Oxide Scale Adherence Research Articles

Microstructures and isothermal oxidation behaviors of CoCrAlYTaSi coating prepared by plasma spraying on the Ni-based superalloy GH202

The microstructures and isothermal oxidation behaviors of the CoCrAlYTSi coating prepared by plasma spaying on the surface of the Ni-based superalloy GH202 were investigated. The cross-sectional sheet of the coating was prepared by focused ion beam (FIB) and the resulting microstructures were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). After oxidization at 800°C to 1000°C for 100h, complex oxides were formed on the coating surface. The oxides included Al2O3, Cr2O3, CoO, CoCr2O4, Ta2O5, and SiO2. The protective oxidation films of Al2O3 formed readily on the coating due to the higher affinity of aluminum and oxygen. The addition of yttrium can increase the fineness of the coating microstructures and improve the adhesion of the coating. The oxidation of tantalum in the coating reduces the oxygen partial pressure in the oxidation scales and accelerates the formation of Al2O3. The addition of silicon element at less than 3wt.% can slow the oxidation rate of the CoCrAlYTaSi coating, enhance the oxide scale adherence, and prevent outward diffusion of refractory elements (such as W and Mo) from the substrate. Overall, the presence of yttrium, tantalum, and silicon in the coating improved the resistance of high temperature oxidation and enhanced the bonding force of the coating and the alloy.

Oxidation of Experimental Ti-Si-Al Based Alloys

Despite the fact that conventional high temperature titanium alloys possess a good combination of low weight, high strength and good corrosion resistance, their operational temperatures do not exceed 540-600 °C, since at higher temperatures they suffer from extensive oxidation, scaling and formation of a brittle oxygen-reach diffusion layer on their surface, so-called ‘apha-case’. The alloying with silicon was regarded as a promising way to raise the working temperatures of titanium alloys, since silicon is known to improve oxidation resistance, oxide scale adherence and high temperature creep behavior of titanium without noticeable deterioration of its ductility. The present paper was focused on studying of the oxidation kinetics and the formation of oxide scale and alpha-case layers on a series of experimental Ti−Al−Si based alloys, additionally alloyed with zirconium and tin. The oxidation kinetics of the experimental alloys upon exposure in air at 700 °С for up to 240 hours was examined and compared with that of commercially available Ті−6242 alloy. The oxide scale thickness, its phase composition and crystal morphology were characterized using X-ray diffraction and scanning electron microscopy (SEM), while the alpha-case layer was analyzed using SEM and microhardness measurements. According to the experimental findings, the experimental Ti−Al−Si based alloys demonstrated a good potential for their use at high temperatures.

Effects of carbon and coiling temperature on the adhesion of thermal oxide scales to hot-rolled carbon steels

The present work applied tensile testing to investigate the adhesion of thermal oxide scales to as-received hot-rolled carbon steels containing 0.04–0.18wt.% C and to steels oxidised in the atmosphere relevant to the hot-rolling process which contained water vapour. Higher carbon content in the steel deteriorated the adhesion of scale formed during hot rolling which was related to the higher amount of carbon existed at scale-steel interface. For the steel with 0.14wt.% C, increasing the coiling temperature could increase the carbon solubility in the matrix, thus reducing the interfacial carbon and improving the scale adhesion.

Effect of doping aluminum and yttrium on high-temperature oxidation behavior of Ni-11Fe-10Cu alloy

Aiming to develop materials for construction of the set-up and electrode of high-temperature molten salt reactors, the effect of Al and Y on the high-temperature oxidation behavior of Ni-11Fe-10Cu at 750 and 950 °C in air were investigated. The oxidation kinetics of Ni-11Fe-10Cu alloy followed parabolic law at 750 °C without spallation and linear law at 950 °C with severe spallation, while that of Ni-11Fe-10Cu-6Al-3Y alloy followed parabolic law at 750 and 950 °C without spallation. The parabolic rate constant (kp) of Ni-11Fe-10Cu was smaller than that of Ni-11Fe-10Cu-6Al-3Y at 750 °C. The oxide scale formed on Ni-11Fe-10Cu at 750 °C was composed of a CuO outer layer, a NiFe2O4 middle layer and a NiO inner layer. The oxide scale formed on Ni-11Fe-10Cu-6Al-3Y at 750 °C was also composed of the similar triplex layers in addition to an internal oxidation zone containing Al, Ni and Cu oxide and the microstructure of the scale changed with increasing temperature. Although the doping Al and Y could improve the adherence of oxide scale, it could aggravate the extent of internal oxidation. Based on the combination of X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDX) analysis, the microstructure and growth mechanism of the multi-layer oxide scale was studied and the effect of doping Al and Y on the oxidation behavior of Ni-11Fe-10Cu alloy was also discussed.

The role of Dy doping on oxidation behavior of Co-40Mn/Co coating for solid oxide fuel cell metal interconnects

Co-38Mn-2Dy and Co-40Mn alloy coatings are prepared by using high-energy micro-arc alloying process (HEMAA) and a Co transition layer is firstly obtained on 304 SS. Microstructures and compositions of Co-Mn(Dy)/Co coatings after preparation and oxidation are analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Coatings are the splash appearance and fine-grained structure with a metallurgical bonding to substrate. The addition of Dy in Co-Mn coating can effectively improve the oxide scale adhesion and reducing the high temperature oxidation rate of coating. The outward diffusion of Fe and Cr from substrate is remarkably suppressed by the external oxide layer for Co-38Mn-2Dy/Co coating. And Dy-rich oxides, Mn-rich oxides and oxide pegs are found in oxide layer after oxidation for 100 h, respectively. Co-rich oxides favor to form on the top scale because of high oxygen partial pressure. The value of area specific resistance (ASR) is measured to be low for Co-38Mn-2Dy/Co coating at 800 °C.

Electrochemical Corrosion of HVOF-Sprayed NiCoCrAlY Coatings in CO2-Saturated Brine

The effect of pre-oxidation treatment and surface preparation of optimized NiCoCrAlY coatings deposited by high-velocity oxygen fuel (HVOF) spraying and exposed to a low-temperature corrosive environment is reported herein. Coatings with two surface finish conditions (as-sprayed and ground) were heat treated under two different oxygen partial pressures (air and argon). The electrochemical corrosion behavior was evaluated in CO2-saturated brine via potentiodynamic polarization, polarization resistance, and electrochemical impedance measurements. The results show that the grinding process and pre-oxidation treatment in argon enhanced growth and formation of α-Al2O3 scale. The potentiodynamic polarization results show that both pre-oxidation and surface treatment had a positive influence on the corrosion resistance of the coating. The reduction of the porosity and the formation of a dense, uniform, and adherent oxide scale through pre-oxidation treatment led to an increase of the corrosion resistance due to a decrease in active sites and blocking of diffusion of reactive species into the coating. However, according to the results, complete transformation from metastable alumina phases to α-Al2O3 in addition to formation and growth of dense α-Al2O3 is required to ensure full protection of the coating and base material over long periods.

High Temperature Oxidation Behavior of High Strength Steel Plates

Three kinds of high-strength steel plates containing (less than 0.07%, or 0.024%, or 0.057%)-Si were oxidized at 700-900 °C isothermally and cyclically in atmospheric air, and their oxidation behavior was compared. The composition of the steels significantly affected the scaling rates, thickness, and adherence of the formed scales. The most important element in terms of oxidation was Si because Si affected the oxidation rates and scale adherence much. Silicon formed quite slowly a growing SiO2–containing scale around the scale/matrix interface. In the Si-deficient steel, quite thick oxide scales formed, and their adherence was poor. An optimum amount of Si was necessary in order to decrease the oxidation rate, and improve the scale adherence.

Effect of Y2O3 contents on oxidation resistance at 1150 °C and mechanical properties at room temperature of ODS Ni-20Cr-5Al alloy

Ni-20Cr-5Al alloy with Y2O3 addition (i.e., 0, 0.2, 0.4, 0.6, 0.8, 1.0, 3.0 and 5.0wt%) are used to prepare oxide dispersion strengthening (ODS) Ni-based superalloy by powder metallurgy technology. The effect of Y2O3 particles on oxidation resistance at 1150°C and mechanical properties at room temperature of Ni-20Cr-5Al alloy was investigated. The results show that the oxidation resistance of alloys is improved when the content of Y2O3 is under 0.6wt%. The oxidation resistance of alloys decreased obviously when the content of Y2O3 is over 0.8wt%. It is due to the small amount of Y2O3 is conducive to form stable oxide scale, and improves the adhesion of oxide scale and matrix. While Y2O3 content is too high, it is easier to result in segregation of Y2O3, which create defects in matrix and decrease exfoliation resistance of oxide scale. Continuous and compact Al2O3 oxide scale can effectively protect matrix. The relative density of alloys can be significantly increased with Y2O3 addition which is 0.2–0.6wt%, it’s speculated that distribution of Y2O3 in matrix is benefit to promote rearrangement and densification of grains during process of sintering. While Y2O3 content is more than 0.8wt%, Y2O3 will hinder viscous flow and reduce relative density due to its strong thermal stability.

Effect of aluminisation characteristics on the microstructure of single phase β-(Ni,Pt)Al coating and the isothermal oxidation behaviour

In the present study, single phase β-(Ni,Pt)Al coatings were prepared in sequence of Pt electroplating and ‘above pack’ aluminisation treatments. Three chief processing factors, including initial Pt thickness, aluminising temperature and time, were selected to investigate their influences on the microstructure of final β-(Ni,Pt)Al coating. Isothermal oxidation behaviour of the coatings with different thickness of Pt was evaluated at 1100°C in static air. An empirical equation was proposed to show relationship between coating thickness and the three processing parameters. The β-(Ni,Pt)Al coating of 5μm Pt showed the best oxidation resistance due to superior adhesion of oxide scale.

Improved oxide scale adherence of low-Pt/Hf co-doped β-NiAlCrSi coating on superalloy IC21 at 1200 °C

Low-Pt/Hf co-doped β-NiAlCrSi and Hf single-doped β-NiAlCrSi coatings were produced onto advanced single crystal (SC) superalloy IC21 containing Mo, respectively. The cyclic oxidation and interdiffusion behaviour of the coatings at 1200°C were investigated. As compared to the single-doped coating, the co-doped coating revealed suppressed interdiffusion and delayed β–γ′ phase transformation. Simultaneously, the interfacial voids formation and scale rumpling were inhibited. As a result, the thermally grown oxide (TGO) grown on the co-doped coating exhibited improved adherence and the roles of Pt and Hf in low-Pt/Hf co-doped coating were discussed.

Breakaway oxidation of Ti3AlC2 during long-term exposure in air at 1100 °C

Catastrophic breakaway oxidation of Ti3AlC2 occurs during long-term oxidation at 1100°C in air up to 4000h. Correspondingly, the oxidation kinetics transforms from cubic law to linear law. The transition time is about 3171h, and the corresponding critical Al content is about 5.99% lower than the initial content. Afterwards, Ti and C start to be oxidized instead of selective oxidation of Al, and Al2O3 scale loses its protectiveness. Meanwhile, voids generated at the Al2O3/Ti3AlC2 interface reduce the oxide scale adhesion. After 3250h oxidation, Ti3AlC2 still maintains its crystal structure, indicating the capability of bearing great Al lack.

Oxidation behavior and tribological properties of multilayered Ti-Al-N/Mo-Si-B thin films

The impact of highly oxidation resistant Mo1−x−ySixBy on the oxidation resistance and tribological properties of arc evaporated face-centered-cubic Ti0.57Al0.43N is investigated in detail through Mo1−x−ySixBy/Ti0.57Al0.43N and Mo1−x−ySixByN/Ti0.57Al0.43N compound coatings as well as Ti0.57Al0.43N/Mo1−x−ySixBy multilayer coatings. The Ti0.57Al0.43N/Mo0.54Si0.30B0.16 and Ti0.57Al0.43N/Mo0.68Si0.12B0.20 multilayers with bilayer periods of 35 and 70 nm (consisting of 6 and 15 nm thin sputtered Mo0.54Si0.30B0.16 and Mo0.68Si0.12B0.20 layers), respectively, significantly outperform all coatings investigated during 900 °C ambient-air-oxidation treatments. Consequently, the oxidation resistance of the multilayer coatings is higher as compared with their individual layers. Even after 1000 min exposure, only ∼1.0 μm of the Ti0.57Al0.43N/Mo0.68Si0.12B0.20 multilayer is consumed to form a dense adherent and protective oxide scale. The latter is composed of Si-, Al-, Ti-, and Al-rich layered outer oxides preventing the volatilization of the Mo-rich layered oxide at the interface to the Ti0.57Al0.43N/Mo0.68Si0.12B0.20 multilayer. Whereas both multilayers, Ti0.57Al0.43N/Mo0.54Si0.30B0.16 and Ti0.57Al0.43N/Mo0.68Si0.12B0.20, exhibit excellent mechanical properties (hardnesses of 32–34 GPa and indentation moduli of 385–405 GPa) and oxidation resistance, the higher Mo-containing Ti0.57Al0.43N/Mo0.68Si0.12B0.20 multilayer outperforms all coatings investigated during ball-on-disk tests. The steady state coefficients of friction are ∼0.5 combined with wear rates below 10−6 mm3/Nm after 500 m sliding against Al2O3 at room temperature, 500, and 700 °C.

Quantification of Adherence of Thermal Oxide Scale on Low Carbon Steel Using Tensile Test

In the present work, a tensile test method was used to investigate the adhesion of thermal oxide scale on low carbon steels oxidised in O2 containing 20 % H2O at 850 °C for up to 120 s. The mechanical adhesion energy was quantified, and a theoretical framework was developed to investigate the factors affecting the quantification i.e., the residual stress and Young’s modulus of the oxide scale. It was found that the quantified adhesion energies were in the range of 18–240 J m−2. When a higher value of the residual stress was used for the quantification, the quantified mechanical adhesion energy was decreased to a critical value and afterwards turned to be higher because of the increased strain energy accumulated in the oxide due to the stress in the direction perpendicular to the tensile loading. Furthermore, when a higher value of Young’s modulus of the oxide was used for the quantification, a higher quantified mechanical adhesion energy was obtained.

Effects of different alloying additives X (X = Si, Al, V, Ti, Mo, W, Nb, Y) on the adhesive behavior of Fe/Cr2O3 interfaces: A first-principles study

This study investigated the segregation behavior of alloying additives X (X=Si, Al, V, Ti, Mo, W, Nb, Y) on the Fe(111)/Cr2O3(0001) interface as well as the effects of these additives on the interfacial adhesive strength by using the first-principles method. The results indicated that W, Mo, and Nb atoms were easily segregated at the Fe(111)/Cr2O3(0001) interface, however, the introduction of them would weaken the adhesive strength of the interface through weak-electron effects. Moreover, Y, Al, Si, Ti, and V were difficult to segregate at the Fe(111)/Cr2O3(0001) interface. Comparison of separation energies and interfacial structural properties suggested that introduction of Si and Al improved the adhesive strength of the Fe(111)/Cr2O3(0001) interface through strong interactions between Si/Al and O. Thus, Si and Al improved the adhesion of surface oxide scales and enhanced oxidation resistance.

Determination of Mechanical Adhesion Energy of Thermal Oxide Scales on Steel Produced from Medium and Thin Slabs Using Tensile Test

The mechanical adhesion of thermal oxide scales formed on industrial hot-rolled steel strips produced through the electric-arc-furnace route was studied. The samples as-received steel were prepared with the specific shape fitting to the micro-tensile machine in the SEM chamber for observation of surface failure during the test. It was found that oxide transverse cracking and scale spallation are observed. This paper also presented a theoretical model for evaluate adhesion energy from strain and stress values at the first spallation. It was found that the oxide scales on the medium slab exhibited high mechanical adhesion energy. This might be due to the existence of oxide contained Si at steel-scale interfaces. It can promote adhesive interactions between steel-scale interfaces.

Microstructure And Mechanical Properties Of Crofer 22 APU Ferritic Stainless Steel

Abstract The objective of this work was to expand the knowledge on mechanical properties of the oxidized Crofer 22 APU Ferritic Stainless Steel. To examine adhesion of oxide scale formed on steel the scratch test was performed. Scratch test as an appropriate method for qualitative evaluation of the film adhesion to substrate has been used in many studies. Scratch properties were investigated before and after oxidation at 800°C for 500 hours in laboratory air.

Cyclic oxidation behavior of Cr-/Si-modified NiAlHf coatings on single-crystal superalloy produced by EB-PVD

The Cr-/Si-modified NiAlHf coatings were produced on single-crystal (SC) superalloy N5 by electron beam physical vapor deposition (EB-PVD). The cyclic oxidation behavior of the coatings at 1100 °C was investigated. The microstructures of the oxide scales grown on the coatings were characterized by scanning electron microscope (SEM) with energy-dispersive X-ray spectrum (EDX), electron probe micro-analyzer (EPMA) and X-ray diffraction (XRD). The effects of Cr and Si on the cyclic oxidation behavior of the NiAlHf coatings were discussed. The addition of Si to the NiAlHfCr coating not only reduces the oxidation rate but also enhances the oxide scale adherence. Owing to the addition of Si in the coating, the segregation of Cr and Mo beneath the oxide scale is effectively avoided, which contributes to enhancing oxide scale adherence.

Influences of MCrAlY Coatings and TBCs on Oxidation Behavior of a Ni-Based Single Crystal Superalloy

DD98M alloy is a second generation nickel-based single crystal superalloy without Re addition, which is developed by Institute of Metal Research, Chinese Academy of Sciences. It is a combination of attractively strong points including high strength and low cost. In this work, Ni-based single crystal superalloy DD98M was adopted as the substrate material. Two types MCrAlY (M denote metal) coatings were deposited on DD98M specimen by arc ion plating and YSZ topcoat (TC) were deposited on the substrate by electron beam physical vapor deposition (EB-PVD) on the NiCrAlY bond coat (BC). Experimental results showed that the application of the NiCrAlY and NiCoCrAlYHfSi coatings improved the oxidation resistance of DD98M obviously at 1000 °C. The adhesion of oxide scale of NiCoCrAlYHfSi coating was much better than that of NiCrAlY coating. TBCs application greatly enhanced the operating temperature and significantly improved the durability of the substrate. The thermal growth oxidation (TGO) between the bond coat and topcoat play an important role in adhesion of the whole coating system.

Effects of alloyed Si on the oxidation behaviour of Co–29Cr–6Mo alloy for solid-oxide fuel cell interconnects

To evaluate the suitability of the Co–29Cr–6Mo alloy as an interconnect in solid-oxide fuel cells (SOFCs), the oxidation behaviour of Co–29Cr–6Mo alloys with various Si concentrations was investigated in air at 700–1000°C. The presence of alloyed Si improved the oxide-scale adhesion by promoting the formation of a continuous Cr2O3 film. The SiO2 particles in the inner layer and the grain boundaries of alloy matrix beneath the inner layer inhibited the inward oxygen diffusion and outward chromium diffusion. The results indicate that the Co–29Cr–6Mo alloy with added Si is appropriate for SOFC applications.

Cyclic oxidation resistance of Ce/Co modified aluminide coatings on nickel base superalloys

Ce/Co modified aluminide coatings with different CeO2 content were prepared on nickel base superalloys by pack cementation method. The microstructure and cyclic oxidation behavior of the coatings were investigated. The results show that the Ce addition is beneficial to improving adhesion of oxide scales by forming the “oxide pegs” structure and reducing voids at the scale/coating interfaces. When the content of CeO2 addition in the pack mixture is 2wt.%, the Ce/Co modified aluminide coating has the highest content of Ce in the outer layer and exhibits the best cyclic oxidation resistance at 1323K.