Contraction also caused some distortion in the shapes of modules: over time, indentations and corners of the modules tended to became rounded (Figure 2A B).
The net extension of the piezo element, the speed, the time of indentation, the time between indentations and the number of indentations were controlled using the Asylum MFP3D software in IgorPro 6.22 platform.
By plasma-nitriding at a nitrogen pressure of 130 Pa and a nitriding power of 50 W, about 1.3 times larger indentation resistance than that of the as-sputter-etched protrusions was obtained after a long nitriding time of 14 ks.
The amorphized zone in B4C extends to a depth of almost seven times the indentation depth.
At the same time, nano-indentation investigations suppose that forest or Orowan strengthening, due to particles-dislocations interactions, is unlikely to occur.
On the other hand, an experimental limitation of our study was that the quantitative results may be affected by the properties of sound enamel as the thickness of tested materials should be at least 10 times the indentation [22]; this value was estimated to reach 45 μm in this study, which is significantly deeper compared to the nominal thickness of 20 μm of etched enamel.
The indentation time was 30 s. Indent diagonals were visually measured in optical microscopy and converted into hardness.
Figure 3 Load versus time for various indentation depths.
The indentation time was kept as 5 s for all the loads.
The output parameters such as crack length, healed crack length, hardness and fracture toughness of the samples were correlated with appropriate inputs such as contents of SiC and Y2O3, crack-healing temperature, healing time, compaction pressure, indentation load using statistical analysis.
