1997 TMS Annual Meeting: Monday Abstracts

MATERIALS, COATINGS AND PROCESSES FOR IMPROVED RELIABILITY OF HIGH TEMPERATURE COMPONENTS: Session II: Materials and Process II

Session Chairman: Dr. K. G. Kubarych, Solar Turbines, 2200 Pacific Highway, P.O. Box 85376, San Diego, CA 92186

2:00 pm

MODELING ENGINE COMPONENT CREEP DEGENERATION: A.K. Koul, X.J. Wu, Structures and Materials Propulsion Laboratory, Institute of Aerospace Research, National Research Council of Canada, Ottawa, Ontario, Canada K1A0R6

The paper presents a mechanistic approach to modeling creep degeneration of superalloy components with a view to developing residual life prediction algorithms. In accordance with the deformation decomposition rule: E = Eg + Egbs, we classify degeneration mechanisms into two categories: 1) grain boundary deformation controlled degeneration mechanisms, including grain boundary sliding (GBS), cavitation and GBS assisted oxidation; and 2) intragranular deformation controlled degeneration mechanisms. The evolutionary creep equation for each strain component is thus mechanism-based. Generally, GBS is responsible for the transient, while intragranular deformation mechanisms, particularly dislocation glide-plus-climb and dislocation multiplication, contribute to tertiary creep deformation during short term tests. When coupled with cavitation and oxidation, GBS also contributes to tertiary creep. The total creep strain is a result of the summation of all above contributions, and the entire creep, as a continuous process, is thus described. Superimposed on these mechanisms are various fracture criteria to predict the eventual event of creep rupture.

2:30 pm

THE EFFECT OF DEFECTS ON THE LCF BEHAVIOR OF AN ADVANCED SINGLE CRYSTAL SUPERALLOY: K.A. Dannemann, H. Jang, W.T. King, GE Power Generation, Schenectady, NY 12345

The defect propensity in single crystal castings is enhanced with increased casting size. As the industrial gas turbine community moves towards the application of large single crystal castings, there is increasing concern regarding the effects of grain and casting defects on part life. Although aircraft engine experience provides a basis for single crystal grain limits, the cycle and life requirements of large industrial gas turbines differ considerably. The effect of several types of defects on the low cycle fatigue behavior of an advanced single crystal alloy will be discussed. Tests were run on cast-to-size LCF bars with intentional defects (freckles, inclusions, low angle boundaries, recrystallized grains, slivers, mis-oriented grains) in the gage section. A correlation between defect size and LCF life was observed. Work to date indicates LCF life is more dependent on defect size than type.

2:50 pm

HOT FORMING CHARACTERISTICS OF NI-BASE SINGLE CRYSTAL SUPERALLOY CMSX-6: D. Zhao, H. Dong, M. Zelin, A. Dalley, Concurrent Technologies Corporation, 1450 Scalp Ave., Johnstown, PA 15904

High temperature deformation processing of Ni base single crystal superalloy CMSX-6 has been shown to be a feasible process. However, it is essential that the single crystal material be deformed at a low strain rate and within an appropriate temperature range to prevent recrystallization and fracture. In order to establish these limits, the hot forming behavior of Ni base single crystal superalloy CMSX-6 was investigated by performing high temperature compression, bending, and rolling tests. Stepwise deformation and annealing tests were also conducted to simulate multi-pass rolling practice. The flow stress and recrystallization behavior were characterized over a range of temperatures, strain rates, and strains. Metallurgical phenomena, such as changes in size and morphology of 1 particles, orientation change of the single crystal specimens, subgrain boundary formation, recovery, and recrystallization, occurred during the high temperature deformation processes. These phenomena were analyzed to understand their influence on forming of single crystals. Deformation at too high temperatures resulted growth of 1 particles and deteriorated the service properties of single crystals. Highly mis-oriented subgrain formation around 1 particles lead to recrystallization. Deformation mechanisms were investigated by analyzing the results of compression and indentation tests. The primary slip systems activated were of (111)<110> type. This work was conducted by the National Center for Excellence in Metalworking Technology, operated by Concurrent Technologies Corporation under contract No. N00140-92-C-BC49 to the U.S. Navy as part of the U.S. Navy Manufacturing Technology Program.

3:10 pm

EFFECT OF TEMPERATURE ON THE DEFORMATION CHARACTERISTICS OF A NI-MO-CR ALLOY: W.C. Johnson, D.L. Klarstrom, Haynes International, 1020 W. Park Avenue, P.O. Box 9013, Kokomo, IN 46904; M. Dollar, Haynes International, Engineering 1 Bldg., 10 W. 32nd Street, Chicago, IL 60616

The high temperature, age hardenable, Ni-Mo-Cr alloy HAYNES 242 shows a change in deformation characteristics dependent upon the testing temperature. Aged material shows microtwinning to be a dominant deformation mechanism at all testing temperatures. However, this does not preclude the occurrence of slip at room temperature and elevated temperature. Grain boundaries also seem to play a role in the fracture propagation mechanism at work in tested samples. Samples in the aged condition fracture with a combined mode of dimple rupture and cleavage as opposed to annealed samples which fracture through a dimple rupture mode alone. The fracture surface shows microvoid coalescence but the fracture takes place in a shear-type mode as opposed to the traditional cup and cone ductile fracture.

3:30 pm BREAK

3:50 pm

SOLID PARTICLE EROSION RESISTANCE OF IRON, NICKEL AND COBALT-BASED ALLOYS: B.F. Levin, J.N. DuPont, A.R. Marder, Lehigh University, Energy Research Center, Bethlehem, PA 18015

The erosion behavior of commercially available iron, nickel and cobalt-based alloys was evaluated and a relative ranking of their erosion resistance was developed. Microhardness tests were conducted in the vicinity of the eroded surface to measure the size of the plastic zone beneath the eroded surface. It was found that all alloys deformed plastically and a new toughness parameter has been proposed which shows good correlation with erosion resistance. To find a relationship between mechanical properties and erosion resistance, elevated temperature mechanical test were conducted for all alloys. The erosion resistance of tested materials exhibited good correlation with their tensile toughness. Relationships between the ability of materials to deform plastically, mechanical properties (i.e., hardness and tensile properties) and erosion resistance are discussed.

4:10 pm

THERMAL AND MECHANICAL PROPERTIES OF THERMAL BARRIER COATING ON CU-SUBSTRATE PREPARED BY DETONATION-GUN THERMAL SPRAY METHOD: Y.M. Rhyim, H.W. Jin, C.G. Park, Center for Advanced Aerospace Materials, Pohang University of Science & Technology, Pohang 790-784, Korea; S.B. Kim, M.C. Kim, Research Institute of Industrial Science & Technology, Pohang 790-600, Korea

Thermal barrier coating (TBC) consisting of Y2O3-stabilized ZrO2 top coat on a MCrAlY bond coat has been developed for thermal protection of hot components used in steel plant, especially the tuyeres in blast furnace. Since the tuyere is used under extremely harsh chemical environment and high temperature (up to 2300°C) within the blast furnace, it is essential to develop a strong and tough protective coating, that is fully compatible to the tuyere's pure copper substrate, by applying the detonation-gun thermal spray method. As fuel gas amount increased, the porosity of MCrAlY coat layer generally decreased to less than 1%, but microcracks can be formed with extreme fuel gas amount. The metallic bond coat with the thickness greater than 100 µm is required to sustain the ceramic top coat. In obtaining the best top coat, the spraying condition with maximum detonation temperature was found as an optimum condition from the computer simulation. A partially stabilized zirconia top coat layer deposited by this condition exhibited the low porosity with high hardness (~640 DPH) which is better than the coating made by plasma spraying. The thermal fatigue resistance of the present TBC was revealed to depend on both the thickness of ceramic top coat and the composition of the stabilizer. The result on the thermal conductivity is also discussed.

4:30 pm

ELECTROCHEMICAL PROCESSING OF THERMAL BARRIER COATINGS: S.W. Banovic, K. Barmak, A.R. Marder, C.M. Petronis, D.G. Puerta, D.F. Susan, Lehigh University, Department of Material Science and Engineering, 5 E. Packer Ave., Bethlehem, PA 18015

Multilayer, graded thermal barrier coatings have been fabricated using electrochemical methods. The inner two layers of the coatings are electro-deposited from aqueous baths and consist of 18 vol. % Al and 20 vol. % Al + 7 vol. % alumina, respectively, in a Ni matrix. The outer two layers are electrophoretically deposited form non-aqueous baths and contain an oxidation-resistant alumina 1 zirconia layer and a thermal-resistant yttria-stabilized zirconia outer layer, respectively. The alumina + zirconia layer was formed by reaction bonding of an aluminum-alumina-zirconia precursor powder. In addition to the details of the fabrication, the results of thermal cycling and mechanical testing of these four-layer coatings will be presented.

4:50 pm

ELECTRON BEAM PHYSICAL VAPOR DEPOSITION OF NICKEL-BASE ALLOYS USING REFRACTORY ADDITIONS: D.A. Madey, A.M. Ritter, S. Tin, M.R. Jackson, S. Rutkowski, R.A. Nardi, GE Corporate Research & Development, P.O. Box 8, Schenectady, NY 12301

Many potential applications of electron beam evaporation demand tight compositional control in the deposits and high deposition rates. Adding tungsten to nickel-based evaporation pools can increase evaporation rates and improve compositional control in deposits. Effects of tungsten addition on several alloys, NiCoAl, NiCoCr, and NiCrAl were investigated. Magnitudes of compositional gradients in the deposits, measured using electron microprobe techniques, were used to evaluate the sensitivity of vapor cloud chemistry to fluctuations in processing parameters. Compositional and microstructural gradients in quenched evaporation pools, studied using microprobe and SEM, yielded information about the evolution of steady state in the pools. Tungsten distributions in the pools, which may significantly affect temperature distribution, fluid flow, and heat transfer, were mapped using back scattered electron microscopy and energy dispersive X-ray analysis. Currently, pool surface temperatures are being mapped using an infrared imaging radiometer and effects of refractory additives other than tungsten are being evaluated.

5:10 pm

RF MAGNETRON SPUTTERING OF MOSI2+X SIC COMPOSITE THIN FILMS: S. Govindarajan, J.J. Moore, Advanced Coatings and Surface Engineering Laboratory, Dept. of Met. & Materials Eng., T.R. Ohno, Dept. of Physics, Colorado School of Mines, Golden, CO 80401-1887

A critical component of a prototype coating system being developed to protect molybdenum against high temperature oxidation (i.e. at 1600°C for 500 hours) is a functionally graded layer based on MoSi2+x SiC (where x is the variable mole fraction of SiC in the film). Different approaches for synthesizing composite films include sputtering from elemental or compound targets, reactive sputtering, and direct sputtering of composite targets. This paper will explore the feasibility of synthesizing composite films by RF magnetron sputtering of a composite target. Results of compositional depth profiling using Auger Electron Spectroscopy, microstructural evaluation and X-Ray diffraction analyses of the films will be presented. In particular, the diffusion of silicon and carbon in to the substrate will be characterized using a "ball-cratering" technique followed by auger electron spectroscopy (AES). This technique will help to overcome the disadvantages associated with ion-beam sputtering during depth profiling (e.g. different sputter yields for the constituent elements, interface broadening effects, etc.).