The internal oxidation behaviour of Ni-base and Fe-base alloys containing approximately 5 at% Al and both with and without low concentration Cr additions in flowing low-oxygen atmospheres at 1273 K was studied. There were two groups of Febase alloys; ferritic alloys that were Fe-Al-Cr and others that also contained approximately 9.3 at% Ni in order to make them austenitic. Ni?base alloys were oxidised in oxygen partial pressures of either 4.6 ?? 10-11 atm or 9.8 ?? 10-13 atm and Febase alloys were oxidised in an oxygen partial pressure of 1.2 ?? 10-16 atm The aim of this investigation was to examine the effect of internal oxidation on Fe- and Ni-base alloys containing Al or Al with Cr. The morphology of the precipitates formed and rates of reaction were of interest. Oxidation of the ferritic Fe-base alloys produced internal oxidation only at lower solute concentrations. In these alloys steady state diffusion-controlled precipitation was prevented from occurring due to the formation of an oxide barrier at the reaction front, and cracking off of the internal oxidation zone. In all of the austenitic alloys (Ni-base and y-Fe-base) internal oxidation was observed after all exposures. In y-Fe-base alloys and in Ni-base alloys oxidised at the higher oxygen partial pressure (4.6 ?? 10-11 atm) precipitation zones were found to widen according to parabolic kinetics, indicating diffusion control. In Ni-base alloys oxidised at 9.8 ?? 10-13 atm, precipitation zones were observed to widen according to parabolic kinetics up to 40.9 hours. However, the rate slowed for longer reaction times due to coalescence of precipitates at the reaction front. The rate of internal oxidation decreased with increasing Cr, and thus total solute, concentration. The parabolic rate constants measured for internal oxidation were higher than predicted by Wagner's theory of internal oxidation, which is consistent with observations in previous studies. Kinetics were accelerated by the presence of elongated precipitates, aligned approximately normal to the alloy surface. Chromium alloy additions led to precipitate coarsening, and at lower oxygen partial pressures, to loss of elongated morphology. The precipitates formed were found to be a mixture of M2O3 and AM2O4, where M represents either Al or Cr, and A represents either Fe or Ni. Both oxide forms were detected at all depths within the internal oxidation zone. However, Cr-containing oxides were limited to the part of the internal oxidation zone closer to the alloy surface, while Al-containing oxides were present at all depths. This is consistent with thermodynamic predictions.

Zugl.: Karlsruhe, Univ., Diss., 2007

Thesis (Ph.D.)--Murdoch University, 2003. / Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 190-209.

Thesis (Ph. D.)--University of Delaware, 2008. / Principal faculty advisor: Charles G. Riordan, Dept. of Chemistry & Biochemistry. Includes bibliographical references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 107-111). Also available via the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 116-119). Also available via the Internet.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references (p.113-116).

Zugl.: Ulm, Univ., Diss., 2007

Mémoire (M.Sc.T.)--Université du Québec à Chicoutimi, 2002. / Document électronique également accessible en format PDF. CaQCU

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves 120-121).