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Molecular dynamics method was used to simulate and investigate the mechanical behavior of amorphous and crystalline silica during nanoindentation and uniaxial compression tests in the nanoscale. Also, the hardness and elastic moduli were experimentally checked by nanoindentation tests. The MD nanoindentation simulation results show that the amorphous silica has an indentation modulus less than the crystalline one, and the elastic strain of the amorphous silica is higher than crystalline silica. In contrast, the amorphous silica has a lower hardness. The uniaxial compression test results show that both structures have three deformation stages during the tests. The first stage corresponds to the linear elastic region; the second stage indicates the elastic-plastic region for crystalline silica, and yielding stage in the amorphous silica. The last stage corresponds to the fracture region for crystalline structure and densification for the amorphous structure. By comparing the area under stress-strain curves of the two structures, it can be concluded that the absorbed energy under external stress in the amorphous silica is three times greater than that in the crystalline one. Moreover, the nanoindentation tests of SPS samples made of amorphous and crystalline silica were performed, and the results confirmed that the crystalline silica has higher hardness and indentation modulus than the amorphous silica. Also, comparing the indentation moduli obtained by simulation and experimental tests shows that the indentation modulus predicted by simulation is in good agreement with that obtained based on experimental results.

The effects of Ni element on mechanical properties of CoSn2 phase were investigated by means of first-principles calculations and nano-indentation measurements in this work. Theoretical models of Co1−xNixSn2 (x = 0, 0.25, 0.5, 0.75 and 1) were built to research the phase stability, elastic constants and electronic structures of Ni-free and Ni-doped CoSn2 structures. Analyses about phase stability indicated that the Ni solubility in (Co,Ni)Sn2 phase could reach to 33.33 at.%. The calculated results showed that the additional Ni atoms weakened the mechanical properties of CoSn2 and the Young’s modulus decreased from 149.70 to 107.55 GPa. Besides, the ductility of CoSn2-based structures was improved after the doping of Ni. All studied crystal structures were anisotropic. The results of electronic structures demonstrated that the bonding energy of (Co,Ni)Sn2 phase decreased with the adding of Ni, which was the determinant of the decrement of mechanical properties. The experimental results obtained from nano-indentation showed that the Young’s modulus and hardness were 159.9 ± 11.3 GPa and 6.91 ± 0.65 GPa for CoSn2 while 140.5 ± 9.3 GPa and 6.23 ± 0.82 GPa for (Co,Ni)Sn2. By combining theoretical and experimental methods, it was certainly concluded that the introduced Ni element weakened the mechanical properties of CoSn2. Keywords: Intermetallic compounds, Ni additions, Nano-indentation, First-principles calculations, Mechanical properties

The physico-chemical properties of the Uranium intermetallic compound are of technological importance for improvement of the safety and compatibility of nuclear engineering systems. Diffusion couple samples with U and Cu were assembled and U-Cu intermetallic compounds were fabricated at interface by hot pressure diffusion method at a treatment temperature of 350 °C to 650 °C and at a pressure of 168 MPa in a vacuum furnace. The microstructure and element distribution of the compound phase have been studied by means of SEM, EDS, and XRD. The result showed that a new phase was developed to a thickness of approximately 10 μm with a ration of U:Cu with 1:5. Mechanical properties such as elastic moduli and hardness of the compound have been studied by means of nanoindentation. The nanoindentation testing on sample indicated that hardness of Uranium intermetallic compound are higher than that of metal U and Cu. Uranium intermetallic compound and U have a Young’s moduli with 121 GPa, 160 GPa respectively. The elastic/plastic responses of U-Cu intermetallic compound and U under nanoindentation tests were also discussed in detail.

This paper describes a new approach for the extraction of single-crystal elastic stiffness parameters from polycrystalline samples using spherical nanoindentation and orientation measurements combined with finite-element (FE) simulations. The first task of this new approach involves capturing efficiently the functional dependence of the indentation modulus on the lattice orientation at the indentation site and the unknown single-crystal elastic constants. This step is accomplished by probing the function of interest using a suitably constructed FE model of spherical indentation, and establishing a compact spectral representation of the desired function using the discrete values obtained from the simulations. Note that this function needs to be established only once for a selected crystal lattice symmetry. In the second step of the approach presented here, the unknown single-crystal elastic constants for a selected phase are estimated through a regression technique that provides the best match between spherical nanoindentation measurements obtained on differently oriented grains of that phase in a polycrystalline sample (measured by orientation imaging) and the function established in the first step. The accuracy and viability of the proposed approach are demonstrated for an as-cast cubic polycrystalline Fe–3% Si sample.

We present the results of the large-scale molecular dynamics simulations of nanoindentation of a titanium crystal. By considering three different types of the indenter, namely of square, conical and spherical shapes, we observe the dependence of deformations of the crystalline structure on the type of the indenter. Various load-displacement curves are observed for different intender types. For each case study we perform molecular dynamics simulation of a full indentation cycle, which includes the loading and unloading stages. On the basis of such simulations we evaluate elastic properties of the material, namely we calculate the hardness and Young’s modulus. We observe the dependence of the obtained values of hardness and Young’s modulus on the type of the indenter and discuss the origin of this dependence.

The correlations between the crystalline structure and mechanical properties of GaSe thin films were investigated by means of X-ray diffraction (XRD) and nanoindentation techniques. The GaSe thin films were deposited on Si(1 1 1) substrates deposited at various deposition temperatures using pulsed laser deposition (PLD). The XRD results indicate that all the GaSe thin films are pure hexagonal phase with highly (0 0 0 l)-oriented characteristics. Nanoindentation results revealed apparent discontinuities (socalled multiple ‘‘pop-in’’ events) in the load-displacement curve, while no discontinuity was observed in the unloading segment of the load-displacement curve. The hardness and Young’s modulus of GaSe thin films determined by the continuous stiffness measurements (CSM) method indicated that both mechanical parameters increased with the increasing deposition temperature with the hardness and the Young’s modulus being increased from 1.2 ± 0.1 to 1.8 ± 0.1 GPa and from 39.6 ± 1.2 to 68.9 ± 2.7 GPa, respectively, as the deposition temperature was raised from 400 to 475 C. These results suggest that the increased grain size might have played a prominent role in determining the mechanical properties of the PLD-derived GaSe thin films.

The correlation of carbonate content with enamel microstructure (chemical and crystal structure) and mechanical properties was evaluated via linear mapping analyses using Raman microspectroscopy and nanoindentation. Mappings started at the outer enamel surface and ended in the inner enamel near the dentin-enamel junction (DEJ) in lingual and buccal cervical and cuspal regions. The carbonate peak intensity at 1070 cm−1 gradually increased from outer to inner enamel. Moreover, the phosphate peak width, as measured by the full width at half maximum (FWHM) of the peak at 960 cm−1, also increased, going from ~9 cm−1 in outer enamel to ~13 cm−1 in enamel adjacent to the DEJ, indicating a decrease in the degree of crystallinity of hydroxyapatite from outer to inner enamel. In contrast, Young’s modulus decreased from 119±12 to 80±19 GPa across outer to inner enamel with a concomitant decrease in enamel hardness from 5.9±1.4 to 3.5±1.3 GPa. There were also significant correlations between carbonate content and associated crystallinity with mechanical properties. As carbonate content increased, there was an associated decrease in crystallinity and both of these changes correlated with decreased modulus and hardness. Collectively, these results suggest that enamel carbonate content and the associated change in the crystal structure of hydroxyapatite, i.e. degree of crystallinity, may have a direct effect on enamel mechanical properties. The combination of Raman microspectroscopy and nanoindentation proved to be an effective approach for evaluating the microstructure of enamel and its associated properties.

This study evaluated mechanical behavior of the intermetallic compounds (IMCs) formed at the interfaces between potential Pb-free solders (Sn-Ag-Cu and Sn-Zn) and the wires of Cu and Ag under different loading rates. Compared to Ag based IMCs, Cu based IMCs were harder and stiffer, but less strain rate sensitive. The morphology of the indent impression was found depending on the ratio of the modulus to hardness, and the crystal structure of the IMCs.