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| Vickers hardness | |
|---|---|
| Name | Vickers hardness |
| Caption | Micrograph of a Vickers indenter mark on steel |
| Invented by | George E. Sandland and Robert L. Smith |
| Developer | Vickers Limited |
| First published | 1925 |
| Units | Vickers pyramid number (HV) |
| Typical range | 5–3000 HV |
| Related tests | Brinell, Rockwell, Knoop, Mohs |
Vickers hardness The Vickers hardness test is a standardized method for measuring the indentation hardness of materials using a diamond pyramid indenter, yielding a numeric value expressed as a Vickers hardness number (HV). The method is applied across metallurgy, Royal Society, Imperial College London, Fraunhofer Society laboratories and industrial quality control in sectors including Rolls-Royce, Boeing, General Electric, Siemens and Tata Steel. It provides a continuous scale suitable for thin sections, coatings, ceramics and metals where traceable quantification is required by organizations such as ISO, ASTM International and DIN.
The Vickers test uses a square-based pyramidal diamond indenter pressed into a test surface under a specified load, then measures the diagonal of the resulting indentation to compute hardness; results are reported in HV. The technique complements other hardness measurements used by National Institute of Standards and Technology, European Commission, Japanese Industrial Standards Committee and national metrology institutes in comparative studies and round-robin interlaboratory comparisons. Practitioners from University of Cambridge, Massachusetts Institute of Technology, Technical University of Munich, École Polytechnique Fédérale de Lausanne and Tsinghua University commonly reference Vickers values in publications on alloys, Nuclear Energy Agency materials, aerospace components and semiconductor device packaging.
The method was developed in the 1920s by researchers at Vickers Limited aiming to create a universal microhardness test replacing the disparate scales of the time. Early adoption by industrial firms such as British Steel, Société Anonyme de Produits Chimiques, Krupp and US Steel drove standardization. Key contributors included metallurgists who collaborated with institutions like Cambridge University Engineering Department and patent filings in the interwar period influenced uptake by manufacturers including Vickers-Armstrongs and academic labs at University of Manchester.
A diamond indenter in the shape of a right square pyramid with an apex angle of 136° is pressed into a polished surface under loads ranging from 1 gf to 30 kgf (or higher with specialized machines) using a load frame manufactured by vendors such as Mitutoyo, Struers, Buehler and ZwickRoell. After dwell time, the diagonals d1 and d2 of the square impression are measured by optical microscopes or imaging systems from Olympus Corporation, Zeiss, Nikon Corporation and converted to an average diagonal d. Operators follow protocols from ISO 6507, ASTM E92 and JIS Z 2251 with pre-test surface preparation by metallography labs at institutions like Los Alamos National Laboratory and Centre National de la Recherche Scientifique.
Vickers hardness HV is calculated by dividing the applied load by the surface area of the indentation, which for the pyramid geometry yields HV = 1.8544 * (F / d^2), where F is the load in newtons and d is the mean diagonal in millimetres. Laboratories accredited by UKAS, ANAB and DAkkS apply this formula when reporting microhardness for alloys such as AISI 304, Inconel 718, Ti-6Al-4V, and ceramics like Al2O3 and Si3N4. The numerical factor arises from the pyramid angle and is used in conversion tables linking HV to other scales in standards maintained by ISO committees and national standards bodies.
Calibration uses reference blocks produced by metrology laboratories including National Physical Laboratory (UK), PTB (Germany), NIST, and certified materials from suppliers such as Goodfellow and McCrone. Accuracy depends on indenter geometry fidelity, load cell calibration traceable to national standards, surface preparation, operator technique, optical resolution of diagonal measurement and thermal stability in controlled environments like those at CERN or Sandia National Laboratories. Common error sources include imperfect polishing, surface roughness, elastic recovery, tilted indenter seating, machine compliance, and pile-up or sink-in effects in soft or hard substrates; interlaboratory reproducibility is improved by round-robin studies coordinated by International Organization for Standardization committees and research groups at Imperial College London.
Vickers is widely used for microhardness profiling across case-hardened steels in automotive industry gearbox components from Bosch and ZF Friedrichshafen, thin films and coatings in microelectronics from Intel and TSMC, and ceramic composites for General Motors and Airbus structural components. For brittle ceramics and glass, indentation fracture mechanics relating crack lengths to toughness are frequently applied by researchers at University of California, Berkeley and ETH Zurich. For polymers, viscoelastic recovery and time-dependent creep require modified dwell times as studied by teams at Dow Chemical and DuPont. In additive manufacturing, Vickers mapping helps assess anisotropy and heat-affected zones in parts produced by EOS GmbH and GE Additive.
Compared to Brinell hardness test, Vickers provides smaller indentations suitable for thin sections and is applicable over a wider load range. Compared to Rockwell hardness test it offers higher resolution for microstructural phases and precipitates studied at Lawrence Livermore National Laboratory and Oak Ridge National Laboratory. The Knoop test, developed for very thin coatings, uses an elongated diamond indenter and complements Vickers for anisotropic materials such as single crystals examined at Bell Labs and IBM Research. Conversion between scales uses empirical correlations published by ISO and researchers at TMS (The Minerals, Metals & Materials Society) and ASM International.
Standards governing Vickers testing include ISO 6507 series, ASTM E92, JIS Z 2251 and associated calibration guides from national metrology institutes. Instrument specifications address indenter geometry, load application profiles, dwell times, optical magnification, edge detection algorithms in imaging software from ImageJ derivatives and vendor firmware, and environmental control referencing practices from BIPM. Accredited testing labs following these standards often participate in proficiency testing organized by ILAC and regional accreditation bodies to ensure traceability and comparability.
Category:Hardness tests