The micro-hardness of metals at very low loads
TL;DR: The micro-hardness of gold has been investigated over a range of indentation sizes from 0.5 mm to 0.2 μm using loads down to 1.0 mg.
Abstract: The micro-hardness of gold has been investigated over a range of indentation sizes from 0.5 mm to 0.2 μm using loads down to 1.0 mg. The indentations were made using a series of spherical indenters of varying radius. In this way it was possible to keep the shape of indentations geometrically similar over a wide range of indentation sizes and so obtain comparable results. The smallest indenters (0.5 μm radius) were prepared using techniques similar to those used for making field-ion microscope tips and the experiments at the small sizes were carried out inside a scanning electron microscope. The measurements were made on specimens in the annealed condition and in the heavily cold-worked condition; considerable care was taken to exclude any possible effect arising from the preparative treatment of the surface. The results show that the hardness is increased by a factor of between two and three at sizes down to 0.2 μm in both the annealed and cold-worked conditions. Possible reasons for this increas...
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TL;DR: In this paper, an understanding of the molecular mechanisms of tribology in thin films and at surfaces has been presented, which is of fundamental importance in many pure and applied sciences, such as computer simulations.
Abstract: Friction, wear and lubrication between materials in contact are of fundamental importance in many pure and applied sciences. Owing to the development of experimental and computer-simulation techniques for studying these phenomena at the atomic scale, an understanding is beginning to emerge of the molecular mechanisms of tribology in thin films and at surfaces.
1,393 citations
TL;DR: In this paper, Sneddon's analysis for the elastic contact between a rigid, axisymmetric punch and an elastic half space is used to show that a simple relationship exists between the contact stiffness, the contact area, and the elastic modulus that is not dependent on the geometry of the punch.
Abstract: Results of Sneddon's analysis for the elastic contact between a rigid, axisymmetric punch and an elastic half space are used to show that a simple relationship exists between the contact stiffness, the contact area, and the elastic modulus that is not dependent on the geometry of the punch. The generality of the relationship has important implications for the measurement of mechanical properties using load and depth sensing indentation techniques and in the measurement of small contact areas such as those encountered in atomic force microscopy.
1,363 citations
TL;DR: In this paper, the authors measured the hardness of a thin epitaxial gold film embedded in the silver layers and found that the deformation was primarily restricted to the sharp edges of the indentation.
Abstract: The hardness of thick, high-purity, epitaxially grown silver on sodium chloride is found to be dependent on the size of the indentation for sizes below ≃10 μm. The measurement of the size effect has been made in two ways. In one, the hardness has been calculated from the load-displacement curve obtained from an instrumented microhardness testing machine and assuming a geometric self-similarity in the indenter shape. In the other measurement, the hardness was obtained from the load exerted by the microhardness tester divided by the indentation impression area as measured by atomic force microscopy. The observed variation in microhardness with indentation size is consistent with a simplified strain gradient plasticity model in which the densities of the geometrically necessary and statistically stored dislocations are fitting parameters. An equally good fit can also be made with a simple geometric scaling relationship. Transmission electron microscopy observations of a thin (≃50 nm) epitaxial gold film embedded in the silver layers revealed that the deformation was primarily restricted to the sharp edges of the indentation. In addition, deformation twinning within the indentation impression was observed on the {1H} planes.
1,259 citations
TL;DR: In this paper, the authors investigated the properties of indentation hardness on the sub-micrometre scale in nickel, gold and silicon and showed that indent areas and therefore hardness can be determined from penetration depth with reasonable accuracy, and that elastic relaxation can be quantitatively understood.
Abstract: In this paper we investigate the properties of indentation hardness on the sub-micrometre scale in nickel, gold and silicon. Indenter penetration depths as low as 20 nm are used. The area of the indents is determined by electron microscopy, and thus the Meyer hardness calculated. The indenter penetration is monitored continuously during loading and unloading. We show that indent areas, and therefore hardness, may be determined from penetration depth with reasonable accuracy, and that elastic relaxation can be quantitatively understood. We discuss the marked increase of indentation hardness with decreasing indent size on the sub-micrometre scale. Small indents in silicon showed no evidence of cracking, but did show unusual deformation characteristics.
883 citations
TL;DR: Nanoindentation has become one of the most widely used techniques for measuring the mechanical properties of thin films as discussed by the authors, and has been shown to be useful in the study of optical coatings, hard coatings and materials modified by ion implantation and laser treatment.
Abstract: One of the simplest ways to measure the mechanical properties of a thin film is to deform it on a very small scale. Because indentation testing with a sharp indenter is one convenient means to accomplish this, nanoindentation, or indentation testing at the nanometer scale, has become one of the most widely used techniques for measuring the mechanical properties of thin films. Other reasons for the popularity of nanoindentation stem from the ease with which a wide variety of mechanical properties can be measured without removing the film from its substrate and the ability to probe a surface at numerous points and spatially map its mechanical properties. The utility of the mapping capability is illustrated in Figure 1, which shows several small indentations made at selected points in a microelectronic device. The hardness and modulus of the device were determined at each point. In addition to microelectronics, nanoindentation has also proved useful in the study of optical coatings, hard coatings, and materials with surfaces modified by ion implantation and laser treatment.
792 citations
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05 Oct 2000
TL;DR: Hardness measurements with conical and pyramidal indenters as mentioned in this paper have been used to measure the area of contact between solids and the hardness of ideal plastic metals. But they have not yet been applied to the case of spherical indenters.
Abstract: 1. Introduction 2. Hardness measurements by spherical indenters 3. Deformation and indentation of ideal plastic metals 4. Deformation of metals by spherical indenters. Ideal plastic metals 5. Deformation of metals by spherical indenters. Metals which work-harden 6. Deformation of metals by spherical indenters. 'Shallowing' and elastic 'recovery' 7. Hardness measurements with conical and pyramidal indenters 8. Dynamic or rebound hardness 9. Area of contact between solids Appendix I. Brinell hardness Appendix II. Meyer hardness Appendix III. Vickers hardness Appendix IV. Hardness conversion Appendix V. Hardness and ultimate tensile strength Appendix VI. Some typical hardness values
3,562 citations
TL;DR: It is desirable to begin by reviewing the development and the present state of hardness testing under low load, and to say something about the terminology.
Abstract: As the concept of micro-indentation hardness testing has not yet become commonly accepted, nor has any definition of it been universally agreed upon, it is desirable to begin by reviewing the development and the present state of hardness testing under low load, and to say something about the terminology.
148 citations
TL;DR: In this article, the authors investigated the strength properties of annealed metals when the stressed volume is small enough to lie between the existing dislocations in a crystal and found that the strength was strongly dependent on the condition of the interface.
Abstract: Four types of experiment have been carried out to investigate the strength properties of annealed metals when the stressed volume is small enough to lie between the existing dislocations in a crystal. These are (i) indentation experiments of a soft metal surface with a hard stylus, (ii) blunting of a soft metal tip against a hard surface, (iii) compression of individual metal crystals, and (iv) bending of thin filaments. The experiments were performed in either a scanning electron microscope or a transmission electron microscope with the use of micro-loading devices capable of applying loads down to 0.1 mgf (10 -6 N). In the blunting experiments carried out in the transmission electron microscope it was possible to observe dislocations directly in the tip during loading. The majority of the experiments were carried out on gold. The results showed that strengths similar to the theoretical value can be achieved but in the experiments in which the stress was applied at an external surface (experiments (i), (ii) and (iii) above) the strength was strongly dependent on the condition of the interface. The strength that could be sustained by a region of perfect crystal in contact with a hard metallic surface was about five times less than the theoretical strength. These relatively low strengths are probably due to interfacial tractions producing very high local stresses. The introduction of some polymeric or amorphous layer at the interface raised the strength to the theoretical level. It is suggested that this is due to the fact that the polymeric layer removes most of the stress concentration. Transmission electron microscopy through aluminium tips during blunting showed that plastic deformation could take place at quite low stresses in a dislocation-free crystal with no dislocations remaining in the crystal during the early stages of blunting. Dislocation build up only occurred in the later stages of deformation. The yield stress was found to decrease with plastic strain in all the experiments, and could fall to values which were not substantially greater than those observed in large specimens. Comparison of the compressive strength of two spherical gold crystals, 0.5 μ m and 2 mm in diameter respectively, showed that the small crystal was only twice as strong as the large crystal after they had both undergone equal amounts of compression. The maximum strengths observed for gold ( μ /20) are greater than those calculated by Kelly (1966) ( ca . μ /50) and are nearer the value deduced by Brown & Woolhouse (1970) for the generation of dislocations around precipitate particles in alloys. The low strengths observed on deformed crystals are considered in the context of dislocation generation in small volumes and it is concluded that although a source mechanism of the Frank–Read type may be able to operate on this scale, some other source mechanism may also exist.
107 citations