powder productıon and nano materıals - 6th International Powder ...

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6. ULUSLARARASI TOZ METALURJİSİ KONFERANSI ve SERGİSİ
th INTERNATIONAL POWDER METALLURGY CONFERENCE & EXHIBITION
If the mean pressure of the tribosystem is increased to 13.71 MPa the wear thickness is shown in figure 6.
Figure 6. Wear thickness vs. Number of Cycles at 13.71 MPa
Wear thickness further increases, and material SH operates 4x10 5 cycles if IT11 ISO class is required by the failure
criterion.
Equation (3) shows that the wear thickness depends on hardness of the material and on the length of the contact
area L. The length of the contact area in Powder Metallurgy may be increased by increasing the height of the disk,
by “simply” filling more powder without changing the die geometry and the compaction strategy significantly. An
increase in L changes the mean pressure (decrease) and the wear coefficient, accordingly. For instance, figure 7
shows the wear thickness in the case of a 30% larger contact length: the wear coefficient in this new situation was
extrapolated by the available data base.
Figure 7. h vs. N at 2.82 MPa (length of the contact area is increased of 30%)
The comparison between figures 4 and 7 shows that the increase in the length of the parts results in a decrease of
the wear thickness for both TH and SH. The material TH is still not able to operate for 10 6 cycles in any case. On
the other hand, material SH can operate 10 6 if the IT11 is required by the failure criterion.
As an alternative, hardness may be increased by increasing the carbon content of the material. For instance, an
increase of 60 HV in hardness can be obtained by either increasing the carbon content up to 0.7-0.8% (in the case
of TH the sintering temperature should be increased, as well, to enhance hardenability thanks to the homogenization
of the Ni distribution). In this case, the wear thickness decreases, as shown by figure 8, relevant to the lowest
pressure considered. Again, the material TH is still not able to operate for 10 6 cycles in any case. On the other
hand, material SH can operate 10 6 even if the IT10 is required by the failure criterion. The increase in hardness is
equivalent to the 30% increase in the height of the parts. The most attractive solution seems to be the increase in
hardness. The increase in carbon content slightly decreases compressibility of the powder mix but, on the other
side, the increase in height increases the part weight correspondingly. Even from the viewpoint of the cost effectiveness,
the increase in the carbon content has to be preferred.
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