Vickers stress test
The Vickers hardness test is the most versatile Hardness testing method for metallic materials. It is suitable for soft to extremely hard materials, small components, thin layers and (automated) hardness profilesThe hardness value is determined via an optically measured test indentation. Crucial for reliable results are the appropriate test force, a ground and polished sample surface, and evaluation according to standards.
the essentials in brief
- The Vickers hardness test uses a Diamond pyramid as an penetrator.
- The hardness value will be out Test force and the diagonals of the test impression calculated.
- The Vickers hardness testing method is suitable for a very wide range of materials.
- Vickers is particularly relevant in small components, thin layers, edge areas and hardness gradients.
- The test requires ground (and polished) sample surface
- The test impression will optically measured.
- The procedure is part of the standard series. DIN EN ISO 6507 .
- This method is the most commonly used method for Fully automated tests.
What is the Vickers hardness test?
The Vickers hardness test is a standardized indentation test. A diamond pyramid is pressed into the surface of the material with a defined test force. After the force is released, a usually square indentation remains, the two diagonals of which are measured optically.
The procedure was developed as an alternative to BrinellThe hardness test was developed and is today one of the most versatile methods for measuring hardness. The result is indicated using the abbreviation . HV for Härte Vickers. The number after HV indicates the test force used, for example. HV10 or HV30.
For which materials is the Vickers hardness test suitable?
The Vickers hardness test is suitable for a very wide range of materials. It is particularly useful when small, precisely positionable test indentations are required or when different hardness ranges need to be covered by a single method.
Typical applications are:
- soft to extremely hard metallic materials
- hardened steels
- small components
- thin layers and edge areas
- metallographically prepared samples
- Hardness profiles and hardness depths (automatable)
- homogeneous materials and defined test areas
For coarse, porous or inhomogeneous structures, Brinell is often superior because the large ball imprint covers a larger area of the material.
How does the Vickers hardness testing method work?
The Vickers hardness test follows a clear procedure:
- The sample is prepared metallographically (ground, possibly polished) and positioned stably.
- A diamond pyramid is pressed into the surface with a defined test force.
- The test force acts for the prescribed time.
- After the pressure is released, a square test impression remains.
- The two diagonals of the impression are measured optically.
- The Vickers hardness value is calculated from the test force and the mean value of the diagonal lengths.
The geometry of the indenter is crucial for the comparability of the results. In the Vickers test, a diamond pyramid with a square base and an angle of 136 degrees between opposing faces is used. It is important that the tip does not exceed a prescribed ridge length – especially in the micro-Vickers test. The current ISO 6507-1 standard describes the Vickers hardness test for three test force ranges for metallic materials, including cemented carbides and other sintered cemented carbides.
What does a specification like 440 HV30 mean?
Vickers hardness values should be given in full so that the result remains reproducible. A typical value is:
440 HV30
- The components mean:
- 440 is the determined hardness value.
- HV stands for hardness Vickers.
- 30 denotes the test force in kgf.
If the standard test load duration is adhered to, it does not need to be stated separately in the results. If the load duration deviates, the time is added, for example:
440 HV30/20
In this case, the last number represents a load duration of 20 seconds.
Micro, small force or macro: Test force ranges at Vickers
Vickers differentiates between test force ranges.
- Microhardness test (0,01 to < 1 kgf (HV0,01 to HV0,5)
- Small force test (1 to < 10 kgf (HV1 to HV5)
- classic Vickers hardness test (10 to 100 kgf (HV10 to HV100)
This classification is important because it directly influences equipment selection, sample preparation, and application. Modern hardness testers, equipped with multiple force measuring cells, are capable of covering the entire test force range with a single machine.
| Area | common name | Inspector | Typical application |
|---|---|---|---|
| Vickers microhardness test | micro hardness testing machine | < 1,961 N | Very small test impressions, thin layers and structural components |
| Vickers small-power test | low-force hardness testing machine | 1,961 N to < 49,03 N | Small components, edge areas and hardness gradients |
| Vickers hardness test | Vickers hardness testing machine | ≥49,03N | Classical materials testing on larger test surfaces |
Why Vickers is particularly important for hardness levels
Vickers is particularly well-suited for hardness profiles because the test indentations are small and can be positioned precisely. This allows multiple measurement points to be placed along a defined profile, for example, from the surface towards the core of a component.
Typical applications are:
- CHD / EHTCase hardening depth
- SHD / RHT: Surface layer hardening depth
- NHD / NHTNitriding case depth
- hardness gradients on components
- Edge areas after heat treatment
- thin layers and coated surfaces (see also Button)
- Weld seam inspection
- Jominy hardness test (forehead shock test)
Automated Vickers systems are useful for numerous measuring points or recurring testing procedures. They can automatically generate test patterns, visually capture the impressions, and document the results.
Sample preparation and surface requirements
Vickers hardness testing is an optical method. Therefore, the quality of the surface directly influences how reliably the indentation diagonals can be detected and measured.
For simple tests, a suitable, clean, and flat surface may suffice. However, for hardness profiles, edge zone tests, or small test loads, metallographic preparation down to a polished surface is often necessary. Only then can small indentations be clearly identified and reproducibly evaluated.
Sufficient spacing between the test indentations and the edge of the sample is also important. Insufficient spacing can distort the result because adjacent indentations can locally affect the material.
Advantages and limitations of the Vickers hardness test
| Benefits | boundaries |
|---|---|
| Very wide range of use | The surface must be well prepared. |
| Suitable for small components and thin layers | Optical evaluation required |
| Precise positioning of individual test points is possible | Inappropriate preparation can lead to unreliable measurement results. |
| Important for hardness profiles and hardening depths | Often less suitable than Brinell for inhomogeneous or porous materials. |
| One procedure for many testing force areas | High testing effort with many manual measuring points |
Standards for Vickers hardness testing
The Vickers hardness test is part of the standard series. DIN EN ISO 6507 regulated. For practical application, the following areas are particularly relevant:
- DIN EN ISO 6507-1 describes the testing procedure.
- DIN EN ISO 6507-2 It covers the verification and calibration of testing machines and diagonal measuring systems.
- DIN EN ISO 6507-3 This concerns the calibration of hardness comparison plates.
- DIN EN ISO 6507-4 Contains tables for determining hardness values.
- ASTM E384 This standard is relevant for microhardness testing with Vickers and Knoop indenters in the American standards environment. ASTM E384 covers microindentation tests with Knoop and Vickers indenters in the test force range of 1 to 1000 gf.
The standard should be clearly defined before testing, especially if measurement results are to be used for test reports, customer requirements or audits.
Common errors in the Vickers hardness test
Errors in Vickers hardness testing often arise from an unsuitable test force, an unsuitable surface, or an uncertain evaluation of the indentation diagonals.
Typical sources of error include:
- unsuitable sample surface
- Incorrect sample preparation (hardening during grinding)
- incorrect examiner
- Insufficient distances between test impressions
- incorrect positioning in hardness gradients
- Inaccurately detected or measured diagonals
- Testing in porous or highly inhomogeneous areas
- Result given without examiner
- Uncritical comparison of hardness values from different test force ranges
- Insufficient magnification at low test forces and high hardness
Suitable sample preparation and a suitable test plan are particularly important when using small test loads, hardness profiles or automated measurement series.
What types of Vickers hardness testers are available?
Various instrument concepts are available for Vickers hardness testing. The selection depends on the test force range, application, specimen geometry, degree of automation, and required documentation.
Possible device types include:
- manual Vickers hardness testers
- Micro hardness testing machines
- Small-scale hardness testing machines
- Vickers hardness testing machines for higher test forces
- Universal hardness tester with Vickers function
- Fully automatic Vickers systems for hardness profiles
- Systems with camera, image analysis and motorized XY table
Automated systems are particularly helpful for hardness profiles or recurring measurement series, as they can reproducibly approach measuring points and evaluate results using software. At the same time, they relieve the materials tester of time-consuming test series and free up time for more demanding tasks such as result evaluation, root cause analysis, or research and development.
When is Vickers the right method?
| Application | Suitable for Vickers? |
|---|---|
| Small components | Ja |
| Thin layers | Yes, depending on the test force and preparation. |
| Hardness profiles and hardness depths | Yes, often preferred |
| Very hard materials | Ja |
| Soft to hard metals | Ja |
| Coarse or porous cast structures | Rather Brinell |
| Rapid serial testing without optical measurement | Rather Rockwell |
| Severely unprepared surfaces | Rather not |
FAQ: Frequently Asked Questions
What is the Vickers hardness test?
The Vickers hardness test is a standardized hardness testing method in which a diamond pyramid is pressed into the material with a defined test force. The diagonals of the indentation are then measured optically.
How does the Vickers hardness test work?
A diamond pyramid produces a square indentation. The two diagonals are measured and, together with the test force, used to calculate the Vickers hardness value.
For which materials is Vickers suitable?
Vickers coating is suitable for a very wide range of materials, from soft metals to very hard materials. The process is particularly relevant for small components, thin films, and hardness gradients.
What does 440 HV30 mean?
440 is the hardness value, HV stands for Vickers hardness and 30 denotes the test force in kgf.
What is the difference between Vickers and Knoop?
Both methods use a diamond indenter and optical evaluation. Knoop produces an elongated, diamond-shaped indentation and can be useful for very thin layers or specific edge areas. Vickers, on the other hand, produces an almost square indentation and is more widely used.
When is Vickers not suitable?
Vickers is less suitable if the surface is not adequately prepared or if highly porous or coarsely inhomogeneous materials are to be tested. In such cases, Brinell may be more appropriate.
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