The Vickers Hardness Test (HV) is one of the most versatile hardness testing methods in materials science. Developed in 1921 by British engineers Robert L. Smith and George E. Sandland at Vickers-Armstrongs Ltd., it can be applied to virtually all solid materials — from the softest aluminium alloys to the hardest ceramics and cemented carbides.
Test Principle
The Vickers hardness test uses a square-based diamond pyramid indenter with a face angle of 136° (Vickers indenter), pressed perpendicularly into the test specimen surface under a specified test force (F) for a fixed dwell time. After removal of the indenter, the lengths of the two diagonals of the indentation are measured and averaged (d), and the hardness value is calculated using the formula below.
1.8544 is a constant derived from the geometry of the 136° indenter
The square pyramid design ensures that the geometry of the indentation remains similar across different test forces, meaning Vickers hardness values are highly consistent regardless of the load applied — an advantage that the Brinell hardness test (HB) does not possess.
Key Advantage: The 136° face angle creates a fixed geometric ratio between the diagonal length and the test force, making HV values comparable across loads — enabling cross-material and cross-batch comparisons.
Test Force Classifications
According to ISO 6507, Vickers hardness testing is classified into three categories based on test force:
| Category | Test Force Range | Symbol Examples | Typical Applications |
|---|---|---|---|
| Macro Vickers | 5 kgf (49 N) and above | HV 5 ~ HV 100 | Steel, castings, bulk hardness of large components |
| Low-Load Vickers | 0.2 ~ 2 kgf | HV 0.2 ~ HV 2 | Thin specimens, coatings, surface-hardened layers |
| Micro Vickers | Below 0.2 kgf (1.96 N) | HV 0.001 ~ HV 0.1 | Individual grains, inclusions, thin films, microstructural analysis |
Standard Test Procedure
- Specimen Preparation: The specimen surface must be ground flat and polished to a mirror finish, free of grease and oxide layers, to ensure the indentation is clearly measurable. Surface roughness Ra is recommended to be below 0.4 μm.
- Select Test Force: Choose the appropriate test force (HV 0.001–HV 100) based on material thickness, expected hardness range, and the test objective (bulk hardness or local microstructure).
- Indent and Dwell: Press the indenter perpendicularly into the specimen surface at the specified test force and hold for 10–15 seconds (per ISO 6507) to ensure full plastic deformation.
- Measure Diagonals: After removing the indenter, use an optical microscope or imaging system to measure the lengths of both diagonals d₁ and d₂. Calculate the mean value d = (d₁ + d₂) / 2.
- Calculate and Record: Apply the formula HV = 1.8544 × F / d² to calculate the hardness value, or allow a fully automated hardness tester to output results and reports directly.
Spacing Requirements: The distance between adjacent indentation centres must be at least 3× the diagonal length; the distance from an indentation centre to the specimen edge must be at least 2.5× the diagonal length, to avoid mutual influence.
Micro Vickers Hardness & Case Depth Analysis
Micro Vickers hardness testing (HV 0.01–HV 1) is one of the most important tools for analysing surface treatment layers. Measurement of the "effective case depth (CHD/NHD/SHD)" for heat-treated components — such as carburised, nitrided, and induction-hardened parts — relies on a series of micro-indentations arranged along the cross-section, forming a "hardness profile."
Automated hardness testers (such as the DuraScan series) can define indentation array paths and automatically complete the measurement of dozens or hundreds of indentations, plotting the profile curve in real time. Based on standards such as ISO 2639 (carburising) and ISO 18203 (nitriding), the system automatically determines the case depth, greatly improving testing efficiency and consistency.
Comparison with Other Hardness Scales
Vickers (HV)
136° diamond pyramid indenter. Widest application range — from soft to ultra-hard materials, covering micro to macro scales.
Brinell (HB)
Tungsten carbide ball indenter. Suitable for castings and coarse-grained materials, but not for very hard materials or micro hardness testing.
Rockwell (HRC/HRB)
Conical diamond or ball indenter measuring indentation depth. Fast operation, suitable for production lines, but not suitable for thin specimens or surface layers.
Key Application Areas
- Heat Treatment Quality Control: Verify the hardening effect and depth of quenching, tempering, carburising, nitriding, and related processes
- Weld Joint Analysis: Measure hardness profiles across the heat-affected zone (HAZ), fusion zone, and base metal to evaluate weld quality
- Surface Coating Evaluation: Measure hardness and adhesion of hard chromium, DLC, PVD/CVD coatings
- Failure Analysis: Locate embrittled, overheated, or decarburised zones through hardness profiles
- R&D Verification: New alloy development, material qualification, cross-batch consistency confirmation
- Aerospace & Automotive Components: Cross-section hardness acceptance testing for turbine blades, gears, bearings, and other critical parts