Program Organizers: Narendra B. Dahotre, Center for Laser Applications, University of Tennessee Space Institute, Tullahoma, TN 37388; Janet M. Hampikian, School of Materials Science & Engineering, Georgia Institute of Technology, Atlanta, GA 30332; Jacob J. Stiglich, PO Box 206, Sierra Madre, CA 91025
Tuesday, PM Room: B1
February 6, 1996 Location: Anaheim Convention Center
Session Chairpersons: Alejandro Sanz, Laboratoire de Metallurgie, Ecole Nationale Superieure, De L'Aeronautique Et De L'espace, 10, Av. Edouard Belin, BP 4032, 31055 Toulouse Cedex, France; Janet M. Hampikian, School of Materials Science of Engrg, Georgia Institute of Technology, Atlanta, GA 30332
2:00 pm Invited
MODELING THE INTERDIFFUSION OF HIGH TEMPERATURE COATINGS: J.E. Morral, Cheng Jin, W.D. Hopfe, Department of Metallurgy and Institute of Materials Science, University of Connecticut, 97 N. Eagleville Road, Storrs, CT 06269-3136
During processing and service, high temperature coatings can interdiffuse with their underlying substrate. The microstructure of the interdiffusion zone depends on the initial coating and substrate compositions in a way that can be predicted using newly developed principles of diffusion in complex systems. As an example, these principles will be applied to predicting the microstructure of MCrAlY coatings when they diffuse into Ni-base superalloys at 1200deg.C. It will be shown, both by computer modeling and experiments on diffusion couples, that a variety of microstructures are possible even when the initial coating is a [[gamma]]+[[beta]] alloy and the substrate is a [[gamma]]+[[gamma]]' alloy.
CUBIC PHASE (Al,Cr)3Ti COATINGS FOR TITANIUM AND TITANIUM ALUMINIDE ALLOYS: Dale K. Dewald, Waubik, Inc., P.O. BOX 457, Hancock, MI 49930; Donald E. Mikkola, Department Metallurgical & Materials Engineering, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931
Chromium alloyed forms of cubic-modified Al3Ti have been identified as potential high temperature protective coatings for titanium-based structural alloys. Coatings of the nominal composition Al67Cr8Ti25 have been applied to both Ti and TiAl alloy substrates by the Low Pressure Plasma Spray (LPPS) and Electro-Spark Deposition (ESD) processes. The coatings have been subjected to long term cyclic oxidation tests. Details of the coatings and methods will be presented along with the micro-structure and protective behavior of the coatings.
THE FORMATION AND RELEVANCE OF "MARTENSITIC" STRUCTURES WHICH DEVELOP IN ALUMINIDE COATINGS ON A RHENIUM CONTAINING NICKEL BASE SUPERALLOY: S.B. Newcomb, A.E. Dent, W.M. Stobbs, Department of Materials Science and Metallurgy, Cambridge University, Pembroke St., Cambridge CB2 3QZ, UK
The compositional and structural changes that occur in aluminide and platinum aluminide coatings on a rhenium containing nickel base superalloy during high temperature thermal cycling have been assessed using "edge-on" TEM approaches. It is found that Al diffusion, up into the oxide and down into the substrate, happens differently for the two tvpes of coating with, in particular, differing relative effects on the development of the sub-coating substrate [[gamma]]/[[gamma]]' structure in relation to the relative segregation of the other elements present. Highly defective "martensites" based on Ni5Al3 form in the coatings and their role will be discussed. Their defective nature suggests that thev enhance the rates at which the coatings degrade but there is evidence that they are also important in relation to stress relief.
COATING INDUCED LIFE REDUCTIONS OF SINGLE CRYSTAL SUPERALLOY GAS TURBINE
BLADE MATERIALS: J. Bressers, Institute for Advanced Materials, Joint
Research Centre, EC Petten, The Netherlands
Single crystal nickel-based alloys are widely used as materials in aero gas turbine blades because of their excellant resistance to high temperature deformation. Coatings are used in order to provide the blades with adequate protection against environmental degradation. An issue of major concern is the effect of the presence of the coating on the operational life of the blades. This paper reports the results of a study evaluating the life of the single crystal nickel-based superalloy SRR99 under thermo-mechanical fatigue (TMF) loading, in the uncoated condition as well as protected with a nickel aluminide diffusion coating and with an MCrAlY overlay coating. Different TMF cycle types with a minimum temperature of 300[[ring]]C and maximum temperatures of 850[[ring]]C and 1050[[ring]]C, and with different minimum-to-maximum strain ratios were used to simulate the thermal and mechanical loads at critical volume elements of a blade. At strain ranges relevant to aero engine blade service, the presence of both coatings causes the TMF life of SRR99 to decrease, the reduction by a factor of five being largest in the case of the overlay coating. The results are analyzed in terms of the effect of the coating on the number of cycles for microcrack initiation and on the crack growth rate. The faster crack growth in the coated material, which is found to be largely responsible for the observed reduction of the TMF life, is due to a combination of poor coating properties and composition/microstructure changes in the substrate layers just beneath the coating.
THE HIGH TEMPERATURE OXIDATION PERFORMANCE OF ALUMINA COATINGS ON NI-BASE ALLOYS: M.R. Hendrick, J.M. Hampikian and W.B. Carter, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA
Alumina coatings were applied to nickel-base alloys by combustion chemical vapor deposition (CCVD). CCVD is an open air CVD technique performed in a flame produced from a nebulized liquid fuel solution. As- deposited alumina coatings on fused quartz were analyzed by transmission electron microscopy (TEM) and found to be crystalline. The oxidation kinetics of coated specimens were ascertained by oxidation tests carried out in pure flowing air at 800-1100[[ring]]C and compared to the kinetics of uncoated specimens. The morphology and composition of the alumina coatings were determined by scanning electron microscopy, energy dispersive X-ray spectroscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy.
3:45 pm BREAK
THE RESISTANCE OF SOME GAS TURBINE HOT COMPONENTS COATINGS TO HIGH TEMPERATURE CORROSION AND THERMAL CYCLING DAMAGE: G.P. DeGaudenzi, F. Uberti, CISE spa-P.O. Box 12081, I-20134 Milano, Italy; A. Colombo, G. Rocchini, ENEL Spa, DSR/CRAM, Milano, Italy
Structural materials and coatings used for industrial gas turbine hot components are designed to resist high temperature corrosion attack through the development of protective scales of Cr2O3, Al2O3 or SiO3. The effectiveness of these scales can be reduced by thermal cycling induced stresses which can lead to crack nucleation and growth and to consequent spallation. Synergistic interaction phenomena with HTC can play an important role in accelerating the process. A Dean Test was devised at the HTC Lab of CISE to simulate the gas turbine environment; a 48 hours thermal cycling from test (850 and 900[[ring]]C) to room temperature was performed. The behavior of some Ni and Co-based superalloys, conventional coatings (both PtAl and NiCoCrAIY) and thermal barrier coatings was studied through gravimetric kinetics, loss-of-metal data and SEM/EDS analyses of corrosion products morphology and composition after exposure up to 3000 hrs. Based on the results, a model was applied to predict scale service life reduction due to this mechanism.
IMPROVING CORROSION RESISTANCE OF CAST IRON BY SOLID-GAS CHROMOSILICONIZING: Xiaoxing Qiu, Dev Venugopalan, Materials Department, College of Engineering and Applied Science, University of Wisconsin-Milwaukee
Siliconizing and chromosiliconizing are an inexpensive method of chemically treating for corrosion and high-temperature oxidation resistance in ferrous materials. Conventionally, siliconizing and chromosiliconizing by the powder-pack method are used to improve the above properties in cast iron. However, limited success has been attained for gray cast iron. For example, corrosion resistance has been raised only two times in hydrochloride acid solution test. This poor performance is due to a high density of porosites and flake graphite in the case layer. The solid-gas method is a way of producing vapor from a solid treating agent directly within the retort. The present word was done on cast iron using solid-gas chromosiliconizing. A very dense layer was obtained on the surface of the cast iron with this processing. This results in a greatly improved resistance to corrosion in the test with hydrochloric acid and hot alkaline solutions.
HIGH TEMPERATURE CORROSION PROTECTION BY LASER-SURFACE MODIFICATION: Rahul Asthana, Anil Gupta, Ashish Gupta, Ajay Singh, E- 277 'Nirupam', Kanla Nagar, AGRA282005, India
Laser treatment of metallic materials has gained wide interest due to great potentialities of the technique. It has several advantages i.e. localized heating, high temperature and high cooling rates, etc. Laser surface alloying or coating is a good way to prepare barrier layers on to metals. This paper deals with the method of elaboration of several alloys or coating on to iron, nickel, or nibomium by melting a predeposited solid powder and the substrate. The behaviour of the formed coating in O2 at high temperature have also been presented.
CORROSION RESISTANT Pd- Si COATINGS: L.P. Efimenko, E.A. Antonova, L.P. Petrova, Institute of Silicate Chemistry of Russia Academy of Sciences, ul.Odoevskogo,24, korp.2, St. Petersburg, 199155, Russia
The Pd-Si coating with palladium content more than 95 weight percent has been
formed by powder-annealing technology for protecting superalloys and steels.
The influence of temperature, time, and Si content in the composition on the
coating structure were studied. The coating is formed at 1000[[ring]]C for ten
minutes in the presence of liquid phase. After formation the base metal content
in the coating is less than one weight percent. The solid solution formation in
the transition zone provides the high adhesion of the coating to the protected
metal. The oxidation resistance of the coating at 800[[ring]]C for fifty hours
is practically equal to that of pure palladium. The corrosion of Pd-Si and
Pd-Ir-Si coatings in HNO3 is studied. It is shown the iridium increses
corrosion resistance by ten to twenty times. The aging at 700[[ring]]C for
twenty hours improves the corrosion resistance additionally by a factor of 1.5
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