Effects of Electron Beam Processing on Fatigue Fracture Propagation Pattern and Formation of Deformation Zone on the Fracture Surface in Titanium Nickelide.

The effect of surface treatment using an electron beam is explored as a factor influencing the nature and the rate of fatigue fracture propagation in titanium nickelide samples undergoing cyclic stretching under a low-cycle loading regime before and after irradiation with low-energy high-current electron beam (L-EHCEB). A correlation is established between the stage of fatigue fracture propagation and the stage of forming deformation zones on the fracture surfaces in unirradiated and in irradiated samples. The surfaces of the samples are treated using the electron beam installation RITM-SP having the following parameters of electron beam: energy density E_S = 3.7 J/cm², pulse duration τ = 2.5 μs, number of pulses n = 5. The difference in propagation sequence of main fatigue fractures is revealed under cyclic stretching of unirradiated and irradiated titanium nickelide samples. Preferential mechanisms of quasi-static and fatigue fracture are established at various stages of fracture propagation. It is shown that LEHCEB treatment shifted both the onset of fatigue destruction of material and all the following stages by ΔN ≥ +3000, increasing, thereby, the cycling resistance of samples by a factor of ~1.5. The greatest impact of surface modification is observed at stage I of fatigue fracture propagation. At this stage, the low propagation rate of fatigue fractures in irradiated samples results in increasing the duration of the stage as compared with unirradiated samples. The conclusion is made that, in order to increase the resilience of titanium nickelide samples effectively using LEHCEB treatment, it is required to set up conditions to increase the number of cycles before the start of stage I and to maximize the duration of this stage. [ABSTRACT FROM AUTHOR]