Effects of Cell Orientation on Compressive Behaviour of Electron Beam Powder Bed Fusion Ti6Al4V Lattice Structures
Electron beam powder bed fusion (EBPBF) is suitable for making porous (or lattice) structures for medical implant applications. However, it is challenging for a lattice structure with a high porosity level to have sufficient strength, while lattice structures with sufficient strength are required for orthopedic applications. Furthermore, strength anisotropy needs to be understood for the design of femoral stems as load direction (LD) is location dependent. The present study aims to understand the effects of cell orientation on the compressive behavior of simple cubic lattice structures built using EBPBF and Ti6Al4V alloy, with [0 0 1]//LD or [1 1 1]//LD. It has been found that the apparent yield strength (σy-L) of [0 0 1] lattices is 1.8 times higher than that of [1 1 1] lattices, by experimental determination and also by numerical simulation. Simulation has shown that, with the [0 0 1]//LD condition, σ1 in vertical load supporting struts is low when the structure yields. But locally, σ1 (>1,000 MPa) is positive and high for the [1 1 1]/LD condition when yielding of the structure occurs with the load value only 57% of the value that is required for causing yielding in the [0 0 1]//LD condition. The predictive yield strength values by simulation of both [0 0 1] and [1 1 1] lattices have been found to be slightly lower than the experimentally determined values. Explanation for this will be provided by considering the effect of the struct effective diameter with EBPBF strut irregularity on the strength of the lattice structures.