Microstructural Characterization of Oxides Formed on Model Zr Alloys Using Synchrotron Radiation

To understand how alloy chemistry and microstructure impact corrosion performance, oxide layers formed at different stages of corrosion on various model zirconium alloys (Zr-xFe-yCr, Zr-xCu-yMo, for various x, y) and control materials (pure Zr, Zircaloy-4) were examined to determine their structure and the connection of such structure to corrosion kinetics and oxide stability. Microbeam synchrotron radiation diffraction and fluorescence of oxide cross sections were used to determine the oxide phases present, grain size, and orientation relationships as a function of distance from the oxide-metal interface. The results show a wide variation of corrosion behavior among the alloys, in terms of the pretransition corrosion kinetics and in terms of the oxide susceptibility to breakaway corrosion. The alloys that exhibited protective behavior at 500°C also were protective during 360°C corrosion testing. The Zr-0.4Fe-0.2Cr model ternary alloy showed protective behavior and stable oxide growth throughout the test. The results of the examination of the oxide layers with microbeam X-ray diffraction show clear differences in the structure of protective and nonprotective oxides both at the oxide-metal interface and in the bulk of the oxide layer. The nonprotective oxide interfaces show a smooth transition from metal to oxide with metal diffraction peaks disappearing as the monoclinic oxide peaks appear. In contrast, the protective oxides showed a complex structure near the oxide-metal interface, showing peaks from Zr3O suboxide and a highly oriented tetragonal oxide phase with specific orientation relationships with the monoclinic oxide and the base metal. The same interfacial structures are observed through their diffraction signals in protective oxide layers formed during both 360°C and 500°C corrosion testing. These diffraction peaks showed much higher intensities in the samples from 500°C testing. The results for the various model alloys are discussed to help elucidate the role of individual alloying elements in oxide formation and the influence of oxide microstructure on the corrosion mechanism.

[1]  A. Motta,et al.  Corrosion Behavior of Model Zirconium Alloys in Deaerated Supercritical Water at 500°C , 2007 .

[2]  A. Motta,et al.  Advanced Corrosion-Resistant Zr Alloys for High Burnup and Generation IV Applications , 2006 .

[3]  A. Motta,et al.  Zirconium alloys for supercritical water reactor applications: Challenges and possibilities , 2006 .

[4]  A. Motta,et al.  Transmission electron microscopy examination of oxide layers formed on Zr alloys , 2006 .

[5]  Martine Blat,et al.  Comparison of the High Burn-Up Corrosion on M5 and Low Tin Zircaloy-4 , 2006 .

[6]  Arthur T. Motta,et al.  Microstructure and Growth Mechanism of Oxide Layers Formed on Zr Alloys Studied with Micro-Beam Synchrotron Radiation , 2005 .

[7]  B. Cox,et al.  Some thoughts on the mechanisms of in-reactor corrosion of zirconium alloys , 2005 .

[8]  B. Lai,et al.  CHARACTERIZATION OF OXIDES FORMED ON MODEL ZIRCONIUM ALLOYS IN 360°C WATER USING MICRO-BEAM SYNCHROTRON RADIATION , 2005 .

[9]  Y. Chu,et al.  Corrosion of zirconium-based fuel cladding alloys in super critical water. , 2005 .

[10]  J. Szpunar,et al.  A model of texture formation in ZrO2 films , 2004 .

[11]  B. Lai,et al.  Structure of zirconium alloy oxides formed in pure water studied with synchrotron radiation and optical microscopy: relation to corrosion rate , 2004 .

[12]  O. Delaire,et al.  Observation of second-phase particles in bulk zirconium alloys using synchrotron radiation , 2001 .

[13]  M. Lallemant,et al.  In situ XRD analysis of the oxide layers formed by oxidation at 743 K on Zircaloy 4 and Zr–1NbO , 2000 .

[14]  Jean Senevat,et al.  Influence of Composition and Fabrication Process on Out-of-Pile and In-Pile Properties of M5 Alloy , 2000 .

[15]  P. Barbéris,et al.  Multi-Scale Characterization of the Metal-Oxide Interface of Zirconium Alloys , 2000 .

[16]  A. Frichet,et al.  Characterization of Zircaloy-4 oxide layers by impedance spectroscopy , 1999 .

[17]  M. Lallemant,et al.  Phase analysis by variable-incidence X-ray diffraction: Application to zirconium oxidation , 1997 .

[18]  B. Hutchinson,et al.  A theory of the resistance of Zircaloy to uniform corrosion , 1994 .

[19]  J. Godlewski.  How the Tetragonal Zirconia is Stabilized in the Oxide Scale that is Formed on a Zirconium Alloy Corroded at 400°C in Steam , 1994 .

[20]  M. Lambertin,et al.  Raman Spectroscopy Study of the Tetragonal-to-monoclinic Transition in Zirconium Oxide Scales and Determination of Overall Oxygen Diffusion by Nuclear Microanalysis of O 18 , 1991 .

[21]  M. G. Balfour,et al.  Development of a Cladding Alloy for High Burnup , 1989 .

[22]  R. Garvie,et al.  Stabilization of the tetragonal structure in zirconia microcrystals , 1978 .

[23]  G. Sabol,et al.  The Origin of the Cubic Rate Law in Zirconium Alloy Oxidation , 1975 .

[24]  K. K. Srivastava,et al.  Martensitic transformation in zirconia , 1974 .

[25]  P. Nicholson,et al.  Phase Analysis in Zirconia Systems , 1972 .

[26]  G. David,et al.  Etude de la croissance de l'oxyde sur le zirconium et le zircaloy-2 , 1971 .

[27]  P. Lacombe,et al.  Influence de l'orientation de monocristaux de zirconium sur les textures de croissance de la zircone monoclinique , 1971 .

[28]  P. Heuer,et al.  The influence of oxide stress on the breakaway oxidation of zircaloy-2 , 1970 .

[29]  C. Roy,et al.  X-ray diffraction analyses of zirconia films on zirconium and zircaloy-2 , 1970 .

[30]  B. Cullity,et al.  Elements of X-ray diffraction , 1957 .