Fatigue strength of an (α + β)-type titanium alloy Ti-6Al-4V produced by the electron-beam physical vapor deposition method

Abstract

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.

Theoretical estimation of fatigue life under regular cyclic loading

“…During deposition, some big droplets depart from the surface of the melt, settling in the condensate and forming columns, which grow and reach the condensate surface. These columns are efficient surface stress concentrators and adversely affect on the fatigue resistance characteristics of the Ti-6Al-4V alloy condensate [11]. The investigation of specimen fatigue fracture surfaces revealed that for almost all but three specimens, crack initiation occurred within the concentrator on the condensate surface.…”

“…To confirm the validity of the above-proposed model for calculating the fatigue life of specimens with surface notches, fatigue test results for specimens of ) (    -titanium alloy Ti-6Al-4V condensate obtained by the ЕВ PVD method [11] were used. ЕВ PVD coatings of the Ti-6Al-4V alloy were prepared by deposition of the same but cast alloy onto flat substrates.…”