Extended characterization of materials based on continuous instrumented indentation diagrams

In addition to the traditional determination of hardness and elastic moduli from continuous diagrams of instrumental indentation, it is proposed to determine the yield stress, the characteristic of plasticity, the characteristic relative size of the elastoplastic zone under the indenter, and the volumetric deformation of the material in the area of contact of the indenter with the sample. The indentation diagram shows the transition point to the unconstrained material flow under the indenter. Keywords: indentation, hardness, elastic moduli, contact stiffness, elastic-plastic strains.

ANALYSIS OF THE REASONS FOR SPECIFIC DEFORMATION BEHAVIOR OF TOPOCOMPOSITE OF THE ALN-D16T SYSTEM DURING INSTRUMENTAL INDENTATION

The reasons for obtaining the unloading curves of the indentation diagrams of topocomposites coated with aluminum nitride with a nonlinear section of the end of the unloading curve are investigated. The influence of the plasticity of the base and the structure of the coating of aluminum nitride of coatings deposited by the magnetron method on the base made of aluminum alloy D16T on the mechanism of deformation and destruction of the topocomposite was evaluated. The assessment of these characteristics was carried out based on the results of the analysis of model and experimental indentation diagrams of topocomposites with coatings of aluminum nitride and titanium nitride, as well as using the results of materials science studies of the behavior of materials of topocomposite components at high specific loads known in the literature. It was found that the nonlinear shape of the end of the unloading curves is associated with solid-phase structural changes in the coating material. The level of solid-phase structural changes in the coating can be estimated from the width of the hysteresis loops during repeated indentation cycles.

Research of polymers strength properties for 3D printing under normal conditions

An article is devoted to the study of the strength properties of interlayer adhesion and determination of Young's modulus by the ball instrumental indentation method for samples, made of various plastics using additive technology under normal conditions. This production method is chosen as the most appropriate for creating lightly stressed parts of complex geometry (up to 30 MPa) in the shortest possible time. One of the possible options for such products is full-size centrifugal wheels layouts of low power gas turbine units (up to 250 kW) for testing them in model conditions. It will ensure the work of the material in the elastic zone. The samples are considered, obtained by FDM method from various polymers such as: acrylonitrile butadiene styrene thermoplastic resin (ABS+), acrylonitrile butadiene styrene thermoplastic resin with addition of carbon fibers (ABS Carbon), nylon with addition of carbon fibers (Nylon Super Carbon), polyethylene terephthalate glycol (PETG) and a compound based on polylactide (PLA HP). Plastics, made by this method, have anisotropic properties. Therefore, in this work, the strength characteristics of the test samples interlayer adhesion under tension are determined.

Evaluation of Adhesion Properties of Hard Coatings by Means of Indentation and Acoustic Emission

In general, the mechanical properties of hard thin coatings are investigated using indentation methods. Material characteristics of hard coatings, such as elastic modulus and hardness, are evaluated by means of nanoindentation and an appropriate evaluation methodology. The most popular method used to obtain the coating properties required using nanoindentation is the evaluation based on the Oliver and Pharr methodology. Adhesion and wear properties can be calculated using these data. In this study, we used a novel method to evaluate the wear and adhesion of coatings. A special measuring device combined with static indentation and acoustic emission signal detection was developed to evaluate the adhesion of coatings. The device consists of a macrohardness instrumental indentation device equipped with an acoustic emission measuring gauge. It was used to investigate crack formation and adhesion of coatings deposited on different substrates using acoustic emissions data. The results using both the existing and novel methods were compared and evaluated.

THE INFLUENCE OF ION IMPLANTATION ON THE PROPERTIES OF Ti6Al4V TITANIUM ALLOY IN BIOTRIBOLOGICAL SYSTEMS

The article is devoted to the assessment of the geometrical structure of the surface as well as the mechanical and tribological properties of the surface layers obtained in the process of ion implantation. The titanium alloy Ti6Al4V used in biotribological systems was implanted with nitrogen and argon ions. Investigations of the geometrical structure of the surface before and after the tribological tests were carried out using confocal microscopy. The hardness of the tested materials was determined by the instrumental indentation method using a Vickers indenter. A nanotribometer was used for tribological tests. The tests were carried out in a reciprocating motion under conditions of technically dry friction and friction with the lubrication of Ringer's solution. SEM scanning microscopy was used to determine the width of the wear pattern and the wear mechanism. The conducted research showed that the hardness of the tested materials increased as a result of ion implantation. The tribological tests showed that the use of ion implantation improves the tribological properties, and the dominant wear mechanism was abrasive wear.

Features of Measuring the Hardness of a Metal Surface Modified with Ultrafine Particles of Minerals

One of the important characteristics of the surface properties of metal parts subjected to friction is hardness. Hardness measurements are important for determining the operational characteristics of parts and monitoring the technological regimes of surface modification. However, hardness measurements of thin modified layers made by different methods can lead to differences in measurement results. The aim of the article was to study the hardness of a metal surface modified with ultrafine particles of minerals by two different methods (instrumental indentation and Vickers hardness measurement) and a comparative analysis of the measurement results obtained by these methods.Standard Vickers hardness measurements at loads of 0.025, 0.1 and 0.5 kgf showed a qualitative difference between the hardness values of the two samples modified with different mixtures of ultrafine particles of minerals and a large heterogeneity of the hardness values over the area. By the method of instrumental hardness, standard measurements were performed without preliminary selection of the indentation site (at a load of 1.05 N) and measurements during indentation into even sections (at low loads of 10 mN).It is noted that the high precision of measurements implemented by instrumental indentation, due to the large roughness of the samples, leads to large values of the error in calculating the measurement results. An additional difference in the results of measurements performed by two methods at shallow indentation depths may be due to the fact that the object under study has a complex structure consisting of a metal matrix and particles distributed over the depth of the sample. A possible way out of the situation lies in the transition from the use of hardness measures when calibrating instruments to standard samples of properties for which the constancy of mechanical properties in the measured range of indentation depths will be ensured, but which are not yet available in research practice. Therefore, at present, when carrying out work related to the search for optimal conditions for obtaining thin wear-resistant layers on the surface of metals modified with ultrafine particles of minerals, comparative measurements performed by one measurement method are recommended.

Assessment of Mechanical and Tribological Properties of Diamond-Like Carbon Coatings on the Ti13Nb13Zr Alloy

The paper presents the results of tests on the geometric structure of the surface, hardness and tribological tests of coatings produced by the method of physical vapor deposition (PVD) on the Ti13Nb13Zr alloy. Hardness was determined using MCT3 from Anton Paar, by instrumental indentation. A diamond indenter with Berkovich geometry was used for the measurement.Model tribological tests were carried out in reciprocating motion under conditions of technically dry friction, friction with lubrication of synovial fluid and Ringer’s solution. The counter-sample in the tested friction nodes was a ball of Al2O3 with a diameter of 6 mm. Nanometer hardness measurements showed that as a result of the diamond-like carbon coating (DLC), the hardness increased by an 7-fold. The lowest friction coefficients among all tested friction nodes were obtained for the material combination Ti13Nb13Zr a-C:H - Al2O3 regardless of the conditions of testing. In the case of technically dry friction, the coefficient of friction decreased by 80%, synovial fluid by 70%, and in the case of Ringer’s solution by 88% compared to the results obtained for Ti13Nb13Zr.

Исследование свойств конструкционных материалов методом инструментального индентирования с помощью портативного нанотвердомера

A modification of the "NanoScan-4 D" nanohardness meter, which allows of measuring the mechanical properties of articles by the instrumental indentation according to GOST R8.748-2011 under conditions close to industrial fabrication, has been developed. The main advantage of the described device, unlike most modern portable hardness testers, is the ability to work with a wide class of materials (from metals to solid polymers) since the study of the mechanical properties of products does not require preliminary information on the elastic modulus of the material being tested. Presented are the experimental data obtained on standard samples of the enterprise: polycarbonate and aluminum, as well as on various metal articles used as parts of machines and mechanisms of the oil and gas industry. The measured values of hardness coincide with the values obtained on a laboratory nanohardness meter taking into account the inherent errors of this type of equipment.