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. was evaluated with c3rrosion fatlgue tests This material was compared witn 2124.T851 in ory helium ana hydrogen-bearing atmospneres of dry nydrogen and water vapor saturated He Tne mcrostructures of both a:,oys were characterize0 using microscopy witn mage ana ys s The monotonic mechanical propenies were determined by tensife testing BotP 8090-T8 and 2124-1851, in snort transverse orientation. suffereo loss of dLctiIdy from the presence of large precipitate partcles This was more severe tor 8090.T8. Fatqgue crack inittat,on specmens were eVaiJa!ed ;sing replicas and SEM examination Atmosphere anb stress amplitdoe were variables Tne env,. ronments were ory He. dry H. and saturated He at ambient temperatures Tne response of tne a loys to these environments was evaluated ~y qualitative observation of slip bands, Sdace crack count. a?v3 numDe. of cycles 13 failure LOW cyc8e corrosion fatig-e tests prov.ded data for evaluating strain haroen ng cnaracteristics and determining the fat,gue strengtn. ductility. and cyclic strengtn con. stants Fatigue performance tn inert and nydrogen-bearing env ronments was compared over a range of strain amplitudes. The variation of fat,gce o,cti. t y coeflicients an0 exponents with environment aggressiveness clearly snows effects by environment on strain controlled fatlade behavior. e.g the fatigue ductility exponents changed Dy 50". or more between Ory an0 saturated He Loaa control.ed fatigue under fully reversed loadinq in ory He. H. or Saturated he, provlded S N pots to illustrate tne effects of aggressive environments. The presence of water vapor decreased the fat1gt.e life 01 8090-T8 Dy an order of magnituoe at iow stress amp Itudes The fatigue life of 2124-T851 decreased in dry H. but was unaffecteo .n satJrated He. At hlgh stress ampdtudes. 2124-T851 is superior to 8090-T8 in ail tested environments At low stress amplitudes. 8090-T8 is superior in dry environments In saturated He. 2124.T851 is superior at all stress amplitudes A mWei was proposed to rationalize the Observed effects 01 the aggressive hydrogenoLs atmosphere This model suggests that panicle-matr#x decoheston is ennanceo in the aggressive e-vironmeT!s If tnis is true, then part cle-matrix decohesion wodld occur at smaller panicles than in men atmospheres. Decohesion would m n t nue to occur at large panicles (AAD93-12615) 0 H Hilliard (Jniversity of IOahOj. DISS. Abstr lnt . June 1993. 53. (12). N P.. [in English]. ISSN 0419-4217 95-0162 The Characterization of the Coarsening of Dealloyed Layers by EIS and Its Correlation With Stress-Corrosion Cracking. (Conference Paper).
The origin of the reversibility of the environmental embrittlement of an Ag-20 at.% gold alloy in 1 M HC104 has been investigated. The structure of the porous Au layer formed on this alloy under potentiostatic polarization has been studied by electrochemical impedance spectroscopy (EIS). In the as-dealloyed state. a 50 pm layer has impedance behavior electrically equivalent to a layer containing 10" cylindrical poresicm2 (geometric area) each with a radius of 9 nm. Upon aging. the pores closest to the substrate coarsen first. destroying the ability of the layer to inject a brittle crack into the uncorroded substrate. This change in structure is Observable as a change in the low-frequency portion of the impedance spectrum. The observed potential dependence of this coarsening indicates that it occurs due to surface diffusion of Au atoms. Photomicrographs. Spectra. Graphs. 21 ref.
R.G. Kelly (University of Virginia). A.J. Young (UMIST). R.C. Newman (UMIST). Electrochemical Impedance: Analysis and Interpretation [Roc. Conl.],
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## 96-0475 Environmental effects on crack Initiation In bollw t W . (Cow ference Paper). Corrosion fatigue is one of the main causes of boiler tube failures h fossil fuel power plants As part of a wide-ranging study into the phenomenon, lnboratory investigations have been performed to examine the