ICMCTF2014 Session A1-2: Coatings to Resist High Temperature Oxidation, Corrosion and Fouling

Wednesday, April 30, 2014 1:30 PM in Sunrise

Wednesday Afternoon

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1:30 PM A1-2-1 Some Results About the Interactions Between Reactivity, Interdiffusion and Creep in Coated Thin Wall Superalloy Systems
Daniel Monceau, Eric Andrieu (CIRIMAT laboratory, University of Toulouse, France); SébastienDryepondt Dryepondt (CIRIMAT laboratory, University of Toulouse, France; present address: ORNL, US); Aymeric Raffaitin (CIRIMAT laboratory, University of Toulouse, France; present address: AIRBUS, France); Damien Texier (CIRIMAT laboratory, University of Toulouse, France; present address: ENSMA, France)

Single crystal nickel-based superalloys are used as structural materials for hot pressure blades in aeronautic gas turbines. Cooled and uncooled blades both include thin-wall sections, sometimes less than 1 mm thick. These parts are always coated with a typically 50 µm thick metallic alloy to improve their resistance to high temperature corrosion and cyclic oxidation. These architectures result in large gradients of microstructure and material properties. Moreover, these systems are subjected to thermal gradients in addition to cyclic temperature, cyclic loading and aggressive atmosphere. The thickness of the area where the substrate microstructure is affected by selective oxidation or by interdiffusion with the coating cannot be neglected anymore for thin components. Interactions among surface reactivity, interdiffusion and creep properties have hence to be considered.

In order to model the lifetime of these components, first generation Ni-based single crystal superalloys were creep tested at high temperature under controlled atmospheres. Flat thin (1mm) and ultra-thin (down to 20 µm) specimens were machined. Aged systems were also machined to extract mechanical samples from the various layers of these architectural materials. The main objective is to characterize the mechanical properties of each individual layer (coating, interdiffusion zone). This approach has been made possible by the development of new test rigs dedicated to high temperature mechanical testing of ultra-thin specimens. In addition, thicker specimens were also creep tested at constant or cyclically changing temperatures, with in some cases a switch of atmospheres during the test (high/low P O2) in order to understand the nature of the coupling between the various degradation mechanisms. For example, creep tests were performed on coated and uncoated specimens in the exact same conditions to discriminate between the effects of surface reactivity and thermal cycling on creep rate. As an overall result, it was found that two kinds of interactions need to be distinguished. The first “static” interaction ,- well-known in the literature – consists of the formation of a non load-bearing section due to the irreversible evolution of the microstructure affected by oxidation and/or interdiffusion. , The building of creep database for graded materials is required to estimate the impact of the non load-bearing section. The second kind corresponds to the “dynamic” interaction between thermal cycling, “in progress” oxidation or interdiffusion, and creep. One example is the increased creep rate of a superalloy being oxidized with vacancies injection leading to a reversible vacancy super-saturation. Fundamental research is needed to better understand these dynamic coupling effects and some available examples of the research in progress will be shown .

2:10 PM A1-2-3 Characterization of the Gradient of Mechanical and Physical Properties Existing in β-NiAlPt Coated Ni-based Single Crystal Superalloy by using Ultrathin Specimens
Damien Texier, Eric Andrieu (CIRIMAT, France); Serge Selezneff, Arnaud Longuet (Snecma, SAFRAN Group, France); Daniel Monceau (CIRIMAT, France)

In service, turbine blades are subjected to thermo-mechanical solicitation at elevated temperature and evolve in severe environmental conditions (oxidation and corrosion). Due to these harsh specifications, the use of Ni-based single-crystal superalloys overlaid with Thermal Barrier Coating (TBC) has proven to insure the integrity of this microstructure graded system for several thousands of hours of flights. NiAlPt or MCrAlY alloys generally constitute the bond coating between the superalloy and the thermally insulating zirconia. Nevertheless, microstructure and properties of the different layers constitutive of the TBC system evolve with time due to interdiffusion, oxidation and mechanical solicitations. These evolutions as rumpling/ratcheting, edge delamination, phase transformations, voids formation are deleterious for the lifetime of turbine blades. Therefore, improvements in the prediction of mechanical behavior and the lifetime of turbine blades require a data base related to the intrinsic properties of each layer at different ageing times. Such data are missing for the modeling of the overall behavior of the TBC systems.

This study deals with the local characterization of the mechanical and physical behaviors of a β-NiAlPt coated AM1 superalloy up to 1100°C. Specimens, 25 to 35 µm thick, have been machined in order to assess the mechanical behavior of the specific layers of the graded materials having experienced different creep ageing conditions. Tensile experiments have been carried out in a temperature range of 700 to 1100°C. A database on mechanical and thermal expansion properties has been set up to describe the gradient of properties existing in such a system at operating temperatures.
2:30 PM A1-2-4 The Effect of a Cr Adhesion Layer on the Protective Behavior of Al2O3 Coatings Against Metal Dusting
Esmerelda Uribe-Lam, Olimpia Salas, Dulce Melo-Maximo (ITESM-CEM, Mexico); Lizbeth Melo-Maximo (IPN, Mexico); Joaquin Oseguera (ITESM-CEM, Mexico); RicardoDiego Torres (PUCPR, Brazil); Roberto De Souza (USP, Brazil)
Metal dusting is a form of corrosion that attacks Fe, Ni, and Co alloys in environments of high carbon potential in the 400-900°C range. The application of oxide thin films on various Fe-based materials has proven to be a promising method of protection against metal dusting. In the present work, Al2O3 coatings were applied on 304L stainless steel substrates by reactive magnetron sputtering using an adhesion interlayer of Cr. Uncoated and coated samples were then exposed to a carburizing atmosphere via thermogravimetry (TGA) to test the protective potential of the coatings. The exposed coated substrates showed a marked decrease in weight gain respect to the uncoated sample. The structure of the uncoated and coated samples prior and after the TGA runs were investigated in detail to determine the mechanisms of protection provided by the coatings.
2:50 PM A1-2-5 The Use of Advanced Surface Analytical Techniques to Investigate Early Oxidation Stages of Aluminides
Philippe Marcus (Chimie ParisTech (ENSCP), France)

A detailed understanding of Al2O3/Ni-aluminides interfaces is a key issue for Thermal Barrier Coatings adhesion. Similarly the evolution of the oxide - intermetallic interface during the early stage of oxidation of TiAl is of primary importance in the context of increasing implementation of these alloys for high temperature applications.

The aim of this lecture is to show how advanced surface analytical techniques, Scanning Tunneling Microscopy (STM), X-Ray Photoelectron Spectroscopy (XPS), and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) can be used to address these interfacial problems.

The selected examples will include the question of vacancies generated at the Al2O3/TiAl interface, studied by STM, and the Al2O3/NiAl interface, studied by XPS and ToF-SIMS.

The use of DFT for modeling the interface at the same scale as STM data (i. e. the atomistic scale) will also be discussed (vacancies and nanovoids).

3:30 PM A1-2-7 Study of the Electrochemical Behaviour of Aluminized Steel
Babs Lemmens (Ghent University, Belgium); Beril Corlu, Joost De Strycker (Arcelor Mittal Global R&D Gent, Belgium); Iris De Graeve (Vrije Universiteit Brussel, Belgium); Kim Verbeken (Ghent University, Belgium)

Zinc-based coatings effectively protect steel against corrosion but have some drawbacks related to environmental issues arising from zinc dissolution and to scarcity of zinc resources. Consequently, aluminium-based coatings gain importance both from a scientific as an industrial point of view. Despite the fact that these Al-based coatings are already being applied industrially, the electrochemical behaviour of the different intermetallic layers formed during the hot dipping process still remains under debate.

When the hot dipping process is performed in a pure Al bath, it gives rise to the formation of different intermetallic layers. The outer layer comprises nearly pure aluminium. This layer is on top of a first intermetallic layer commonly referred to as FeAl3. The second intermetallic layer is a Fe2Al5 layer and adjacent to the steel substrate. In case Si is added to the bath, this element also affects the intermetallic layers.

In order to clarify the electrochemical nature of the different layers with respect to each other, both macroscopic and local electrochemical measurements were performed. To evaluate the performance of the different layers, craters with different depths were produced using a GDOES system, to expose the different layers to the atmosphere. Within those craters the electrochemical behaviour of each specific layer was analysed by immersion in a chloride solution. Afterwards a characterisation of the craters was performed by material characterization techniques such as SEM-EDX and XRD.

3:50 PM A1-2-8 Effects of Ceramic Particle Size on Corrosion Behaviors of Cold Sprayed SiCp/Al 5056 CComposited Coatings
Yingying Wang, Bernard Normand, Nicolas Mary (Insa De Lyon, France); Hanlin Liao (UTBM, France)
Silicon carbide (SiC) particles reinforced Al 5056 (SiCp/Al 5056) composite coatings were deposited by cold spray. Effects of ceramic particles on microstructure and corrosion behaviors were investigated. Microstructures were examined by optical microscopy (OM) and Field Emission Scanning Electron Microscopy (FE-SEM). Results showed that the coatings became more compact with the addition of ceramic particles. Porosity of as-sprayed composite coatings was all less than 1 % and decreased with the increase of SiC particles size. XRD patterns showed that the width of peak widened and the position shifted to higher degrees as a result of increased residual compressed stress with the increase of SiC particles size. Open circuit potential (OCP) measurements and potentiodynamic polarization scans in 0.1 M sodium sulfate (Na2SO4) solutions of different pH values were used to evaluate the corrosion performance. Corrosion potential and corrosion current decreased with the increase of SiC size in both solutions. Surfaces after corrosion were also checked by XRD, FE-SEM and Energy-dispersive X-ray spectroscopy (EDS). Corrosion products were AlO(OH) and Al2O3.
4:10 PM A1-2-9 Corrosion Resistance of Ni Coatings on Steel Deposited with Electrolytic Plasma Processing
Adam Smith, Efstathios Meletis (University of Texas at Arlington, US)
Electrolytic Plasma Processing (EPP) is a surface modification technology that can encompass surface cleaning and sequential coating. Deposition of both metallic and ceramic coatings is feasible by utilizing respectively, the cathodic or anodic version of the process. The EPP process is attracting significant interest from the engineering community due to its simplicity, economic advantages and its green character. For metallic coating deposition, the workpiece is the cathode of an electrical circuit and a conductive nozzle in close proximity is the anode. An aqueous electrolyte is then flowed through the nozzle and over the sample, closing the circuit, and a voltage is applied. The voltage, typically in the low hundreds, forms plasma on the sample surface resulting in metal deposition at a high rate. In the current study, low carbon steel was subjected to an EPP treatment with a nickel containing electrolyte in an effort to create a hard and corrosion resistant surface coating. The effect of deposition power and electrolyte concentration were examined by XRD, along with cross sectional SEM/EDS and microhardness measurements to determine their relationship to coating thickness, composition, and uniformity. The corrosion resistance was assessed by corrosion potential measurements and anodic polarization testing.
4:30 PM A1-2-10 Effects of Mg on Morphologies and Properties of Hot Dipped Zn-Mg Coatings
Caizhen Yao, See Leng Tay, Tianping Zhu, Wei Gao (The University of Auckland, New Zealand)
Zn-Mg-Al coating was prepared by hot dipping method on carbon steel substrate. The phase structure, surface morphology, elemental composition, microhardness and corrosion property of the coatings were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM-EDS), microhardness tester, and electrochemical workstation. Zn coating and Zn-Al coating were also prepared and tested for comparison purpose. The microhardness of Zn-Mg-Al coating is improved from 43 HV of Zn coating and 89 HV of Zn-Al coating to 178 HV. The improvement of microhardness may due to the formation of intermetallic phases. Mg addition also has the ability to decrease the crystal size of Zn, reduce the corrosion rate of Zn coating, and leading to a better anticorrosion property of Zn-Mg-Al coating.
4:50 PM A1-2-11 Influence of Ruthenium as an Alloying Element on the Corrosion Behaviour of Laser Treated AISI 316-NiTi
Babatunde Obadele, Masego Lepule, Peter Olubambi (Tshwane University of Technology, South Africa)

Recently, surface modification of AISI 316-NiTi with elements such as Nb, Co, Mo and ZrO2 have been attempted. The aim of the study is to investigate the influence of ruthenium (Ru) additions and laser speed on the corrosion behaviour of AISI 316 austenitic stainless steel (ASS) reinforced with NiTi. Ni54.6Ti45.4 and Ni54.60Ti45.32Ru0.08 feedstock powders blended in a Turbula mixer were laser deposited onto 316 ASS using a 4.4 kW Nd:YAG laser. Their corrosion behaviour was investigated in 0.9 % NaCl solution using potentiodynamic polarisation technique. It is well known that the corrosion performance of NiTi based alloys, especially the passivation depends on the surface conditions. Corrosion potential, Ecorr, calculated for 316 ASSS, 316-NiTi and 316-NiTiRu were -0.38, -0.28 and -0.26 V respectively. A positive shift in Ecorr and negative shift in Icorr shows a lower tendency and high resistance to corrosion for the 316-NiTiRu alloys as compared to 316 ASS. Ruthenium affects the cathodic Tafel constant (βc) in the chloride solution, which indicates that it influences the cathodic part of the corrosion reaction. SEM micrographs revealed that the alloys were attacked by chloride ions, with different pit morphologies and depths.

5:10 PM A1-2-12 Microstructure, Mechanical and Anti-corrosion Property Evaluation of Iron-based Thin Film Metallic Glasses
Li-Ting Chen, Yung-Chin Yang (National Taipei University of Technology, Taiwan); Jyh-Wei Lee (Ming Chi University of Technology, Taiwan)

Recently thin films metallic glasses (TFMGs) represent a class of promising engineering materials for structural applications. Lots of efforts have been done on the research and development of TFMG materials. Nevertheless, the Iron-based thin film metallic glasses have rarely been investigated. In this work, the Iron-based Fe-Zr-Ti thin film metallic glasses with different Fe contents were prepared by magnetron co-sputtering system using pure Zr, Ti and Fe targets. The thermal behavior of each TFMG was determined using a differential scanning calorimeter (DSC). The crystal structure of the samples was determined by a grazing incidence X-ray diffractometer (GIXRD). Compositions of thin films were analysed by a field emission electron probe microanalyzer (FE-EPMA). Surface and cross-sectional microstructures of thin films were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. The surface roughness of thin films was explored by atomic force microscopy (AFM). A nanoindenter and scratch tester were used to evaluate the hardness and adhesion properties of TFMGs, respectively. The potentiodynamic polarization test in sodium chloride aqueous solution was conducted for each TFMG. It was discovered that the mechanical property of TFMG was enhanced as Fe content increased. The influence of Fe concentration on the amorphous state, microstructure, mechanical and anti-corrosion properties of Iron-based thin film metallic glasses was further discussed in this work.

Keywords: Iron-based, thin film metal glass, scratch tester, nanoindenter, potentiodynamic polarization test

Time Period WeA Sessions | Abstract Timeline | Topic A Sessions | Time Periods | Topics | ICMCTF2014 Schedule