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In the industrial world especially in metallurgy and materials science accurately measuring hardness is of critical importance. This is because understanding a component’s resistance to wear, impact, or deformation directly affects its service life and safety.
The Vickers test offers high accuracy even at the micro scale, making it an indispensable method in modern engineering applications. Its measurement principle is simple: a diamond pyramid-shaped indenter is pressed into the material surface with a specific force, and the diagonals of the resulting indentation are measured to calculate hardness. Despite this simplicity, the method yields highly repeatable and reliable results.
One of the key differentiators of the Vickers test is the ability to vary both the indenter load and the test force across a wide range. This flexibility allows for both microhardness and macrohardness measurements, enabling the test to be adapted to a wide variety of materials and applications.
Imagine a test method that has remained valid for over a century and continues to serve as one of the fundamental tools of modern materials science. The Vickers hardness test is precisely such a method.
When and by Whom Was It Developed?
The Vickers hardness test was developed in 1921 by engineers Robert L. Smith and George E. Sandland at Vickers Ltd., a British company. At that time, they were seeking a new measurement system that would better meet the industry's evolving needs.
Although the Brinell method was widely used, its requirement for large loads and its limited effectiveness on thin materials exposed certain limitations.
Smith and Sandland aimed to develop a more precise, more flexible test applicable across a broader range of materials and they succeeded. As a result, the Vickers test became not just an alternative, but often the preferred method from that point onward.
Industrial Adoption
Beginning in the 1930s, the Vickers test began to spread rapidly across metallurgy laboratories in Europe. Especially after World War II, as defense production gave way to broader industrial manufacturing, the need to test a wider range of materials with greater precision became more prominent further highlighting the advantages of the Vickers method.
From the 1980s onward, the evolution of digital microscopes and automated load control systems led to the advancement of Vickers testing devices. Today, many modern systems use digital loading, automated indentation measurement, and computer-assisted analysis.
The global adoption of this method was also bolstered by the formalization of testing procedures by international standards organizations such as ISO and ASTM, making it a globally recognized testing language.
When choosing a hardness testing method, the key considerations are not only the type, size, and surface condition of the material, but also the desired accuracy and repeatability of the results. This is where the Vickers hardness test stands out in many ways. Its widespread use in both laboratories and production facilities is rooted in these advantages:
Applicable to Very Small and Thin Materials
Brinell and Rockwell tests struggle to evaluate small-scale materials because their large indentations can damage the test piece or yield inaccurate results.
In contrast, the Vickers test uses a diamond pyramid indenter capable of applying very low forces (as low as 1 gf). This is a major advantage for researchers working on the micro scale or manufacturers testing delicate components.
Usable at Both Micro and Macro Scales
Thanks to the wide range of adjustable loads, the Vickers test can measure hardness at both micro and macro levels:
• Micro-Vickers: Uses low loads (1 gf – 1 kgf), creating tiny indentations.
• Macro-Vickers: Uses higher loads (1 kgf – 100 kgf), suitable for larger components.
This flexibility allows the same principle to be applied across parts of various sizes, and since the indenter remains the same, methodological consistency is maintained.
One Indenter for All Loads
In the Rockwell method, different indenters and load combinations are used for each scale, requiring complex procedures and equipment changes.
However, the Vickers test uses only one type of diamond pyramid indenter regardless of the load applied. This simplifies testing procedures and reduces the chance of operator error.
Additionally, because the indenter remains constant, results from different materials can be compared consistently only the applied force changes, enhancing the comparability of data.
High Accuracy and Repeatability via Indentation Measurement
In the Vickers method, hardness is calculated by measuring the diagonals of the indentation left on the surface under a microscope. This ensures high precision, especially in surface hardness analysis.
Unlike other tests where values are read directly from a gauge, Vickers requires manual measurement of the indentation. This allows better control of variables such as surface roughness, localized defects, or plastic deformation that might otherwise skew the results.
Applicable to a Wide Range of Materials
The Vickers method is not limited to metals. It can also be used on ceramics, composites, polymer-based engineering materials, coatings, and more.
Regardless of whether the material is very soft or extremely hard, a suitable load can be selected to perform the Vickers test effectively.
The most commonly encountered hardness testing methods are Vickers, Brinell, and Rockwell. Each relies on different principles, offers distinct advantages, and suits different applications. However, the Vickers test stands out when precision and versatility are the priority.
1. Differences in Testing Method
• Vickers: A four-sided diamond pyramid is pressed into the surface with a specified load. The diagonals of the indentation are measured under a microscope to calculate hardness.
• Brinell: A hard steel or tungsten carbide ball is pressed into the surface with a specific force. The diameter of the circular indentation is measured to determine hardness.
• Rockwell: A diamond cone or steel ball applies a minor load followed by a major load. The hardness value is read directly from the machine based on the depth of indentation.
2. Indenter Types and Load Ranges
• Vickers: Uses a single type of diamond pyramid indenter. Load ranges from 1 gf to 100 kgf.
• Brinell: Typically uses a 10 mm steel or tungsten carbide ball. Loads usually range from 500 to 3000 kgf.
• Rockwell: Includes various scales (HRC, HRB, HRA, etc.) depending on the indenter and load used. Both vary according to the material.
3. When to Use Which Method?
• Vickers: Ideal for very small parts, thin coatings, hardened surfaces, or precision zones. Suitable for both micro and macro testing.
• Brinell: Best suited for larger, homogeneous metal parts. Commonly used for cast iron and soft steels.
• Rockwell: Preferred for fast, direct readings on production lines. The test surface should be clean, smooth, and of adequate thickness.
4. Measurement Accuracy and Surface Preparation
• Vickers: Offers high accuracy due to microscopic measurement. However, surface smoothness is important.
• Brinell: Requires a very flat and smooth surface. Leaves large indentations, which can damage the test area.
• Rockwell: Less sensitive to surface preparation but may yield incorrect results on dirty or rough surfaces.
Thanks to its high precision and wide applicability, the Vickers hardness test is a preferred method in many industries. Its broad scope of use stems from its ability to provide reliable results for both microhardness and macrohardness testing across a wide variety of materials and forms.
Key Industries of Use:
Aerospace Industry
In this sector where high-strength and lightweight materials are essential—the Vickers test is widely used for hardness control of specialty metals, particularly titanium and nickel-based superalloys.
Automotive Industry
Frequently used in the quality control of high-stress components such as engine parts, gears, and bearings. It verifies surface hardness and wear resistance of critical components.
Medical and Biomedical Sector
Used to evaluate the surface hardness of biocompatible materials in implants, prosthetics, and surgical instruments. It is especially effective for analyzing the microstructural properties of titanium alloys and stainless steels.
Electronics and Microelectronics
Micro Vickers testing is ideal for small-scale components, such as thin-film coatings and micro-mechanical parts, where precise surface hardness measurement is required.
Ceramic and Composite Materials
Also effective in evaluating hard but brittle materials. When combined with fracture toughness analysis, the Vickers test helps assess the performance of such materials.
Applicable Material Types:
• Steels and alloys
• Metals such as aluminum, titanium, and copper
• Hardened or surface-treated materials
• Ceramics and carbides
• Thin film coatings
• Biomedical alloys
• Composite materials
• Polymer-based engineering materials (at micro scale)
The Vickers test's ability to cover such a broad material spectrum makes it indispensable for both production and R&D. Regardless of the material’s size, shape, or surface condition, reliable hardness measurements can be obtained with appropriate test parameters.
The accuracy and repeatability of the Vickers test depend on its correct application. While the method may seem simple, each step requires attention to detail, proper surface preparation, and the correct use of equipment.
1. Required Equipment:
• Diamond pyramid indenter: A four-sided diamond tip with a 136° angle. It remains fixed during the test and is not changed.
• Load application system: Can be manual, motorized, or digital. Load is adjustable from 1 gf to 100 kgf.
• Microscope/optical measurement unit: Measures the diagonals of the indentation after the load is applied usually integrated into the testing machine.
• Sample holding stage: Keeps the sample fixed and level especially important for small specimens.
• Surface preparation tools: Sandpaper, polishing, and cleaning equipment. A smooth and reflective surface is required.
2. Surface Preparation
Many errors occur before the test even begins, making surface preparation critical.
• The surface must be clean, oil-free, and dry.
• It should be polished and smoothed using sanding and polishing techniques.
• Rough or dirty surfaces can lead to inaccurate results.
• For thin or soft materials, extra care is required to avoid altering the surface.
3. Applied Force (Load)
One of the advantages of the Vickers test is its flexibility in applied load:
• Loads between 1 gf and 100 kgf can be selected based on the device.
• The load should match the test purpose and material type.
• For micro-scale testing, low loads such as 25 gf are preferred.
• For larger, thicker materials, higher loads (e.g., 10–50 kgf) are suitable.
Load dwell time is typically held constant between 10–15 seconds, in accordance with ASTM E384 and ISO 6507 standards.
4. Test Procedure
The Vickers test follows a straightforward but precise sequence:
• Step 1: Secure the specimen on the test stage.
• Step 2: Select and apply the appropriate load.
• Step 3: Press the diamond pyramid indenter perpendicular to the surface.
• Step 4: Maintain the load for the specified dwell time (e.g., 15 seconds).
• Step 5: Remove the indenter and observe the indentation under a microscope.
• Step 6: Measure both diagonals (d₁ and d₂) of the indentation.
• Step 7: Calculate the average of the two diagonals and determine the hardness value.
The Vickers test is based on measuring the diagonals of the indentation left on the surface after applying a known force. The final hardness value is calculated using a mathematical formula not visual estimation ensuring both accuracy and repeatability.
Formula Used
HV = 1.854 × (F / d²)
Where:
• HV = Vickers hardness value
• F = Applied force in kilograms-force (kgf)
• d = Average length of the two diagonals (in millimeters)
• 1.854 = Geometrical constant specific to the pyramid indenter
The formula works by dividing the applied load by the surface area of the indentation. Since the indenter geometry is fixed, the area can be represented by the square of the diagonal length.
Example Calculation
Scenario:
A 1 kgf load is applied, and the measured diagonal lengths are 0.062 mm and 0.060 mm.
Step 1: Calculate the average diagonal
d = (0.062 + 0.060) / 2 = 0.061 mm
Step 2: Apply the formula
HV = 1.854 × (1 / 0.061²)
HV = 1.854 × (1 / 0.003721)
HV ≈ 1.854 × 268.71
HV ≈ 498.3 HV
This result shows that the surface being tested has a hardness of approximately 498 HV, a value typically found in heat-treated steels.
The reliability of a hardness test depends not only on correct application but also on adherence to established standards. These standards clearly define the conditions under which the test must be conducted, the specifications of the equipment used, measurement tolerances, and reporting requirements.
The Vickers hardness test is governed by two major international standards:
ISO 6507 outlines the general rules for Vickers hardness testing. It consists of multiple parts:
• ISO 6507-1: General principles, indentation measurement, and calculation method
• ISO 6507-2: Calibration and verification of testing machines
• ISO 6507-3: Repeatability and accuracy of test results
• ISO 6507-4: Use and verification of automated testing systems
The standard specifies how to apply the test in laboratories and quality control environments, paying close attention to factors such as load dwell time, indentation symmetry, and device accuracy.
ASTM E384 is the primary American standard for both micro and macro Vickers hardness testing. It provides detailed procedures on:
• Testing methods
• Microhardness measurement techniques
• Tolerances in indentation measurement
• Operator effects and equipment calibration
This standard is especially focused on minimizing operator error in micro-scale testing.
a) Data Comparability
For companies operating internationally, test results must be valid and understandable across borders. Without standardization, comparisons between labs become meaningless.
b) Quality Assurance and Certification
For organizations certified under systems like ISO 9001 or IATF 16949, compliance with test standards is mandatory. Non-compliance may result in invalid product certifications.
c) Generation of Undisputed Data
Hardness is a critical material property used in accept/reject decisions. Its reliability depends not only on proper testing devices but also on adherence to internationally recognized standards.
