating single and triple bonds and displaying intriguing electronic and optical properties. Pulsed laser ablation in liquid (PLAL) is a well assessed technique for the physical synthesis of hydrogen-capped polyynes in solution, however, their limited stability prevents further exploitation in materials for different applications. In this work, polyynes in poly(vinyl alcohol) (PVA) were produced in a single-step PLAL process by ablating graphite directly in aqueous solution of PVA, investigating the role of polymer concentration. The presence of PVA solution, as a participating medium for PLAL, is shown to favour the formation of polyynes. The addition of Ag colloids to the aqueous PVA/polyynes solution allowed surface-enhanced Raman spectroscopy (SERS) measurements, carried out both on liquid samples and on free-standing nanocomposites, obtained after solvent evaporation. We show that polyynes in the nanocomposite remain stable at least for 11 months, whereas the corresponding PVA/Ag/polyynes solution displayed a strong polyyne reduction already after 3 weeks. These results open the view to further characterizations of the properties of polyyne-based films and materials.
Magnesium and its alloys are ideal for biodegradable implants due to their biocompatibility and their low-stress shielding. However, they can corrode too rapidly in the biological environment. The objective of this research was to develop heat treatments to slow the corrosion of high purified magnesium and AZ31 alloy in simulated body fluid at 37{deg}C. Heat treatments were performed at different temperatures and times. Hydrogen evolution, weight loss, PDP, and EIS methods were used to measure the corrosion rates. Results show that heat treating can increase the corrosion resistance of HP-Mg by 2x and AZ31 by 10x.
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