Oxide Scale Layer Research Articles

A study on the machinability of DMLS In718 alloy using an electro-spark machining process

ABSTRACT The direct metal laser sintering process is used to develop the nickel base superalloy DMLS In718 for the experimentation. The DMLS In718 alloy is evaluated to ensure the metallurgical qualities and mechanical properties. Microstructure of the DMLS In718 alloy is anisotropic in nature and the hatch bands are clear to infer. The hardness of the DMLS In718 is 275 Hv which equivalent to the commercially available inconel718 material. the mechanical strength and density of the DMLS In718 alloy is justifiable to the commercial material. The machining studies are performed with electro spark erosion process to report on surface quality, kerf taper and material removal rate. the minimum pulse on time has produced a fine surface quality compared to the maximum process condition. The surface topography in terms of oxide scale and recast layers are identified during to inefficient process conditions. This paper was an opportunity to deliberate the machining quality of the wire electro spark process.

Thermodynamic Analysis of Chloride Corrosion in Steel for Energy System Applications in Fe-O-Cl-Na Environments

The assumptions of contemporary energy policies are increasing the share of renewable energy sources. Biomass combustion is developing as an alternative to fossil fuels. However, it faces challenges such as limited corrosion resistance of steel boiler components due to chloride compounds in flue gases and fly ash. This paper provides a comprehensive thermodynamic analysis of chloride-induced corrosion in steel in the Fe-O-Cl-Na environment, focusing on the influence of steam concentration in the gas phase. The study was performed by using the general thermodynamic rules, the thermodynamic properties of the pure components involved in the reaction, and the properties of the solutions formed in the liquid and gas phases. The study also examined the impact of alkali metal chlorides, particularly NaCl, on the formation of NaFeO2 in the passive oxide scale layer Fe3O4/Fe2O3. Furthermore, it investigated the condensation of NaCl vapour formation of low-melting eutectic mixtures in deposits and the resulting consequences on the corrosion process. The role of HCl in the chlorination and oxidation process of steel in melted ash deposits was also discussed. The presented thermodynamic analysis was compared with assumptions of an “active oxidation” model. This study can be a valuable resource for experimental research planning and a guide for preventing corrosion in industrial settings.

High-temperature oxidation of Haynes 282 microtubes in CO2

ABSTRACT The oxidation characteristics of Haynes 282 microtubes measuring 1 mm in diameter and 200 µm thick exposed to CO2 at elevated temperature are reported. After 215 hours at 700°C and 1 atm, a thin, protective chromia scale accumulates up to 2.03 µm from the outer surface, approximately 1% of the thickness, and internal aluminum oxidation is observed 2.59 µm from the inner surface. The results suggest that oxidation is limited by oxygen diffusion through the growing oxide scale layer. The average grain size in the microtube is 10 µm, and it decreases to 5 µm closer to the inner surface. Severe plastic deformation and variable dynamic recovery and recrystallization from the manufacturing process were observed throughout the microtube. Overall grain size and distribution in the microtube were found to be independent of thermal exposure, despite the occurrence of recrystallization. The superalloy microtube geometry shows promising performance in high-temperature thermal applications.

Effect of solid oxidation products on the ablation mechanisms of ZrC and HfC based coatings above 2000°C

Solid and liquid oxidation products have been considered to be the key issues to influence the ablation resistance of UHTCs coatings. However, the effect of solid oxidation products on the ablation performance is not clear. In the present work, four kinds of UHTCs coatings (ZrC, ZrC-30vol.%SiC, HfC, HfC-30vol.%SiC) were selected to study the effect of different solid oxides on the ablation behaviors of UHTCs coatings. The results showed that the HfC-based coatings had thinner oxide scale and SiC-depleted layer, which shown better ablation resistance than the ZrC-based coatings. Based on the characterization of oxygen vacancy and density functional theory (DFT) calculation, it is thought that the solid oxidation products of HfO2 possesses higher defect formation energy compared with ZrO2, which can help to restrain the diffusion of oxygen and contribute to the better ablation resistance.

Optimal investigation of the reheating furnace based on a 3D numerical model with the formation of both oxide scale layer and skid marks

The performance of reheating furnace is highly dependent on the slab temperatures which further determine energy consumption. In general, the oxide scale layer and skid marks have a huge impact on the temperature distributions of the slab. Thus, an optimal control problem with a 3-dimensional (3D) numerical model is proposed to reduce the generation of skid marks, oxide scale layer and energy losses for the reheating furnace. Firstly, a 3D numerical Partial Difference Equation (PDE) model is built by considering the formation of the oxide scale layer and skid marks. The proposed model is implied by the parallel implementation strategy of GPU to reduce the computational time. Secondly, the 3D PDE-constrained optimal control problem is developed for the reheating furnace and solved by the proposed modified conjugate gradient (MCG) method. Finally, the accuracy of the proposed 3D model is verified by the industry measurement data, and the fast convergence performance of the MCG method is also validated. This work can significantly reduce the generation of oxide scale layer and energy consumption.

The Microstructure Formation of a Protective Oxide-Scale Layer on Small-Diameter FeCrAl Fibers

FeCrAl fibers, at high temperatures, form a protective oxide-scale layer dominated by aluminum oxide on the surface to prevent further oxidation of the base metal alloy. This study investigates the effects of heat treatment on the microstructure formation of the oxide-scale layer on small-diameter FeCrAl fibers, 12 and 17 µm, produced using a bundle drawing process. The morphology examination and chemical analyses of the small-diameter fibers exhibit the microstructure and chemical compositions of the surface and cross-section areas, revealing a distinctive interface layer with a high aluminum concentration between the base metal and the oxide-scale layer. Furthermore, thermogravimetric analysis results show that the 12 µm fibers have about a 60% higher oxidation rate than the 17 µm fibers-caused by the high outward diffusion of aluminum to the surface of the fibers due to their high surface-area-to-weight ratio. Consequently, the high growth rate of the nonuniform oxide-scale layer and the limited aluminum reservoir of the 12 and 17 µm diameter fibers lead to faster depletion of aluminum from the base metal alloy-limiting the lifetime and durability of the smaller-diameter fibers in high-temperature applications.

Validation of the Cooling Model for TMCP Processing of Steel Sheets with Oxide Scale Using Industrial Experiment Data

To verify the mathematical model of the water-jet cooling of steel plates developed by the authors, previously performed experimental studies of the temperature of the test plates in a roller-quenching machine (RQM) were used. The calculated temperature change in the metal as it moved in the RQM was compared with the readings of thermocouples installed at the center of the test plate and near its surface. The basis of the model is the dependence of the temperatures of the film, transition and nucleate boiling regimes on the thickness of the oxide scale layer on the cooled surface. It was found that the model correctly accounts for the oxide scale on the sheet surface, the flow rates and combinations of the RQM banks used, the water temperature, and other factors. For all tests, the calculated metal temperature corresponded well with the measured one. In the experiments with interrupted cooling, the calculated temperature plots repeated the characteristic changes in the experimental curves. The main uncertainty in the modeling of cooling over a wide temperature range can be attributed to the random nature of changes in the oxide scale thickness during water cooling. In this regard, the estimated thickness of the oxide scale layer should be considered the main parameter for adapting the sheet temperature-control process. The data obtained confirm the possibility of effective application of the model in the ACS of industrial TMCP (Thermo-Mechanical Controlled Process) systems.

A Mathematical Model for the Prediction of the Scale Layer Formation on ASTM A510/A853 Cold-Drawn Hypoeutectoid Steel Wire After Batch Annealing

Annealed hypoeutectoid ASTM A510/A853 steel wire is widely used in the construction industry due to its mechanical properties, which makes it a very versatile material to work with. This work concerns the prediction of the thickness of the scale layer of the hypoeutectoid steel wire once subjected to a batch annealing process. We propose a mathematical model to approach oxidation occurring during the process. The model treats this phenomenon as a non-isothermic instance; it takes as input a heating curve, a cooling curve, and a holding time that corresponds to the heating and cooling cycles and a heating holding cycle. We assume the temperature of material outer spiral segments as the furnace atmosphere temperature. With the aid of this model, it is possible to predict the oxide scale layer of the outer spirals segments of the annealed drawn wire coils after batch annealing with reasonable accuracy. We did not find visible evidence of decarburization; the steels of the study in this work do not decarburize. As an approximation, we assumed that the temperature of the outside of the drawn wire coils equals the furnace atmosphere.

Anti-friction mechanism of VAlTiCrMo high-entropy alloy coatings through tribo-oxidation inducing layered oxidic surface

VAlTiCrMo-based high-entropy alloy coatings with BCC structure were successfully prepared by magnetron sputtering, and the tribological properties were improved by changing Mo content. It is revealed that friction force changed the composition of lubricating phase in the oxide scale of VAlTiCrMo1.6 coating, that is, a complex oxide Al2(MoO4)3 as dominant lubricating phase was formed on the surface of oxide scale through tribochemical reaction between simple oxides. And the phase separation in the layered oxide scale caused by thermal diffusion, which is favorable to form continuous lubricating film during friction, was the prerequisite for VAlTiCrMo1.6 coating to acquire low friction and wear. In this process, the addition of Mo played a key role in uphill diffusion and segregation of elements.

Microstructure and stress analyses in nano-structured alumina layers developed on Fe-Al single crystals

In the present work low index single crystal surfaces of a binary Fe-Al alloy were oxidized in atmospheric air at 700 °C. The oxide layer composition, microstructure and texture were investigated by XPS, TEM and XRD. The oxidation stresses were determined in situ by synchrotron XRD. The results revealed the presence of a dual layered oxide scale, consisting of an inner layer of α-Al2O3 and an external layer of α-Fe2O3 and α-Al2O3. Differences in crystal orientation led to variations in the internal stress distribution in the oxide scales, with compressive stress values α-Al2O3 following (110) > (111) > (100).

A Phase-Field Study on Internal to External Oxidation Transition in High-Temperature Structural Alloys

Structural alloys applied at high temperatures rely on an external dense layer of oxide scale for protection. As some reactive alloy components are selectively oxidized internally, understanding how these dispersed metal oxide particles reach the surface to form a protective scale—the so-called internal to external oxidation transition—is crucial for designing these alloys. While the literature is replete with experimental studies on oxidation of alloys, there is a lack of computational studies in this realm due to the complex nature of coupled reaction and diffusion processes in multicomponent multi-phase alloy systems. In this work, we apply a recently developed phase-field model to simulate the oxidation processes under different compositions and nucleation scenarios to gain insights into how a continuous oxide scale can be established. The results show that while alloy composition is critical for internal to external oxidation transition, the oxide nuclei size, shape and distribution also have significant impact on the transition kinetics.

Studies on different oxidation behaviors of TiAlN on titanium alloy and stainless steel under thermal cycling

This paper aims to explore the different oxidation behaviors of TiAlN coatings on two various substrates under thermal cycling at 750 °C. Thin oxide scale layer formed and Ti2N phase generated in TiAlN-TC4 system. IDZ composed of nitride phase appeared at TiAlN/TC4 interface after thermal cycling. By contrast, for TiAlN on stainless steel, thick oxide scale layer formed on the surface. There were no phase transitions in TiAlN and IDZ at coating/substrate interface after oxidation. The various oxidation cracking behaviors also occurred to the two systems. The relative oxidation mechanisms are discussed in detail in this study.

The Atmosphere’s Effect on Stainless Steel Slabs’ Oxide Formation in a CH4-Fuelled Reheating Furnace

Utilising the oxyfuel practice for CH4-fuelled combustion has positive effects on the emissions, efficiency and cost of high temperature furnace practices. However, especially in older installations, oxyfuel usage requires retrofitting and alters the atmosphere in which the oxidation of the steel occurs, when compared to using air as the oxidiser. Stainless steel slab oxide growth during reheating was studied in different atmospheres. The simulated post-burn atmospheres from oxyfuel, lean oxyfuel and air-fuel practices were used to compare oxide-scale layer growth and morphology during simulated typical AISI 304 stainless steel slab reheating prior to hot rolling. Thermogravimetric measurements, glow discharge optical emission spectrometer (GDOES) and field-emission scanning electron microscope energy dispersive X-ray (FESEM-EDS) methodology were applied to discern differences between oxide growth and inner oxide layer morphology between the three practices. Switching from air to oxyfuel practice at a single temperature had the same increasing effect on the scale formation amount as a 25 °C temperature increase in air atmosphere. Inner oxide layer depth profiling revealed C, Si and Ni to be the main elements that differed between temperatures and atmospheres. A morphology study showed Si and Ni behaviour to be linked to breakaway oxidation.

Silicon as a component of ferric oxide scale covering ductile iron pipes after annealing

All ductile iron pipe producers use the annealing process to improve the metal structure. It lasts several hours in a hot air atmosphere, when the surface of pipes is covered by ferric oxide scale, consisting usually of two significantly different layers, being the subject of the research reported here. In the U.S.A., commercially produced pipes are not protected by zinc coatings, because it is believed that ferric oxides are not a solid undercoat for such coatings, while the EN 545:2010 standard used in Europe requires the use of zinc or zinc-aluminum coatings, depending on soil corrosivity. To evaluate which approach has more potential, it is necessary first of all to recognize the structure of ferric oxides after the annealing process and then to understand their role as a base for zinc coatings. The microstructure of oxide scales grown on the external surface of industrial ductile iron pipes was investigated using scanning electron microscopy. In the ductile iron matrix, the concentration of silicon is reported to be much lower than in the layer of oxide scale growing directly on the pipe surface. In several samples, some cracks between the oxide layers were not successfully avoided in spite of using a professional saw with a continuous cooling process. Each time the cracks were horizontal and occurred along two boundaries: between the ductile iron matrix and the first oxide layer or between the two oxide layers rich in silicon and essentially silicon free.

Multistage heat treatment and the development of a protective oxide-scale layer on the surface of FeCrAl sintered-metal-fibers

This study investigates the effects of Multistage Heat Treatment (MSHT) on the development of an oxide-scale layer on the surface of FeCrAl sintered-metal-fibers. The oxide-scale layer was developed using an MSHT cycle at 930 °C for 1 h, followed by 960 °C for 1 h, and finally at 990 °C for 2 h. In this study, three samples were considered: Sample 1 was kept without thermal oxidation, while Samples 2 and 3 were exposed to one and eighteen MSHT cycles. Thermo-gravimetric analyses show that the weight gain of the heat-treated sample slows with time, confirming the growth of the protective oxide-scale layer. Scanning electron microscope images, after one MSHT cycle, reveal nonuniform oxide-scale growth with platelet-like on the surface. After eighteen MSHT cycles, however, clumped particles formed on the surface of the fibers. Atomic force microscopy was utilized to study the surface topography of the fibers. The results show that MSHT increases the surface roughness, where the surface roughness of one and eighteen MSHT cycles are the same. The x-ray diffraction analyses of the baseline sample and the sample with one MSHT cycle show pattern peaks of crystalline Fe2CrAl. In contrast, the results of eighteen MSHT cycles displayed diffraction pattern peaks of crystalline Cr and stable α-Al2O3. In summary, the results of this study reveal the changing nature of the oxide-scale layer. The findings of this study form the foundation for new techniques to protect and prepare the FeCrAl fibers as a support for catalysts.

Oxidation and electrical properties of chromium\u2013iron alloys in a corrosive molten electrolyte environment

Chromium–iron (CrFe) binary alloys have recently been proposed to serve as the “inert” anode for molten oxide electrolysis (MOE). Herein, the effects of anodic polarization on physical and functional properties of CrFe anodes in the corrosive environment of MOE are studied via empirical observations and theoretical calculations. The findings indicate that the alloys form an inner chromia–alumina solid-solution covered by an MgCr2O4 spinel layer. A survey into the electrical properties of the detected oxides suggests that the layered oxide scale function as an efficient conductor of electricity at elevated temperature. The formation mechanism of the oxides is also investigated.

Kinetics and evolution of oxide scale during various stages of isothermal oxidation at 1300 °C in spark plasma sintered ZrB2 – SiC – LaB6 composites

The kinetics and oxide scale evolution during isothermal exposure of spark-plasma sintered ZrB2-20 SiC–LaB6 (7, 10 or 14 vol%) composites at 1300 °C for 1, 8, or 24 h have been examined. Random mass change observed during the first hour stems from a non-protective scale. The variation of mass gain with time is expressed by near-parabolic rate law during 0−8 h time period, and by relations indicating slower kinetics during 8−24 h, with parabolic rate constants (kp) decreasing sharply. Microstructural examination has shown a continuously evolving layered oxide scale comprising La2Si2O7, borosilicate glass (BSG), ZrSiO4, and ZrO2, where the BSG layer growth rate scales linearly with LaB6 content during 0−8 h, but shows an opposite trend on further exposure. During both time periods (0−8 and 8−24 h), kp decreased following a linear relationship with increasing BSG layer thickness, indicating its key role as diffusion barrier for oxygen.

High-efficiency reduction behavior for the oxide scale formed on hot-rolled steel in a mixed atmosphere of hydrogen and argon

In this study, a novel double-stage reduction method of “low temperature and high temperature” was proposed to improve the reaction efficiency of the hydrogen reduction technology of the oxide scale formed on hot-rolled steel. The reduction behavior of the oxide scale in 20 vol% H2–Ar at various reduction methods was investigated in detail. The weight change of specimen under various reduction methods was measured by thermogravimetric analysis, and then the reduction degree and the reaction rate were calculated based on the measured value. Scanning electron microscopy was used to observe the surface and the cross-sectional morphologies of the oxide scale after the reduction reaction, and the mass percent of oxygen and iron in the cross-sectional reduction layer was measured by energy-dispersive spectroscopy. X-ray diffraction was applied to characterize the phase transformation of the oxide scale in the heating process, and the phase composition of the oxide scale and reduction layer. The experimental results indicated that the reduction degree and the reaction rate of the oxide scale during the double-stage reduction method increased significantly compared with the traditional single-stage reduction method in the range of 500–800 °C. The mechanism of the double-stage reduction method was discussed from two aspects of the phase transformation of the oxide scale and the restrictive link of the gas (H2)–solid (Fe oxides) reduction reaction.

Microstructure and properties of Ti(C, N)–TiB2–FeCoCrNiAl high-entropy alloys composite cermets

The FeCoCrNiAl high-entropy alloys (HEA) was used as binder of the Ti(C, N)–TiB2 composite cermets. The Ti(C, N)–TiB2–FeCoCrNiAl HEA composite cermets were successfully fabricated by mechanical alloying (MA) and vacuum hot-pressing sintering (VHPS) at different sintering temperatures. The microstructure, room-temperature hardness, fracture toughness, bending strength, high-temperature hardness and oxidation behavior were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Vickers hardness testing, indentation method, three point bending method, high-temperature vacuum hardness testing and cyclic oxidation. For the Ti(C, N)–TiB2-HEA composite cermets, apart from Ti(C, N) and TiB2 phases, also a minority Fe2B were detected in the XRD patterns. TEM observation revealed that the structure of the HEA binder was a solid solution where the Ti(C, N) and TiB2 were tightly bound. The Ti(C, N)–TiB2 composite cermets with a Ni/Co binder was selected as a reference. The experimental results indicated that the composite cermets with the HEA binder possesses excellent oxidation resistance. This is attributed to the formation of a continuous and dense external oxide scale and TiO2 layer that effectively impede inward oxygen transport, which leads to a remarkable improvement in the oxidation resistance. The Ti(C, N)–TiB2-HEA composite cermets sintered at 1500 °C showed excellent fracture toughness of 7.9 ± 0.1 MPa.m1/2. And the Ti(C, N)–TiB2-HEA composite cermets sintered at 1550 °C showed excellent hardness and bending strength of 1977.3 ± 20 HV10 and 768.6 ± 20 MPa, respectively. The high-temperature hardness of the HEA binder composite cermets was 993.7 ± 30 HV20, which was superior to the Ni/Co binder value of 668.1 ± 30 HV20 at 1000 °C.

Characterization of the Oxide Scale Formed on T12 Water Wall Tube After Long-term Service in Supercritical Power Plant

Oxide scale control is one of the critical maintenance issues in fossil fuel power plant. Hence, the water treatment of the feed water has been changed from all-volatile treatment (AVT) to oxygenated treatment (OT) by added some amount of oxygen in the system to form a stable oxide and minimize the scale growth rate. In this work, the oxide scales formed on T12 water wall tube after one cycle of chemical cleaning treatment under OT condition in a supercritical coal power plant were characterized by using various methods. It was found that the oxide scale formed on the inner surface of the tube had a multi-layer structure with a porous outer layer consisting of Fe3O4 and Cr-rich α-Fe2O3 oxides and a dense inner layer consisting of Cr-rich spinel oxide. A Cr- and Mn-enriched outermost layer was also observed. Cavities, pits, and exfoliation were observed in the oxide scales. The cavities and grain boundaries behaved as the short path of the diffusion of oxygen into the metal. Intergranular oxidation was observed between the inner layer of oxide scale and matrix. The distribution, morphology, and chemical compositional of these oxides were assessed and discussed from a point of view of the suitability of current chemical cleaning solution and procedure which has been used for AVT descaling.