Internal oxidation of a nickel-based superalloy TMS-75 at 900 degrees C
Date
2012-06-29
Authors
Bill, Oleary Moshe
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Nickel-base superalloys have a wide range of use as high temperature materials of high
mechanical integrity and good oxidation resistance. In most cases where a protective external
adherent alumina scale does not develop, internal oxidation is prevalent. A study was
undertaken to investigate the internal oxidation of an experimental, single crystal, nickelbased
superalloy TMS-75 in air for 100h at 900oC. Transmission electron microscopy (TEM),
scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to
characterize the internal oxidation of this alloy. Internal oxidation was observed in the
presence of a non-protective (Ni,Co)O outer scale. Immediately beneath and in contact with
this scale was a thin layer of relatively fine grained spinel oxide inner scale. The internal
oxidation or reaction zone was located below these two scales. This zone, of around 20
micrometres in thickness, was found to have had lost its original two phase γ-γ´
microstructure, this being replaced with a relatively course grained structure containing
facetted precipitates. The precipitates were identified as being hexagonal AlN and
rhombohedral -Al2O3. A study was made of the orientation relationships between the
different precipitates and matrix. None of the precipitates were found to exhibit an epitaxial
relationship with the surrounding matrix material. The zone axes of the matrix and
precipitates were typically misaligned from a minimum of 1.5o up to about 5o. The
orientation relationships found between the AlN precipitates and the Ni-based solid solution
matrix were:
1) [013]M // [1230 ]P with (200)M // ( 0002 )P and ( 031)M // ( 2110 )P
2) [110]M // [ 0110 ]P with ( 220 )M // (1012)P within 2o
3) [ 011]M // [ 0110 ]P with ( 200 )M // (0002 )P and (311)M // (1010)P
while the orientation relationships found between the -Al2O3 precipitates and the Ni-based
solid solution matrix were:
1) [114 ]M // [ 2112 ]P with (131)M // (1011)P within 2o
2) [112 ]M // [1011]P with (153 )M // (1121)P