Scratch hardness method defines the resistance of a material to plowing by a hard stylus. It measures the hardness of the material and its ability to resist scratches and abrasions. Generally, a scratch hardness tester consists of a stylus, portable sample holding stage, load-applying device, and a data processing and display unit.
The earliest scratch hardness tests were conducted by Friedrich Mohs in 1820 who also developed the Mohs scale. The scratch hardness test measures the resistance of the specimen to fracture or permanent deformation due to friction caused by the stylus along its surface.
This test uses a harder material to scratch the specimen surface which is made of a relatively softer material. When you need to test coatings, then scratch hardness refers to the force which is necessary to cut through the film to the substrate. Mohs scale is used for measuring the scratch resistance of material along with a measuring device known as sclerometer.
Indentation hardness refers to the hardness of a material which is determined by making an indentation on its surface using an appropriate indenter under a test load.
有其测量压痕的用于测量其硬度的深度在试样表面上形成由许多不同的压痕试验方法。 压痕硬度测试可以进一步细分为两个类别 - 宏压痕试验和微压痕测试。 宏压痕试验使多余的值; 1kgf的使用大测试负载，并能上去3000Kgf在某些情况下。
The test loads applied for micro-indentation hardness tests are much lower and can range between 1 to 1000gf. Micro-indentation tests can be used for measuring changes in hardness on a microscopic scale. Vickers method and Knoop hardness testing methods are two popular micro-indentation hardness testing methods.
Indentation hardness tests can be prone to errors. The main sources of errors while measuring hardness include poor technique, improper calibration of the testing equipment, improper finishing of the specimen surface, etc. The test surface needs to be free from any dirt, oxidation, or lubrication to get reliable estimates of hardness. The indenter should also be perpendicular to the specimen surface as any inclination will result in faulty hardness measurements.
回弹硬度是使用里氏回弹硬度试验通常测定。 此方法是通过使用便携式硬度仪在1975年开发了由里氏和Brandestini。 该测试仪提供了新的替代通常错综复杂传统硬度测试仪器。
里氏回弹硬度检测方法如下标准化程序。 所述主体的速度范围米1.4 3米/秒之间，以/秒。 根据这种方法，所述主体的前和后的冲击速度被测量以确定样品的硬度。
The ratio of the impact velocity to the rebound velocity gives the dynamic Leeb hardness of the test specimen. The object used for making the impact on the specimen can be tungsten carbide cobalt, ceramic or diamond, or a ball-shaped indenter with different radius.
The sample hardness determined by this method is represented as (example) 750 HL D in which 750 denotes the hardness value, HL denotes “Hardness according to Leeb” and D represents Leeb method with spherical impact body of tungsten carbide-cobalt with a radius of 1.5 mm and weight of 4.5 grams.
The hardness of a material depends on a number of factors like homogeneity of the material, type of material, its size, and condition.
There are different types of methods for hardness testing which needs to be selected carefully for getting the most accurate and reliable hardness measurements.
Factors which need to be considered before selecting the ideal hardness testing methods include- the type of material to be tested, the hardness of the material to be tested, homogeneity of the material, size of the specimen, if mounting is necessary for hardness testing, thickness of the specimen, etc.
Rockwell hardness testing is the most common and fast method for testing hardness. It is generally ideal for testing hardness of larges sized samples.
It can be used either on the assembly line or in laboratories for testing hardness. It uses a steel ball or diamond-tipped cone indenter for measuring hardness depending upon the hardness of the material to be tested.
To start the Rockwell test, a minor load of generally 10Kgf is applied on the indenter. The indenter then moves under the test load on to the specimen surface. While the indenter is still under the influence of the minor test load, an additional major test load is also applied to it. This ensures better indentation on the specimen surface which is clear and measurable.
The Rockwell method of hardness testing is popular as it is not influenced by either the operator’s bias or the roughness of the surface whose hardness is being tested.
It does not make use of any sophisticated or costly optical equipment for measuring the hardness of specimen, which makes it a cost-effective method for hardness testing. It is a non-destructive method for hardness testing which means that the sample specimen being tested is not destroyed and it can be used for other purposes after the testing procedure is completed.
This method has its drawbacks also as it is not very accurate compared to other methods of hardness testing. Small deviation in measuring the indentation depth can throw off the hardness readings considerably.
If the indenter in this method is worn out, then it can provide faulty hardness measurements which are non-reliable.
Rockwell hardness value is calculated using the conversion charts. There are nearly 30 Rockwell scales but most of the materials are covered by Rockwell C and B scales. The hardness values in Rockwell testing are represented as (example) 70 HRB where 60 is the hardness reading on the B scale.
The Brinell hardness test is one of the oldest and most widely used methods for hardness testing of materials. This method was developed by JA Brinell in the year 1900. It is ideal for measuring the hardness of specimens which are too rough or course to be measured by other methods.
The Brinell method involves usage of higher test loads which can go up to 3000Kgf and a ball indenter generally 10mm in diameter.
For measuring the hardness of softer metals and alloys, smaller test loads of up to 500Kgf are also used. The predetermined test load is applied to the spherical indenter which is held to the specimen surface for generally for 10-15 seconds and then moved.
The indentation depth made by the indenter on the specimen surface is then measured and studied using advanced optical equipment which ensures better accuracy and reliability.
The Brinell conversion chart is then used to convert the average diameter of the indentation made to the corresponding Brinell hardness value. Using the conversion charts, the Brinell hardness value can also be converted into the corresponding tensile strength.
The Brinell method of hardness testing comes with few drawbacks also. The operator can make mistakes in measuring the indentation depth on the specimen surface which can considerably impact the hardness measurements.
Since the method involves advanced and sophisticated optical equipment for measuring the specimen hardness, it is costlier compared to the Rockwell method. It also takes more time to test hardness as the specimen surface needs to be prepared before testing.
The Brinell method will also not work accurately if the specimen surface is too thin i.e. less than 9.6 mm.
The hardness readings using the Brinell method are represented as 600 HBW where 600 denotes the hardness value and HBW denotes “Brinell Hardness” with tungsten ball indenter. If steel ball indenter is used then the readings will be represented as 600 HBS where HBS denotes “Brinell Hardness” with steel ball indenter.
The Vickers test uses the same principle as the Brinell method with the only exception being the type of indenter being used.
The type of indenter needs to be changed under the Brinell method depending on the type of material being tested. However, the same diamond indenter is used in the Vickers method for measuring the hardness of all specimen types.
The indenter used in this method is in the form of a right pyramid. A test load is applied on the indenter which presses itself against the specimen surface thereby leaving an indentation.
The diagonal lengths of these indentation marks are measured using optical systems, resulting in highly accurate hardness readings. The dwell time- the time for which the test force is applied through the indenter on the specimen surface- is generally between 10-15 seconds in this method.
The Vickers test using micro-test loads which are much lesser compared to the Brinell method. It is a microhardness testing method which is best suited for measuring the hardness of materials which are too thin or small for macro hardness testing.
不推荐用于在组装线成批生产维氏试验和更适合用于实验室测试。 在维氏试验的硬度测量被表示为700 HV / 10，其中700是已经在通过使用10公斤力试验力被到达的维氏硬度值。
努普硬度测试方法是将维氏方法的替代方法。 它是显微硬度测量方法，该方法适用于测量像陶瓷易碎和脆性材料的硬度。 这也是像涂料小的细长区域硬度测试非常有用。
努普方法也使用一个锥形钻石压头为，但压头是长形的而不是被右金字塔作为维氏方法。 由于该方法是用于易碎材料的硬度测试，它使用的至多值; 1kgf微负载。
Due to the shape of the indenter, the Knoop method is better suited for measuring longer elongated specimens like coatings. It is important to note that the specimen surface should be prepared properly before conducting the Knoop test for ensuring accurate and reliable hardness measurements.