Papers by Keyword: Oxidation

Abstract: Understanding damage mechanisms across scales is crucial to ensure the structural integrity of nickel-based superalloy components under demanding conditions. This study highlights key aspects of a multi-scale experimental approach for analyzing oxygen-induced cracking in Alloy 718. Microcantilever bending tests on specific grain boundaries were combined with corrosion tests and detailed analyses using high-resolution scanning electron microscopy, electron backscatter diffraction, and energy-dispersive X-ray spectroscopy. The results suggest that susceptibility to oxidative attack is significantly impacted by the type of grain boundary, emphasising the importance of local crystallography in oxygen diffusion and elemental redistribution. By bridging local microstructural features with global mechanical response, the presented multi-scale approach allows the parameterization of physically based material models and identifies grain boundary engineering as a promising strategy for improving damage tolerance.

Abstract: The origin of the thermal creep of zirconium cladding tubes in all light water reactors is still the subject of deep confusion and intricate controversies. The reason for this inconvenient situation is obviously that microstructural processes in thermal creep remain poorly understood and this is due to the relatively small number of studies that have been carried out. In this study uniaxial creep tests in tension of zirconium alloy cladding tubes in the as-received and pre-hydrided states are followed by metallographic analysis of the as-received and crept specimens by light microscopy and SEM to explain the observed high-temperature creep behavior of the tubes.

Abstract: Developing titanium aluminides (Ti-Al) based alloys by means of Laser Engineered Net Shaping (LENS) in-situ manufacturing presents attractive properties as compared to other fabrication methods. Ti-Al alloys have attracted much attention for high-temperature performance in gas turbine and automobile applications because of their attractive properties such as low density, high strength, high stiffness, and good oxidation resistance. In this work, laser in-situ fabricated Ti-Al-Nb-Cr quaternary alloys were developed. The samples were exposed to 1350°C and cooled in air for stress relief and for homogenizing phase distribution before characterization, corrosion behaviour and oxidation properties were investigated. From the electrochemical performance results, sample QT1 and QT2 displayed high potential and high current densities with the values of-0.33931V, -0.36934V and 5.77E-05A/cm², 4.89E-05A/cm², respectively and the corroded SEM proves that the samples had minimal structural damage. The minimum mass gain was observed during oxidation test proving that Ti-Al-Nb-Cr alloys have outstanding oxidation properties for potential high temperature application.

Abstract: Gray iron, a widely used engineering material, is favored for its desirable properties such as good damping capacity, thermal conductivity, and corrosion resistance. However, when exposed to elevated temperatures over time, issues like oxidation and graphite depletion can impact its durability. High-silicon gray iron, with elevated silicon content exceeding 3.0%, is known for its ability to withstand heat and oxidation, making it suitable for many applications, including cookware. This study investigates the impact of varying silicon levels (2.00-4.56%Si) on the solidification behavior, microstructure, and oxidation resistance of gray iron. Three heats with different silicon concentrations were produced and analyzed. Results indicated that higher silicon content increases the eutectoid temperature, stabilizes the ferritic structure, and introduces Type-D graphite in the microstructure. Graphite depletion was observed only in samples with 2.00%Si. The oxidation resistance improved with higher silicon content, as evidenced by a decrease in weight gain after exposure to 800 °C for 4 hours. This suggests the potential of using lower silicon levels in gray iron for cookware applications, balancing material cost with good impact resistance.

Abstract: Currently, native starch as a binder and sizing component is used extremely rarely due to its inherent disadvantages. It has been replaced everywhere with modified starches of various kinds. Studies have shown that polyelectrolyte flocculants can be created on the basis of starch if ionizable groups are introduced into the macromolecules of amylose and amylopectin. At the same time, it was found that the treatment of starch with oxidizing agents (of various natures and activities) can significantly improve the functional properties of native starch when gluing, used for surface sizing, and as a binder for corrugated cardboard. In this work, we also obtained oxidized starch in order to create an adhesive binder on its basis, and only local raw materials were used. It is shown that this method makes it possible to regulate the number of functional groups (oxidizing effect, or OE) in oxidized starch and its paste viscosity within a wide range. This is achieved by changing the molar ratio of the catalyst and oxidizer. During the oxidation process, it is possible to vary the concentration ratios of the oxidizer, catalyst, and conditions. Using FeSO₄ as a catalyzer, the oxidized starch pastes show a less pronounced pseudoplasticity and are characterized by reduced viscosity. The analysis showed that during the oxidation of corn starch with hydrogen peroxide, changes in the supramolecular structure of starch are insignificant: a certain repeated decrease in the level of crystallinity takes place, which leads to a decrease in the gelatinization temperature and also the viscosity of starch pastes.

Abstract: In Atmospheric Plasma Spraying (APS), it is important to understand the controlling factors dominating molten metal droplets’ reaction dynamics to control final coating compositions and properties. The present paper focuses on a novel Computational Fluid Dynamics (CFD) modeling of mass transfer mechanisms of an inflight molten metal droplet leading to droplet oxidation control during APS. The onset conditions of droplet internal circulation and its effect on the deoxidizer oxidation behavior during APS are theoretically examined. Moreover, rapidly supplying these elements from the inside to the droplet surface requires the rapid switching of the mass transfer mechanism to rapid convective flow due to a very limited in-flight time of less than 1ms. The temperature and velocity variations within the droplet would influence the thermo-physical properties of the droplet and the plasma gas and it controls the onset of the internal circulations within the droplets. A novel User Defined Function (UDF) is developed to capture the onset of Hill’s vortex formation and its effect on the rapid-rate convective mass transfer mechanism during APS. Further, a detailed analysis of particle size effect on in-flight in-situ deoxidation during APS of NiAlC droplets was performed. It is observed that the smaller size droplets will undergo more severe oxidation during a flight than larger size droplets due to more molecules of O2 available for reaction in the smaller droplet.

Abstract: To investigate the behaviour of oxidation and chromium volatilisation, AISI 430 stainless steel was oxidised in O₂-H₂O and Ar-CO₂-H₂O atmospheres for 96 h at 800°C with varying water vapour content. In the O₂-H₂O environment, the volatilisation rate of Cr and Mn increased as the water vapour content increased from 5% to 20%. In the case of Ar-CO₂-H₂O conditions, the presence of water vapour in the Ar-20%CO₂ environment reduced the oxidation rates of the steel. However, increasing the H₂O content in Ar-20%CO₂ had an insignificant effect on the oxidation rate. Water vapour was found to accelerate the volatilisation rate of Cr and Mn. Breakaway oxidation occurred in Ar-20%CO₂-40%H₂O, resulting in the highest volatilisation rates of Cr and Mn.

Abstract: After treating industrial wastewater efficiently and adequately to avoid harm from it being reused and disposed of in the past, the majority of countries in the world have moved to integrated planning and sound management to reuse it. The efficiency of water treatment and reuse depends on a set of environmental standards and controls that are connected to the nature of this water and the eventual purpose of treating and reusing it in order to prevent the environmental repercussions of an integrated method. A framework that assures environmental protection must be employed for this treatment and reuse. The emphasis is on developing reusable resources in order to transition from a linear to a circular economy. Finding the primary pathway for heterogeneous and homogeneous catalysis to pollutant degradation, optimizing the layout for integrating Fenton processes into large-scale treatment plants, particularly its coupling with biological treatment, and analyzing or enhancing heterogeneous catalyst lifetime are all important. are some of the main challenges mentioned in this research. This study intends to analyze the efficacy of the Fenton process in treating water in an effective and economical way compared to other conventional techniques.

Abstract: The two-phase titanium alloy Ti6Al4V (often referred to as GRADE 5 or Ti64) is currently probably the most widely used type of Ti alloy. It is characterized by an excellent combination of strength - toughness - chemical stability. However, at temperatures above 500 - 800 °C it is prone to the diffusion of oxygen into surface layers, where the increased oxygen content creates the so-called “alpha-case” layer. The formation of this layer is associated with a reduction mainly in the deformation characteristics of the alloy. The paper focuses on the metallographic analysis of the "alpha-case" layer after annealing at 1050 °C with a holding time of 3 hours and cooling at different cooling rates (500 °C/s, 1 °C/s and 0.08 °C/s). Microstructure changes were observed by light microscopy using polarized light – PL, dark field – DF and phases were identified by SEM methods. The influence of changes in the microstructure on the mechanical properties was determined by measuring the microhardness HV0.2 /10 (STN EN ISO 6507) with Zwick / Roell ZHµ and measuring the resistance to impact stress KU (Charpy system STN EN 10045-1). Based on the microhardness measurement, an increase in the microhardness of the surface layers was observed at all cooling rates and at the same time, a decrease in the impact resistance was observed compared to the initial state.

Abstract: Aluminum Oxide thin films are potential candidate for anti-reflection, anti-soiling, and self-cleaning applications for solar cell panels, solar water heating panels, exterior windows of buildings, glasses, car windows, fabrics, and clothes. This paper reports on effect of chopping during deposition on the intrinsic stress and adhesion of Al₂O₃thin films deposited by electron beam evaporation. The kinetics of the growth and structure of the thin films is governed by adhesion. The durability and its wear are related to the certain extent adhesion of the thin film to the substrate. Effect of ambient aging on the adhesion and the internal stress in the films are also reported. The effect of chopping the thin film growth, phase change and presence of Al₂O₃ studied using scanning electron microscopy (SEM) and x-ray diffraction (XRD). The accumulation of strain energy in the thin film appears as internal stress and the binding of the vapor atoms to the substrates is referred to as adhesion. In this work, adhesion of thin films measured by direct pull off method and the internal stress is measured by interferometric method.