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Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 69-74). Also available via the Internet.

Thesis (Ph.D)--Materials Science and Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Preet M. Singh; Committee Member: Arun M. Gokhale; Committee Member: Miroslav Marek; Committee Member: Naresh N. Thadhani; Committee Member: Richard Neu; Committee Member: Thomas H. Sanders, Jr.. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The stress corrosion cracking (SCC) of an At ST C-1018 mild steel was investigated in three solutions, composed of 12.5 mol/kg NaOH, 3.35 mol/kg NaOH and 2.5 mol/kg NaOH + 0.42 mol/kg Na₂S, respectively. The potential of maximum susceptibility to SCC of steel in the latter two solutions was assessed by a slow strain rate technique. It was found to be slightly higher than the active-passive transition in each solution (-1.00 Vsce in 3.35 mol/kg NaOH and -0.88 Vsce in 2.5 mol/kg NaOH + 0.42 mol/kg Na₂S). A fracture mechanics technique, utilizing fatigue precracked double cantilever beam specimens, was then used to study the effects of stress intensity, temperature and electrochemical potential on crack velocity in all three solutions. Both stress intensity dependent (region I) and stress intensity independent (region II) crack velocity behavior was found. Apparent activation energies for region II of ~ 24 kJ/mol were determined at both Ecorr and -1.00 Vsce in 12.5 mol/kg NaOH. Crack velocities of the order of 10⁻⁹ m/s were measured at Ecorr in 12.5 mol/kg NaOH and at -1.00 Vsce and -0.88 Vsce 3.35 mol/kg NaOH and 2.5 mol/kg NaOH + 0.42 mol/kg Na₂S, respectively. The crack velocities measured at -1.00 Vsce in 12.5 mol/kg NaOH were of the order of 10⁻⁸ m/s. The fractography of the cracks was transgranular in 12.5 mol/kg NaOH at Ecorr. A mixed intergranular-transgranular fractography was observed at the active-passive transition in all three solutions. The results of the two techniques were compared and discussed, as was the role of stress intensity and passivation rate in fracture mechanics experiments. Anodic dissolution, hydrogen embrittlement and adsorption mechanisms were considered. It was decided that the results at Ecorr in 12.5 mol/kg NaOH could best be accounted for by a hydrogen embrittlement mechanism, perhaps assisted by anodic dissolution. Hydrogen embrittlement was eliminated as a possible mechanism at the active-passive transition in all the solutions. The most likely mechanism was thought to be one involving mixed activation-diffusion controlled dissolution. Applications of the results to the pulp and paper industry were considered. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The stress corrosion cracking (SCC) behaviour of Mg alloy AZ31B was investigated with respect to surface condition. Salt fog U-bend testing was used to identify changes in SCC as a result of surface conditioning pre-treatments. Six surface conditions were investigated: as-received, mechanically-polished, sulphuric acid (H2SO4)-cleaned, mechanically-polished then H2SO4-cleaned, aged H2SO4-cleaned, and acetic acid (C2H4O2)-cleaned. Results showed that the rate of SCC was accelerated and the SCC mode was intergranular for all surface conditioning treatments involving H2SO4-cleaning. It was found that the accelerated intergranular SCC was a result of three contributing factors: a low pH, the presence of aggressive ions, and a porous film which allowed direct contact between the metal surface and the electrolyte. Characterization of the surfaces using potentiodynamic polarization and cross-sectional images of sample surfaces showed that in the absence of one of these three contributing factors intergranular SCC would not occur. / Thesis / Master of Applied Science (MASc)

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The objective of this study was to investigate the stress corrosion behaviour of BioglassTM 4555 in order to predict the lifetime of the glass in use as a load-bearing prosthetic device. As part of this study, the development of BioglassTM and the medical tests conducted to assess the glass's biocompatibility are reviewed. The results of implant tests in laboratory animals which indicate that stress corrosion cracking of the glass may be a prohibitive factor to its use are presented. The theories of glass corrosion and stress corrosion cracking of silica based glasses are discussed and an extensive review of the literature presented. The corrosion behaviour of the glass was analysed and found to be similar to that obtained by previous workers. The depths of the corrosion layers were found to be smaller. This was attributed to alumina contamination of the glass. The fatigue parameters of the glass were measured by slow crack-growth studies and strength measurements in a corrosive solution simulating the physiological environment. The values of A and n in the equation relating crack velocity (v) and stress intensity (K1) v=AK1n, were found to be 1x10-173 and 30 respectively. Lifetime predictions for the glass were performed. It was determined that the glass was suitable for use as a prosthetic device if the maximum tensile stress encountered in vivo did not exceed 15MPa. / Thesis / Master of Engineering (ME)

The interactions between engineering materials and their environment which give rise to stress corrosion cracking are reviewed and industrial examples from the petrochemical industry are described. In one of the examples, cracking took place in carbon steel exposed to pressurised gas containing carbon monoxide, carbon dioxide and water. The crack morphology in this system was studied by metallography of samples from industrial gas processing plants and the crack growth rates were determined using precracked specimens. Constant extension rate tests, U-bend specimens and potentiodynamic studies were used to evaluate alternative materials and inhibitor additions in CO-C02-H20 environments. Electrochemical noise was accessed as a technique to monitor sec on line. It was found that the CO-C02-H20 system was characterised by a time dependent adsorption of carbon monoxide at anodic and cathodic sites. The adsorption produced a critical balance between crack tip corrosion rate and the repassivation process comparable to the behaviour at the active-passive transition zone in more conventional systems. The anodic passivation exhibited a breakdown potential near to -400 mV (Ag/ AgCI) that defined the zone of sec susceptibility. Inhibition by CO and hence sec was virtually independent of CO partial pressure provided there was a sufficient reservoir of CO. The addition of commercial film forming inhibitors did not greatly influence the system and sec was still observed in CO-C02-H20 environments to which inhibitors had been added. Steels containing alloy additions of more than 9 % chromium were found to be resistant to sec but austenitic-ferritic weld joints cracked. A low alloy 3% nickel steel performed well in the constant extension rate tests but was not wholly resistant to sec. The morphology of stress corrosion cracks in CO-C02-H20 mixtures was influenced by carbon monoxide partial pressure. More corrosion was observed on the crack walls at low carbon monoxide partial pressure and widened cracks resembling •mesa• corrosion were common. This increased corrosion was probably due to difficulty in maintaining passivity in the crevice formed by the growing crack. Similarly, crevicing in precracked specimens appeared to inhibit sec and no crack extension was observed. Electrochemical noise proved to be a useful tool for monitoring. / Thesis (PhD)--University of Pretoria, 1994. / gm2013 / Materials Science and Metallurgical Engineering / PhD

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