Failure mechanisms of titanium VT1−0 and zirconium alloy E110 in ultrafine-grained, fine-grained and coarse-grained states under cyclic loading in gigacycle regime

Abstract

Fatigue tests were carried out on samples of titanium VT1−0 and zirconium alloy Zr−1 wt % Nb in the ultrafine-grained, fine-grained and coarse-grained states in a gigacycle fatigue regime. It was found that the formation of an ultrafine-grained structure led to an increase in the fatigue limit in the gigacyclic region (10 9 cycles) by 1.3 times for titanium and 1.7 times for zirconium alloy when compared to the fine-grained and coarse-grained states. An evolution of the temperature field for titanium and zirconium alloy samples in various structural states in the process of cyclic loading was studied by the method of infrared thermography. It was shown that the process of cyclic deformation in all types of structural states was accompanied by an initiation and expansion of a heat source in a local volume of samples which has a significant impact on the fatigue strength. The increment of the maximum temperature on the surface of ultrafine-grained samples of titanium VT1−0 and zirconium alloy Zr−1 wt % Nb is significantly lower than that for the fine-grained and coarse-grained states. This fact indicates a qualitative change in the mechanism of energy dissipation which is associated with characteristic features of the ultrafine-grained state. When comparing the dynamics of thermal fields for the titanium and zirconium alloy samples in coarse-grained, fine-grained and ultrafine-grained states, it was found that the energy dissipation zone covered a considerable volume of the sample in the process of fatigue tests in case of ultrafine-grained state, whereas in case of coarse-grained and fine-grained states the growth of thermal energy was localized in the gauge area of the sample.

Development of Ultrafine–Grained and Nanostructured Bioinert Alloys Based on Titanium, Zirconium and Niobium and Their Microstructure, Mechanical and Biological Properties

“…The number of cycles increased to N = 1.9 × 10 9 before the destruction of UFG titanium. Up to 10 9 cycles, the fatigue strength of UFG titanium was 200 MPa, which is 1.3 times higher than that of CG titanium [106].…”

“…The manifestation of the bulk NS and UFG structures via combined SPD methods increases the mechanical characteristics (yield strength, tensile strength, hardness, endurance limit, wear resistance, cyclic fatigue, etc.) [99][100][101][102][103][104][105][106]. This is due to the fact that NS and UFG metals have a number of specific characteristics, such as small grain size, the predominance of large-angle disorientation at the grain boundaries, and the predominance of high internal stresses as a result of significant defect density inside and at the subgrain and grain boundaries.…”

“…Producing NS and UFG alloys is important for improving characteristics such as fatigue strength [103][104][105][106]. It leads to an increase in not only high-cycle (10 6 cycles) but also gigacycle (10 9 cycles or more) fatigue.…”

“…The fatigue strength increased in the UFG zirconium alloy under a gigacycle load regime [106]. Figure 12 illustrates the experimental fatigue points and curves for the zirconium alloy in different states.…”

Characteristic Features of Ultrafine-Grained Ti-45 wt.% Nb Alloy under High Cycle Fatigue

“…The method provides detailed information on the processes of the initiation and propagation of fatigue cracks, as well as energy conversion and accumulation during mechanical testing. Unfortunately, there is little information about the application of IR thermography for investigating the heat-generation processes in UFG metals during fatigue-testing [ 30 , 31 , 32 , 33 ]. Non-linear vibration analysis [ 34 , 35 , 36 ] is widely used to define the initiation and growth of fatigue cracks [ 37 , 38 ].…”