The Spectrum of Crystallographic Misorientations of Intercrystalline Boundaries for BCC-HCP Phase Transformation in Additively Manufactured Ti-6Al-4V

Electron backscatter diffraction is a modern experimental method for local structure and texture investigation, which makes it possible to establish the presence and types of the various boundaries between the elements of the mesostructure such as low or high angle, special and interphase boundaries. Moreover, this technique can demonstrate the migration of boundaries during structural and phase transformations. This study estimated the possible spectrum of crystallographic misorientations of intercrystalline boundaries in additively manufactured titanium alloy Ti-6Al-4V using orientation microscopy and crystallographic calculations based on Burgers orientation relationship during β→α-transformation. The study has established that the boundaries between grains of α-phase are characterized by the misorientation angles of 11±2 °, 61±5 °, 89±3 °. The majority of high-angle boundaries are characterized by misorientation angles in the range of 57-65 °. The study also ascertained that the experimental spectrum of intercrystalline boundaries in the α-phase reveals the displacive nature of β→α-transformation in titanium alloys.

Causes of residual stresses during machining of workpiece surfaces

The basic data about residual stresses are considered, and the classification of residual stresses that occur in the surface layer of parts is provided. At the moment, it is customary to divide residual stresses by the volume of balancing into macro-stresses, micro-stresses and submicron stresses, and by the sign — compressive and tensile. The main causes of residual stresses are analyzed, and the factors influencing their occurrence are identified. There are three main causes of residual stresses: uneven plastic deformations in the cutting zone, as a result of the force of the tool on the workpiece, high temperatures accompanying the cutting process, and structural and phase transformations occurring on the surface of the workpiece.