SUMMARRY
PM2000 is a mechanically alloyed, Ni-base ODS alloy. Excellent high
temperature strength makes it a strong candidate for application in high
temperature industrial processes. In order to exam its useful for high
temperature structural components in which the Pm2000being in contact and
from interface with plainvarbon steel, the oxidation behaviour of PM2000
and plain carbon steel, in terms of the oxides morphology and effect of the
plain carbon steel on the oxidation behaviour of PM2000, also the influence
of the elements migrating between the substrate and mild steel will be the
point of study after different oxidation temperature, using several
techniques: SEM, optical microscopy.
The isothermal behaviour of this component has been examined in air at
1200C for exposure times up to 3hr. Different shapes and positions, also at
some stages of this work it was necessary to use another PM2000 sample to
be in contact with the original PM2000 sample, During exposure all the
samples formed an external scale of alpha alumina (a-Al203). The growth
rate of the scale on the interface area between the PM2000 and Plain carbon
steel samples was significantly faster than that formed on un covered area
of PM2000, resulting in an oxide layer which was about twice as thick after
(1- and 3hr). The oxide grain morphology on the cross-section area of the
interface between the samples was essentially equiaxed containing
irregularly shaped, discontinuous titanium-rich particles, whereas the oxide
formed on uncovered area was slightly finer, clearly alumina and contained
elongated Cr-rich particles. Spalling of the oxide layer occurred after
approximately 1 hr in the centre of the area, probably due to the separation
of the Plain carbon steel from the substrate of PM2000 during the work,
whereas an spalling observed on PM2000 and Plain carbon steel substrate
when a another PM2000 sample used to be contacted with it, Fe oxide
showed rapid growth at the interface area, in another word, the oxidation
behaviour of the joint between PM2000 and Plain carbon steel for (1 & 3 hr)
showed same behaviour of the PM2000 individual at high temperatures and
long term up to (200 hr) Experiments revealed that the initial surface
roughness of PM2000 can contribute significantly to spalling by enabling the
growth of highly convoluted scale layers which are mechanically unstable
under compressive stresses (buckling).
Internal oxidation is also observed in PM2000 substrate after exposure. The
internal oxidations were generally spherical with small Fe, Cr and Al- rich
particles distributed over their internal surfaces.
Ca oxide has been observed as a discontinues layer at the interface,
this particle has been examine, the results showed that Ca oxide
probably diffused from the furnace itself to the substrate or due to the
impurity of the upper surface of Plain carbon steel