Cyclic Oxidation Resistance Research Articles

Improvement of oxidation resistance of Ti–47Al–2W–0.5Si alloy modified by aluminizing method

The presented study defines the impact of aluminizing process by out-of-pack method on the oxidation resistance of cast Ti–47Al–2W–0.5Si alloy after homogenising and hot isostatic pressing. The surface condition was characterized, as well as chemical and phase composition of scale formed on examined alloy with and without protective coating, when subjected to cyclic oxidation at 950°C. It was established that the generated hermetic and compact aluminium diffusion coating with a thickness of about 7.5μm, consisting mainly of TiAl2 phase, has a significant effect on the improvement of cyclic oxidation resistance in the case of investigated alloy. It was confirmed that the scale formed after the oxidation process on the surface of alloy with protective coating was composed mainly of Al2O3 oxide, contrary to the scale formed on the alloy without protective coating, which was mainly consisting of TiO2 oxide.

Effect of TiC self-healing coatings on the cyclic oxidation resistance and lifetime of thermal barrier coatings

Thermal barrier coatings (TBC) are getting great importance in industry as the inlet temperature of advanced gas-turbine engines is continuously being pushed higher in order to improve efficiency. It is well known that the thermal growth oxide (TGO) could decrease the durability of the TBC. In order to slow the growth rate of TGO, oxidation barrier coatings were designed and fabricated. Among these coatings, self-healing coating is the most promising.The present study shows that TiC acts as a self-healing agent releasing its oxide (TiO2) by reaction with oxygen in air and heals the cracks/pores present in the coatings. A TiC-self-healing coating after pre-oxidation treatment in the furnace at 600 °C could suppress the growth of the detrimental oxides by the formation of a low-porosity self-healing layer at the top coat (TC)/bond coat (BC) interface. The porosity of healed coatings decreased three times from 12% to 3% as compared to the as-sprayed coating. This lower porosity could attribute to the lower growth rate of self-healing TBC. The gained weight versus the development of the TGO exhibited 30% slower oxidation rate than the conventional TBC while less than 10% oxide area percentage in BC of TiC-self-healing. The treated coatings demonstrated better oxidation resistance up to 28.8% than the conventional coatings. TiC-self-healing coatings reduce the growth rate of TGO which promote the TBC to survive twice thermal cycles at higher temperature of 1000 °C.TiC-self-healing TBCs could be considered as a promising TBC with better oxidation resistance and thermal cycle resistance.

Cyclic oxidation resistance of In718 superalloy treated by laser peening

The aim of this study was to improve the cyclic oxidation resistance of In718 superalloy by laser peening(LP). Specimens were treated by LP from one to three times, respectively. The cyclic oxidation tests at 900 ° for periods up to 2 h were conducted. Changes of the top surface morphology and microstructure were analyzed by scanning electron microscope (SEM), energy-dispersive spectra (EDS), transmission electron microscope (TEM) and X-ray diffraction technique (XRD), respectively. The weights were measured between the oxidation cycles to assess the oxidation of the specimens. The top surface microstructure after LP was characterized by highly tangled and dense dislocation arrangements and a high amount of twins. Protective oxidation layer was generated more quickly on the surface treated by LP. The average oxidation rate was about 50 % lower. A tiny homogeneous oxidation layer containing (Fe,Cr)2O3, NiCrO3 and Ni(Al,Cr)2O4 spinel was generated on the surface. The experimental results of cyclic oxidation tests show that specimens treated by LP have a better high temperature oxidation resistance, and the antistrip performance of the oxidation layer improves. Moreover, the effects of LP are strengthened with the increase of laser peening.

Formation of the β-NiAl Containing Hf by the Simultaneous Electrodeposition of Al and Hf using a Molten-Salt and the Cyclic Oxidation Behavior

The formation of a coating layer consisting of a Ni aluminide containing Hf on a Ni substrate was attempted by the electrodeposition of Al and Hf. Especially, the effects of the HfF4 concentration in the electrolytic bath, electrodeposition temperature and potential on the type of Ni aluminide phase and the morphology of the Hf-rich precipitates in the Ni aluminide were investigated. The cyclic oxidation resistance of the Ni covered with the coating was then evaluated. Al and Hf were deposited by molten salt electrolysis. For the sample treated with the Al and Hf deposition at 1023 K, a Ni2Al3 layer was formed, and no Hf in the layer was observed. On the other hand, for the sample treated with the Al and Hf deposition at 1173 K and −1.25 to −1.8 V, a NiAl layer containing Hf was formed. It was found that a thick NiAl layer was formed at 1173 K and −1.5 V. The cyclic oxidation test result showed that the oxidation rate of the untreated sample, the sample coated with a Ni2Al3 layer without Hf and the sample coated with a thin NiAl layer, were high. However, for the sample coated with a NiAl layer containing a small amount of Hf, the mass gain rate was low. On the sample after the cyclic oxidation test, a scale consisting of α-Al2O3 and HfO2 adhering to the substrate was formed.

Cyclic oxidation behavior of Hf/Zr co-doped EB-PVD β-NiAl coatings at 1200 °C

The reactive element of Hf or Zr doped and Hf/Zr co-doped β-NiAl coatings was prepared by electron beam physical vapor deposition (EB-PVD). Cyclic oxidation behavior of the coatings at 1200°C was compared. The Hf/Zr co-doped NiAl coating revealed finer grain size than the Hf or Zr single-doped coatings. Hf/Zr co-doping led to lower oxide scale growth rate than Hf or Zr single-doping. No oxide scale spallation was observed on the surfaces of the NiAlHf and NiAlHfZr coatings after 100h cyclic oxidation, indicating improved high-temperature cyclic oxidation resistance, as compared to the NiAlZr coating. Related mechanisms were preliminarily discussed.

Oxidation behaviour of electron beam physical vapour deposition β-NiAlHf coatings at 1100 °C in dry and humid atmospheres

NiAl intermetallic compounds attract increasing attention for high-temperature applications due to their combination of excellent properties, especially as metallic protective coatings on superalloys or as bond coats in thermal barrier coatings (TBCs). Oxidation behaviour of the β-NiAlHf coatings prepared by electron beam physical vapour deposition (EB-PVD) was investigated at 1100 °C for short time and 100 h in 20 % O2 + Ar and 15 % H2O + Ar, respectively. The results of mass changes reveal that the addition of minor reactive element Hf significantly improves the cyclic oxidation resistance of the β-NiAl coatings in both dry and humid atmospheres. During the initial oxidation stage, water vapour retards the phase transformation from θ-Al2O3 to α-Al2O3. Moreover, compared with the case in dry atmosphere, water vapour significantly reduces the surface roughness of the oxide scales formed on EB-PVD β-NiAlHf coatings after 100 h cyclic oxidation, which corresponds with the difference of surface morphologies of the oxide scales.

Effect of Yttrium Addition on Cyclic Oxidation Behavior of Co-10Cr-10Al Alloys at 1073K

The effect of rare earth element yttrium on cyclic oxidation behavior of Co-10Cr-10Al alloys in ambient atmosphere of 1 atm at 1073K was investigated. The results indicated that the addition of 0.05 at.% Y in the alloy enhanced the formation of protective oxide scales with compact smooth surface, and improved cyclic oxidation resistance of the alloy. On the contrary, the addition of 0.1-0.3 at.%Y greatly increased the oxidation rate of the alloy, with formation of a rapidly growing Co oxides layer with the porous and rough surface appearance.

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.

Preparation of Ni-Al-Pt Coating on Ni-6 at%Cr Alloy by Electrodeposition Method and Cyclic-Oxidation Resistance

Preparation of Ni-Al-Pt Coating on Ni-6 at%Cr Alloy by Electrodeposition Method and Cyclic-Oxidation Resistance

Effect of Ce2O3 on microstructures and oxidation resistance of laser melting deposited composites on a Ti alloy

AbstractTo our knowledge, here is the first time that Stellite SF12-Si3N4-B4C-Ce2O3 powders are deposited on a TA1 titanium alloy as the composites by a laser melted deposition (LMD) technique. It is noted that compared with a TA1 alloy substrate, an improvement of cyclic oxidation resistance is obtained for such LMD composites. Scanning electron microscopy results indicate that many nanocrystalline/amorphous phases are produced, which improve the oxidation resistance of such composites. Such composites exhibit better oxidation resistance than the composites without Ce2O3 due to the formation of denser and finer-grain scale. The effect of Ce2O3 on the formation mechanism and oxidation behavior of such composites is discussed in detail.

Effect of high temperature on the surface morphology and mechanical properties of nanostructured Al2O3–ZrO2/SiO2 thermal barrier coatings

Nanostructured Al2O3–ZrO2/SiO2 multilayer coating was applied on 316L SS specimens using dip-coating method. Then, the coated specimens on heat treatment to 800, 900, and 1000°C for 100h showed the formation of a stable structural phase of t-ZrO2-toughened Al2SiO5 along with ZrSiO4. The microstructural images of the heat-treated specimens observed the level of porosity and that of BHJ-pore size distribution was decreased in the coating along with crack splats. Then, the coating was subjected to cyclic oxidation and hot corrosion test for 20cycles. The obtained results showed that the rate of cyclic oxidation resistance enhanced when compared to that of hot corrosion resistance. The results of X-ray diffraction analysis showed hot corrosion resistance in molten salt, with non-leaching t-ZrO2 structural phase of ceramic coating. The mechanical properties of the nanostructured coating improved with an increase in the heat treatment. The maximum hardness (H) and reduced elastic modulus (Er) values of the coating were approximately 18.43±0.62 and 68.30±1.35GPa, respectively. Spallation and oxidation resistance of the coating were explored through mechanical properties, in situ scanning probe microscopy, and atomic force microscopy. The results showed that silicate-based thermal barrier coating provided better protection to SS specimen from high-temperature corrosion.

Cyclic Oxidation Resistance of Hot-Dipping Aluminized GH169

GH169 superalloy steel was coated by hot-dipping in a molten aluminum bath, and then diffusing annealing at 950 °C for 2h. The cyclic oxidation behaviors of the hot-dipped aluminized steel and GH169 were tested at 900 °C for 24 cycles using resistance furnace. Morphology of surface and cross-section, element distribution of the oxide scale were characterized by SEM and EDS. The results showed that protective Cr2O3 and Al2O3 oxide scales were formed on GH169 and aluminized steel after 24 cycles, respectively. The inner oxidation was found on GH169 after 24 cycles. It was composed of surface Al2O3 oxide film, outer Al-rich layer scattered with NiAl phase, and inner NiAl layer on aluminized steel after 24 cycles at 900°C.

Existence patterns of Dy in β-NiAl from first-principles calculations

Intermetallic compound β-NiAl is a promising material in high temperature applications due to its high melting temperature, high strength, low density, and good oxidation resistance. However, its application remains limited because of its relatively poor cyclic oxidation resistance. Addition of reactive element (RE) Dy can improve the cyclic oxidation of NiAl alloys significantly. However, the mechanism of Dy addition is not clear. Even the existence pattern of Dy in NiAl is unspecified. Therefore, in the present study, the impurity formation energies of Dy in stoichiometric NiAl, Ni-rich, and Al-rich NiAl for the substitution cases were studied by first-principles density functional theory. The results show that Dy could hardly substitute for either Ni or Al atoms in NiAl. However, calculations for dissolution energies show that Dy could be easily dissolved in Al vacancies in all three types of NiAl, which provides a new existence pattern of Dy in NiAl beyond experimental detection.

Improvement of cyclic oxidation resistance of Y-containing Ti–6Al–2.5Sn–4Zr–0.7Mo–0.3Si alloys

The cyclic oxidation behavior of Y-containing Ti–6Al–2.5Sn–4Zr–0.7Mo–0.3Si alloys was studied at 650–750°C. The oxidation kinetics of the alloys was investigated by measuring weight gains at different temperatures. The microstructure characterization of the alloys was carried out using XRD and SEM. It was found that oxidation resistance of the alloys at 650–750°C is improved by Y-addition. The excellent oxidation resistance obtained in the Y-containing alloys is mainly attributed to the significant refinement of oxides and consequently retarding the inward diffusion of oxygen. Y addition is also found very effective in improving the adhesion between oxidation layer and matrix.

HfC nanowire-toughened TaSi2–TaC–SiC–Si multiphase coating for C/C composites against oxidation

To prevent carbon/carbon (C/C) composites from oxidation at high temperature, a HfC nanowire-toughened TaSi2–TaC–SiC–Si multiphase coating was prepared by a two-step technique including chemical vapor deposition (CVD) and pack cementation. The microstructure and oxidation resistance of the coating were investigated. The HfC nanowires can effectively reduce the size of microcracks and avoid the formation of through-thickness microcracks in the multiphase coating. Due to the toughening mechanisms including nanowire pullout and debonding, the cyclic and isothermal oxidation resistance of the coating are both improved.

Cyclic oxidation and interdiffusion behavior of Pt modified NiAlHfCrSi coatings on single crystal superalloy containing Mo

β-NiAlHfCrSi coatings were deposited on a Mo-containing single crystal (SC) superalloy with or without an electro-plated Pt film by electron beam physical vapor deposition (EB-PVD), respectively. Co-doping of Cr and Si caused grain refinement of the coatings and retarded outward diffusion of Pt during heat-treatment in vacuum at 1050°C. During cyclic oxidation at 1150°C, severe scale spallation occurred in the Pt-free coating due to the formation of voids beneath the oxide scale. The Pt modified coating effectively suppressed the formation and growth of voids and exhibited improved cyclic-oxidation resistance. Si-doping not only reduced the oxidation rate of the coating but also enhanced the oxide scale adherence, one of mechanisms for which is that the addition of Si in the coating prevented outward diffusion of refractory elements such as Mo from the alloy substrate.

The cyclic oxidation behaviour of Ni-based superalloy GTD-111 with sulphur impurities at 1100 °C

The effect of sulphur on the cyclic oxidation of Ni-based superalloy GTD-111 was investigated. A cyclic oxidation experiment was performed for up to 200 cycles of 1h exposure at 1100°C. Even at the initial stage of 15 cycles, porosity increased with increasing sulphur content. The formation of pores along Cr2O3 layer grain boundaries was particularly pronounced. Increased porosity leads to an increase in spallation, which results in accelerated depletion of Cr and Al. As a result, continuity of an Al2O3 layer and cyclic oxidation resistance reduced with increasing sulphur content.

Effect of different B contents on the mechanical properties and cyclic oxidation behaviour of β-NiAlDy coatings

NiAlDy coatings doped with 0.05at.% and 1.00at.% B were produced by electron beam physical vapour deposition (EB-PVD). The mechanical properties and cyclic oxidation behaviour of the coatings were investigated. Compared to the undoped NiAlDy coating, the B doped coatings exhibited improved ductility, higher micro-hardness and elastic modulus. The NiAlDy alloys revealed similar thermal expansion behaviour in a temperature range of 200–1100°C. However, the addition of B did not show significant improvement in the cyclic oxidation resistance of NiAlDy coatings, on the contrary, the addition of 1.00at.% B accelerated the scale growth rate and aggravated the scale rumpling, which led to severe spallation. Related mechanisms were preliminarily discussed.

Effects of substrate material and TBC structure on the cyclic oxidation resistance of TBC systems

The effects of different substrates (CMSX-4 and IN738LC) on cyclic oxidation behavior of two thermal barrier coatings (TBCs) were investigated in this study. Cyclic oxidation test was conducted at a peak temperature of 1080°C with 30min hold time. The TBC systems tested consisted of two nickel-base superalloy substrates (CMSX-4 and IN738LC), a platinum aluminide bond coat and two types of 8YSZ top coat (vertical cracks (VC) and columnar structure). Samples with CMSX-4 substrate showed greater cyclic oxidation lifetimes than that with IN738LC, and VC YSZ on CMSX-4 offered longer cyclic life than those with columnar structure. After the oxidation test, the samples were analyzed using a scanning electron microscope (SEM) and an X-Ray diffractometer. The failure location of all TBC systems examined was found to be in the vicinity of TGO, consistent with past research of similar coating systems. Alumina and spinels (CS) were detected on all spalled surfaces although the amount of each phase differs from sample to sample. Ta-rich oxide was found on spalled coating surfaces with CMSX-4 substrate while islands of YSZ on the exposed TGO surface of samples with IN738LC substrate. It is believed that alloy composition, TGO rumpling and stresses induced by TGO growth and coefficient of thermal expansion (CTE) mismatch between different layers all contributed to the reduced cycles to failure of TBC systems with IN738LC substrate.

Effect of Annealing Treatment on the Isothermal and Cyclic Oxidation Behavior of an Electrodeposited Alumina-Forming Ni-Al Microcomposite

In this study, an electrodeposited alumina-forming Ni-Al composite having a nanocrystalline Ni matrix dispersing Al microparticles was produced and annealed in vacuum at 500°C for different time (3hr, 5hr and 8hr, respectively). Effect of annealing time on the microstructure, isothermal and cyclic oxidation behavior of the Ni-Al composite at 1000°C was comparably investigated. The results indicated that Al microparticles slowly dissolved into nickel grain to form an ultrafine-grained Ni3Al/NiAl composite with micro-sized pores dispersion due to volume shrinkage. The increased distribution uniformity of Al with the increasing of annealing time favors the formation of a protective alumina layer in a short time, and then significantly reduced the isothermal oxidation rate. Besides, the reduction of pores size with the increasing of annealing time also helps the ultrafine-grained Ni3Al/NiAl composite to grow an adherent alumina scale with increased cyclic oxidation resistance.