Prediction of machining induced microstructure in Ti–6Al–4V alloy using 3-D FE-based simulations: Effects of tool micro-geometry, coating and cutting conditions

Abstract

Machining process affects surface integrity of Ti–6Al–4V titanium alloyed end-products. During thermal-mechanical loading and subsequent processing that take place in machining, grain size is altered at the subsurface through dynamic recrystallization and subsequent recovery. This can cause softening or hardening of the machined surfaces affecting surface integrity depending on the resultant grain sizes and phase fractions. Prediction of machining induced surface integrity specifically microstructure and grain size can be achieved by using Finite Element-based process simulations and calculated temperature, strain, stress and strain rate fields. This study presents experimental and numerical investigations in machining induced subsurface microstructure, microhardness and grain size in Ti–6Al–4V titanium alloy. Machining surfaces are investigated by measuring subsurface microhardness and grain size and phase fractions in each cutting conditions through scanning electron microscopy and image processing. 3-D FE machining simulations are conducted at the same cutting conditions and tool geometry to predict dynamic recrystallization (DRx) and resultant grain size by utilizing the Johnson–Mehl–Avrami–Kolmogorov model for Ti–6Al–4V alloy. The study also presents investigations and discussions about the effects of machining conditions (tool geometry, coating, and cutting conditions) on the microhardness and grain size in machining Ti–6Al–4V. Numerical modeling results are compared with experimental results and distinct effects of tool edge radius, coating, and cutting conditions on machining induced subsurface microstructure specifically on the changes in grain size due to dynamic recrystallization and recovery have been reported.