Accepted articles

L.E. Afanasieva, V.V. Izmailov, M.V. Novoselova
Tver State Technical University

Abstract: The article is devoted to an experimental study of the influence of microstructure features of the Ti – 6Al – 4V alloy obtained by electron beam melting technology on the tribological properties: hardness; friction coefficient; abrasive wear resistance. The microstructure of the alloy consists of colonies α′-plates 1.5…2 μm thick and interlayers of the β-phase 0.2 μm in size. Hardness was measured at low loads N = 1-2 N (microhardness) and at loads N = 90–180 N (indentation hardness). The friction coefficient was determined on a microtribometer according to the ball-plane scheme in a pair with a steel indenter at loads of 2-5 mN. Wear resistance was studied by friction against a fixed abrasive according to the ball-plane scheme. The microstructure and properties of the samples were studied in two mutually perpendicular planes: in the layer and in the direction of synthesis. Anisotropy of microhardness and friction coefficient under low loads was revealed. In the layer plane, the microhardness under loads of several newtons is 900…1000 MPa lower than on the lateral surface of the sample. Under low contact loads, the friction coefficient in the contact of a spherical steel sample with a flat layer surface is approximately 20% lower than in the contact of the same steel sample with the lateral surface of a titanium alloy sample. With increasing contact load, the difference in properties disappears. Abrasive wear resistance in the direction of sample synthesis is 30% higher than in the layer plane, which is explained by the role of the structural factor. It is shown that the orientation of the colonies of α′-plates has a decisive effect on the tribological properties.
Keywords: titanium alloy, selective electron beam melting, microstructure, hardness, friction coefficient, wear resistance

A.V. Tvardovskiy
Tver State Technical University

Abstract: Classical ideas about the adsorption process have always been based on the fact that the adsorbent remains inert and does not change its size when interacting with gases or vapors. Its role is limited to creating an adsorption field where the adsorbate molecules fall. It is on the basis of this principle that the well-known adsorption equations of Henry, Langmuir, Fowler-Guggenheim, Brunauer-Emmett-Teller and others were derived. However, modern experimental studies show that adsorbents are deformed in the adsorption process. This fact significantly changes the entire picture of the consideration of this phenomenon. For example, when the geometric dimensions of the pores of the adsorbent change during deformation of the latter, the adsorption field into which the adsorbate molecules fall changes significantly. And this affects the value of the calorimetric heat of adsorption removed during the studies. Thus, the adsorbent is an equal participant in the adsorption process along with the adsorptive, and the adsorption system should be considered as a two-component one. In this regard, when conducting adsorption studies, a comprehensive approach is needed, including taking isotherms, measuring calorimetric heats of adsorption, and conducting dilatometric experiments to study the adsorption deformation of adsorbents. Such a comprehensive approach was used for the Na-montmorillonite – methanol vapor system. The differential heat and adsorption isotherm at T = 293 K were obtained using a Calvet-type microcalorimeter and a McBain-Bakr microbalance. The adsorbent deformations were measured using a highly sensitive dilatometer. The main part of this dilatometer was a linear differential transformer, the core of which was connected to the adsorbent by means of a rod. Any changes in the geometric dimensions of the adsorbent changed the position of the core in the transformer, which affected the signal taken from the secondary winding of the transformer. Having calibrated the dilatometer, the adsorption deformation of the adsorbent was determined. Such a comprehensive approach allowed us to significantly detail the description of the adsorption process for this studied system.
Keywords: adsorption, adsorbent, adsorption isotherm, calorimetric heat of adsorption, adsorption deformation of the adsorbent, dilatometric method