Chemical and morphological changes at Al{sub 2}O{sub 3}/NiAl interfaces and their relationship to scale adhesion
Ni-(40,50)at%Al alloys with different C and S contents were oxidized at 1000-1150 C for various times in oxygen. Auger electron microscopy was used to study the interface chemistry after scale spallation in ultra high vacuum. The interfacial failure stresses were determined with a tensile pull tester and they were related to the interfacial pore density. Results show that sulfur did not segregate to the Al{sub 2}O{sub 3}/Ni50Al interface even after extended oxidation times. Small amounts, however, segregated to the Al{sub 2}O{sub 3}/Ni40Al interface. The difference in behavior may be related to the surface energy difference between Ni50Al and Ni40Al. On the interfacial void faces of Ni50Al, C first segregated, then it was replaced by S after longer oxidation times; the amount of segregants varied with different crystallographic orientation of the void face. On Ni40Al, S segregated much earlier on the void faces due to a faster diffusion rate in the Ni-rich NiAl. The apparent S diffusivity in Ni50Al and Ni40Al at 1000 C was determined to be 10{sup -9} and 6 x 10{sup -9} cm{sup 2}/s respectively. Excess sulfur in Ni40Al greatly increased the interfacial pore density. Preliminary results on interfacial failure stress showed that it decreased with increasing pore density, regardless of whether S was present at the interface, indicating that the major detrimental effect of S on scale adhesion may be to enhance interfacial pore formation.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Director. Office of Science. Basic Energy Sciences (US)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 823940
- Report Number(s):
- LBNL-52664; R&D Project: 503001; TRN: US200417%%51
- Resource Relation:
- Conference: ECS Spring meeting, Symposium High Temperature Corrosion and Materials Chemistry, IV, Paris (FR), 04/27/2003--05/02/2003; Other Information: PBD: 15 Mar 2003
- Country of Publication:
- United States
- Language:
- English
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