Nanoindentation of Macro‐porous Materials for Elastic Modulus and Hardness Determination

Effects of Micro-Arc Oxidation Process Parameters on Characteristics of Calcium-Phosphate Containing Oxide Layers on the Selective Laser Melted Ti13Zr13Nb Alloy

“…Young's modulus was higher for all specimens treated under 200 V with the highest value equal to 80.94 ± 6.71 GPa obtained during the MAO process in 50 mA conditions, while specimens treated at 300 and 400 V showed the significantly decreased Young's modulus. The results are in line with the literature, where the lowest values of Young's modulus and hardness correspond to materials with less dense microstructure and the highest levels of porosity [65][66][67][68]. The MAO process carried out at 400 V indicated from two to four times bigger pore size compared to the MAO process at 200 V. Similarly, Souza et al [69] suggested that the elastic modulus obtained for porous film was related to the actual elastic response of the film.…”

“…According to the literature, to minimize the effect of the substrate, the indenting should be provided to a maximum depth (h max ) less than 10% of the coating thickness (t f ) (h max /t f < 0.1) [37], and some authors indicate 20% of the film thickness for the porous thin ceramic films (h max /t f < 0.2) [78], while others pointed out that for hardness measurements, the substrate effect would be relatively small as long as the indentation depth would be below 50% of the film thickness [79]. On the other hand, taking into consideration the roughness effect, the elastic modulus results are more consistent and reproducible when the indentation depth is bigger, in the range of 10%-20% of the film thickness [65], since when the indenter tip is similar to the value of the surface roughness, the stresses at the initial point are much greater and result in variability in the first stages of indentation [80]. It can be noticed that in our research all MAO coatings fulfill the relations h max /t f < 0.5, while MAO_300 and 400 fulfill the relations 0.1 < h max /t f < 0.2, which according to the literature should improve the reliability of the film-only properties.…”

Production and Properties of the Porous Layer Obtained by the Electrochemical Method on the Surface of Austenitic Steel

“…Surface roughness could induce underestimation of E and H at shallow indentation depth (i.e., small load) [ 65 , 66 ]. The highest values of the Young’s modulus were obtained for 316L and sample I, which at the same time revealed the lowest value of layer thickness, with a heterogeneous structure of the layer and the largest pore diameter.…”