On the reverse indentation size effect and microhardness measurement of solids

In an attempt to elucidate the processes involved in the formation of indentation impressions, Vickers hardness measurements have been made on soda-lime silica glass, fused silica, and crystalline quartz indented at room temperature and 77 K. The hardness of all three materials increases by a factor of ∼2.5 on cooling to liquid nitrogen temperature. High-magnification SEM photographs revealed that the deformation and cracking patterns of the glasses changed strikingly: no shear lines were observed within the indentations, and ring cracking occurred instead of radial/median cracking. In addition, cracking occurs at much higher loads than at room temperature. The hardness results have been explained in terms of volume flow (densification) rather than shear flow (viscous or plastic) for the glasses at low temperature. The quartz crystal, on the other hand, deformed plastically at both room temperature and 77 K. Cracking differences result from changes in both flow and water activity

Indentation Behavior of Soda‐Lime Silica Glass, Fused Silica, and Single‐Crystal Quartz at Liquid Nitrogen Temperature

The mechanism of deformation under the indentation of MgO crystals has been studied by transmission and scanning electron microscopy. The dislocation structure and Burgers vectors of rosette dislocations are determined. The nature and geometry of cathodoluminescence around indentation have been also investigated. The luminescence radiation is shown to be caused by interstitial point defects built up under indentation.



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Investigation of the deformation mechanism of MgO crystals affected by concentrated load

The effect of crystallographic anisotropy on the room-temperature Knoop microhardness of silicon carbide has been studied on each of three major sections of alpha single crystals (namely: {0 0 0 1}, {1 ¯1 0 0} and {1 1 ¯2 0}), measurements being made at 10° angular intervals over a range sufficient to include all the non-equivalent indenter orientations on each crystal section. The results are presented graphically and compared with a number of possible anisotropies computed for different slip systems using a model based on the effective resolved shear stress (ERSS) model of Brookes et al. [1] with a modification suggested by Arnell [2]. The results are interpreted to show that plastic deformation appears to occur preferentially on the {1 ¯1 0 0}〈1 1 ¯2 0〉 and {0 0 0 1}〈1 1 ¯2 0〉 slip systems over different ranges of orientations of the indenter. Further, it has been possible to estimate the ratio of the critical resolved shear stresses of these systems, the {0 0 0 1} 〈1 1 ¯2 0〉 system having a CRSS between 1.2 and 2.1 times that of the {1 ¯1 0 0}〈1 1 ¯2 0〉 system. Computation has also been used to investigate the detailed effect of the form of Brookes' constraint factor and the reliability of hardness anisotropies predicted in this way. The possible roles of slip and other deformation mechanisms in governing the response of brittle solids subjected to indentation hardness tests are also discussed.

Microhardness anisotropy of silicon carbide

This review summarises the state of knowledge on acoustic emission (AE) techniques applied to material property evaluation during indentation (e.g. hardness) testing. There are two aspects of application of AE technique to indentation which makes it unique, i.e. (1) enhancing the understanding of the evolution of material accommodation mechanisms under loading and (2) qualitative and quantitative evaluation of mechanical properties such as fracture toughness and bond strength from the AE signal. Both of these aspects have the potential to improve our understanding of the structure property relationships of current and future generation materials. In addition, the knowledge developed here can be incorporated to improve the AE based condition monitoring systems for stress critical applications. This review concentrates on the phenomena which occur during indentation and how its examination can be used to study more fundamental behaviour of materials such as deformation and fracture. The uncertainty ...

Indentation testing and its acoustic emission response: applications and emerging trends

The plastic deformation regions near the indentations on the (0 0 1) plane of MgO single crystals were investigated for an indentor under load and after unloading. It was established that the completion of slip-line structures arising during indentor penetration occurred during indentor removal. The presence of prolonged plastic deformation has been explained by considering the impulse character of the microindentation process of MgO at room temperature.

Prolonged plastic deformation related to the microindentation of MgO single crystals

Anomalies in the Knoop microhardness anisotropy of crystals

The deformation of the (001) plane of LiF and NaCl by indentation and scratching at high temperatures was performed. The dislocation patterns arising from deformation were sharply different from those observed at room temperature. It was proposed the explanation of these results.



The model of plastic flow in (001) indentation and scratching were considered. Anisotropy of hardness by the scratch method was revealed clearly at high temperatures. It was proposed the explanation of the anisotropy of hardness. The correlation was established between the dislocation structures observed near the indentations and scratches.



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Some features of plastic deformation of LiF and NaCl single crystals at high temperatures

The influence of the three types of hardening (1 – radiation hardening; 2 – the hardening in lowering of temperature; 3 – the hardening in the series of KCl-NaCl-NaF-LiF-MgO crystals) on the length of dislocation rosettes arms is investigated. This length characterizes the dislocation ensemble mobility in the nonuniform stress field. It is shown that the change of microhardness and that of mobility of dislocations correlate well while introducing the radiation damage. In contrast to it the microhardness rise does not cause marked decrease of the length of rosettes arms in the other two cases. The conclusion is made that the length of rosettes arms depends not only upon the value of crystal hardness but also upon the mode of origin of this value. On the (001) plane of the crystals under investigation it is found that the length of dislocation rosettes arms depends on the indentor orientation. A possible explanation of this phenomenon is proposed.



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The influence of the mode of hardness increase on the dislocation mobility of the crystal with NaCl lattice

The complex investigations of microhardness and dislocation mobility in temperature interval 77–873 K have been performed on ionic crystals, semimetals and covalent crystals It is shown that the correlation between the microhardness and dislocation mobility exists as a whole only The temperature change of microhardness is not often connected with the change of dislocation mobility An “anomalous” behaviour of semimetals has been established – they have a small microhardness and a low dislocation mobility at a time



[Russian Text Ignored]

D. Z. Grabko

Papers

Prolonged plastic deformation related to the microindentation of MgO single crystals

Anomalies in the Knoop microhardness anisotropy of crystals

Some features of plastic deformation of LiF and NaCl single crystals at high temperatures

The influence of the mode of hardness increase on the dislocation mobility of the crystal with NaCl lattice

Correlation between microhardness and dislocation mobility in crystals with a different type of bond