Oxidation Behavior Of Coatings Research Articles

Study of oxidation behavior of nanostructured NiCrAlY bond coatings deposited by cold spraying

Nanostructured NiCrAlY bond coating was deposited using a milled powder by cold spraying. A shot-peening treatment was then applied to the as-sprayed coating to modify the coating surface morphology. The oxidation behavior of the coating with the as-sprayed surface and shot-peened surface was investigated under isothermal oxidation at 900 °C and 1000 °C for different times. The oxidation behavior of the coating was characterized through surface morphology and cross-sectional microstructure by scanning electron microscopy. It was found that a uniform oxide layer was formed on the surface of the shot-peened nanostructured NiCrAlY coating during oxidation at temperatures of 900 °C and 1000 °C. The surface morphology of the coating has significant effect on the morphology of the oxide. The surface geometry of the cold-sprayed MCrAlY coating must be modified to promote formation of a protective oxide film during oxidation, through application of a post-treatment process such as shot-peening.

Preparation and oxidation of an Y 2O 3-dispersed chromizing coating by pack cementation at 800 °C

Preparation and oxidation of an Y 2O 3-dispersed chromizing coating was investigated by chromizing an as-electrodeposited Ni–Y 2O 3 composite film using a conventional pack-cementation method but at a greatly decreased temperature (800 °C). For comparison, chromizing was also performed in the same condition on an as-deposited Ni film without Y 2O 3 particles. Oxidation at 900 °C indicated that compared to the Y 2O 3-free chromizing coating, the Y 2O 3-dispersed chromizing coating exhibited an increased oxidation resistance, due to the formation of purer and denser chromia scale. The Y 2O 3 effects on the coating formation and the coating oxidation behavior are discussed in detail.

Evaluation of arc ion plated NiCoCrAlYSiB coatings after oxidation at 900–1100 °C

NiCoCrAlYSiB coatings were deposited on DS M11 Ni-based superalloys by arc ion plating (AIP). In order to study the effect of Si and B additions on the oxidation behavior of NiCoCrAlY-type coatings, isothermal oxidation tests were carried out from 900 °C to 1100 °C. The results indicated that Si and B additions had little effect on the isothermal oxidation behaviors of coatings at 900 °C and 1000 °C, while the additions improved the oxidation resistance at 1100 °C. The reasons for Si and B improving the oxidation resistance are discussed through analyzing the oxidation kinetics, phase compositions of oxide scales, morphology and elemental distributions through the coatings after oxidation.

Oxidation models of the growth of corrosion products on the intermetallic coatings strengthened by a fine dispersive Al 2O 3

In this paper, the cyclic oxidation test of intermetallic coatings with iron and nickel aluminium is presented. The oxidation behavior of coatings strengthened by a fine dispersive Al 2O 3 was investigated in aggressive gases for exposure times of up to 500 h. The surfaces of the composite coatings after the corrosion test in air were analyzed by light and scanning microscopy observation. An analysis of the corrosion products’ phase composition was conducted by an X-ray diffraction method. The results obtained from the presented investigations enable the elaboration of the two models of the growth of corrosion products on the intermetallic coatings strengthened by a fine dispersive Al 2O 3, first, on the coating with FeAl phase and second on the coating with NiAl intermetallic phase. The results show that the composite, thermally sprayed coatings have very good high-temperature corrosion resistance.

Oxidation of a Novel Chromium Coating with CeO2 Dispersions

Chromium coatings have been in widespread use to enhance the high-temperature oxidation resistance of low-alloy steely since the 1950s [Samuel and Lockington, Metal Treatment and Drop forgeing 18, 354 (1951); Sully and Brandes, Chromium, 2nd edn. Butterworths, London 1967]. In this work, a novel CeO2-dispersed chromium coating with a fine-grain structure was manufactured on a mild-carbon steel by Prior composite electrodeposition of Ni with CeO2 particles, followed by chromizing using a conventional halide activate, pack-cementation method. For comparison, chromizing was also performed on the carbon steel and on the one with Ni-plating pretreatment. Cyclic oxidation at 840degreesC for 120 h showed that among the three various samples chromized, the CeO2-dispersed chromium coating exhibited the best oxidation resistance, while the worst for the coating on the carbon steel The samples after oxidation were investigated using X-ray diffraction (XRD), scanning-electron microscopy equipped with energy dispersive X-ray analysis (SEMI/EDAX) and electron-probe microanalysis (EPMA). The results indicated that although all three coatings grew chromia scales during oxidation, the one formed on the CeO2-modified coating Was thinner, denser and had a fine-grain structured Moreover, the formation of "Kirkendall" voids and new precipitates, which occurred during oxidation below the scale in the chromium coating on the Ni-plated sample, was prevented in the presence of CeO2 particles in the coating The CeO2 effects on the coating formation and the coating oxidation behavior are discussed in detail.

Oxidation behavior of molybdenum nitride coatings

Molybdenum nitride coatings were deposited onto H13 hot working tool steel and alumina substrates by arc PVD. The coatings were characterized with respect to their mechanical and structural properties. Oxidation behavior of the coatings on alumina substrates was investigated by TG/DTA. Coated H13 substrates were oxidized in a tube furnace under atmospheric conditions at specific temperatures determined from TG/DTA tests of the same coating on alumina substrate. The oxide scale morphology was characterized by scanning electron microscopy and X-ray diffraction. Resistance to oxidation of Mo–N coatings is poor because of the non-protective nature of their oxides and the volatility of the oxides at moderately high temperatures. The oxides formed during the oxidation were determined as MoO 2 and MoO 3. The oxidation reaction product MoO 3 is a volatile oxide and its evaporation reaction starts at after 550 °C. In addition, decomposition of Mo 2N starts at 681 °C and the decomposition reaction product is metallic molybdenum, which also oxidizes to volatile MoO 3.

The behavior of MCrAlY coatings on Ni 3Al-base superalloy

This work is concerned with NiCrAlY and NiCoCrAlY coatings deposited on the superalloy IC-6 (Ni 3Al-base superalloy) by arc ion plating (AIP). The results indicated that the presence of Al and Mo in alloy IC-6 impeded Cr atoms moving from coatings to substrates during the deposition process. As a consequence, the distribution of Cr is well proportioned in both NiCrAlY and NiCoCrAlY coatings. Vacuum heat treatment drastically increased diffusivities and the coating became more uniform. The interdiffusion also led to the phase transformation in the coatings. Although γ′-Ni 3Al and γ-Ni were still the major phases in the coating, their lattice constant a 0 decreased. The results of isothermal oxidation showed that the oxidation behavior of coatings obeyed the parabolic rate law. The oxidation resistance was not influenced very much by the presence of Co in the NiCrAlY coating at 900 °C static atmosphere. NiCoCrAlY coating had poorer oxidation resistance than NiCrAlY coating when they were exposed at 1000 °C.

The Influence of the Ion Bombardment Conditions on the Oxidation Behavior of Sputtered TiN Coatings / Der Einfluss der Bedingungen beim lonenbeschuss auf das Oxidationsverhalten von gesputterten TiN-Schichten

In this investigation, the oxidation behavior of TiN coatings deposited by non-reactive unbalanced d.c. magnetron sputtering from TiN targets at different ion bombardment conditions was investigated. The oxidation behavior of the coatings was determined by means of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The samples were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX) and X-ray diffraction (XRD). The results obtained indicate that the oxidation behavior of the coatings is related to its microstructure and morphology where coatings with fine-grained dense structures showed the best resistance against oxidation.

Oxidation kinetics of sputtered Cr–N hard coatings

Hard coatings are nowadays successfully applied for applications where they are subjected to high temperatures. Although the oxidation threshold of hard coatings has been investigated by several authors, there is only limited information on the oxidation kinetics. Within this paper, the oxidation behavior and kinetics of sputtered Cr–N coatings were studied systematically. All coatings investigated were prepared by means of reactive unbalanced DC magnetron sputtering using a Cr target and argon/nitrogen discharges. The N/Cr ratio was varied systematically to achieve coatings with phase compositions of single phase Cr 2N or CrN, respectively. For the single phase CrN coatings, the macrostresses were adjusted to values between −211 and 400 MPa using different ion bombardment conditions to evaluate the stress influence. The oxidation behavior of coatings deposited onto hot-working tool steel was investigated using thermo-gravimetric analysis in an argon/oxygen atmosphere. Dynamical measurements were carried out to determine the oxidation threshold and to provide basic information on suitable temperatures (between 725 and 825°C) for isothermal measurements. The activation energies for oxidation calculated by means of Arrhenius plots range between 102 and 465 kJ mol −1 for the different Cr–N coatings. The oxidation products were characterized using scanning electron microscopy, energy-dispersive X-ray analysis and X-ray diffraction and were found to be Cr 2O 3. Based on the results obtained in this study it can be concluded that the activation energy for oxidation provides a suitable basis for comparison of the oxidation behavior of different hard coatings.