Oxide Spallation Research Articles

An innovative strategy against oxide spallation of hot formed steels

An innovative strategy against oxide spallation of hot formed steels

Synergistic effects of Pt and Y addition in (Ni, Pt)CrAlY bond coat on oxide spallation resistance and growth of interdiffusion zone between bond coat and Ni-based single crystal superalloy

This study shows the beneficial effect of Pt addition to the (β+γ)-NiCrAlY coating. Adding Y in NiCrAl increases oxide growth kinetics but improves spallation resistance. Pt with Y does not change the oxidation rate compared to only adding Y but significantly reduces spallation when cooled to room temperature. Continuous layers of Al2O3 and Cr2O3, along with other oxides such as YAlO3, NiCr2O4, and NiAl2O4, are observed. Moreover, Pt addition reduces the thickness of the interdiffusion zone where Al goes through an uphill diffusion profile, minimizing Al loss and significantly decreasing the growth of deleterious TCP phases.

High temperature oxidation behavior of a Ni–Co-based superalloy

Oxidation behavior of a Ni–Co-based superalloy prepared by vacuum induction melting (VIM) plus electron beam smelting layered solidification technology (EBSL) and VIM plus electro slag remelting (ESR) at 1180 °C was investigated. The predominant oxides from the outer layer to the inner layer are TiO2, Cr2O3, (Al, Ti)-rich oxide and Al2O3, respectively. The (Al, Ti)-rich oxide is considered to be Al2Ti4O9, which is formed by TiO2 and Al2O3. At high temperature, the external oxides experienced significant spalling, particularly in ESR-alloy, which indicated that the EBSL-alloy is more preferable in terms of oxidation resistance. This can be attributed to the presence of finer grains in EBSL-alloy, which facilitates the diffusion of elements and promotes the rapid formation of oxidation scales on the surface of the alloy. Additionally, the presence of a TiO2 layer cover on Cr2O3 reduces the degree of spalling of oxides in EBSL-alloy.

Oxidation behaviour of austenitic stainless steel 304HCu in Advanced Ultra Supercritical (AUSC) steam and the efficacy of shot-peening treatment

Effect of shot-peening on the oxidation behaviour of alloy 304HCu in controlled advanced ultra-supercritical (AUSC) steam at 650 ◦C, 31 MPa for 600 h was investigated. Non-shot peened surfaces form thick Fe-rich oxides, undergo internal oxidation, and suffer oxide spallation sooner than those reported in literature. Shot-peened surfaces form a thin, external chromia scale with Mn(Cr,Fe)2O4 and MnCr2O4 spinels growing above and below it respectively. Shot-peening enhances Cr and Mn diffusivity through grain refinement and increased dislocation density, which aids in resisting chromia scale breakdown, eliminating iron oxides, and preventing oxide spallation. Oxide growth mechanism in AUSC steam is discussed.

A study of fretting fatigue in a contact pair of DZ125/GH4169: its mechanical behavior and life prediction

In this paper, the fretting fatigue test of DZ125/GH4169 contact pair was carried out. Observation and analysis of the wear and fracture were needed to get the fretting damage law. A hardness parameter was introduced to modify the existing life prediction model. The specimen was exposed to both normal and fatigue loads, as indicated by the results, which resulted in the formation of a black oxide layer that stuck to the contact zone's edge. Oxide spalling formed grits and abrasive wear, accelerating the loss of fatigue resistance. At high temperatures, the oxidation was intensified. The life prediction results were all within the double error band. The error range was reduced and the life prediction effect was significantly improved.

Theoretical study of the effects of alloying elements on TiO2/Ti2AlNb interface adhesion properties.

Ti2AlNb-based alloys are expected to be applied in the manufacture of parts of aeroengines to achieve the goal of increasing the thrust-to-weight ratio. However, the poor high temperature oxidation resistance of these alloys may hinder their applications. Alloying has been proven to be effective in improving oxidation resistance properties. However, the selection of alloying elements and their influence mechanisms are rarely studied. The TiO2/Ti2AlNb interface bonding interactions and the effects of alloying elements of Si, Sc, Y, Zr, Mo and Hf were investigated via first principles calculations. The separation energy and electronic structure were studied to explore the bonding interactions between the oxide scale and Ti2AlNb matrix. When Zr and Hf are used to replace Al, the bonding properties of the TiO2/Ti2AlNb interface are improved. The tensile and shear deformations of the interfacial zones are applied to study the influence of alloying elements on the TiO2 oxide spalling on Ti2AlNb. The tensile strength is increased by more than 2 GPa when Nb is substituted by the Sc, Zr and Hf elements. Therefore, Sc, Zr, and Hf are beneficial for inhibiting oxide spalling and will have great potential to improve the oxidation resistance properties.

Fabrication of yttria-stabilized zirconia/La2O3 composite coating by electrophoretic deposition to improve high-temperature oxidation resistance of stainless steel

Nanoscale yttria-stabilized zirconia (YSZ) and La2O3 were used to prepare a composite coating by electrophoretic deposition (EPD) and sintering to improve the high-temperature oxidation resistance of AISI430 stainless steel. SEM, XRD, and TEM were used to identify the microstructure of the YSZ/La2O3 composite coating and the oxide film formed at 900 °C. The effect of the EPD voltage on the coating thickness was studied. The microstructure properties and phase transition of the composite coatings during sintering were identified. The oxidation behavior of the composite coating at 900 °C was investigated by analyzing the oxidation kinetics curve, oxidation spallation, the formation of the interfacial oxide film, and the evolution of the coating microstructure. A model of the microstructure evolution of the YSZ/La2O3 composite coating during EPD, sintering, and high-temperature oxidation was proposed and discussed.

On the oxidation and interdiffusion behavior of an AlCoCrFeNiY high-entropy alloy bond coat on a directionally solidified Ni-based superalloy

The oxidation and interdiffusion behavior of a novel AlCoCrFeNiY bond coat deposited on a directionally solidified Ni-based superalloy were systematically studied at 1050, 1100 and 1150 °C, and compared with a conventional NiCoCrAlY coating deposited on the same substrate. The AlCoCrFeNiY bond coat exhibits lower oxide growth rates due to its large columnar grains and low Al activity at the oxide scale/bond coat interface. Meanwhile, AlCoCrFeNiY has higher resistance to oxide spallation than NiCoCrAlY, which is attributed to the formation of a clean and defect-free metal/oxide interface. Significant interdiffusion occurs across the AlCoCrFeNiY/superalloy substrate interface. Our experimental evidence and thermodynamic modelling suggest that Fe accelerates interdiffusion and destabilizes the γ’ phase, thereby causing the formation of a thick and γ’-depleted interdiffusion zone. In addition, the AlCoCrFeNiY bond coat undergoes more Al depletion and subsequent β to γ transformation compared with NiCoCrAlY. Based on the findings in this work, a novel AlCoCrFeNiY/NiCoCrAlY double-layer bond coat was designed, tested and validated to achieve optimal balance between oxidation and interdiffusion.

Cyclic and Isothermal Oxidation Behavior of a Directionally Solidified Ni-Al-Ti-Co-Cr Superalloy

Nickel based superalloys are widely used in such applications as gas turbine blades due to their excellent mechanical properties at elevated temperatures. Oxidation is one of the life limiting factors at such temperatures since it accelerates failure mechanisms, e.g. fatigue and creep. In this project, oxidation behavior of Ni-3Al-4.8Ti-9.5Co-14Cr (wt.%) superalloy was investigated under various testing conditions. The alloy was investment-cast with preferential crystal growth direction [100]. Isothermal oxidation tests were carried out at 800°C for 150h. Cyclic oxidation tests were then conducted between 100-800°C for 150 one-hour cycles. An additional one-hour cycle was tested to replicate real-life working condition of the alloy, which consisted of heating the samples up to 800°C followed by slow cooling to 400°C. During the testing, samples were periodically taken from the furnace and weighted with an accuracy of 10-4 g to calculate the weight gain and to analyze the microstructure of formed oxide. Scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS) and X-ray diffraction were used to study the microstructure of oxidation products. The results reveal that the highest amount of weight gain is obtained in isothermal testing, while the lowest in cyclic. Diffusion of Ti and Ni to the free surface results in the early-stage formation of needle-shaped oxide phases followed by severe oxidation of Cr and Al. The layer of chromium oxide is continuous while aluminum oxide is blocky at the deepest position from the free surface. Cracks form at the interface of carbide particles and gamma phase near the free surface of cyclic oxidation samples due to concentration gradient of Ni and Al. Precipitate-free zone are observed near the free surface of all the samples at the end of the tests, but internal oxidation does not occur significantly in all the samples. It is found that temperature fluctuation increases oxide spallation, which causes crack formation. At the same time, in isothermal testing, dense, crack-free layer of oxide form on the surface of superalloy.

Modeling hydrogen localization in Zircaloy cladding subjected to temperature gradients

In light water reactors, Zr-based alloys used for nuclear fuel cladding undergo oxidation and absorb hydrogen, which can precipitate as brittle zirconium hydrides. During reactor normal operation conditions, hydrogen concentration varies locally due to various factors, where local high concentration can significantly degrade cladding mechanical properties and, hence, its service life. This study aims to quantify the redistribution of hydrogen within the fuel rods caused by temperature gradients, considering geometric irregularities such as inter-pellet regions, oxide spallation, and missing pellet surfaces. Through simulations, we have discovered that these temperature variations can lead to significant local hydrogen enrichment, even under normal operational conditions. Consequently, the Zircaloy cladding may suffer from critical weakening in its mechanical performance due to excessive hydride precipitation at specific locations. These findings underscore the importance of accounting for local hydrogen concentrations when evaluating the overall reliability of the cladding.

Comparing the oxidation of FeCrAl alloys in isothermal and cyclic high-temperature steam environments

This study investigates the oxidation behavior of FeCrAl (APMT and C26M) alloys in high-temperature steam at 1000 °C using isothermal and cyclic conditions. The FeCrAl alloys exhibited a fully ferritic body-centered cubic structure with no significant phase transformation, and the manufacturing procedures of the alloys resulted in varying grain sizes and porosity. In the 5 h isothermal test, the protective alumina film provided corrosion resistance without cracking in the high-temperature steam environment. However, thermal cycling seemed to compromise passivity; expansion and contraction during heating and cooling allowed oxygen penetration into the underlying metal in local regions, leading to transgranular crack-like features. Spallation of oxides was also observed. Post-exposure analysis of the oxide film formed on the FeCrAl alloys revealed two distinct oxide layers on the alloy: an outer Al-rich oxide film and an inner mixed oxide enriched in Cr and Fe.

Long-term effects of soft-chromising Ni-electroplated AISI 441 commodity steel for SOC stack interconnects

Using commodity steel AISI 441 with Ni-based oxide coatings can facilitate large-scale interconnect manufacturing for solid oxide cell stacks, but adverse Ni-diffusion limits the high-temperature suitability. As a remedy, chromium is here added to the steel by a soft-chromising treatment. The (cyclic) oxidation resistance of virgin and soft-chromised AISI 441 is evaluated up to 8300 h at 780 °C, and further benchmarked against more commonly used Crofer 22 APU, with a Co(Mn)-spinel coating. Results revealed lowest isothermal oxidation kinetics for the soft-chromised, Ni-coated AISI 441, further preventing oxide spallation otherwise observed during thermal cycling of the virgin AISI 441 counterpart.

Revealing High-Temperature Oxidation and Tensile Behaviors along with Underlying Mechanisms of a Titanium Alloy with Precipitated Titanium Silicide

Titanium alloys, with their impressive strength relative to their weight, resistance to corrosion, and compatibility with biological systems, have found extensive applications in various industries. In high-temperature environments, especially within the aerospace sector, it is essential to advance titanium alloys that boast enhanced resistance to oxidation and superior mechanical characteristics. This work investigates the oxidation characteristics and mechanical performances at high temperatures of a titanium alloy with titanium silicide particles. Oxidation at temperatures of 600–700 °C over a span of 8–32 h led to the formation of protective oxide layers and moderate oxidation rates. However, accelerated oxidation and oxide spallation occurred after exposed at 800 °C for a period of 16 h, indicating inadequate oxidation resistance over 800 °C. Subsequent tensile tests at 650 °C revealed intricate dislocation patterns in the α-Ti matrix and their strong interaction with interfaces of α-Ti/Ti5Si3, which is indicative of an efficient load transfer between the precipitates and the matrix. Overall, this study offers fresh perspectives on the oxidation kinetics and the deformation processes of titanium alloys with in-situ Ti5Si3 particles at high temperatures. These insights will guide subsequent alloy development endeavors aiming to broaden the use of titanium alloys in increasingly challenging high-temperature settings.

A comparative study on the oxidation behavior and failure mechanisms of conventional NiCoCrAl alloy and in-situ composite AlCoCrFeNi2.1 eutectic high-entropy alloy at 1300 °C

We present a comparative study on oxidation behavior and failure mechanisms of conventional NiCoCrAl alloys doped with Y and Hf (CNA) and in-situ composite AlCoCrFeNi2.1 eutectic high-entropy alloy doped with Y and Hf (ISC-EHEA) at 1300 °C. We demonstrate that the ISC-EHEA has much stronger resistance to surface rumpling and oxide spallation than CNA. Hybrid molecular dynamics (MD) and Monte Carlo (MC) simulations show that the diffusion coefficients of the metal elements in the Al-depletion layer of the ISC-EHEA are 50 % lower than those in the CNA. The low diffusion coefficients lead to low growth stress in the thermally grown Al2O3 scale on the ISC-EHEA and improve the creep resistance of the metal in contact with the scale, thus preventing the occurrence of rumpling. The oxidation rate constant of the ISC-EHEA is ∼32 % lower in comparison to those of the CNA, which is attributed to the coarser columnar Al2O3 grains that effectively mitigate grain boundary diffusion. The rumpling-free metal/oxide interface, the low residual stress and the low oxide growth rate for the ISC-EHEA result in strong resistance to scale spallation. Owing to the strong scale/alloy bonding at the interface and the build-up of strain energy during prolonged oxidation, damage in the Al2O3 scale on the ISC-EHEA is initiated as surface cracks rather than interface decohesion. When re-oxidized at 1300 °C, the ingress of oxygen along the surface cracks results in fast growth of new oxides at the metal/oxide interface, which causes local stress concentration, interface crack propagation and scale spallation.

Insights into the role of W/B alloying on high-temperature oxidation behavior of Ti42Al5Mn alloy

In this study, the oxidation behavior of Ti42Al5Mn, Ti42Al5Mn0.5 W, Ti42Al5Mn0.5W0.1B, and Ti42Al5Mn0.8 W was investigated at 800 °C. Due to the inability to form a dense protective Al2O3 layer, Ti42Al5Mn suffered severe spallation during oxidation at 800 °C and the mass gain was significant. The intermediate layer between the scale and the substrate was first composed of Laves/Z phase but changed to α2/Z phase with prolonged oxidation. The intermediate layer with high Ti/Al ratio favors the formation of a thick Al2O3 + TiO2 mixed layer in the oxide scale which is prone to initiate cracks and cause the spalling of oxides. The doping of W in TiO2 effectively inhibited its generation and promoted the formation of a dense Al2O3 layer, resulting in a significant improvement in the oxidation resistance of the alloy. Compared to Ti42Al5Mn alloy, Ti42Al5Mn0.8 W showed no spallation after 300 h cyclic oxidation and the kinetic curve changed from liner law to parabolic law. The intermediate layer of Ti42Al5Mn0.8 W alloy was composed of a single Laves phase and remained unchanged even after 1000 h oxidation at 800 ℃, offering a favorable basis for the generation of a stable protective oxide layer in the alloy. The addition of 0.1 at.% B to Ti42Al5Mn0.5 W alloy refined its microstructure and further improved its spallation resistance to a level close to that of Ti42Al5Mn0.8 W alloy.

Comprehensive damage and deformation mechanisms during out-of-phase thermal mechanical fatigue of the fourth-generation single crystal superalloy

To shed light on the stability and reliability of the fourth-generation single crystal (SX) superalloy during in-service operation, out-of-phase (OP)- thermal mechanical fatigue (TMF) experiments were systematically carried out. The TMF behavior, deformation and damage mechanisms were thoroughly investigated. The results showed that at comparatively low strain ranges (0.5% and 0.6%), the dislocation movements were basically concentrated in γ matrix and the TMF life was basically governed by high-temperature oxidation. More locally, the fatigue cracks initiated from the spalling of surface oxides, while the discontinuous Al2O3 layer could only provide limited protective resistance to crack propagation. Additionally, deformation twins could nucleate in the vicinity of micropores or crack tips, which further induced more complex defects and accelerated the fatigue fracture of the alloy. Nevertheless, as the strain range reached 0.8% and 0.9%, the nucleation and extension of micro-twins were independent on the defects, the mechanisms of twinning-shearing and anti-phase boundary (APB)-shearing were observed throughout the specimen. Under these conditions, the fatigue cracks basically initiated from the severe plastic deformation, which resulted in the much-reduced TMF life of the specimen. Ultimately, salutary guidance for the further application of fourth-generation SX superalloys was rationally summarized.

Effect of Solution Heat-Treatment on the Oxidation Resistance of Ni-Base Single-Crystal Superalloy

To clarify the effect of solution heat-treatment on the oxidation resistance of Ni-base single-crystal superalloy TMS-238, the evaluation of dendrite/inter-dendrite segregation of alloying elements in the as-cast and heat-treated samples, and its effect on cyclic oxidation resistance were investigated. Cyclic oxidation test results at 1100 °C for up to 150 cycles clearly showed that the as-cast samples with element segregations had lower oxidation resistance compared to heat-treated samples with homogeneous structure. Further, for the as-cast sample, rapid growth and spallation of oxide consisting of NiO, Cr2O3, and Al2O3 were observed around the dendrite core for 10 cycles of oxidation. Analysis of sub-surface on sample isothermally oxidized at 1100 °C for 10 minutes showed that rapid oxide growth is due to the formation of discontinuous Al2O3 layer at dendrite core with lower Al concentration. Furthermore, in this study, the threshold value of Al concentration and Gibbs energy for the formation of continuous Al2O3 layer were estimated and determined to be around 5.2 wt pct and − 556.6 ± 0.5 kJ/mol, respectively. This indicated that the solution heat-treatment for TMS-238 should be conducted above 1305 °C for exhibiting oxidation resistance at 1100 °C, to meet the threshold value within the whole region between dendrite and inter-dendrite.

Coupled abrasion Erosion-Oxidation wear from particles in Concentrating solar thermal power facilities

Solid particles represent an attractive heat transfer and energy storage media for next generation solar thermal power facilities for their ability to operate at high temperatures without concerns for freezing or corrosion. A potential outstanding issue that still remains for particles as heat transfer media is the wear on components operating with particles flowing (sliding) in, along, or over them. Prior work has shown that even at the low velocities (∼1 cm/s to ∼ 1 m/s) expected in solar thermal facilities, material wear will still occur, and the lifetime and performance of components undergoing wear needs to be well understood. Abrasion erosion occurs when particles come into contact with containment materials at extremely shallow angles, and is likely to be seen in heat exchangers, storage bins, and flow control mechanisms. Additionally, because of the open nature of most of these systems to air, oxidation of metals is also of concern. Here, we show how critical the coupled erosion-oxidation mechanism is to understanding particle/material durability and therefore need for greater in-depth analysis. Abrasive wear experiments are conducted on metals such as SS316 (L and H grades), Inconel 740H, Haynes 230 with different particles (HSP 40/70, Wedload 430, and CarboMax HD) for different operating conditions. Results clearly indicate that oxide spallation and removal is critical to the overall wear seen at high temperatures.

Effect of microstructure and microtexture evolution of oxide layer over J82B steel on mechanical descaling properties

The oxide layer covering a high-carbon steel wire rod must be efficiently removed to form ‘a well-adhered yet easy-to-remove oxide scale’ during the mechanical descaling process. In this study, the relationship between the microstructural characteristics of the oxides and the efficiency of mechanical descaling was investigated. An electron backscatter diffraction analysis was conducted prior to bending and microscratch testing to clarify the microstructural discrepancies, namely, the phase distribution and texture orientation of the oxide constituents within the oxide scale system over the steel wire rod. The oxide scale system exhibits a double-scale layered structure, primarily consisting of FeO and Fe3O4. The low-angle and low-Σ coincident site lattice (CSL) boundaries in the Fe3O4 grains inhibit crack propagation without diffusion interactions, supporting oxide spallation in the large flake state during descaling. However, if the Fe3O4 grains were distributed along the boundary between the oxide scale and the iron substrate and had a high orientation consistency with the α-Fe grains, the grown oxide scale spalled into fine fragments, and a considerable amount of oxide scale residue firmly adhered to the descaled steel specimen. Stress relief and ion vacancy diffusion mechanisms govern the growth of Fe3O4 grains near the surface and at the interface of the matrix. These results provide guidelines for adjusting the oxide scale heterogeneity of high-carbon steels to improve their descaling performance.

Effect of molybdenum on cyclic oxidation behavior of 4th generation nickel-based single crystal superalloys

The cyclic oxidation behavior of fourth-generation nickel-based single crystal superalloys with 2–4 wt% Mo content were studied at 900 ℃ and 1100 ℃. At 900 ℃, with the increase of Mo content, the oxide layer accumulates more growth stress, resulting in the interface between the outer oxide layer and the inner oxide layer more prone to crack initiation. At 1100 ℃, the oxidation layer accumulates more growth stress and thermal stress, so the oxidation layer occurs large scale spalling, which is more severe in 4Mo alloy. The results show that the increase of Mo content of alloy promotes the oxidation of containing W-Re alloy, which promotes the volatilization of oxides and the spalling of oxide, decreases the protection of oxide layer, and deteriorates the oxidation resistance of the alloy.