Nanoindenter

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A nanoindenter Nanoindenter holder.jpg
A nanoindenter

A nanoindenter is the main component for indentation hardness tests used in nanoindentation. Since the mid-1970s nanoindentation has become the primary method for measuring and testing very small volumes of mechanical properties. Nanoindentation, also called depth sensing indentation or instrumented indentation, gained popularity with the development of machines that could record small load and displacement with high accuracy and precision. [1] [2] The load displacement data can be used to determine modulus of elasticity, hardness, yield strength, fracture toughness, scratch hardness and wear properties. [3]

Contents

Types

A round end cone indenter ConicalTip.jpg
A round end cone indenter
A filament rod indenter FilamentRod.jpg
A filament rod indenter
A standard Berkovich indenter, which is a 3-sided pyramid where a = 65.03deg Berkovich.jpg
A standard Berkovich indenter, which is a 3-sided pyramid where a = 65.03°

There are many types of nanoindenters in current use differing mainly on their tip geometry. Among the numerous available geometries are three and four sided pyramids, wedges, cones, cylinders, filaments, and spheres. Several geometries have become a well established common standard due to their extended use and well known properties; such as Berkovich, cube corner, Vickers, and Knoop nanoindenters. To meet the high precision required, nanoindenters must be made following the definitions of ISO 14577-2, [4] and be inspected and measured with equipment and standards traceable to the National Institute of Standards and Technology (NIST). The tip end of the indenter can be made sharp, flat, or rounded to a cylindrical or spherical shape. The material for most nanoindenters is diamond and sapphire, although other hard materials can be used such as quartz, silicon, tungsten, steel, tungsten carbide and almost any other hard metal or ceramic material. Diamond is the most commonly used material for nanoindentation due to its properties of hardness, thermal conductivity, and chemical inertness. In some cases electrically conductive diamond may be needed for special applications and is also available.

Holders

Nanoindenters are mounted on holders which could be the standard design from a manufacturer of nanoindenting equipment, or custom design. The holder material can be steel, titanium, machinable ceramic, other metals or rigid materials. In most cases the indenter is attached to the holder using a rigid metal bonding process. The metal forms a molecular bond with both material be it diamond-steel, diamond-ceramic, etc.

Angular measurements

Nanoindenter dimensions are very small, some less than 50 micrometres (0.0020 in), and made with precise angular geometry in order to achieve the highly accurate readings required for nanoindentation. Instruments that measure angles on larger objects such as protractors or comparators are neither practical nor precise enough to measure nanoindenter angles even with help of microscopes. For precise measurements a laser goniometer is used to measure diamond nanoindenter angles. Nanoindenter faces are highly polished and reflective which is the basis for the laser goniometer measurements. The laser goniometer can measure within a thousandth of a degree to specified or requested angles. [5]

Related Research Articles

Structural geology Science of the description and interpretation of deformation in the Earths crust

Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover information about the history of deformation (strain) in the rocks, and ultimately, to understand the stress field that resulted in the observed strain and geometries. This understanding of the dynamics of the stress field can be linked to important events in the geologic past; a common goal is to understand the structural evolution of a particular area with respect to regionally widespread patterns of rock deformation due to plate tectonics.

Rockwell scale

The Rockwell scale is a hardness scale based on indentation hardness of a material. The Rockwell test measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload. There are different scales, denoted by a single letter, that use different loads or indenters. The result is a dimensionless number noted as HRA, HRB, HRC, etc., where the last letter is the respective Rockwell scale . When testing metals, indentation hardness correlates linearly with tensile strength.

Brinell scale

The Brinell scale characterizes the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test-piece. It is one of several definitions of hardness in materials science.

Superhard material Material with Vickers hardness exceeding 40 gigapascals

A superhard material is a material with a hardness value exceeding 40 gigapascals (GPa) when measured by the Vickers hardness test. They are virtually incompressible solids with high electron density and high bond covalency. As a result of their unique properties, these materials are of great interest in many industrial areas including, but not limited to, abrasives, polishing and cutting tools, disc brakes, and wear-resistant and protective coatings.

Vickers hardness test

The Vickers hardness test was developed in 1921 by Robert L. Smith and George E. Sandland at Vickers Ltd as an alternative to the Brinell method to measure the hardness of materials. The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the indenter, and the indenter can be used for all materials irrespective of hardness. The basic principle, as with all common measures of hardness, is to observe a material's ability to resist plastic deformation from a standard source. The Vickers test can be used for all metals and has one of the widest scales among hardness tests. The unit of hardness given by the test is known as the Vickers Pyramid Number (HV) or Diamond Pyramid Hardness (DPH). The hardness number can be converted into units of pascals, but should not be confused with pressure, which uses the same units. The hardness number is determined by the load over the surface area of the indentation and not the area normal to the force, and is therefore not pressure.

Indentation hardness tests are used in mechanical engineering to determine the hardness of a material to deformation. Several such tests exist, wherein the examined material is indented until an impression is formed; these tests can be performed on a macroscopic or microscopic scale.

Knoop hardness test

The Knoop hardness test is a microhardness test – a test for mechanical hardness used particularly for very brittle materials or thin sheets, where only a small indentation may be made for testing purposes. A pyramidal diamond point is pressed into the polished surface of the test material with a known load, for a specified dwell time, and the resulting indentation is measured using a microscope. The geometry of this indenter is an extended pyramid with the length to width ratio being 7:1 and respective face angles are 172 degrees for the long edge and 130 degrees for the short edge. The depth of the indentation can be approximated as 1/30 of the long dimension. The Knoop hardness HK or KHN is then given by the formula:

Nanotribology is the branch of tribology that studies friction, wear, adhesion and lubrication phenomena at the nanoscale, where atomic interactions and quantum effects are not negligible. The aim of this discipline is characterizing and modifying surfaces for both scientific and technological purposes.

Hardness is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard metals such as titanium and beryllium are harder than soft metals such as sodium and metallic tin, or wood and common plastics. Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore, there are different measurements of hardness: scratch hardness, indentation hardness, and rebound hardness.

Nanoindentation, also called instrumented indentation testing, is a variety of indentation hardness tests applied to small volumes. Indentation is perhaps the most commonly applied means of testing the mechanical properties of materials. The nanoindentation technique was developed in the mid-1970s to measure the hardness of small volumes of material.

Shore durometer

The Shore durometer is a device for measuring the hardness of a material, typically of polymers, elastomers, and rubbers.

Berkovich tip

A Berkovich tip is a type of nanoindenter tip used for testing the indentation hardness of a material. It is a three-sided pyramid which is geometrically self-similar. The popular Berkovich now has a very flat profile, with a total included angle of 142.3 degrees and a half angle of 65.27 degrees, measured from the axis to one of the pyramid flats. This Berkovich tip has the same projected area-to-depth ratio as a Vickers indenter. The original tip shape was invented by Russian scientist E.S. Berkovich in the USSR c. 1950, which has a half angle of 65.03 degrees.

Ceramography Preparation and study of ceramics with optical instruments

Ceramography is the art and science of preparation, examination and evaluation of ceramic microstructures. Ceramography can be thought of as the metallography of ceramics. The microstructure is the structure level of approximately 0.1 to 100 µm, between the minimum wavelength of visible light and the resolution limit of the naked eye. The microstructure includes most grains, secondary phases, grain boundaries, pores, micro-cracks and hardness microindentions. Most bulk mechanical, optical, thermal, electrical and magnetic properties are significantly affected by the microstructure. The fabrication method and process conditions are generally indicated by the microstructure. The root cause of many ceramic failures is evident in the microstructure. Ceramography is part of the broader field of materialography, which includes all the microscopic techniques of material analysis, such as metallography, petrography and plastography. Ceramography is usually reserved for high-performance ceramics for industrial applications, such as 85–99.9% alumina (Al2O3) in Fig. 1, zirconia (ZrO2), silicon carbide (SiC), silicon nitride (Si3N4), and ceramic-matrix composites. It is seldom used on whiteware ceramics such as sanitaryware, wall tiles and dishware.

Meyer hardness test

The Meyer hardness test is a hardness test based upon projected area of an impression. The hardness, , is defined as the maximum load, divided by the projected area of the indent, .

Meyer's law is an empirical relation between the size of a hardness test indentation and the load required to leave the indentation. The formula was devised by Eugene Meyer of the Materials Testing Laboratory at the Imperial School of Technology, Charlottenburg, Germany, circa 1908.

The Leeb Rebound Hardness Test (LRHT) invented by Swiss company Proceq SA is one of the four most used methods for testing metal hardness. This portable method is mainly used for testing sufficiently large workpieces.

Fiber pushout test

The fiber pushout test is a mechanical test performed on composite materials where a fiber is mechanically pushed out of the material. This test is carried out with the purpose of measuring the matrix/fiber interface de-bonding energy and the effects of frictional sliding between the matrix and the fiber.

Materials that are used for biomedical or clinical applications are known as biomaterials. The following article deals with fifth generation biomaterials that are used for bone structure replacement. For any material to be classified for biomedical application three requirements must be met. The first requirement is that the material must be biocompatible; it means that the organism should not treat it as a foreign object. Secondly, the material should be biodegradable ; the material should harmlessly degrade or dissolve in the body of the organism to allow it to resume natural functioning. Thirdly, the material should be mechanically sound; for the replacement of load bearing structures, the material should possess equivalent or greater mechanical stability to ensure high reliability of the graft.

The Korsunsky work-of-indentation approach is a method of extracting a values of hardness and stiffness for a small volume of material from indentation test data.

Indentation size effect Property of materials at small scales

The indentation size effect (ISE) is the observation that hardness tends to increase as the indent size decreases at small scales. When an indent is created during material testing, the hardness of the material is not constant. At the small scale, materials will actually be harder than at the macro-scale. For the conventional indentation size effect, the smaller the indentation, the larger the difference in hardness. The effect has been seen through nanoindentation and microindentation measurements at varying depths. Dislocations increase material hardness by increasing flow stress through dislocation blocking mechanisms. Materials contain statistically stored dislocations (SSD) which are created by homogeneous strain and are dependent upon the material and processing conditions. Geometrically necessary dislocations (GND) on the other hand are formed, in addition to the dislocations statistically present, to maintain continuity within the material.

References

  1. Nanoindentation Lecture 1 Basic Principle, by Do Kyung Kim, Dept. of Material Science and Engineering KAIST, Korea.
  2. Fischer-Cripps, A.C. Nanoindentation. (Springer: New York), 2004.
  3. W.C. Oliver and G.M. Pharr. An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments, J. Mater. Res., vol. 7, No. 6, June 1992.
  4. ISO 14577-2 = Instrumented indentation test for hardness and materials parameters. Part 2: Verification and calibration of testing machines. Section 4: Direct verification and calibration.
  5. "Archived copy" (PDF). Archived from the original (PDF) on 2015-12-23. Retrieved 2015-11-16.CS1 maint: archived copy as title (link)