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Mechanical Properties of Diamond, Diamond Films, Diamond-Like Carbon and Like-Diamond Materials
Published in Mark A. Prelas, Galina Popovici, Louis K. Bigelow, Handbook of Industrial Diamonds and Diamond Films, 2018
The composite hardness expressions incorporate the dependence of hardness on load at small indentation sizes, the so-called “indentation size effect” (ISE) and a “plastic zone size term”, to account for (indentor imparted) deviations from the spherical cavity approach. The load bearing profile under an indentor on a stiff film is likely to be non- uniform as well, with further adjustments necessary for substrate materials with a low yield stress to Young’s modulus ratio (σy/E). All these effects need be incorporated in the value of the interface parameter, α, which is to be experimentally determined for each material.
Evaluating the irradiation hardening of reactor pressure vessel steels by nanoindentation hardness test and micropillar compression test
Published in Journal of Nuclear Science and Technology, 2022
Yuyang Zheng, Diancheng Geng, Hao Yu, Sosuke Kondo, Akihiko Kimura, Hideki Yuya, Ryuta Kasada
Nanoindentation hardness tests are the most fundamental and conventional USTTs used because they can evaluate the changes in hardness and elastic modulus without the need for micro-specimen fabrication on the ion-irradiated surface. However, at the micrometer and sub-micrometer scales, it has been often observed in various materials that the hardness increases with decreasing in the indentation depth, as known to be the indentation size effect (ISE). The mechanism of ISE has been well explained by the Nix-Gao model [10]. One of the authors proposed the extended Nix-Gao model to estimate the bulk-equivalent hardness from the depth-dependent nanoindentation hardness [6]. Although this method has been widely used in ion-irradiated materials, including RPV steels [11–13], further studies are required to determine the relationship between the bulk-equivalent hardness and traditional Vickers hardness.
On the breakdown of the Nix-Gao model for indentation size effect
Published in Philosophical Magazine, 2021
Indentation size effect (ISE), i.e. size-dependent increase in hardness, occurs in crystalline plastically deformable materials when the size of the indent approaches the average dislocation spacing, so that the plastic deformation under the indenter is controlled by a limited number of defects [7]. This makes it difficult to compare the results obtained at different (in particular small) loads that are needed for characterisation of small particles or thin layers. Experimental hardness data obtained for decreasing penetration depths can be effectively fitted, e.g. by power-law relation (using log H–log h plot) [8,9] or by an exponential (decay) function [10]. For the physical basis, it was concluded that the ISE is related to dislocation generation rather than to interaction between existing dislocations [11].
Characterization of thermal sprayed Si on sintered SiC for space optical applications
Published in Surface Engineering, 2021
Tayaramma D. P. V. Jalluri, S. Somashekar, Arjun Dey, R. Venkateswaran, S. Elumalai, B. Rudraswamy, K. V. Sriram
The nanoindentation investigations have been carried out on polished Si-SSiC sample using Berkovich indenter under controlled loading and unloading conditions. The various P-h plots are shown in Figure 11(a), corresponding to the load of 5, 10, 20 and 50 mN, respectively. It is very important to note that, the signature of pop-outs or elbow is evident from unloading curve of the P-h plots. This is a characteristic phenomenon of Si which is extensively discussed in literature and it is linked with increase in volume during phase change while experiencing loading [39]. The variation H, E and plastic/elastic energy consumed during indentation process as function of load are shown in Figure 11(b–d), respectively. The hardness is superior (∼11.8 GPa) at the lowest load e.g. 5 mN as compared to the hardness value (∼10.4 GPa) at higher loads e.g. 10–50 mN and it remains almost constant. The decrease in hardness with increase in indentation load is observed due to indentation size effect (ISE) which is well documented in the literature [40]. As expected, Young’s modulus almost remains unaltered (∼146.2 GPa). Young’s modulus is intrinsic property of material and hence it is not expected to change on alteration of indentation load as well as depth. However, for the plasma sprayed ceramic coatings such as ZrO2 [41,42] and hydroxyapatite [43], the significant reduction of Young’s modulus reported is primarily linked with process-induced volumetric/planar defects and porosities. Thus, the constant modulus data (Figure 11(c)) with increase in indentation depth/load implies the microstructural uniformity and homogeneity of flame sprayed Si coating not only with respect to the planar surface but also through thickness of the material.