Cyclic Oxidation Resistance Research Articles

Enhancement of cyclic oxidation resistance and effect of transition oxides on wear mechanism of yttrium plus aluminium modified tribaloy T-900 alloy

This paper investigated the microstructure, cyclic oxidation behaviour and wear mechanism of modified and unmodified Tribaloy T-900. Yttrium and aluminium addition promoted the selective oxidation of Al, which reduced the oxidation rate by forming continuous protective layer of Al2O3 at 1000 °C. Al2O3 layer hindered the formation of simultaneous internal oxidation and nitridation zone. Yttrium addition transforms the mechanism of grooving wear to rolling wear by increasing the surface passivation and adherence of transition oxides scale during sliding wear. Hardness of T-900Al and T-900AlY was increased due to refinement of Laves phase and precipitation of grey intermetallic phase.

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.

Microstructure and oxidation resistance of spark plasma sintered Yttria-Zirconia ODS steels

In this experiment, the effect of Y2O3 and ZrO2 additions on the microstructure and cyclic oxidation resistance of 17-Cr ODS steel containing Al consolidated using spark plasma sintering method were studied. In addition, density, porosity and hardness were also observed. Four compositions of ferritic steels as Fe-17Cr-3.5Al-Ti-Y (‘FP’), Fe-17Cr-3.5Al-Ti-Y-0.4Y2O3 (‘FY’), Fe-17Cr-3.5Al-Ti-Y-0.4ZrO2 (‘FZ’), and Fe-17Cr-3.5Al-Ti-Y-0.2Y2O3-0.2ZrO2 (‘FYZ’) were prepared by mechanical alloying and followed by sintering at 1000 °C. Microstructure characteristics were observed for different aspect, viz. elemental distribution, composition, and phase identification. Cyclic oxidation tests were carried out at 800 °C for 8 cycles. The results show that ZrO2 addition suppresses the formation of Y-Al-O clustering and promotes the formation of Y-Zr-O clustering and the enhancement of oxidation resistance of the alloy. However, in some condition it also has a deleterious effect on crack resistance. In contrast, the addition of Y2O3 decreases the oxidation resistance but increases the hardness.

Oxidation behavior of reactively synthesized porous Ti3(Si,Al)C2 compound at 800 °C in ambient air

Abstract Porous MAX compound combines the advantages of metals and ceramics, and has great filtration application prospects in harsh environments. In this work, porous Ti3(Si,Al)C2 was prepared by reaction synthesis of elemental powders, and its cyclic oxidation resistance at 800 °C for 100 h was studied. The synthesized Ti3(Si,Al)C2 has the MAX phase purity above 99 vol% with the maximum aperture, open porosity and permeability of 5.3 μm, 42.9% and 16.27 m3·m−2·kPa−1·h−1, respectively. The oxidation kinetics of porous Ti3(Si,Al)C2 is divided into two stages, which includes the linear law for the initial period within the first 10 h and the parabolic law for the subsequent stable period with their oxidation rate constants of 1.37 × 10−2 h−1 and 4.76 × 10−4 h−1, respectively. The final oxide layer is composed of rutile TiO2 and Al3Ti5O2 phases. In the stable stage, the maximum aperture and open porosity remain nearly constant with slight linear reduction rates of 4.32 × 10−3 μm·h−1 and 5.58 × 10−2%·h−1, which are 2.1% and 3.6% of those in the initial stage, respectively. In the last oxidation procedure of 40 h, the permeability decreases by 2.8%, showing a high stability. The high-temperature oxidation process for porous Ti3(Si,Al)C2 maintains a high and stable permeability and enhances the filtration accuracy by 96.3%, which improves the filtration performance.

Impact of frequency, hold time and atmosphere on creep-fatigue of a 9–12% Cr steel from 300 °C−600 °C

In this study the impact of frequency or rather hold time and atmosphere on the transition from fatigue dominated crack growth to creep fatigue of the ferritic/martensitic steel X20CrMoV12-1 was investigated from 300 °C−600 °C. This temperature range is most important for power plants operated in a flexible manner. Due to the increased share of renewable sources of energy, modern thermal power plants must be operated in a flexible manner to compensate fluctuating power supply from renewables. More damaging loading scenarios, including frequent start-up and shut-down cycles as well as load fluctuations, occur much more frequently than in the past as a consequence. Fatigue damage becomes more and more important, while creep damage reduces due to shorter full power operation durations. Furthermore, loss of passivation by fatigue induced cracking and delamination of protective oxide layers may constitute strong interdependencies of increased cyclic operation and steam oxidation resistance. This results in the necessity for a innovative surveillance concepts including operation mode dependent inspection intervals of thermal power plants. Application of a damage tolerance concept, based on fracture mechanics, can help to improve remaining life assessment of existing and fatigue tolerant design of future power plants. In order to develop codes for flexibly operated components, based on damage tolerance analysis by linear elastic fracture mechanics, its validity range and especially its limitation have to be evaluated first. The study has shown that the transition from pure fatigue to creep fatigue interaction begins at 500 °C and 3.33 × 10−3 Hz (300 s hold time). Furthermore this transition was found to be independent from steam atmosphere. The corresponding fracture mechanisms were investigated in detail.

Alumina growth behaviour on the surface-modified NiCoCrAl alloy by Pt and Hf at high temperature

The growth behaviour of the modified surface of NiCoCrAl alloy by Pt and Hf was investigated at 1050 °C in air atmosphere. The undoped NiCoCrAl alloy exhibited an extremely serious oxide scale spallation. Compared to the undoped alloy, the Hf and Pt depositing on the surface of NiCoCrAl can greatly increase the alumina scale lifetime. Furthermore, altering the deposition order of Pt and Hf influences the cyclic oxidation resistance. The higher content of Hf on the alumina scale of NiCoCrAl alloys resulted in the formation of spinel (NiCr2O4). The spinel as a second phase in the oxide layer of NiCoCrAl + Hf alloys led to the internal oxidation. Internal defects were caused by the diffusion of Al during the oxidation process. Due to the phase transformation and grains growth, the internal stress of alumina scale increased, so that the spallation occurred on the surface of NiCoCrAl + Pt alloys. Pt particles agglomerated on the NiCoCrAl + Hf + Pt alloy surface to form irregular particles, and a lower TGO growth rate has been observed for the NiCoCrAl + Hf + Pt alloy.

Cyclic oxidation resistance of Co-9Al-9W new cobalt-based superalloy

Cyclic oxidation resistance of Co-9Al-9W new cobalt-based superalloy

Formation of High-Oxidation-Resistant NiAl Surface Layer by Simultaneous Electrodeposition of Al and Zr in Molten Salt

A coating layer consisting of Zr-containing NiAl was prepared by the simultaneous electrodeposition of Al and Zr using a molten salt as the medium. In particular, the morphology and chemical composition of the coating layer were investigated based on the influence of the ZrF4 concentration of the bath and the electrodeposition potential. Furthermore, in the surface layer consisting of the NiAl phase, the Zr concentration was measured by ICP analysis of the solution in which the surface layer was dissolved. For the prepared samples, the cyclic oxidation resistance was evaluated in air at 1423 K. For the Ni sample after the electrodeposition in a NaCl–KCl–3.5 mol%AlF3 bath without ZrF4 at − 1.5 V, a surface layer consisting of Ni2Al3 was formed. On the other hand, when the simultaneous electrodeposition of Al and Zr was carried out in a NaCl–KCl–3.5 mol%AlF3 salt containing 0.05 mol%ZrF4 at − 1.3 V and the molten salt containing 0.1 mol%ZrF4 at − 1.3 ~ − 1.5 V, the formation of a surface layer consisting of NiAl was observed. In particular, by the simultaneous electrodeposition in the molten salt containing 0.1 mol% ZrF4 at − 1.5 V, a thick surface layer consisting of NiAl (about 40 μm) was formed. Furthermore, the detailed analysis of the Zr concentration in the surface layer revealed that the Zr content in the layer was 0.05 at%. Cyclic oxidation tests revealed that a mass loss was observed for the samples coated with the NiAl layer formed by the electrodeposition of only Al. However, for the sample coated with the NiAl layer containing a small amount of Zr, no decrease in the mass due to exfoliation of the oxide was observed. After the cyclic oxidation tests, a scale consisting of α-Al2O3 with good adhesion to the substrate metal was formed on the samples coated with the NiAl layer containing a small amount of Zr. This scale included ZrO2 particles.

Effect of Chromium Addition on the Cyclic Oxidation Resistance of Pseudo-Binary (Mo,Cr)3 Si Silicide Alloy

AbstractThis paper describes the performance under cyclic oxidation of (Mo,Cr)3 Si compound with different Cr additions for possible coating application. Cyclic oxidation was carried out at 1,000 °C at different intervals during 250 h. Oxidized surface samples were analysed by scanning electron microscope where epitaxial oxide scales were observed mainly in samples with higher Cr content which may provide protection against surface oxidation. X-ray diffraction studies have shown the Cr2O3 and SiO2 formation as the main oxide scale; after analyses, it was found that these oxides are responsible for the best oxidation protection, with 36 at.% Cr being the optimal chromium concentration. At lower chromium concentrations, pest reaction occurred in the oxidized samples at times less than 25 h as a result of the formation of the unstable molybdenum oxide.

Oxidation behavior of a glass-based composite coating with a low expansion cermet bond-coat and an AlN diffusion barrier on K417G superalloy

A ceramic particle reinforced glass matrix composite coating with a novel Ni + CrAlYSiN cermet bond-coat and an AlN diffusion barrier was prepared on K417G superalloy, and its oxidation behavior at 1000 °C was investigated. The oxidation rate of the coating was significantly reduced compared with the Ni + CrAlYSiN coating, because the glass-based top-coat promoted selective oxidation of Al within the bond-coat due to the oxygen barrier effect. Furthermore, cyclic oxidation resistance of the coating was improved by the low expansion bond-coat while weakened by the microstructure degradation of the top-coat. Additionally, the AlN diffusion barrier effectively restrained interdiffusion between bond-coat and substrate.

Effect of Y2O3 content in the pack mixtures on the cyclic-oxidation of Y2O3-modified low temperature aluminide coatings on 309 stainless steel

By using Y2O3 nanoparticles, instead of part or all of Al2O3, acting as filler, Y2O3-modified aluminide coatings were produced on 309 stainless steel using a conventional pack-cementation method at 700 °C for 6 h. Effect of Y2O3 content in the pack mixtures on the cyclic-oxidation resistance of different aluminide coatings was comparably investigated. The results show that the phase of aluminide coatings was Fe24Al76.8. With the increase of Y2O3 content in the pack mixtures, the thickness of aluminide coatings decreased but the cyclic-oxidation resistance at 900 °C in air increased, because of prevention of cavities at the alumina scale/coating interface, and because of mitigation of degradation of the aluminide coating due to decreased outward diffusion and inward interdiffusion between the aluminide and the 309 stainless base. The reasons for the results are discussed.

Fabrication and Oxidation Resistance of TiAl Matrix Coatings Reinforced with Silicide Precipitates Produced by Heat Treatment of Warm Sprayed Coatings

Ti-Al-based intermetallics are promising candidates as coating materials for thermal protection systems in aerospace vehicles; they can operate just below the temperatures where ceramics are commonly used, and their main advantage is the fact that they are lighter than most other alloys, such as MCrAlY. Therefore, Ti-Al-Si alloy coatings with five compositions were manufactured by spraying pure Ti and Al-12 wt.% Si powders using warm spray process. Two-stage hot pressing at 600 and 1000 °C was applied to the deposits in order to obtain titanium aluminide intermetallic phases. The microstructure, chemical composition, and phase composition of the as-deposited and hot-pressed coatings were investigated using SEM, EDS, and XRD. Applying of hot pressing enabled the formation of dense coatings with porosity around 0.5% and hard Ti5(Si,Al)3 silicide precipitates. It was found that the Ti5(Si,Al)3 silicides existed in two types of morphologies, i.e., as large particles connected together and as small isolated particles dispersed in the matrix. Furthermore, the produced coatings exhibited good isothermal and cyclic oxidation resistance at a temperature of 750 °C for 100 h.

High-temperature oxidation behaviour of minor Hf-doped β-NiAl single crystals in dry and humid atmospheres

Oxidation behaviour of undoped β-NiAl and β-NiAl-0.05Hf single crystals were investigated at 1100 °C in 20 vol% O2 + Ar and 15 vol% H2O + Ar, respectively. On contrary to the well-known beneficial effect of Hf additions on the oxidation behaviour of polycrystalline β-NiAl, severe-scale spallation is observed for β-NiAl-0.05Hf single-crystal alloy, especially in dry atmosphere. It is proposed that the presence of the grain boundaries in the polycrystalline substrate enables proper content of Hf segregating at the grain boundaries of the oxide scale and at the scale–substrate interface, which promotes the conditions required for reactive element effect. Once the reactive element effect of Hf does not work, its strong affinity with oxygen will accelerate the process of high-temperature oxidation. However, the absence of the grain boundaries as fast diffusion paths partially compromises the adverse influence of water vapour on cyclic oxidation resistance of β-NiAl single crystal, resulting in considerable suppression of the oxidation rate and less loss of protection compared with that in dry atmosphere. In addition, interfacial cavities are observed in dry and humid atmospheres, which may eventually result in the spallation of the oxide scale.

Contribution of Mg addition to the high temperature cyclic oxidation resistance of NiAlCr alloys

Cyclic oxidation tests of NiAlCr-Mg (Mg = 0–3.8 at.%) alloys were carried out at 1027 °C under airflow. Small amount of Mg addition (1 at.%) increased the cyclic oxidation resistance while further addition of Mg increased the oxidation rate of the alloys. A distinct and continuous MgAl2O4 spinel layer formed on Mg containing alloys. Additional MgO layer formed on the alloys containing 2.5 and 3.8 at. % Mg.

Engineering an ultrafine intermetallic eutectic ternary alloy for high strength and high temperature applications

We introduce a novel material based on microstructural engineering of intermetallics at an ultrafine scale. A unique microstructure was developed in a ternary alloy composition (Ni-12 at.% Al-11 at.% Zr) containing two coupled intermetallic phases (Ni3Al and Ni5Zr) consisting of colonies with interconnected lamellae that degenerate into irregular morphologies during growth. This architecture exhibits excellent high temperature microstructural stability, exceptional high strength with adequate tensile ductility at room temperature, and outstanding cyclic oxidation resistance.

Cyclic oxidation behaviour of Co/Si co-doped β-NiAl coating on nickel based superalloys

Co/Si co-doped β-NiAl coating on nickel based superalloys was prepared using pack cementation method. Microstructure and cyclic oxidation behaviour of the coating were investigated. The weight loss of the coating is less than 3 mg/cm2 after 3200 cycles at 1050 °C. The coating exhibits a good cyclic oxidation resistance. The addition of Si decreases the growth stress in the oxide scale by inhibiting the formation of harmful NiO. The formation of SiO2 particles at the scale/coating interface decreases the growth rate of the Al2O3 scale. Moreover, Si addition promotes the formation of the high Al-content phase β-NiAl.

Oxidation behaviour of plasma surface alloying on Ti6Al4V alloy

ABSTRACTTi–CrNi alloy coatings with 20, 40, 60 and 80 at-%Ni were prepared on Ti6Al4V alloy surface by double glow plasma surface alloying technique. The cyclic oxidation behaviour of the coatings was investigated at 750, 850 and 950°C. The results show that each coating has a complete structure of settled layer, mutual diffusion layer and sputtering affected zone. When the Ni content was 40 at-%, the Ti–CrNi alloy coating showed the best cyclic oxidation resistance. The oxide scale with ‘Cr2O3 film+NiO film’ structure showed the best resistance to peeling.

High temperature cyclic oxidation resistance of 50Cr-50Al coatings mechanically alloyed on low carbon steel

In the present study, the 50Cr-50Al coatings were mechanically alloyed on low carbon steel at two different milling times of 1 h and 4 h, and subsequently annealed in vacuum at 800 °C for 2 h. The resistances of coatings with and without annealing against high temperature cyclic oxidation were studied at 800 °C for up to 8 cycles. The phase compositions and structures of oxidized samples were analyzed by X-ray diffractometer and SEM-EDX analyzer. The results showed that carbon steel is susceptible to oxidation. The resistance of low carbon steel towards oxidation at high temperature was improved by applying 50Cr-50Al coatings due to the formation of Al2O3. However, Fe atoms from the substrate had a tendency to diffuse outwards through defects in the coating layer, resulting into the formation of Fe-oxides nodules. The coated sample that was prepared for 4 h showed a better oxidation resistance than that of 1 h. Then, the annealing treatment significantly enhanced the coating's oxidation resistance. Based on the results of present work, the annealed 50Cr-50Al coating prepared for 4 h exhibited the lowest mass gain. The details are presented in this paper.

Cyclic oxidation behavior and oxide scale adhesion of Al/NiCrAlY coating on pure titanium alloy

Al and Al/NiCrAlY coatings were deposited on pure titanium substrate by air plasma spraying method. Cyclic oxidation behavior and oxide scale adhesion at 800 °C for 100 cycles were investigated. For the single Al coating, a severe spalling of oxide scale and elemental interdiffusion occurred after 100 cycles. The mass loss of the single Al coating has reached to 1.39 mg/cm2. The oxide scale on the duplex Al/NiCrAlY coating kept a good bonding with the underlay coating. The addition of NiCrAlY layer inhibited the outward diffusion of Ti atoms and inward diffusion of Al atoms. The propagation of cracks and the formation of pores were also suppressed by NiCrAlY layer. As a result, the duplex Al/NiCrAlY coating possessed a superior cyclic oxidation resistance.

Effect of minor alloying elements La, C and B on the cyclic oxidation behavior of Ni-Cr-W-Mo superalloys

The cyclic oxidation behavior of Ni-Cr-W-Mo base alloys with various La, C and B contents is investigated at 1150 °C in ambient air with 15 min of high-temperature exposure and 5 min of air cooling. Oxidation resistance is evaluated by the weight change during cyclic oxidation. The cross-section of the oxide scale is observed by scanning electron microscopy after the cyclic oxidation test. The oxide scale mainly consists with spinels and a chromia layer. NiWO4 oxide particles and NiO are also observed in some areas. The addition of La improves the cyclic oxidation resistance significantly. However, the addition of 0.03 wt% B reduces the beneficial effect of La. The additions of B and C increase the spallation at the initial stage such that severe weight loss is observed. However, the spallation is reduced at the later stage. The addition of a proper amounts of B and C can be beneficial to improve the cyclic oxidation resistance of Ni-Cr-W-Mo alloys.