indicates that the data in Figure 11.6 demonstrate, for the example of palladium,
only a trend and not the actual correlation.
11.2.2
Influence of Grain Size
A comparison of the strength of nanocrystalline and conventional materials with
grain sizes in the micrometer range shows that the yield stress of nanocrystalline
materials is found at significantly higher values. A comparison of the stress–strain
diagrams for palladium of 50 mm and 14 nm grain size is shown in Figure 11.7.
Figure 11.6 Relationship between grain size and porosity for the specimen used for the
mechanical measurements plotted in Figure 11.5. It is clear that, especially for palladium, the
grain size was far from constant [5].
0
0.005
0.01
0.015
0.02
0.025
0
100
200
300
strain Δl/l
stress [MPa]
Figure 11.7 Comparison of the stress–strain diagram of palladium with different grain sizes.
Note the significant increase in yield stress and reduction in Young’s modulus for the
nanocrystalline material in comparison with the coarse-grained material [6].
304j 11 Mechanical Properties of Nanoparticles