The Vickers hardness test is a popular method used for measuring the hardness of materials. It can be used for both macro and microhardness testing and is a static test. The method involves measuring the size of the indentation made by an indenter on the surface of a test specimen. This measurement is used to determine the material’s hardness value.
This testing method relies on optical techniques for measurement. The indentation size is typically observed under a microscope, and the length of the diagonals is measured. This measurement is used to calculate the Vickers hardness number of the material. The Vickers hardness test is widely used in industry and research settings due to its high precision and accuracy.
Microhardness testing is a widely recognized and recommended method for evaluating the hardness of various materials, such as metals, ceramics, and composites. This testing technique conforms to the standards established by ASTM E384, ISO 6507, and JIS Z 2244. The microhardness testing method can be applied to almost any type of material, making it a versatile and valuable tool in the field of materials testing. By using microhardness testing, researchers and engineers can obtain precise and accurate measurements of a material’s hardness, which is a critical factor in determining its suitability for specific applications.
Equipment Required
The Vickers hardness tester is a device commonly used to measure the hardness of materials. It works by pressing a pyramid-shaped indenter into the surface of the material and measuring the size of the resulting indentation. The indenter used in a Vickers hardness tester is typically made of diamond, which is one of the hardest materials known to man. This ensures that the indenter will not be damaged or deformed during the testing process. The size of the indentation left by the indenter is proportional to the hardness of the material being tested. The Vickers hardness test is often used in quality control and research and development to determine the strength and durability of materials.
Theory and Principle of the Test
A penetrator with a four-sided diamond pyramid shape will be utilized for the testing process. The angle between the sides facing each other is 136 degrees. In the load stage, three options are available, namely 10 kg, 30 kg, and 60 kg, with 10 kg being the most frequently used load.
During the testing process, the depth of the specimen must be at least 1.5 times the diagonal measurement of the impression created by the penetrator. Additionally, to ensure that the impressions do not interfere with each other, the distance between the center of an impression and the edge of adjacent impressions or the edge of the specimen must be at least 3 times the diagonal measurement of the impression.
Surface Preparation
To ensure accurate results from microhardness testing, it is important to properly prepare the sample material before placing it in the testing machine. The surface condition of the sample plays a critical role in determining the accuracy of the Vickers hardness test, which in turn depends on the load used during the testing process.
When conducting macro hardness testing, loads greater than 1 kgf must be applied to the sample. In addition, the surface of the sample must be ground to a suitable finish to ensure accurate results.
On the other hand, microhardness testing requires loads that are equal to or less than 1 kgf. Furthermore, the surface of the sample must be mechanically polished or electropolished, depending on the specific requirements of the testing procedure. By ensuring that the surface of the sample is properly prepared, the accuracy and reliability of the microhardness test results can be maximized.
Test Procedure
To perform a test on a specimen, it is important to set the machine to the appropriate stage of test load and dwell time. Once this is done, the specimen should be placed on the testing table with care. To ensure accurate testing, the objective should be brought to the “set” position and the hand wheel should be turned slowly in a clockwise direction to focus the specimen sharply on the front screen.
After the specimen is properly focused, the inventor should be brought to the “set” position and the loading, dwell, and unloading cycle should be turned on. Once this is complete, the objective should be brought back to the “set” position. The indentation resulting from the test will now be projected onto the front focusing screen.
To accurately record the results of the test, it is important to measure the diagonals along both axes of the impression and record them accordingly. By following these steps, an accurate and reliable test can be performed on the specimen.
Results
The context given appears to be a mathematical formula involving two variables, F and d. The variable F represents the load applied in kilograms of force, while the variable d represents the arithmetic mean of the two diagonals, d1 and d2, in millimeters.
The formula is not explicitly stated, but it is implied that the variables F and d are related in some way. It is possible that the formula is used in a specific context, such as engineering or physics, where it is used to calculate the force applied to a structure or object based on its dimensions.
Overall, the given context is brief and lacks specific details, making it difficult to provide a more comprehensive analysis.
Formula and Calculation
Vicker’s Hardness (HV) =
The obtained results for a material’s hardness are reported as 800 HV/10, where 800 represents the Vickers hardness and 10 is the load applied during testing. However, it is common practice in the scientific community to report the Vickers hardness in the International System of Units (SI), specifically in mega-Pascals (MPa) or giga-Pascals (GPa).
To convert the Vickers hardness from HV to MPa, it is necessary to multiply the HV value by a conversion factor of 9.807. This conversion factor is derived from the relationship between force and pressure in the SI units, where 1 MPa is equal to 1 N/mm². Therefore, when the Vickers hardness is reported in MPa, it reflects the amount of pressure required to create an indentation on the material’s surface.
Similarly, to convert the Vickers hardness from HV to GPa, the HV value must be multiplied by a conversion factor of 0.009807. This conversion factor reflects the relationship between force and pressure in the SI units, where 1 GPa is equivalent to 1,000 MPa or 1,000 N/mm². Therefore, reporting the Vickers hardness in GPa provides a measure of the material’s resistance to indentation on an even finer scale than MPa.
In summary, converting the Vickers hardness from HV/10 to SI units, specifically MPa or GPa, requires multiplication by the corresponding conversion factor of 9.807 or 0.009807, respectively. This conversion allows for more precise and accurate reporting of a material’s hardness in standardized units that can be easily compared across studies and industries.
Application of Vickers Method Depending on the respective Load Range
Advantages of the Vicker’s Method
The Vickers method is a versatile testing procedure that can be employed with a wide variety of materials and test specimens, spanning from those that are soft to those that are hard. One of the benefits of this method is that it covers the entire hardness range, making it a valuable tool for a range of applications.
Unlike other hardness testing methods that may require different types of indenters depending on the material being tested, the Vickers method utilizes only one type of indenter that is suitable for all testing scenarios. This simplifies the testing process and makes it more efficient.
Another advantage of the Vickers method is that it is non-destructive. This means that the test specimen can be used for other purposes after testing is complete. This is particularly useful in scenarios where the material being tested is rare or difficult to obtain, as it allows for multiple tests to be performed without sacrificing the entire specimen.
Disadvantages of the Vickers Method
To ensure accurate evaluation, the specimen’s surface quality must be of high standard as the indentation is optically measured. Hence, the test location must be adequately prepared by grinding and polishing. Failure to do so will result in imprecise evaluation.
Compared to the Rockwell method, the Vickers hardness testing process is relatively slow. The test cycle typically takes 30 to 60 seconds, excluding the time required to prepare the specimen.
Vickers hardness testers require an optical system to conduct optical indent evaluation, making them more expensive than Rockwell testers.