Study of the Fatigue Strength of Titanium aLloys Modified by Vacuum Ion Nitriding in the Pulse Mode Under High-Frequency Loading
DOI:
https://doi.org/10.32515/2664-262X.2026.14(45).163-171Keywords:
ion nitriding, pulse mode, titanium alloy, endurance limit, loadAbstract
In the work presented, a study was carried out of the effect of the coating (modification of the surface layer by vacuum ion nitriding in the pulse mode on endurance at a high frequency (about 10 kHz) of variable load. Samples with a length of 24.1 mm had a cross section measuring (6x0.5) mm in the fatigue failure zone. It is absolutely necessary that for a correct comparison of future results, the size of the corresponding cross section the cross-section of samples for the case of tension - compression should be similar; the frequency of tests should also be the same.
Calculations show that the resonant length of a metal rod that oscillates at a frequency of 10 kHz along its basic form should be quite significant - about 240÷250 mm. Since with such lengths it is practically impossible to ensure the required size (6x0.5) mm of the cross-section of the sample without losing its stability, due to the minimal stiffness during bending, in this case it is necessary to find a solution to this problem. Plates made of such materials, collected in a package, work exactly under conditions of cyclic stretching-compression at frequencies (3,10,20,40) kHz. In order to further increase the stability during longitudinal oscillations of such samples, their test was carried out at frequencies higher than (3;10) kHz, because, for example, at 20 kHz the length of the sample will be less than the length at 10 kHz by exactly 2 times.
Experiments were performed to determine the fatigue strength of thin sheet titanium VT1-0 before and after modification of the surface layer using vacuum ion nitriding technology in the pulse mode.Fatigue tests of prismatic samples during their resonant bending vibrations were carried out at a high frequency of loading - (11-12) kHz. Preliminary modification of the samples was carried out using the technology of vacuum ion nitriding in isothermal mode.
Fatigue curves based on 107 load cycles were constructed as a result of the tests. Five groups of samples were tested - one group in the state of delivery without processing and four groups after technological modification of the layer. From the fatigue curves, the values of endurance limits σ-1 under symmetrical variable load were obtained. It is shown that regardless of the variation of the parameters of the vacuum ion nitriding technology in the pulse mode in their given range, the value of the endurance limit σ-1 of titanium VT1-0 with a modified surface is higher by (12-17)% compared to the value of σ-1 of unmodified titanium VT1-0.
It is assumed that, based on the apparent coincidence of the fatigue curves for groups of samples 2, 3, 5 in the section N≥3×106 cycles, one can hope for guaranteed strengthening of titanium VT1-0 in the given (selected) range of parameters.
The calculation-experimental method of determining the durability of materials on thin-walled samples under cyclic tension-compression loading under high-frequency conditions is described. Given its proven performance and theoretical validity, it is quite suitable for studying the fatigue strength of thin-sheet materials depending on the influence of various physical, mechanical and technological factors, including surface modification in another way.There is an opportunity to compare the fatigue strength of titanium alloys before and after nitriding under cyclic bending and homogeneous tension-compression under conditions of complete identity of the initial characteristics and factors, except for the type of the given load.
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Copyright (c) 2026 Anatoly Rutkovskіy, Oleksandr Trapezon, Sergiy Markovych, Oleg Bevz
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