Functionally graded bimodal Ti6Al4V fabricated by powder bed fusion additive manufacturing: Crystal plasticity finite element modelling

The paper investigates the effects of secondary α_s phase lath thickness and the primary α′ phase content in microstructural functionally graded Ti6Al4V through a dual-phase crystal plasticity finite element (CPFE) model. Existing experimental studies have identified two microstructure parameters that were varied in the microstructure of dual phase Ti6Al4V, namely α_s lath thickness and primary α′ phase content. However, existing FGM simulation studies to date only focused on the gradient in grain size. Therefore, the present study examined lath thickness and primary phase content as design inputs. A total of 12 parameters combinations were studied in homogeneous crystal plasticity models. The α′ phase content was varied from 60% to 95%. Within the remaining phase lamellae structure, the lath thickness was varied from 0.15 μm to 6.20 μm. As a result, a rule of mixtures relation was found between the α’ phase content and both the resulting elastic and plastic properties. A proportional Hall-Petch like correlation between α_s lath width and yield strength was established. Based on these findings, microstructures with varying the lath thickness were studied in a newly developed finite element model. Uniform stress and uniform strain boundary conditions were applied to this FGM, and the resulting behaviour was predicted.