Laser powder-bed fusion of titanium with multifunctional CaCl2 spaceholders

Titanium with porosity created by removal of spaceholders has reduced stiffness which can address longstanding orthopedic challenges of aseptic loosening and stress shielding. Here, we show that CaCl2 powder can have a dual use when integrated in titanium, (i) as a chemically inert pore-former (spaceholder) during laser powder-bed fusion (L-PBF) additive manufacturing and (ii) as a proposed osteogenic enhancer in the resulting Ti-CaCl2 composite. During L-PBF of powder blends, both Ti and CaCl2 are melted, creating elongated CaCl2 inclusions in Ti upon solidification, enabled by the immiscibility of the two liquid phases and, after solidification, the two solid phases. After subsequent CaCl2 dissolution in water, interconnected porosity is formed in the metallic matrix, either in bulk specimens or within struts of microlattices. As laser energy density decreases, more CaCl2 is trapped in Ti, creating less elongated, more homogenous porosity from smaller meltpools during manufacturing. Micro-computed tomography shows that most porosity is attributable to the CaCl2 spaceholder after its removal, but additional porosity is also generated from the L-PBF process via vaporization of the CaCl2. Uniaxial compression testing illustrates that lower overall porosity produces higher elastic modulus and yield strength specimens.