High Temperature Isothermal Oxidation Research Articles

A new strategy for improving TBCs performance through tailoring the bond coating interface with laser texturing

The parallel micro-hole texture was manufactured to tailor the bond coating interface morphology by a one-step process with the assistance of nanosecond pulsed laser technique. It is demonstrated that the interface stability of the laser-textured TBCs was improved through the evaluation of high-temperature isothermal oxidation under different durations and water-quenching thermal shock at 1050 ℃. The interfacial TGOs formed in the laser-textured TBCs were composed of the continuous alumina strip and grew more slowly compared to that of the as-sprayed TBCs during isothermal oxidation. In addition, as for the laser-textured TBCs, no transverse cracking was noticed along the TGOs interface and the alumina-only TGOs developed a thickness of approximately 1.4 µm after thermal shock testing. The high surface density of micro holes on the bond coating interface enhanced the interfacial toughness and suppressed TGOs growth, which contributed to improving the TBCs durability.

Development of Gd2O3 doped yttria stabilized zirconia based thermal barrier coating for improved high temperature oxidation and erosion resistance

Rear-earth doped advanced thermal barrier coatings (TBCs) have been developed by in-situ doping of Gd into YSZ matrix by atmospheric plasma spray coating of YSZ and Gd2O3 (6 to 15 mol %) premixed powders. These modified TBCs are deposited over CoNiCrAlY bond coated Inconel 718 substrate. Diffusion of Gd or Gd3+ into YSZ matrix resulted in further stabilization of its tetragonal phase which is confirmed by detailed X-Ray diffraction analysis. Microstructure and chemical compositions of doped TBCs are examined by scanning electron microscopy and energy dispersive spectroscopy, respectively. Incorporation of Gd2O3 resulted in relatively denser and smoother coating compared to pure YSZ coating for identical process parameters due to finer particle size and complete melting of Gd2O3 powders. However, in-situ doped coatings are sinter resistant at elevated temperature unlike pure YSZ coating which aids in retention of porosities during high temperature exposure and provide better thermal performances. Modified TBCs showed higher hardness and Young's modulus, as revealed by micro and nano hardness measurements. High temperature isothermal oxidation studies carried out between 1173 K and 1273 K allowed evaluation of the efficacy of modified TBCs for oxidation resistance and related kinetics. The results show that modified TBCs provide better oxidation resistance compared to pure YSZ coating. Erosion tests of TBCs both at ambient and elevated temperature (773 K) showed that modified coatings are more resistant to erosion compared to YSZ coating.

Oxidation and Electrical Property Studies on Ferritic Steels as Potential Interconnects in Electrochemical Devices for Energy Conversion

This work presents the results of oxidation studies on commercially available Nirosta 4016/1.4016 ferritic steel, which contains 16.3 wt.% chromium, as well as the electrical properties of steel/scale layer systems in order to determine the usefulness of this steel for constructing metallic interconnects in solid oxide fuel cell (SOFC) and solid oxide electrolyzer cell (SOEC) stacks. The E-Brite ferritic steel, consisting of up to 26 wt.% chromium, was chosen as a reference material. High-temperature isothermal oxidation kinetics studies were carried out on both steels at 1073 K for 255, 505, 760 and 1010 h in air atmosphere. These conditions are representative of those present in the cathode compartment of a SOFC and the anode compartment of a SOEC. Area specific resistance (ASR) measurements were performed on steel/scale layer systems, obtained after the previous oxidation of both steels in the above-mentioned conditions, in the air in the temperature range of 573–1073 K using the pseudo-DC four-probe method. On the basis of these studies, complemented by morphology observations, as well as chemical and phase composition analysis of the oxidation products, the usefulness of Nirosta 4016/1.4016 ferritic steel for manufacturing interconnects in energy conversion electrochemical devices operating at 1073 K was confirmed.

High-temperature oxidation properties of economical and lightweight Fe-Cr-Ni-Al medium-entropy alloy

This study investigated the microstructure, high-temperature oxidation properties and mechanism of non-equiatomic Fe-Cr-Ni-Al medium entropy alloy (MEA). Microstructural observation of MEA identified coarse grains of mm scale, and cuboidal precipitates with an average size of 125 nm were evenly distributed within grains. Phase analysis confirmed that the alloy consisted of a Fe-Cr matrix (BCC structure) and B2 Ni-Al precipitate. High temperature isothermal oxidation tests measured oxidation weight of 0.08 mg/cm2 at 800 ℃, 0.17 mg/cm2 at 900 ℃, 0.22 mg/cm2 at 1000 ℃, and 0.47 mg/cm2 at 1100 ℃. Compared to other alloys tested with similar conditions, Fe-Cr-Ni-Al MEA presented by this study achieves economic benefits with relatively excellent high-temperature oxidation resistance. The outstanding high-temperature oxidation resistance of the MEA presented by this study is due to the evenly distributed dense stable Al2O3 layer formed regardless of temperature conditions. In addition, the alloy did not have breakaway oxidation, which can occur as oxidation progresses.

Isothermal oxidation characteristics of laser‐treated Al2O3 + Sm2SrAl2O7 composite thermal barrier coatings

AbstractA thermal barrier coating system with Al2O3 + Sm2SrAl2O7 composite top coat was developed on an Inconel 718 superalloy substrate by using an atmospheric plasma spray technique, and the coated samples are treated with an Nd:YAG fiber laser to improve the surface properties. The as‐coated and laser‐treated samples were subjected to high temperature isothermal oxidation test at 1100°C for 150 h duration. The surface of the oxidized samples showed the presence of dissociated SmAlO3, SrAl2O4, and Sm2O3. Thermally grown oxides (TGO) are found at the bond coat top coat interface of the samples. The oxidation kinetics is examined by monitoring weight gain at regular intervals. The electrochemical impedance behavior, oxidation mechanism, and TGO formation in the developed composite coatings are discussed in detail.

Numerical Model For Short-Time High-Temperature Isothermal Oxidation of Fe–Mn Binaries at High Oxygen Partial Pressure

Since the oxidation reactions in the process of steel production occur in harsh conditions (i.e., high temperatures and gas atmospheres), it is practically impossible to observe in situ the compositional changes in the steel and the formed oxide scale. Hence, a coupled thermodynamic-kinetic numerical model is developed that predicts the formation of oxide phases and the composition profile of the steel alloy’s constituents in a short time due to external oxidation. The model is applied to high-temperature oxidation of Fe–Mn alloys under different conditions. Oxidizing experiments executed with a thermogravimetric analyzer (TGA) on Fe–Mn alloys with different Mn contents (below 10 wt %) are used to determine kinetic parameters that serve as an input for the model. The mass gain data as a function of time show both linear and parabolic regimes. The results of the numerical simulations are presented. The effect of different parameters, such as temperature, Mn content of the alloy, oxygen partial pressure, and oxidizing gas flow rate on the alloy composition and oxide phases formed, is determined. It is shown that increasing the temperature and decreasing the oxygen partial pressure both lead to a thicker depleted area.

Effect of minute element addition on the oxidation resistance of FeCoCrNiAl and FeCoCrNi2Al high entropy alloy

The effect of Ti0.1 and Ti0.1Si0.1 addition on the high temperature isothermal oxidation behavior of dense FeCoCrNiAl and FeCoCrNi2Al high entropy alloy (HEA) consolidated by vacuum hot pressing were investigated by X-ray diffraction, Scanning Electron Microscopy and Raman Spectroscopy. Mechanical properties such as hardness, Young’s modulus, and thermal properties such as differential scanning calorimetry (DSC) and coefficient of thermal expansion (CTE) were also investigated. The weight gain recorded after isothermal oxidation for 5,25,50 and 100 h at 1050 °C was found to be parabolic in nature. X-ray diffraction analysis (XRD), as well as Raman spectroscopy analysis of HEA’s oxidized at 1050 °C for 100 h, shows the formation of the Al2O3 phase. A homogeneous thin oxide scale without any discontinuity was observed throughout the cross-section. Ti and Si addition in 0.1 at. % improves mechanical properties, oxidation resistance, and reduces waviness of the oxide scale.

High temperature isothermal oxidation behavior of electron beam melted multi-phase γ-TiAl alloy

The γ-TiAl alloys fabricated by additive manufacturing have gathered significant attention in recent years due to their unique microstructural features and properties. However, the oxidation kinetics of additively manufactured γ-TiAl alloys have not been studied thoroughly. Herein, the TNM-B1 alloy was fabricated with the help of electron beam melting (EBM) for the first time and tested for 100 h over a temperature range of 800 °C-1000 °C; this was aimed at investigating its isothermal oxidation kinetics. Subsequently, the exposed samples were systematically analyzed to study the oxide scales, which was achieved with the help of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Spallation was observed at 900 °C and 1000 °C after an exposure of 30 h and 5 h, respectively. The results showed that the oxide comprises alternative layers of Al2O3, TiO2, and mixture phases. The oxidation resistance of the EBM-processed TNM-B1 alloy was observed to be superior to those of the conventionally processed TNM-B1 and other γ-TiAl alloys. Finally, the significance of a fine fully lamellar microstructure on the oxidation kinetics of TNM-B1 alloy was explained.

Characterization of the High Temperature Isothermal Oxidation Behaviour of an ATI425® Titanium Alloy

Characterization of the High Temperature Isothermal Oxidation Behaviour of an ATI425® Titanium Alloy

An investigation of oxidation, hot corrosion, and thermal shock behavior of atmospheric plasma-sprayed YSZ–Al2O3 composite thermal barrier coatings

Abstract In the current study, different types of thermal barrier coatings with various mass fractions were investigated in terms of oxidation, hot corrosion, and thermal shock resistance. The thermal barrier coatings consisted of six different samples, which included the usual YSZ, Al2O3, hybrid composites with 65 wt.% YSZ and 35 wt.% Al2O3, 50 wt.% YSZ and 50 wt.% Al2O3, 35 wt.% YSZ and 65 wt.% Al2O3 and the final one, which was a double layer composite (Al2O3 and YSZ). High temperature isothermal oxidation behavior of the coatings was tested at 1050 °C, using an air furnace for 48 h, 80 h, and 120 h respectively. Hot corrosion tests were applied at 1050 °C using a 45 wt.% Na2SO4 and 55 wt.% V2O5 mixture of salts. The microstructure and phase stability of coatings were evaluated by means of scanning electron microscopy and X-ray diffraction techniques. The usual YSZ showed better hot corrosion and thermal shock resistance, while Al2O3 showed the lowest hot corrosion and oxidation resistance. Thermally grown oxide formation, thermal expansion coefficient mismatch and phase transformation in the thermal barrier coatings could be the main causes of degradation after thermal shock testing.

An investigation of oxidation, hot corrosion, and thermal shock behavior of atmospheric plasma-sprayed YSZ–Al2O3 composite thermal barrier coatings

Abstract In the current study, different types of thermal barrier coatings with various mass fractions were investigated in terms of oxidation, hot corrosion, and thermal shock resistance. The thermal barrier coatings consisted of six different samples, which included the usual YSZ, Al2O3, hybrid composites with 65 wt.% YSZ and 35 wt.% Al2O3, 50 wt.% YSZ and 50 wt.% Al2O3, 35 wt.% YSZ and 65 wt.% Al2O3 and the final one, which was a double layer composite (Al2O3 and YSZ). High temperature isothermal oxidation behavior of the coatings was tested at 1050 °C, using an air furnace for 48 h, 80 h, and 120 h respectively. Hot corrosion tests were applied at 1050 °C using a 45 wt.% Na2SO4 and 55 wt.% V2O5 mixture of salts. The microstructure and phase stability of coatings were evaluated by means of scanning electron microscopy and X-ray diffraction techniques. The usual YSZ showed better hot corrosion and thermal shock resistance, while Al2O3 showed the lowest hot corrosion and oxidation resistance. Thermally grown oxide formation, thermal expansion coefficient mismatch and phase transformation in the thermal barrier coatings could be the main causes of degradation after thermal shock testing.

Modeling and simulation of coupled phase transformation and stress evolution in thermal barrier coatings

The thermally grown oxide layer is known to be responsible for the failure of coating systems due to the generation of severely high stresses. In this work, oxidation induced stresses generated in thermal barrier coating (TBC) systems are investigated for high temperature isothermal oxidation. In that sense, a comprehensive model, where phase transformation is coupled with mechanics is developed for the life-time estimation of TBC systems and a modified version of the Allen-Cahn type phase field approach is adopted in order to model the generation of thermally grown oxide (TGO) in finite strain constitutive framework. The top-coat material behavior is modeled using a rate-dependent Gurson type plasticity for porous materials which also accounts for creep. The results for the isothermal phase transformation analysis and the model validation using experimental results are demonstrated. The capability of the model in predicting the local stresses which is the main variable in the analysis of possible delaminations and accurate lifetime estimation of TBC systems is shown.

High Temperature Isothermal Oxidation of Heat-treated HR-120 Ni-based Alloys

The effect of heat treatment of HR-120 Ni-based alloys on the isothermal oxidation at high temperature was studies. HR-120 Ni-based alloys was undergo a heat treatment process at two different temperatures, namely 1000 °C and 1200 °C for 3 h soaking time, followed by water quench. The heat-treated samples were then undergoing an isothermal oxidation test at 500 °C for 500 h exposure time in air. Oxidized samples have been characterized in terms of the kinetics of oxidation, phase analysis using x-ray diffraction (XRD) and oxide surface morphology using scanning electron microscope (SEM) and field emission scanning electron microscope (FESEM) equipped with energy dispersive x-ray (EDX) spectrometer. The heat treatment process exhibits an increasing of average grain size alloy as the temperature increases. Whereas, the oxidation kinetics of oxidized samples exhibits a parabolic rate law, representing a diffusion-controlled oxide growth rate. The oxidized of heat-treated sample at 1000 °C recorded low oxidation rate with low parabolic rate constant values. The oxide surface morphology of oxidized samples indicates the formation of continuous oxide scales with overgrown Nb-rich oxide particles after exposure for 300 h. At 500 h exposure time, the formation of Nb-rich oxide particles was growing with evidence of crack occurred around the overgrown oxide particles.

Oxide scale growth on Fe-40Ni-24Cr alloy at high temperature oxidation

Fe-40Ni-24Cr alloy is a Ni-based alloy used at high temperature application. In this study, Fe-40Ni-24Cr alloy had undergo a solution treatment at two different temperatures, namely 1050° and 1150°, for 3 hours soaking times followed by water quench. A solution-treated Fe-40Ni- 24Cr alloy was experienced a high temperature isothermal oxidation test at 500° for 500 hours exposures duration. The growth of oxide scale was characterized in terms of oxidation kinetics and surface morphology using field emission scanning electron microscope equipped with energy dispersive x-ray spectroscopy. The oxidation kinetics of all samples shows an increasing weight gain pattern as the exposure durations increases. The oxidation kinetics was obeyed a parabolic rate law, indicating the oxide growth rate was followed diffusion-controlled mechanism. The surface morphology of oxidized solution-treated Fe-40Ni-24Cr alloy displayed a formation of continuous oxide scale with evidence of overgrown Nb-rich oxide particles distributed along the oxidized samples surface. Oxidized Fe- 40Ni-24Cr alloy which undergo solution treatment at 1150° exhibited the formation of oxide spallation. The spallation has a tendency to occur around the area of overgrown Nb-rich oxide particles.

Effect of segmented cracks on TGO growth and life of thick thermal barrier coating under isothermal oxidation conditions

This paper is devoted to a comparative study on the isothermal oxidation of thick thermal barrier coating (TTBC) with and without segmented cracks produced by atmospheric plasma spray (APS) process. Accordingly, the growth of thermally grown oxide (TGO) and its effect on the degradation of the coating were investigated. Thick top coat in both segmented crack and conventional thick TBC reduced the double layered TGO growth rate slightly. The segmented crack thick TBC demonstrated longer isothermal oxidation life in comparison with that of the conventional thick TBC at 1100 °C. The dominant failure mechanism was spallation due to lateral cracking within the TGO and/or within TBC near the TGO layer, called mixed failure. Stress, and consequently strain, induced on the TTBC due to progressive TGO growth, seems to be primarily responsible for the crack initiation and propagation leading to the coating failure. Increment of elastic energy stored within the top coat due to the increasing of TGO thickness, finally causes thick thermal barrier coating failure in high temperature isothermal oxidation.

High-temperature oxidation of Ti–Al–Si alloys prepared by powder metallurgy

The Ti–Al–Si alloys are promising materials for high-temperature use in automotive, aerospace or cosmic industry. The main advantages of these alloys are their low density (approximately 4 g/cm3), good oxidation resistance, and mechanical properties at elevated temperatures. Addition of silicon into the Ti–Al alloys improves the high-temperature behaviour and improves compactness and adhesion of the oxide layer. The resistance against oxidation can be effectively improved also by an appropriate technology of preparation. In this work, the high-temperature cyclic and isothermal oxidation resistance of the Ti–Al–Si alloys are described. The effect of powder metallurgy production route (reactive sintering, mechanical alloying, Spark Plasma Sintering) on high-temperature behaviour was compared. Cyclic and isothermal oxidation tests were carried out at 800 °C and 1000 °C, well above the air-operating limit for TiAl. It was confirmed, that the Ti–Al–Si alloys are resistant at temperature 800 °C, where only very thin oxide layer was formed. Mechanical alloying followed by Spark Plasma Sintering improved the high-temperature behaviour of these alloys, the oxide layer was even thinner.

Effect of Nb Addition on Oxidation Mechanisms of High Cr Ferritic Steel in Ar–H2–H2O

High chromium ferritic steels are being used as construction materials for interconnects in solid oxide electrolysis cells (SOEC). Addition of niobium in the range of a few tenths of a percent is suitable for increasing the high-temperature creep strength of this type of ferritic steel. In the present work, the high-temperature isothermal oxidation behavior of a niobium containing ferritic steel at 800 °C was investigated in Ar–4%H2–4%H2O gas simulating the service environment in an SOEC (cathode side) and compared with that of a Nb-free counterpart alloy. Gravimetric data were correlated with the results from microstructural analyses using, among others, scanning and transmission electron microscopy as well as glow discharge optical emission spectroscopy. Atom probe tomography was used for obtaining atomic-scale insight into the segregation processes in external oxides and their interfaces. The oxidation rate was substantially higher for the Nb-containing than for the Nb-free alloy. Both alloys formed double-layered oxide scales consisting of inner chromia and outer MnCr2O4 spinel. Additionally, a thin layer of rutile-type Nb(Ti,Cr)O2 oxide of 200–300 nm thickness was observed at the scale–alloy interface in the Nb-containing steel. Nb addition to the alloy led to its segregation at chromia grain boundaries which affected the diffusion of Cr and other solute species such as Ti, Mn and Si.

Effect of Fe addition and moist environment on the high temperature oxidation behavior of Mo76-xSi14B10Fex (x = 0, 0.5, 1 at.%) composites

The effect of Fe addition and the moist environment on the high temperature isothermal oxidation behaviors of multiphase Mo76-xSi14B10Fex (x = 0, 0.5, 1 at.%) composites in the range of 1000–1300 °C have been investigated. The microstructure of all the composites with α–Mo solid solution (SS) and eutectic mixture of Mo3Si + Mo5SiB2 phases, has been refined upon Fe addition, which improves the oxidation resistance and reduces the mass loss up to 55% in dry air and 31% in moist air for 24 h exposure. Whereas, the oxidation resistance in moist air improves due to the formation of a protective Fe-rich glassy borosilicate scale, which reduces the vaporization of MoO3 by forming Fe2(MoO4)3. The cross-sectional area of the residual alloy for x = 1 were estimated to be 97% in dry air and 85% in moist air that of unoxidized coupons. The bulk hardness of the as-cast composite is 1031 Hv for x = 1, which reduced only by 6.7% (962 Hv) upon oxidation at 1300 °C in both dry and moist air, showing superior stability of the silicide matrix composites for high temperature application. X-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy studies were performed to identify the various products of oxidation and to explore the mechanism of protection.

Influence of isothermal oxidation on microstructure of YSZ and Mullite-YSZ thermal barrier coatings

Microstructural changes in conventional yttria stabilized zirconia (YSZ) and multilayer Mullite-YSZ/YSZ (M-YSZ) thermal barrier coatings were compared based on high temperature isothermal oxidation at the temperatures of 1050, 1150 and 1250 °C. Both types of thermal barrier coatings were produced from commercially available powders utilizing atmospheric plasma spray technique. Initial M-YSZ powder mixture consisted of 29 vol. % of Mullite and 71 vol. % of YSZ. Inconel Alloy 713LC nickel-based superalloy was used as a substrate material (cylinders, 25 mm in diameter and 10 mm in thickness). The TBCs lifetime, phase stability, thickness of the thermally grown oxide layer, porosity, and changes in microstructure after high temperature testing were evaluated using light microscope, scanning electron microscope equipped with EDX analyzer, and XRD technique.

High Temperature Isothermal Oxidation Behavior of Superheater Materials

Abstract During combustion of biomass, alkali chloride-rich ash deposits condense on the surface of superheater tubes, thereby induce corrosion. A well-developed protective oxide layer formed from pre-oxidation treatment is an environmental friendly and cost effective technique for corrosion protection of superheater materials at high temperature in alkali salt environment. The ability of the pre-oxidized layer to protect the alloys depend on the properties such as porosity, thickness, continuity and composition of the layer. The characteristics of the oxide layer could be controlled by proper understanding on the oxidation behaviour of the materials. The main objective of this work is to obtain information on the oxidation behaviour of Hastelloy C22 (C22) and 304 Stainless Steel (304SS) at high temperature environment, hence to justify the suitability of these alloys to be subjected for pre-oxidation treatment. Oxidation of C22 and 304SS was conducted at temperature 900 °C and 1000 °C for 24 hours by thermogravimetric analysis (TGA). The oxide morphology and elemental analysis were characterized using Field Emission Scanning Electron Microscope (FESEM) equipped with Energy Dispersive X-ray Spectroscopy (EDX). The phases of the oxidation products were determined using X-ray diffraction analysis (XRD). The weight change of 304SS is higher as compared to C22 which indicates higher oxidation rate for 304SS. However, the oxide layer formed on Hastelloy C22 is more protective compared to the oxidation products of 304SS. The finding justifies the high potential of C22 alloy to be subjected for pre-oxidation treatment before used as superheater materials for biomass industry.