Effect of Microstructural Features of Titanium Alloys on Fatigue Properties and Mechanism of Crack Nucleation in Region of Very High Cycle Fatigue

Abstract

This work considers the problem of subsurface fatigue crack nucleation and decrease in fatigue properties in two-phase titanium alloys at very high cycle fatigue (VHCF). Analysis of microstructure of alloy VT3-1 obtained by two different technological processes, punching and extrusion, is performed. It is shown that main features of the microstructure of alloy VT3-1 are inhomogeneity of size and shape of the structural elements of the α phase. Agglomerations of globular structural elements of the α phase as well as “macrozones” of acicular plates are found for the forged alloy. As for the extruded VT3-1 it is shown that the inhomogeneity of the microstructure is connected with the regions where acicular plates of the α phase are formed within the primary β grains. In this case, their direction does not coincide with the direction of extrusion. Nonmetallic inclusions are found neither in the forged nor in the extruded titanium alloy VT3-1.