In-situ investigation on tensile deformation and fracture behaviors of Ti60 alloy rolled sheet with equiaxed microstructure

Abstract

In this work, the deformation mechanism and fracture behavior of Ti60 alloy sheet with equiaxed microstructure (the volume fraction of equiaxed α grains is 68%) using the in-situ tensile test were studied by in-situ scanning electron microscope (SEM) and electron backscattering diffraction (EBSD). The results show that equiaxed α grains activate three coordinated deformation mechanisms, mainly single slip mode, supplemented by slip transfer and grain rotation. The alloy is mainly coordinated by equiaxed α grain deformation, dominated by prismatic< a> and basal< a> slip, and prismatic slip in (101̅0) plane and [12̅10] direction as the most active slip system. With the increase of deformation, the soft oriented equiaxed α grains preferentially occur prismatic slip, while some hard oriented grains rotate in the direction favorable to slip. When there is no slip transfer between adjacent grains, dislocation pile-up at the grain boundary and causes stress concentration, which makes the grain boundary easy to become the crack nucleation point. In SEM and EBSD studies, lamellar α grains have no obvious deformation characteristics. However, TEM study found that some lamellar α grains were kinked, which led to lamellar fracture and the formation of high-density dislocation areas around them. Meanwhile, due to the large difference in coordinated deformation ability between equiaxed α grains and lamellar α grains and between equiaxed α hard and soft oriented grains. Therefore, cracks are initiated, propagated and fractured mainly at the junction of the α colony composed of lamellar α grains and at the equiaxed α grain boundary.