What is a Vickers hardness tester and how does it work?
A Vickers hardness tester is a widely used instrument for measuring the hardness of materials. It is named after its inventor, George Vickers, and is based on the principle of indentation hardness testing. This testing method involves applying a controlled force on the surface of a material and measuring the size of the resulting indentation.
The Vickers hardness tester uses a diamond pyramid-shaped indenter to create the indentation. The indenter has an angle of 136 degrees between opposite faces, creating a square-based pyramid. The size of the indentation is determined by the diagonal lengths of the square impression, which are measured using a microscope or a digital imaging system.
The testing process begins by preparing the material's surface, ensuring it is clean and flat. The material is then placed on the testing stage, which is typically a sturdy platform capable of withstanding high pressures. The indenter is mounted on an adjustable arm that can be positioned accurately above the surface of the material.
To perform the hardness test, a load is applied to the indenter. The applied load is usually within the range of 1 kg to 120 kg, and it remains constant during the test to ensure consistent results. The load is generally applied for a specified duration, typically ranging from a few seconds to a minute.
Once the test is completed, the indenter is removed, and the indentation is measured. A microscope or digital imaging system is used to determine the diagonal lengths of the square impression. These measurements are then used to calculate the Vickers hardness value using the formula: Vickers hardness number (HV) = 1.854 × Applied Load ÷ Surface Area of the Indentation.
The Vickers hardness value represents the material's resistance to indentation. It is a dimensionless quantity, usually expressed in HV units. The Vickers hardness scale is quite extensive, covering a wide range of materials from extremely soft to extremely hard. It is commonly used for testing metals, ceramics, and some polymers.
One of the advantages of the Vickers hardness test is its ability to produce accurate and reproducible results, even with different sample orientations. This makes it a versatile testing method, particularly when dealing with anisotropic materials. Additionally, the Vickers hardness scale is capable of measuring extremely hard materials, with the upper limit reaching up to 2000 HV.
What are some advantages of using a Vickers hardness tester over other hardness testing methods?
There are several advantages of using a Vickers hardness tester over other hardness testing methods. Here are some of them:
1. Versatility: One of the major advantages of the Vickers hardness tester is its versatility. It can be used to test the hardness of a wide range of materials, including metals, ceramics, and even some non-metallic materials. This makes it a valuable tool in industries such as manufacturing, aerospace, automotive, and construction where materials of different types and hardness levels need to be tested.
2. Accurate and Precise Results: The Vickers hardness testing method provides highly accurate and precise results. It uses a diamond indenter to create a square-based pyramid-shaped indentation on the material surface. The diagonals of this indentation are then measured using a microscope, and the Vickers hardness number is calculated based on the size of the indentation. This method allows for more accurate and repeatable measurements compared to other hardness testing methods.
3. Wide Range of Hardness Testing: The Vickers hardness tester can measure a wide range of hardness values, from very soft materials with low hardness to very hard materials with high hardness. It provides a reliable measurement method for materials across the hardness scale, making it suitable for analyzing materials with varying levels of strength and toughness.
4. Small Indentation Size: The Vickers hardness tester creates very small indentations, which is advantageous when testing delicate or thin materials. The small indentation size helps to minimize the effect on the surrounding material, reducing the risk of damage or deformation. This is particularly beneficial for materials that are prone to cracking or fracture under high forces, making the Vickers hardness tester a safer and non-destructive testing method.
5. International Standardization: The Vickers hardness testing method has been internationally standardized, which ensures consistency and comparability of results across different laboratories and industries. The standardized testing procedures and calibration methods allow for accurate hardness measurements that can be directly compared and understood by professionals worldwide.