Determination of Fatigue Strength of VT1-0 Titanium Sheet Under Cyclic Bending On Prismatic Specimens With Surface Layer Modification

The study aimed to determine the nature of the influence of the results of surface layer nitriding on the endurance characteristics of titanium alloy VT1-0. The factor of such a problem statement is the need to strengthen parts and structural elements by their surface modification. The effectiveness of the strengthening technology was checked on the example of fatigue bending load. Preliminary modification of the surface layer of the material specimens was performed using diffusion ion-plasma thermocyclic nitriding (IPTA) technology, the variable parameters of which were pressure, the temperature in the working chamber, and the duration of the diffusion process. To experimentally determine the effect of modification parameters on endurance to conduct experiments in real time, a high-frequency method for determining the endurance limits was used. As one of the most effective methods of accelerated determination of the endurance limit, this method is the most convenient for comparative studies of the fatigue strength of materials. A high-frequency magnetostrictive installation was used. To determine the endurance limit σ –1 under symmetric bending loading, cantilever prismatic specimens were tested by excitation of resonant bending vibrations at a frequency of 11–12 kHz. To ensure fatigue failure of the specimens in a predetermined cross-section, remote from the place of fixing on the installation, a variant of point-hinged fixing of the cantilever specimen was used, in which intense resonant vibrations with two nodal cross-sections were excited. Fatigue failure under such a loading scheme occurs in an entirely determined section between two nodes of oscillations. Calculating the destructive stresses in this section is performed by a method based on measuring the vibration frequency and coordinates of the nodal sections. Fatigue tests of five groups of specimens were carried out – one with specimens in the state of delivery without technological processing and four groups after technological modification of the surface layer. Fatigue curves were built based on 10 7 loading cycles. It was found that regardless of the variation of IPTA technology parameters in their given range, the endurance limits σ –1 of titanium with a modified surface are higher by 12–17% compared to σ –1 for unmodified titanium VT1-0. From the analysis of the correlation between the obtained values of σ –1 and the corresponding technological parameters of nitriding, as well as based on t