Wear resistance of titanium alloy VT1-0 with a modified surface under abrasive action
Authors:   National Academy of sciences of Ukraine G.S. Pisarenko institute for problems of strength, Rutkovskіy Anatoly , Markovych Sergiy ,   Central Ukrainian National Technical University, Mahopets Sergiy ,   Central Ukrainian National Technical University, Markovych Viktor ,   Central Ukrainian National Technical University
Published: April 2024

The cost of rebuilding machine parts as a result of wear is enormous and rising every year. At a US symposium on reducing wear in machinery, the general consensus was that wear management is central to solving national problems such as energy conservation, material reduction, and ensuring the reliability and safety of mechanical systems. Nitriding significantly increases the wear resistance of metals and alloys. The formation of chemical compounds in titanium alloys by introducing nitrogen or increasing its concentration limit changes the rate of chemical reactions and the kinetics of oxide film growth, and increases their adhesion to the substrate. This leads to a decrease in the intensity of adhesive node formation and improves the tribological characteristics of titanium alloys. Therefore, it is necessary to study a titanium alloy with a hardened nitrided layer to obtain experimental results to determine the regularity of the influence of diffusion saturation parameters on wear resistance under abrasive conditions. The universal installation "VIPA-1" was used for vacuum ion nitriding in the pulse mode and the formation of diffusion layers on the surface. Technological parameters of vacuum ion nitriding in the pulse mode: temperature - 550°C, pressure - 25-150 Pa, processing time - 10 hours, ratio of reaction gases - 80% Ag + 20% N2. For experimental studies, samples of VT1-0 titanium alloy with dimensions of 30x30 mm and a thickness of 5 mm were used. The surface hardening of the samples was carried out uniformly around the entire perimeter, which ensures a uniform thickness of the diffusion layer. The analysis of the operating conditions of the friction surfaces of most structural elements made it possible to use the installation for bench tests according to the scheme of wear with a free abrasive (Brinell method). Wear tests were carried out on an experimental setup in accordance with GOST 23.208-79 (Fig. 2). The friction process was modelled in the presence of a free, not rigidly fixed abrasive, which coincides with the American standard ASTM C 6568. The experiment was carried out at a sliding speed of 0.158 m/s, a load of 20 kg (with a shoulder of 272 mm) and a friction path of 50 m. Steel 45, hardened to a hardness of 480-500 HB, was used as a reference. The wear body was a disc made of VT1-0 titanium alloy with a diameter of 100 mm and a thickness of 3.5 mm. On the basis of experimental studies, it has been established that the main mechanisms for increasing the wear resistance of titanium alloys as a result of the process of diffusion saturation of the surface with nitrogen during vacuum ion nitriding in the pulse mode are strengthening of the surface layers; creation of a favourable residual stress pattern; change in the patterns of deformation of the surface layers; change in the chemical and adhesive properties of the surface; transfer of diffusing nitrogen atoms into the depth of the matrix during friction due to the tribodiffusion effect. Conclusions. 1. Maximum wear rate of titanium alloy VT1-0 without hardening. 2. The effect of thermocyclic nitriding increases the wear resistance of VT1-0 alloy: in sand - 3 times; in water + sand - 3.5 times; in salt + sand - 2.5 times. 3. The effect of isothermal nitriding increases the wear resistance of VT1-0 alloy: in sand - 4 times; in water + sand - 3.5 times; in salt + sand - 2.5 times.