High Temperature Oxidation Protection Research Articles

The effect of amorphous coating on high temperature oxidation resistance of Ni-based single crystal superalloy

Amorphous Al2O3 coating was prepared on Ni-based single crystal superalloy via atomic layer deposition (ALD) for high temperature oxidation protection. The oxygen inward transport and outward-cation diffusion were hindered by amorphous Al2O3 coating, and the coated alloy showed high oxidation resistance. The low oxygen partial pressure at the alloy/coating interface altered the alloy oxidation behavior, allowing the priority oxidation of protective Al and Cr elements. The oxidation process was controlled by the growth of Cr2O3 and Al2O3. The coating exhibited high spallation resistance. Degradation of the coating, the formation of NiAl2O4 phase in amorphous Al2O3 layer, was observed.

Microstructure and high temperature oxidation behavior of laser cladding C22 coating

C22 coating was successfully prepared on TP347H tube by laser cladding. The main goal was to assess the possibility of using laser cladding C22 coating for high temperature oxidation protection of boiler tubes in ultra-supercritical power plant. The microstructure, phase composition, microhardness and high temperature oxidation behavior of C22 coating were investigated. The microstructure evolution, phase constitution and high temperature oxidation behavior of C22 coating and TP347H samples were investigated. The oxidation experiment were carried out at 600 °C, 700 °C, 800 °C for 168 h. The results revealed that C22 coating mainly contain Ni-Cr-Co-Mo solid solution. The average microhardness of coating surface is 1.5 time that of substrate. Coating exhibited superior oxidation resistance at 600-800 °C. A dense and continuous Cr 2 O 3 film was observed in inner layer of coatings. C22 coating can be used as an excellent oxidation resistant coating with wide application prospect. Coating exhibited superior oxidation resistance due to the formation of a dense and continuous Cr 2 O 3 film in inner layer at 600-800 °C.

Structure–Property Correlation of Plasma-Sprayed Inconel625-Al2O3 Bimodal Composite Coatings for High-Temperature Oxidation Protection

Structure–Property Correlation of Plasma-Sprayed Inconel625-Al2O3 Bimodal Composite Coatings for High-Temperature Oxidation Protection

Mechanical and high temperature oxidation behavior of HfB2-ZrB2-SiC-B4C-CNT composites joined with and without Ni interlayer

Difficulties associated with the manufacturing of diboride based large and complex shapes mandate them to be joined for extreme applications. In the present work, spark plasma sintering is utilized to join HfB2-ZrB2-SiC-B4C-CNT (HZSBC) based composites with Ni-interlayer at 1100 °C and without interlayer at 1800 °C. Microstructural analysis has elicited the formation of Ni diffused reaction zone (150–200 μm), and unaffected HZSBC composite for HZSBC-Ni-HZSBC joined composite (at 1100 °C), which gets merged into a homogeneous microstructure (without any distinguishable interface) in the HZSBC-HZSBC joint (without Ni-interlayer). An overall reduction of 18% and 14% is elicited in hardness and elastic modulus, respectively, in the HZSBC-Ni-HZSBC joint, whereas in HZSBC-HZSBC joined composite, uniform hardness and elastic modulus of ∼22 GPa and ~398 GPa, respectively, is observed. Further, the bending and shear strength of the joined composites was obtained to be ∼209 MPa and ∼41 MPa, respectively, for HZSBC-Ni-HZSBC, which increased to ~342 MPa and ∼81 MPa, respectively, for HZSBC-HZSBC. In conjunction, though superior high-temperature (1500 °C) oxidation protection is witnessed in HZSBC-HZSBC joint, with a thinner oxide layer, both display SiO2-rich protective glassy layer, making these composites potential candidates for use in atmospheric re-entry conditions.

Amorphous Si–B–C–N coatings for high-temperature oxidation protection of the γ-TiAl alloy

The present work focuses on the preparation of amorphous Si–B–C–N coatings to protect γ-TiAl intermetallic alloys against oxidation above 750 °C that otherwise leads to surface degradation and embrittlement. The film fabrication process included the deposition of an amorphous Si interlayer at a temperature of 700 °C to promote adhesion. Subsequently, Si–B–C–N coatings were prepared by pulsed dc and rf magnetron co-sputtering from Si and B4C targets in Ar + N2 gas mixtures. Specifically, we studied the oxidation behavior of the coatings and the evolution of the microstructure, composition, and mechanical properties upon an isothermal oxidation test performed in laboratory air at 800 °C for 100 h. We found that an optimized Si40B5C2N47 (at.%) coating protects the γ-TiAl alloy substrate against oxidation by a combination of several effects: a) Interdiffusion of Si and Ti results in the formation of TixSiy phases on the film-substrate interface promoting adhesion of the coating, b) Diffusion of Ti to the surface is effectively inhibited and no fast-growing TiO2 is formed at the outer surface, and c) Stable amorphous structure of Si–B–C–N coatings hinders inward oxidation of O. Investigation of the oxidation kinetics at 800 °C up to 1000 h proved that Si–B–C–N coating serves as an efficient oxidation barrier demonstrated by the significantly reduced mass gain and the parabolic oxidation rate constant (1.05 × 10−13 g2·cm−4·s−1) compared to the uncoated γ-TiAl alloy (5.65 × 10−13 g2·cm−4·s−1).

High-temperature oxidation protection of γ-based TiAl by sputtered AlOF films

The implementation of γ-based titanium aluminides in various components of aircraft engines has been motivated by the need to optimize their thrust-to-weight ratio and limit greenhouse gas emissions. The interesting mechanical properties of TiAl alloys make them suitable for use in coldest stages of low-pressure turbines, but their sensitivity to oxidation at temperatures greater than 750 °C limits their use in the hotter sections of aircraft engines. The halogen effect is known to efficiently protect TiAl against high-temperature oxidation and is a promising solution toward increased implementation of TiAl in higher-temperature parts of the engines. Amongst all halogens, fluorine offers the best protection in a wide set of operating conditions. This work demonstrates the possibility of using reactive magnetron sputtering of Al in an Ar, O2, and CF4 atmosphere to fluorinate the surface of γ-based Ti-48Al-2Cr-2Nb and promote the alumina-forming characteristics of the alloys. The chemistry of the reactive plasma is first investigated using mass spectrometry and is then linked to the coating composition, measured by Rutherford backscattering spectrometry. Finally, an array of coating compositions is tested in isothermal oxidation at temperatures up to 875 °C. The coatings are protective, generating an alumina oxygen barrier upon oxidation.

Effects of LaB6 on the high-temperature oxidation behavior of TiC+TiBx reinforced titanium matrix composite coatings fabricated by laser cladding

The effects of LaB6 addition on the oxidation behavior of TiC+TiBx reinforced titanium matrix composite coatings at the temperature of 600 °C were investigated. The results showed that severe oxidation occurred on the Ti-6Al-4V after oxidation at 600 °C for 50 h. The oxidation weight gain of the (TiC+TiBx)/Ti coating without LaB6 addition (2.43 mg/cm2) was reduced to 49.6% that of the Ti-6Al-4V substrate (4.9 mg/cm2). Though (TiC+TiBx)/Ti coatings improved the oxidation resistance for the surface of Ti-6Al-4V substrates, cracks were easily formed between the coarse rod-like TiB2 and the titanium matrix during the high temperature resulting in less high-temperature oxidation protection. When the LaB6 addition gradually increased from 0 wt% to 1.0 wt%, the oxidation weight gain decreased from 2.43 mg/cm2 to 1.30 mg/cm2, and the linear rate constant Kp1 decreased from 0.04752 to 0.02703. The oxidation law gradually changed from the linear law to the parabolic law when the LaB6 addition increased to 1.5 wt%, which indicated the oxide layer gradually became dense and protective. The oxidation weight gain decreased from 1.23 mg/cm2 to 0.87 mg/cm2 when the LaB6 addition increased from 1.5 wt% to 2.0 wt%, while increased instead when the LaB6 addition increased to 2.5 wt%. An appropriate amount of LaB6 (2.0 wt%) addition significantly improved the oxidation resistance of the coating with the lowest parabolic velocity constant Kp2 = 0.01418 due to the refinement of grain sizes of the coating, especially the refinement of the coarse rod-like TiB2 phase, which decreased the crack forming sensibility and increased the compactness and continuity of the oxidation layer. A small amount of in-situ formatted La2O3 at the grain boundaries acted as a barrier also blocked the ingress of oxygen.

Microstructure formation and high temperature oxidation behavior of Ti-Al-Cr-Y-Si coatings on TiAl

The paper presents the application of Closed Hollow Cathode Physical Vapor Deposition (CHC-PVD) method for the depostion of Ti-Al-Cr-Y-Si coatings on γ-TiAl 48-2-2 alloy for high temperature oxidation protection. The study concerned the analysis of the coating’s growth mechanism, initial microstructure as well as phase transformations investigations using high resolution Scanning Transmission Electron Microscopy (STEM) and high temperature X-ray diffraction (HT-XRD). The coated alloy was subjected to high temperature oxidation test at 850 °C where a fivefold lower mass gain compared to bare 48-2-2 alloy was observed. Detailed microstructural investigations allowed to characterize the thermally grown oxide scale, which was found to be composed of nanometric layers of titania, equiaxed (Al,Cr)2O3 and columnar alumina. These investigations provided microstructural evidence for the Cr effect on the formation of Al2O3, which was postulated previously. Yttrium was found to segregate to the grain boundaries of alumina oxide scale during high temperature oxidation, indicating the occurence of the reactive element effect.

A novel phosphate-ceramic coating for high temperature oxidation resistance of Ti65 alloys

A novel phosphate-ceramic coating was developed for high-temperature oxidation protection of Ti65 titanium alloy. Aluminum phosphate binder was strategically mixed with Al2O3+SiC ceramic particles as the filler material and subsequently deposited on Ti65 titanium alloy by air spraying. High temperature oxidation behavior of the Ti65 substrate was studied in coated and un-coated state by performing series of isothermal oxidation and thermal shock tests at 650 °C. Microstructural and thermal evolutions under different conditions were investigated using scanning electron microscopy (SEM), electron-probe microanalysis (EPMA) and X-ray diffraction (XRD). It was revealed that under uncoated condition, the Ti65 alloy experienced severe oxidation and developed non-protective TiO2 oxide film. In contrast, phosphate-ceramic coated Ti65 alloy exhibited excellent oxidation resistance with small weight gain (0.35 mg/cm2) compared with that of the uncoated Ti65 alloy (1.05 mg/cm2). Microscopy results confirmed absence of TiO2 oxide scales at the coating-substrate interface. The significant enhancement in the oxidation resistance of the Ti65 alloy was attributed to the dense nature of the phosphate-ceramic protective coating with great thermal and chemical stability. Furthermore, the coating exhibited excellent thermal shock resistance for having compatible thermal expansion coefficient with the Ti65 alloy substrate.

Polymer derived ceramic materials from Si, B and MoSiB filler-loaded perhydropolysilazane precursor for oxidation protection

Silica-based coating systems were developed using polymer derived ceramics (PDCs) technology. Ceramic composites on the base of a SiO2 and SiNO matrix and homogeneously distributed Mo5SiB2, SiB6, Si and B fillers were manufactured. The coating systems have low porosity and provide a high oxidation resistance up to 100 h at 800 °C and 1100 °C in air. The influence of temperature and atmosphere of pyrolysis on the polymer precursor, the volume fraction of filler materials on the chemical composition of compacts as well as their high-temperature oxidation protection was investigated.

Hot Corrosion Resistance of Hot-Dip-Aluminized AISI 321 Stainless Steel in a Salt Mixture of 60%V2O5 + 40% Na2SO4 at 700 °C

Hot-dip aluminizing (HDA) is an established surface coating technique to deposit aluminium on ferrous substrates. The aluminium deposit forms a compact layer of alumina when exposed to high temperature, providing high-temperature oxidation and corrosion protection. In the present investigation, HDA of AISI 321 stainless steel was carried out in pure aluminium bath at 700 °C. The steel samples were dipped in molten Al bath for 10 min. The HDA sample was given diffusion treatment at 900 °C for 5 h before subjecting to hot corrosion tests. The microstructural features after hot corrosion tests were analyzed using an X-ray diffractometer and a scanning electron microscope. The aluminized and bare steel samples were subjected to hot corrosion test in a salt mixture of 60%V2O5 + 40% Na2SO4 at 700 °C. The tests were conducted for 50 cycles, of which each cycle consisted of 1-h heating at 700 °C in furnace followed by 20-min cooling in air. The corrosion kinetics was studied by thermogravimetric analysis. The study revealed that weight gains for aluminized sample were lower than the uncoated sample. The weight gain for the uncoated sample at the end of 50 cycles was 5.87 mg/cm2, and that of the aluminized sample was 2.3 mg/cm2. Spalling of oxide scales was observed for the uncoated sample, while aluminized sample showed adherent oxide scales resulting in increased hot corrosion resistance.

Improving the High-Temperature Oxidation Resistance of TiAl Alloy by Anodizing in Methanol/NaF Solution

An aluminum- and fluorine-enriched anodic film was fabricated on TiAl alloy by anodizing in NaF-contained methanol solution. The high-temperature oxidation resistance and protection mechanism of the anodized TiAl alloy were investigated. It showed that the formation of aluminum-enriched oxide scale originates from halogen effect and quite small anodization current density is essential to improving the high-temperature oxidation resistance. Upon oxidation at 850 °C for 100 h, no cracks and/or spallation were exhibited on the anodized TiAl alloy. At temperature higher than 300 °C, titanium fluoride will sublimate, accompanying with the transformation of aluminum fluoride into protective Al2O3 layer, as was indicated by XPS analysis. This freshly generated Al2O3 layer, together with the anodization formed one, can efficiently inhibit the outward diffusion of Al and inward diffusion of oxygen, thereby improving the high-temperature oxidation resistance of the TiAl.

In-situ formation of SiC, ZrB2-SiC and ZrB2-SiC-B4C-YAG coatings for high temperature oxidation protection of C/C composites

Si3N4, (ZrO2+B4C + Si) and (ZrB2+SiC + B4C + Y2O3+Al2O3) were used as precursors for in-situ formation of SiC, ZrB2-SiC and ZrB2-SiC-B4C-YAG coatings respectively. The oxidation behavior of coated C/C composites was studied by cyclic oxidation in air at temperatures between 1500 °C and 1700 °C. The SiC coating exhibited the lowest weight loss at 1500 °C and 1600 °C. After initial mass loss for two cycles of oxidation at 1500 °C, the ZrB2-SiC coating was found to provide the best protection by the precipitated ZrO2 in SiO2 glass at 1700 °C. The ZrB2-SiC-B4C-YAG coating performed well at 1700 °C with the formation of a complex YAG glass containing ZrB2/ZrO2.

Surface coating of ceria nanostructures for high-temperature oxidation protection

Stainless steels are used in high-temperature structural applications but suffer from degradation at an elevated temperature of operation due to thermal stress which leads to spallation. Ceria coating over chromium containing alloys induces protective chromia layer formation at alloy/ceria interface thereby preventing oxidative degradation. In the present work, three metals of differing elemental composition, namely, AISI 304, AISI 410, and Inconel 600 were tested for high-temperature stability in the presence and absence of ceria coating. Nanoceria was used as the target to deposit the coating through electron beam physical vapor deposition method. After isothermal oxidation at 1243 K for 24 h, Ceria coated AISI 304 and Inconel 600 exhibited a reduced rate of oxidation by 4 and 1 orders, respectively, in comparison with the base alloy. The formation of spinel structure was found to be lowered in the presence of ceria due to the reduced migration of cations from the alloy.

Optimization of parameters for electrodeposited Silver coating on Inconel 718

Inconel 718 has moderately good oxidation and corrosion resistance along with high temperature strength. However, they are susceptible to oxidation at temperatures above 500°C due to presence of non-uniform and porous oxide. Silver electroplating, conventionally used for decoration has been studied for high temperature oxidation protection on Inconel 718 sheet. Coating thickness of silver has been controlled through optimization of process parameters like current density, bath temperature, pH, process duration, etc. Coated coupons with optimized parameters have been characterized for thickness measurement, surface morphology, thermal shock test and GDOES (Glow discharge optical emission spectroscopic). Coating thickness of ∼ 10 µm has been obtained which is found to be adherent and passing the tape test, thermal shock test and plasma arc test.

Phase evolution of EBPVD coated ceria-zirconia nanostructure and its impact on high temperature oxidation of AISI 304

The present work focusses on the effect of nanocrystalline xCeO2–(1-x)ZrO2 (x=1, 0.75, 0.5, 0.25 and 0 in wt% abbreviated as C100, C75Z25, C50Z50, C25Z75 and Z100) coated by electron beam physical vapour deposition (EBPVD) on AISI 304 and its implication on the high-temperature oxidation protection. The oxidation kinetics indicate that the samples C100, C75Z25 and C50Z50 show 3–4 orders better oxidation protection than uncoated AISI 304. Coating morphology and composition play an important role in developing superior nanostructures against high temperature oxidation. The development of ceria-zirconia coating helps in the realization of structural materials for elevated temperature application.

High temperature oxidation protection of γ-titanium aluminide using (Cr,Al)ON coatings deposited by high-speed physical vapor deposition

In recent years great efforts have been made in the development of γ-TiAl alloys for use in aerospace applications such as turbines, where low densities and high temperature strength are required. However, γ-TiAl alloys show poor oxidation resistance at temperatures T>850°C due to the formation of a non-protective oxide layer consisting of a mixture of TiO2+Al2O3 in air, which could be easily spalled off, resulting in a shortened lifetime of the components. One promising way to overcome this problem is the deposition of an oxidation protective coating with low oxygen permeability at high temperatures. However, the interdiffusion between coating and substrate is still challenging even for advanced oxidation resistant coatings such as MCrAlY (M=Ni or Co) and aluminide. The present work focuses on the (Cr,Al)ON coating system, inspired from its outstanding diffusion barrier properties. Four (Cr,Al)ON coatings with different Cr:Al and N:O ratios were deposited onto γ-TiAl substrate by the innovative High-Speed Physical Vapor Deposition (HS-PVD) technology, which enables the deposition of oxygen-rich coatings in a stable plasma process without target poisoning. Basing on hollow cathode discharge (HCD) and gas flow sputtering (GFS), the HS-PVD made it possible to deposit (Cr,Al)ON coatings at a deposition rate ds/dt>16μm/h. The as-deposited coatings show an X-ray amorphous structure. Subsequently, the transmission electron microscopy (TEM) analysis confirmed the nanocomposite coating structure. The thermal stability and oxidation behavior of the coatings were evaluated by means of differential scanning calorimetry (DSC) and thermogravimetry (TGA) between T=100°C and T=950°C. It was confirmed that the X-ray amorphous structure even remained stable at temperatures up to T=950°C. Moreover, cross-sectional SEM images of the coated samples after the HT-XRD measurements showed neither the formation of oxides at the coating substrate interface nor the interdiffusion of Ti into the coating, indicating a promising performance of the diffusion barrier. The results of the conducted research reveal a high potential of the HS-PVD deposited (Cr,Al)ON coatings for the oxidation protection of γ-TiAl at T>850°C in turbine applications.

Impact of structure and morphology of nanostructured ceria coating on AISI 304 oxidation kinetics

Nanostructured ceria-based coatings are shown to be protective against high-temperature oxidation of AISI 304 due to the dynamics of oxidation state and associated defects. However, the processing parameters of deposition have a strong influence in determining the structural and morphological aspects of ceria. The present work focuses on the effect of variation in substrate temperature (50–300°C) and deposition rate (0.1–50Å/s) of ceria in electron beam physical vapour evaporation method and correlates the changes in structure and morphology to high-temperature oxidation protection. Unlike deposition rate, substrate temperature exhibited a profound influence on crystallite size (7–18nm) and oxygen vacancy concentration. Upon isothermal oxidation at 1243K for 24h, bare AISI 304 exhibited a linear mass gain with a rate constant of 3.0±0.03×10−3kg2m−4s−1 while ceria coating lowered the kinetics by 3–4 orders. Though the thickness of the coating was kept constant at 2μm, higher deposition rate offered one order lower protection due to the porous nature of the coating. Variation in the substrate temperature modulated the porosity as well as oxygen vacancy concentration and displayed the best protection for coatings deposited at moderate substrate temperature. The present work demonstrates the significance of selecting appropriate processing parameters to obtain the required morphology for efficient high-temperature oxidation protection.

Nanostructured CeO2 coating for high temperature oxidation protection

This paper investigates the influence of nanostructured ceria (CeO2) coating on high temperature oxidation behaviour of 2·25 Cr-1 Mo steel. The isothermal corrosion study of the micrometre size and nanostructured CeO2 coated specimens was conducted in air oxidation environment at 973 K for 8 h. The corrosion rate and reaction kinetics were studied, and the post-corroded scales were characterised by field emission scanning electron microscopy and X-ray diffraction. The results clearly indicate that the nanostructured CeO2 coated specimen improves the oxidation resistance in comparison to the micrometre size CeO2 coated specimen. The improvement of oxidation resistance in the case of nanostructured CeO2 coating can be attributed to the formation of semimolten zone, which consists of nanostructured CeO2 particle. On the other hand, in the absence of semimolten nanostructured zone, the micrometre size CeO2 coated specimen shows higher corrosion rate in comparison to the nanostructured CeO2 powder coated specimen.

High-Temperature Corrosion and Radiation Characteristics of Thermal Sprayed Molybdenum Disilicide-Based Coatings

Due to their poor oxidation resistance, most metallic components of industrial furnaces can be used only under high-temperature service conditions in inert atmospheres or vacuum. The operation in oxidizing atmospheres is normally limited to temperatures up to 1200 °C. However, it is known that molybdenum disilicide shows a good oxidation resistance in the temperature range up to 1650 °C. Therefore, the aim of this work is the application of molybdenum disilicide coatings for high-temperature oxidation protection of molybdenum-based substrates. Thermal spraying of agglomerated and sintered powder was carried out by atmospheric plasma spraying (APS). Feedstock and coatings were characterized by means of optical microscopy. The high- temperature oxidation behavior was investigated by exposure tests in air at 500 °C and 1200 °C. All coatings didn't show any degradation after this exposure tests. Additionally the formation of the SiO2 protection layer on the surface of the MoSi2-based coatings was detected by in-situ- measurements of spectral emissivities by Fourier transform infrared spectroscopy (FTIR).