Indentation size effect when measuring Vickers hardness

Abstract

Problem. An important aspect in the study of hardness using the Vickers pyramid is to take into account the indentation size effect. When measuring the hardness by the Vickers method, the applied load is divided by the surface area of the impression. A significant factor influencing the conformity of the hardness measurement results is the indentation size effect. The indentation size effect significantly affects the results of hardness measurements, changing their values by 20-60%. The widespread use of hardness tests is explained by a number of their advantages over other types of mechanical tests. However, to date there are a number of problems in determining the hardness of metals and alloys, for example, it is believed that the hardness of metals is a constant, but in practice the hardness depends on the load. The indenter indentation into the surface of the material is carried out in each method of determining hardness with different loads. The force of loading on the indenter depends on the properties of the material, the size of the prototype and other experimental factors. In turn, Vickers hardness also depends significantly on the load on the indenter. This phenomenon is called "indentation size effect". Goal. The purpose of the study is to assess the nature of the change in hardness with increasing load on the indenter using the functional dependence of hardness on the depth of indenter insertion. Methodology. The study was conducted on three metal samples according to ISO 6507. Results.1. In the study of the dependence of Vickers hardness on the load of samples with 12Х18Н10Т, МА21, БрО5Ц5С5 the direct dimensional effect (indentation size effect) is obviously shown. This indicates that as the load increases during the measurements, the hardness of the materials decreases significantly. 2. In the study of the dependence of Vickers hardness on the load of sample 12Х18Н10Т, it was found that with increasing load from 29N to 196N, the hardness decreases from 252HV29 / 10 to 200HV196 / 10- by 21%. 3. In the study of the dependence of Vickers hardness on the load of sample MA21, it was found that with increasing load from 24N to 196N, the hardness decreases from 128HV24 / 10 to 69HV196 / 10-47%. 4. In the study of the dependence of Vickers hardness on the load of sample БрО5Ц5С5, it was found that with increasing load from 19N to 49N, the hardness decreases from 211HV19 / 10 to 85HV49 / 10- 60%. 5. An increase in Vickers hardness values with a decrease in the test load on the indenter should be kept in mind, especially when studying metals and alloys in the micro- and nanoranges. Originality. A mathematical dependence of hardness on the load was obtained, which demonstrates a decrease in hardness with increasing load. This dependence is also quantitatively shown on various metal alloys. Practical value. The application of the proposed method of studying the dependence of hardness on the load will ensure a more reliable qualitative assessment of metals and their products.