Chemical and morphological changes at Al{sub 2}O{sub 3}/NiAl interfaces and their relationship to scale adhesion

Conference · Sat Mar 15 04:00:00 EST 2003

OSTI ID:823940

Hou, Peggy Y ^[1]

---

1. LBNL Library

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: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Director. Office of Science. Basic Energy Sciences (US)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 823940
• Report Number(s): LBNL--52664
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ADHESION
ALLOYS
CHEMISTRY
CORROSION
DIFFUSION
ELECTRON MICROSCOPY
MORPHOLOGICAL CHANGES
ORIENTATION
OXIDATION
OXYGEN
SPALLATION
STRESSES
SULFUR
SURFACE ENERGY