Cellular lattices of biomedical Co-Cr-Mo-alloy fabricated by electron beam melting with the aid of shape optimization

Abstract With a view to developing a highly biocompatible and highly reliable material for artificial hip joints, cellular lattice structures with high strength and low Young’s modulus ( E ) were designed using computational shape optimization. These structures were fabricated from a biomedical Co-Cr-Mo alloy via electron beam melting. As a starting point for shape optimization, inverse body-centered-cubic (iBCC)-based structures with different porosities and aspects were fabricated. The strength tended to increase with increasing E . Then, the structures were re-designed using shape optimization based on the traction method, targeting a simultaneous increase in yield strength with retention of the low E . The shapes were optimized through minimization of the maximum local von Mises stress and control of E to 3/2 or 2/3 of the original value, while maintaining constant porosity. The re-designed cellular structures were fabricated and subjected to mechanical testing. The E values of the porous structures were comparable to the design values, but the strength of the cellular lattice with E  = 2/3 (design value) was lower than expected. This discrepancy was attributed to inhomogeneities in the microstructures and their impact on the lattice mechanical properties. Thus, shape optimization considering crystal orientation is a significant challenge for future research, but this approach has considerable potential.