ICMCTF2005 Session A1-2: Coatings to Resist High Temperature Corrosion and Wear

Monday, May 2, 2005 1:30 PM in Room Sunrise

Monday Afternoon

Start	Invited?	Item
1:30 PM		A1-2-1 The Effect of Nitrogen on the Formation and Oxidation Behavior of Iron Aluminide Coatings Fabricated by Chemical Vapor Deposition Y. Zhang (Tennessee Technological University); B.A. Pint, K.M. Cooley, J.A. Haynes (Oak Ridge National Laboratory) One of the critical issues for the application of iron aluminide coatings is the possible compatibility problem between the coatings and steel substrates which can have substantially different coefficients of thermal expansion (CTE). Formation of any precipitates or thin reaction products between the aluminide coating and the substrate could worsen the problem. Elements such as C and N are added to commercial austenitic and ferritic steels primarily for strengthening purposes. The present study focused on the effect of N in substrate alloys on the coating formation and oxidation performance by comparing the aluminide coatings fabricated via chemical vapor deposition (CVD) on commercial and laboratory ferritic and austenitic alloys with different N contents. Nitrogen from the substrate alloys not only led to the formation of AlN precipitates in the CVD aluminide coating, but also affected coating adhesion. Spallation sometimes occurred in the as-deposited coating on 304L when an AlN layer was present at the coating/substrate interface. The effect of N on the early stages of coating growth during aluminization was addressed, where the AlN precipitates acted as a diffusion barrier and hindered the growth of aluminide coatings. The cyclic oxidation performance in air + 10vol.% H₂O at 700°C was evaluated and compared for the iron aluminide coatings on steel substrates with various N contents.
1:50 PM		A1-2-2 Aluminum Diffusion in Alumina Scales Grown on Fe-Cr-Al Alloys J.A. Nychka, D.R. Clarke (University of California Santa Barbara) Despite many years of research on alumina forming alloys, little is known about the relative inward diffusion of oxygen and outward diffusion of aluminum during alumina scale growth. This paper presents data taken from experiments designed to give a measure of the outward flux of aluminum during oxidation of Fe-Cr-Al alloys. The outward flux of aluminum during the oxidation of four similar, alumina-forming alloys is determined using two experiments. One is measurement of the characteristic equiaxed layer to the total oxide thickness. The second is measurement of the new oxide formed along grain boundaries of a wedge-polished oxide at the oxide/air interface upon re-oxidation. The former provides information about the ratio of outward diffusion of aluminum to inward diffusion of oxygen during oxidation. The latter experiment directly quantifies the outward flux of aluminum as a function of oxide thickness. Both the outward aluminum flux and the ratio of inward to outward diffusional fluxes are found to vary with the minor concentrations of "reactive element" alloying additions. Specifically, Y in solution in the alloy is found to limit outward aluminum diffusion more than Zr in solution, with Y₂O₃ limiting aluminum diffusion more than Zr, Y, and ZrO₂.
2:10 PM		A1-2-4 Microstructure, Composition and Oxidation Resistance of Nanostructured Ni-Al-N Coatings Produced by Magnetron Sputtering D. Zhong, J.J. Moore (Colorado School of mines); E. Sutter (Brookhaven National Laboratory); B. Mishra (Colorado School of Mines) Thin film materials based on β-NiAl have been used for a wide variety of applications, including: underlayers in magnetic recording media, high temperature protective coatings, surface catalysts, and thin film thermistors in micro-electronic device applications. In this work, nanostructured NiAl and Ni-Al-N thin films were RF magnetron sputtered from a NiAl compound target in different argon-nitrogen atmosphere. The structure and stoichiometry of as-deposited coatings were studied using XRD, SEM, TEM, and XPS. Thermal analyses (DSC and TGA) were also conducted to study their oxidation kinetics at high temperatures. Microstructural and compositional changes of the coatings after isothermal oxidation were investigated using XRD, SEM, and RBS. The results show that: (1) denser and more completely crystallized Ni-Al-N thin films can be tailored through controlled ion bombardment during deposition, (2) nano-composite NiAl-AlN thin films were synthesized with nitrogen atomic concentration up to 30%, and (3) the Ni-Al-N coatings exhibited good oxidation resistance at temperatures above 1273 K.
2:30 PM		A1-2-5 (Ti,Al)N Coatings for Aluminum Die Casting Dies: a Study of the Reactivity Between Ti_1-xAl_xN and Aluminum. E.K. Tentardini (Universidade Federal do Rio Grande do Sul, Brazil); M. Castro (Universidade Federal de Minas Gerais, Brazil); A.O. Kunrath, J.J. Moore (Colorado School of Mines) In aluminum die casting, one of the most frequent causes of failure of the die (soldering) is initiated by the reaction between the surface of the die and the molten aluminum alloy being cast. One way to reduce or eliminate this phenomenon is to produce a coating with good adhesion, tribological and chemical properties capable of isolating the die material from the aluminum. (Ti,Al)N coatings exhibit high hardness, good wear resistance and superior oxidation resistance than TiN and TiCN. The structure of the metastable (Ti,Al)N compound changes from the B1 NaCl type for pure TiN and low aluminum contents to a wurtzite structure as larger amounts of aluminum substitute Ti in the lattice. The properties of (Ti,Al)N are strongly dependent on the composition and film structure. This work investigates the susceptibility to reaction with aluminum of TiN and three compositions of (Ti,Al)N coatings. The investigation was conducted using a novel technique that utilizes DTA experiments to determine reaction characteristics between aluminum and selected coatings. The results obtained indicate that the introduction of Al in the TiN structure and the increase of its concentration in the (Ti,Al)N compound shifts the reactions between coating and aluminum towards higher temperatures and significantly reduces the heat of reaction. Microstructure and mechanical properties of the films were also investigated.
2:50 PM		A1-2-6 Coatings for Extreme Environments in the Bearing Contacts A. Sanz (SKF Engineering and Research Center, Netherlands) Rolling bearings and related products such as ball and roller screws are experiencing increased load demanding and are required to be operational in more and more difficult conditions or extreme environments. Furthermore, environmental concern and related government legislation require use of less mineral lubricant oil and toxic additives. Lubrication free is a technology/market trend Advanced coatings provide good solution for lubrication free needs A successful design of coated components requires detailed knowledge on materials, tribology and contact mechanics. The present paper presents a series of coatings and engineered surface solutions for bearings working in extreme environments and or with limited or non-existing lubrication. The deposition techniques covered in this articles include PVD, CPVD, IPVD, reactive magnetron sputtering and others applied to the domain of wear, false brinelling, smearing, lubricant life and contamination resistance under extremely high loaded rolling contact fatigue conditions. The range of properties cover from the ultrahard Me-DLC multilayered coatings to the superelastic CNx coatings. Description of specific applications for both high temperature, vacuum, chemically aggressive environments and clean sensible applications are provided.
3:10 PM		A1-2-7 Structure, Bonding, and Adhesion of MoSi₂/Fe and SiO₂/MoSi₂ from First Principles D.E. Jiang (University of California, Los Angeles); E.A. Carter (Princeton University) The high-melting-point compound MoSi₂ is a promising candidate for a high temperature coating on iron steels and refractory metals. The high temperature oxidation and corrosion resistance of MoSi₂ results from a coherent silica scale that forms. Although a great deal of experimental work has been devoted to improve the performance of MoSi₂ coatings, atomic level understanding of the bonding at both MoSi₂/metal and SiO₂/MoSi₂ interfaces is lacking. Using periodic density functional theory techniques we examine the adhesion strength, interfacial geometry, and bonding characteristics of MoSi₂/Fe and SiO₂/MoSi₂ interfaces. In particular, we study MoSi₂(001)/Fe(100) and MoSi₂(110)/Fe(110). The former has the lowest interface mismatch of all low-index surfaces and the latter represents the interface between the lowest-energy surfaces of the bulk materials. We predict that both MoSi₂/Fe interfaces have similar intrinsic adhesion energies of ~3.85 J/m², significantly stronger than the adhesion between iron and other ceramic coating materials such as ZrC and TiC. We find that the bonding at the interface is local, with covalent character exhibited between Fe-Si and Fe-Mo across the interfaces. To model silica/MoSi₂, we study the SiO₂(100)/MoSi₂(001) interface, due to its minimal lattice mismatch. We use β-cristobalite to model amorphous silica, since they have similar structural characteristics. We find that Si-O covalent bonding dominates the interfacial adhesion, yielding strong adhesion energy of 5.75 J/m². These very high interfacial adhesion energies suggest that MoSi₂ indeed should be a quite thermally stable coating for steels.
3:30 PM		A1-2-8 On the Strength of TiAlN Following to High Temperature Operations A. Escudeiro Santana (Swiss Federal Institute of Technology - Lausanne, Switzerland); A. Karimi (EPFL, Switzerland); V.H. Derflinger (Balzers Ltd., Liechtenstein); A. Schutze (Tribo Coating) Abstract: The sources of hardness in TiAlN films vary with the type of microstructure namely single-phase and nanocomposite. In the single phase films (Ti-rich) solution hardening generates stable defect configuration and film hardness is stable up to 800°C. Intercolumnar decohesion appears between 800-1000°C due to high thermal stress intensity in the voided columns verified by means of annealing under vacuum and high speed machining (HSM). At 30min/1000°C, the decomposition of B1-TiAlN in B4-AlN accomp an ies recovery and hardness strongly decreases. Fine grain structure in nanocomposite TiAlN (Al-rich) significantly improves ductility and fracture toughness as well as structure stability at high temperatures. Nanocomposites are already decomposed in B1-Ti AlN and B4-AlN in the as deposited state. After 16h/1000°C the hardness of nanocomposite increases from 30 to 35 GPa, mainly attributed to the increase of the volume fraction of B4-AlN. The decrease in the averaged grain size after annealing to values lower than 6 nm and the solution of Ti in the B4-AlN also contribute to hardening at some extent. t. e. p.
3:50 PM		A1-2-9 A Multifunctional Boron Coating on Metal Substrate R. Petrova, N. Suwattananont (New Jersey Institute of Technology) This paper describes the recent investigation of the microstructure, oxidation resistance, and corrosion resistance of boron coatings obtained on the surface of metallic alloys. It has been shown that the properties of the diffusion layers depend on their thickness, structure, chemical and phase composition as well as on kinetic parameters used in the process. The thickness of the boride coating varies by the type of the substrate material. The corrosion resistance of the boronized coating was determined in 5%, 10% and 15% of Hydrochloric acid (HCl), Sulfuric acid (H₂SO₄) and Nitric acid (HNO₃). The oxidation behavior of boron coatings on steel substrate was investigated at elevated temperature. For oxidation process high temperature range 600-900°C was used. Optical microscopy, X-ray diffraction, SEM, EDS was used to investigate the microstructure, phase composition, and oxides formed on the metallic surfaces. The isothermal oxidation behavior was investigated by means of TGA. The boron coatings showed improved corrosion resistance and oxidation resistance at high temperature.
4:10 PM		A1-2-12 Microstructural and Tribological Characteristics of DLC Coated Al₂O₃ at Elevated Temperatures K.Y. Lee, I.S. Jung (Pukyong National University, South Korea); C. Rincon, R. Wei (Southwest Research Institute) Alumina ceramics are commonly used in many severe applications such as in corrosive, high temperature and highly loaded situations especially in hot chemical based extreme environments for sealing application. Presently, polymeric materials are used as the counter part for alumina ceramic seals to reduce the ceramic-to-ceramic wear. As a result, leaks are very commonly observed from water pump during services. Consequently, it is needed to improve the surface properties of the ceramic seals using a surface modification technique such as a thin film coating process to meet the increasing demand of more stable and more durable performance and lower friction of coefficient in those extreme environments. To meet these challenges, we have applied DLC (diamond-like carbon) coatings on alumina specimens using various surface engineering techniques to improve the surface properties. A number of compositions of the DLC films and a number of interfacial bond layers have been studied. The DLC coated specimens have then been tested under a wider range of temperature conditions, from room 25O up to 400°C in dry air to study the survivability of the DLC coatings. Wear tests were carried out using a high temperature pin-on-disk tribo-tester. After that, the wear-tested specimens were analyzed using SEM with EDS to characterize the worn surfaces as well as the cross sections of the DLC films. Morphological changes of the DLC coated surfaces before and after the wear tests were studied using AFM. In addition, STEM, Raman spectroscopy were adopted to characterize microstructure and scratch and nano-indentation for the evaluation film properties, and the elemental changes of the DLC coatings during the wear tests at such high temperatures and to understand the relationship between microstructure and tribological properties of DLC material in high temperature. Finally, the wear characteristics of the DLC coatings on commercial alumina ceramics at the elevated temperature range and microstructures on process are presented in detail.