Biomedical Engineering Reference
In-Depth Information
From an analysis of the surface proile it can be derived that
pores penetrate to a depth of 152 to 460 nm. On the other hand,
their percentage of the entire surface of the material is 9.5% and the
largest pore diameter up to 4 μm.
Compared with the widely used medicine 316L stainless steel
(248 HV0.2), microhardness of sintered nanocrystalline austenitic
nickel-free nitrogen containing stainless steels obtained by
mechanical alloying is signiicantly higher (378 to 520 HV0.2, see
Fig. 6.8). The result is two times greater than in austenitic steel
obtained by conventional methods. This effect is directly connected
with structure reinement and obtaining of nanostructure as well
as the introduction of nitrogen. Nitrogen dissolved in austenitic
stainless steel increases its strength, which is caused by large
amount of solution hardening. The grain size hardening in N-alloyed
austenitic stainless steels is based on the grain size dependence of
the yield strength described by the Hall-Petch equation. The effect
of N content on grain boundary hardening increases proportionally
as the N content of the steel increases. Grain boundary hardening
therefore increases with increasing N content of the steel and is
related to the strong afinity between Cr, Mo and N atoms.
Figure 6.8
Microhardness of FeCrMnMoN materials [29].
As one can see from nanoindentation test (see Table 6.3),
microhardness remains on the level of 500 HV in case of Ni-free
stainless steels with nanostructure and 276 HV for 316L stainless
steel.
