dissertation global and local fracture properties of metal matrix ...

Section 7
Table 7.3. Data on measured CODi-values for the PM-MMC Al6061-20%Al2O3 in as-
fabricated condition and after 7 ECAP.
Data for the as-fabricated MMC
A particle cluster area
Number
of profile
CODi-values
[µm]
An area with local
homogeneous particle
Number
of profile
distribution
96
CODi-values
[µm]
Data for the MMC after 7
Number of
profile
ECAP passes
1 0.5 1 3.0 1 2.5
2 0.2 2 2.5 2 2.0
3 0.5 3 2.0 3 3.0
4 0.2 4 2.0 4 2.0
CODi-values
[µm]
5 2.5
6 2.0
7.5. About possible application of ECAP to improve the particle distribution in different
MMCs
As one can see from the results of our investigation, the ECAP can be useful as an additional
operation during the secondary processing of MMCs produced by powder metallurgy
technology to increase the uniformity of particle distribution. The required number of ECAP
passes can be easily calculated by Eq. 7.8. The ECAP can be employed as a last procedure of
fabrication of MMCs as well as the ECAP and extrusion can be combined during the
fabrication of MMCs. It should be noted that the ECAP does not degrade the microstructure
of the investigated material: no void formation and no particle breaking in the case of small
particles are observed in the sample interior, but due to the occurrence of surface defects, the
number of ECAP passes is limited. The application of heat treatment between the consecutive
ECAP passes to relax the stresses in the sample could solve this problem.
Although no investigations of the influence of ECAP on the uniformity of particle distribution
in cast MMCs have been undertaken, our results suggest that the ECAP might be useful in this
case too. Indeed, the difficulty of achieving a homogeneous distribution of reinforcement in