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The fatigue test results and the mechanical characteristics in static tension are obtained for specimens of titanium alloys belonging to the known classes of materials with a reference globular or bimodal microstructure and the so-called fine-grained b-transformed microstructure provided by the rapid heat treatment technique. The microstructure of the materials under study is analyzed. The microstructural parameters responsible for the fatigue strength of particular material have been found. The comparison is made between the fatigue limits obtained experimentally and calculated using the models previously developed by one of the authors.Introduction. Titanium alloys, due to their unique combination of physical-mechanical properties, are among the basic materials used in aerospace engineering. For this reason, the study of the effect of various types of microstructures on the mechanical properties of these alloys and the development of new, more efficient technologies for their production is certainly a pressing problem. As found by many researchers, the main factor determining the mechanical characteristics of titanium alloys, and especially the fatigue resistance characteristics, is the alloy microstructure [1]. Two main microstructural types are distinguished, such as globular and lamellar microstructures, with each of them having its own advantages and disadvantages [2]. A globular microstructure exhibits high characteristics of static strength and plasticity (especially, in the case of thermal hardening treatment) and also the high levels of fatigue resistance characteristics, whereas the creep and fatigue crack propagation resistance characteristics are low. Instead, the lamellar microstructure has good high-temperature creep and crack propagation resistance characteristics, with the strength and plasticity characteristics being too low.As an alternative trade-off, a microstructure of the so-called bimodal type can be used between these kinds of microstructures which is characterized by the presence of residues of the primary a?-phase of a globular morphology and a two-phase (a b + )-matrix of a lamellar structure in the spacings between a-globules. Such

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The fatigue test results are presented for an (α β + )-type titanium alloy in the form of two-layered smooth specimens (the first layer is a condensate prepared by the electron-beam physical vapor deposition method, the second one is a substrate from a standard sheet material of the same type) and condensate specimens. It has been found that the presence in the condensate of deposition defects such as droplets lowers the fatigue limit of the material by approximately 1.5 times as compared to that of the condensate which is free of defects. It is shown that in the absence of droplets, the fatigue limit of the condensate is no lower than that of the substrate material. The microstructure, texture and fracture surfaces of the materials under study are analyzed, on the basis of which the fatigue limits of the defectless condensate and substrate material are calculated using approaches of linear fracture mechanics. Good agreement has been obtained between calculated and experimental data.

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