Thermal barrier coating life prediction model development

service failures can have severe economic consequences for the operating company, m

additionto the risk caused to personnel. This outlines oil production and utilities systems and r o v i ~ the metallurgical failures experienced by one North Sea operator over the last ten years, describing actionstakento prevent further incidence. 6 refs. L i q u i d b r e e d e r materials. Taw, H., Malang, S., Reit~, F. and Sennier, J. J. Nucl. Mater. J u l y (11) 1 9 8 8 , 1 r ~ - - 1 8 7 A , 1 7 8 - 1 8 7 The potential and limitations of a particular breeder material for application in a fusion reactor device depend, to a large extent, upon the ability of the reaeamh community to generate suitable designs, develop efficient tritium extraction systems and solve the major materials problems. Design. T extraction and material compatibility issues are discussed for blankets (SS316. 316L. 4914. vanadium alloys) based on the eutectic Pb-17Li, pure Li and. to a lesser extent, molten selta and aqueous salt solutions. In spite of the relatively limited research effort evolved, liquid breeder blankets continue to be attractive solutions for T generation. However, the experimental programs need to be extended and include more integrated experiments. 62 refs

Fatigue r e s i m n c e a n a l y s i s o f c o r r o d e d w i r e . Sesaki, Y., Kiuchi, A. and Shinke, T. Kobeico Technol. Ray, 1 5 - 1 8 Aug. 1988, (4) Fatigue strength of corroded galvanized steel wires was investigated, both experimentally and analytically, for the purpose of estimating the residual life of parallel wire strand cables new in use. Three kinds of wire specimens with different degrees of corrosion were prepared by salt spray testing. The periods of SST were 50. 100 and 150 days. Fatigue strength tensile strength, and reduction ratio of sectional area of these wires, according to the respective SST period, were clarified experimentally. Taking these results into account. adequate formulations of fatigue strength of corroded wires at 2 x 1(7=cycles are presented using the Weibull distribution. 15 refs.

General Thrust chamber thermal barrier coating techniques. Quentrneyer, R.J. NASA Tech. Memo. TM-I00933 1988 Methods for applying Thermal barrier coatings to the hot-gas side wall of rocket thrust chambers to significantly reduce the heat transfer in high heat flux regions has been the focus of technology efforts for many years. A successful technique is developed by the Lewis Research Center that starts with the coating on an AI mandrel and then builds the thrust chamber around it by electroforming Cu This results in a smooth coating with exceptional adherence, as has been demonstrated in hot fire rig tests. The low cycle fatigue life of chambers with coatings applied in this manner has been increased dramatically compared to uncoated chambers, 20 refs.

Isothermal and 'bithermal" thermomachanical fatigue behavior of a NiCoCrAIY-coated single crystal superalloy. Gayda, J., Gabb, T.P. and Miner, R. V NASA Techn, Memo. TM-100907 1988 Specimens of single crystal Ni base superalloy PWA 1480 with <001 > orientation, bare or with NiCoCrAIY coating PWA 276, were tested in low cycle fatigue (LCF) at 650, 870, and 1050°C. and in simplified 'bithermal' thermomechanical fatigue (TMF) tests bel:ween these temperatures, These tests were examined as a bridge between isothermal LCF and general TMF On a k i n basis, isothermal LCF life of bare crystals exhibited classic dependence on ductility, decreasing with temperature from 1050-650"C Coated crystals exhibited the same life at 1050"C, but at 650"C, cracks initiating in the coating reduced life in the Iow-~,si,. long-life regime. Life for various bithermal TMF tests in the high-ruEn regime was also controlled by ductility, and approached the life exhibited for isothermal LCF at the Tminof the cycle. However, in the Iow-AEin regime, the OP bithermal test (which imposes tension at Train) reduced lives of both bare and coated crystals, and drastically so. for the 650-1050°C cycle. Surface cracks initiated and propagated rapidly in the 65(~1050"C OP cycle. Damage mechanisms in the low-tUrin regime for OP bithermal test were different, however, for bare and coated crystals. A 650-1050°C OP vacuum test of a bare crystal was discontinued after 10000 cycles, five times the life observed in air tests, without evidence of cracking. Yet. coated crystals tested in vacuum formed cracks through the coating nearly as fast as those tested in air. The total OP bithermal lives of the coated crystals were. however, longer in vacuum than in air tests, due to slower crack entry and propagation through the crystal itself Additional tests illustrated the effects of other OP bithermal cycle variables on the life of coated crystals in air. As expected, life decreased with increasing AT, increasing Tmax. and decreasing Tmin, since, respectively, they increase the ductility of the crystal (in the range 650-1050°C). Time at Tm,x, however, had only a small detrimental effect, 14 refs b a r r i e r c o a t i n g l i f e p r e d i c t i o n m o d e l d e v e l o p m e n t . Cruise, T.A., Stewar~ S.E. and Ortiz, M. J. Eng. Gas Turbines Power (Trans. ASME) Oct. 1988, 110, (4), 6 1 0 - 6 1 6

Thermal

Ceramic thermal barrier coating tests show that the coating fails by ceramic spalletion, Analysis of life data indicates that cyclic thermal loading and thermal exposure play synergistic roles in controlling the spellatlon life of the coating. A life prediction algorithm has been developed, based on a damage accumulation algorithm that includes both cyclic and time-dependent damage, The cyclic damage is related to the calculated cyclic inelastic strain range in the ceramic coating: the time-dependent damage is related to the oxidation kinetics at the bond/cerernic interface. Cyclic inelastic strain range is calculated using a modified form of the Walker viscopieatic material model. Calculation of the oxidation kinetics is based on traditional oxidation algorithms using experimentally determined parameters. A relation between oxide growth and cycle parameters was derived from test data. The life prediction model was evaluated by predicting the lives of a set of thermal cyclic tests whose heating and cooling rates were significantly greater than those used to correlate the life parameters. Correlation between the actual and predicted spallation lives is within a factor of three. This is judged to be satisfactory, relative to fatigue life prediction scatter in metals (B1900 + Hf Ni superalloys). 4 refs.

One-minute CBN hard-finishing. Am: Mech. Autom. Manuf J u l y 1988, 132, (7), 1 2 4 - 1 2 5 Advantages of precision finishing of steal gear teeth after case hardening are discussed. Methods for using faster cutting cubic-boron-nitride abrasives are described Results

Int J Fatigue May 1989

obtained from an eiectropleted abrasive coating on a worm wheal type cutter are discussed. An automated finishing machine, developed for use with this cutter, is described, A high pressure coolant system is discussed,

Method of heat treating b e a r i n g m a t e r i a l s ( P a t e n t EP0241ar~W). Btyda, K.A., Lanner, G., Stu~r~n, R.W. and Yahraus, W.A. Aus. Eur. Patentanmeld. I 9 Dec. 1987, 3, (50), 2 9 1 0 An improved method of prOducing a powered metal AI base bearing material is provided. A bearing strip composed of three layers of sintered Ai base particles which has been roll clad to a rapid backing layer is subjected to a heat treatment procedure in a continuous manner at a temperature of from about 700 to about 900 F for at least 30 s and then cooled at a rate of at least 100 F/h Bearings made from the resulting material show dramatic fatigue life improvement in comparison to that obtainable with currently available powdered metal AI bearing materials.

A c r i t i c a l r e v i e w o f p r e c i p i t a t i o n behaviour in 1 C r - M o - V r o t o r steels Senior, B.A. Mater. Sci. Eng. A Sept. 1988, A 1 0 3 , (2), 263-271 Precipitation in 1 Cr-Mo-V rotor steels is reviewed with respect to crystal structure, composition. nucleation behaviour and morphology In addition, the effects of ageing on precipitation are described, and the major effects of ageing on precipitation are described, and the major effects of tensile and cyclic deformation discussed. Where data relating to 1CrMo-V are not available, reference has been made to work in which similar steals have been examined 57 refs

Elastic strain energy analysis of the dislocation structures in fatigue. Kwon, LB., Fine, M.E. and Mute. T Acta Metal/. Sept. 1988, 36, (9), 2 8 0 6 - 2 6 1 4 The dislocation structures which evolve during fatigue have been investigated in terms of the elastic strain energy Mathematical models for the configuration of dislocation dipoles such as the ladder structure and vein structure are introduced. The elastic strain energy for these models is calculated and evaluated using the eigen strain method. This analysis may provide insight as to why persistent slip bands in fatigued Cu are created after the vein structure reaches a certain stage and why persistent slip bands consist of ladder rungs with an equal spacing of approx 1.3 Ira1at room temperature. 13 refil. F a t i g u e damage accumulation in nickel modified by ion beam s u r f a c e m i c r o a l l o y i n g . Grumrnon, D.S., Jones, J.W. and Was, G.S. Metal/. Trans. A Nov. 1988, 1 9 A , (11 ), 2 7 7 5 - 2 7 8 8 The formation, distribution, and surface morphology of persistent slip band (PSB) structures have been studied in polycrystalline Ni with ion beam microalloyed Ni-AI (nickel 270 alloy) surface layers Both supersaturated solid solutions of AI in Ni and 7-7 dual-phase structures were formed on surfaces of low cycle fatigue specimens by ion beam mixing vapour-deposited Ni and AI layers, using 1 x 10 '6 ions/cm2 of Kr + at 0.5 MeV, When cycled to saturation at constant plastic strain ranges between 6 x 10-~-7 x 10 -~ ion beam modified specimens showed a retardation in the appearance of PSBs at the surface. and a reduction in their numbers and intensities at cyclic saturation. Slip bands that eventually emerged at ion beam modified surfaces displayed morphological features which differed sharply from the PSB notch-peak topographies usually found in fatigued fcc metals, Further, it was found that subsurface strain localization occurred in the presence of the modified surface layer, generating PSBs in the bulk which extended the underside of the layer, but did not penetrate it. This behaviour may be understood in terms of the resistance of the surface layer to plastic deformation, and the localized stresses produced in the surface film as a result of subsurface strain localization. 27 refs.

Strain softening, grain boundary migration and dynamic recryatalllzation of nickel during high temperature low c y c l e f a t i g u e . Chen, S. and Gottatein, G. Acta Metall. Dec. 1988, 36, (12), 3093-3101 The flow stress behaviour and microstructura[ development of Ni polycrystals during high temperature low cycle fatigue were studied. All specimens exhibited a flew stress decrease at large cycle numbers, even at total strain amplitudes as IoN as 0.4%. but distinctly before crack initiation. The microstructure revealed a tendency toward grain coarsening due to grain boundary migration, but Iocatly grain refinement owing to dynamic recwstallization is the major softening mechanism at large cumulative strains end the cause of the observed flow stress maximum. Observation on AI, which does not recrystallize dynamically, support this conclusion, After large cycle numbers, the dislocations were arranged in a well recovered ceil structure, and the average cell size scaled with the reverse flew stress. The results substantiate that dynamic recrystallization can be set off at drastically lower stress in cyclic deformation than in monotonic deformation. This supports the stipulation that occurrence of dynamic recystatlizetion is nucleation controlled. 25 refs.

Irradiation effects F a t i g u e l i f e of helium-implanted AISI 316L at 500 and @(X)'C. Leeser, A. and UIImaier, H. J. Nucl. Mater. J u l y (11) 1988, 15rP-1§TB Fatigue tests of helium-implanted AISI 316L (CHe approx 600 appm) were carried out at 500 and 600"C Nf, the number of cycles to failure, was determined for different frequencies and total strain ranges Whereas at high frequencies He did not influence the fatigue beheviour, a drastic reduction in fatigue life, a change of fracture mode from transgranular to intergranular, and a different structure of surface cracks were observed below a critical frequency v c (approx 3 Hz at Co00°C) TEM revealed that in this case the mean bubble size in grain boundaries in implanted and fatigued specimens was larger than in those which have been implanted only Lower temperature and MC-strengthening (JPC Alloy 8206) reduce the critical frequency and the magnitude of the drop in fatigue life These results agree qualitatively with a model of high temperature embrittlement by Trinkaus 12 refs i n f l u e n c e of light ion irradiation on fatigue crack propagation in a u s t e n i t i c s t a i n l e s s s t e e l . Fen/c/, P. J. Nucl. Mater. J u l y (11) 1988, 1EE-lb'TB, 9 6 3 - 9 6 7

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