Microspherical diamond single crystal indenter as a means of obtaining stress – strain diagrams

Obtaining a stress – strain diagram using tensile machines involves testing a large volume specimen. An alternative to such tests is the automated ball indentation test (ABI test — automatic ball indentation), which is designed to determine the stress-strain curves of metallic materials and structural elements. The purpose of this work is to study the applicability of the technique, which is developed for the obtaining of the stress – strain diagram using large spherical indenters (diameter 250 – 1500 μm), to work with a microspherical indenter with a diameter of 5 μm. The use of small diameter spherical indenters allows the study of small sized samples of material from which it is not possible to produce samples for a standard uniaxial tensile experiment. It can be applied to study individual phases of heterogeneous materials, intergrain boundaries, as well as thin films, coatings and near-surface layers of the sample. In this work, the shape of the obtained imprints on the surface of the studied samples was studied both by non-contact method — by means of confocal optical 3D profilometry, and by means of contact method — atomic force microscopy. The non-contact method, as having a higher speed, was used to reveal the grain sizes of alloys, the contact method — to measure the diameter of imprints — due to its higher lateral resolution. A series of experiments were carried out on tensile testing of alloys on a universal testing machine and on indentation of specimens made of the same alloys. The values of elastic moduli and time resistances of alloys V95, VT1 and VT6 were obtained, which coincide within the error limits in the results of two different experiments. In this study, stress – strain diagrams were experimentally plotted using tool indentation and residual indentation geometry analysis when a spherical tip made of diamond single crystal with a small radius of curvature (2.5 μm) was used.

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