Influence of anisotropic microstructure on chip formation mechanism in additively manufactured Ti6Al4V

Abstract

Integrating machining and additive manufacturing (AM) can improve the machining quality of titanium alloy components. However, the anisotropic characteristics of the microstructure in AM titanium alloys significantly affect chip morphology, which influences the vibrations in the cutting process, resulting in lower machining quality than isotropic materials. Therefore, this study explores the effects of the anisotropic microstructure on the chip formation mechanisms of AM Ti6Al4V. The morphology and microstructure of the chips and the Adiabatic Shear Bands (ASBs) were observed, and the crystal orientation and grain size of the chips and those near the ASBs were discussed. The results demonstrate that the microstructure type, texture, grain size, and grain boundary of the AM Ti6Al4V cause the bending and bifurcation of the ASBs, and the chip morphology depends on the slip path of the ASBs. Widmanstätten and the pyramidal slip system are more susceptible to dislocation movement and ASB slip; the large grains decrease the critical resolved shear stress of the slip system, which is more conducive to shear slip; the grain boundaries along the columnar crystals are prone to shear slip and crack propagation, leading to the bending of ASB and unusual chip morphology. As the cutting speed increases, the effects of the anisotropic microstructure on the chip formation become more significant, leading to more complex chip morphology. This research, for the first time, discovered the influence of anisotropic microstructures on adiabatic shear bands and chip morphology by analyzing the crystal orientation and grain morphology within the chips. The findings can help reduce cutting vibrations and tool wear, thereby improving the cutting quality of AM Ti6Al4V.