When it comes to material quality control, hardness is often an important factor. With microhardness testing equipment, you can learn a great deal about a material’s resistance to permanent deformation and assess variations in hardness across very small features, even those that are particularly small or thin.
Vickers and Knoop are the main methods of microhardness testing. Here, hardness testing machine manufacturer INNOVATEST explains how the two methods work and their distinct uses.
In simple terms, a microhardness test measures how resistant a material is to permanent indentation. A microhardness test measures how much a material can resist deformation under pressure. It looks for changes in the shape and size of a material caused by physical force.
Microhardness testing measures the hardness of small features, thin sections and surface layers with very high precision. Microhardness testing typically uses test forces up to approximately 10 newtons (N). Macrohardness testing can be used for larger samples and involves different methods and equipment.
Microhardness testing uses an indenter to press the material surface under a predetermined force for a standardised duration. This indentation is measured to calculate a hardness value. There are two primary microhardness tests, the Vickers and Knoop methods, which vary in the equipment and measurements used.
Hardness testing is often crucial for selecting the right material for an application and is therefore widely used in industries where material performance is key, such as automotive, aerospace, manufacturing and metalwork.
Microhardness testing can indicate the performance potential of materials such as thin films, coatings, anodised layers and plating. It is useful for assessing the hardness of ceramics, polymers, and metals and for predicting a material’s ability to withstand heavy use and resist wear.
The Vickers microhardness test uses the Vickers indenter. This is shaped like a square pyramid, and its 136-degree angle makes it squat.
The Vickers hardness tester typically applies the test force for 10–15 seconds, depending on the applicable standard and material.
After 10-15 seconds, the remaining indentation is measured optically by taking the lengths of the diagonals to calculate the size of the impression.
The indenter on the Knoop hardness tester is rectangular and elongated, with a length-to-width ratio of just over 7:1. The long edge has an angle of 172 degrees and the short edge 130 degrees. Knoop hardness tests are usually performed at test forces ranging from 10 gf to 1,000 gf.
After 10-15 seconds of pressure, the Knoop indenter creates a shallow indentation. Only the long axis is measured, and it is used to calculate hardness.
The process of testing is documented in ISO 4545, ASTM E92 and JIS B 7725.
The Vickers and Knoop methods are sufficiently different to have distinct applications and optimal uses. Here are the key differences.
Higher Vickers test loads may produce cracking in some brittle materials. The Knoop method indentation is about half as deep as the Vickers method indentation, so the Knoop method is better for very thin or delicate materials, such as coatings or ceramics. Vickers is best suited to metals and heat-treated components.
Vickers and Knoop create indentations of different shapes.
The symmetrical square indentation makes Vickers well suited to general-purpose hardness testing and mapping.
The elongated indentation makes Knoop particularly useful for thin coatings, brittle materials and closely spaced hardness measurements.
Choosing between Vickers and Knoop microhardness testing depends on the material, its thickness, and the level of precision you need. Both methods offer reliable, repeatable results when using the right equipment and technique.
Innovatest designs and manufactures a full range of manual and automated microhardness testers, built to comply with international testing standards including EN ISO and ASTM and support multiple industries. Whether you’re testing thin coatings, heat-treated metals or an unusual material, our team can help you find the right solution for your lab.
Get in touch with INNOVATEST today to discuss your microhardness testing needs or request a personalised recommendation.
The best microhardness tester is one that offers precise load control, reliable optics, and compatibility with both Vickers and Knoop methods. Units with automatic turret indexing and calibrated load cells typically offer the best balance of accuracy and efficiency for most quality control settings.
Automatic microhardness testers are generally better suited to high-volume testing, since they reduce operator error and speed up measurement through automated indentation and optical analysis. Manual testers remain a cost-effective option for labs with lower testing volumes or simpler quality control needs.
Microhardness testing typically requires magnification typically between 100x and 500x, depending on indentation size and the material being tested. Vickers indentations are usually measured at 400x to 500x for accuracy, whereas Knoop indentations, being shallower and elongated, may require higher magnification to clearly define the long axis.
Microhardness tester costs vary significantly based on automation level, load range, and software features, with basic manual models priced lower than fully automated systems with advanced imaging and reporting tools. Indenter type, calibration certification, and after-sales support also affect price.
The most important features of microhardness testing software are automated measurement, data traceability, and multi-standard reporting. Automated image analysis reduces human error in measuring indentations, while traceable data logging supports compliance with standards such as EN ISO 6507 and EN ISO 4545, widely used across European labs.