Additive manufacturing of a porous titanium layer structure Ti on a Co–Cr alloy for manufacturing cementless implants

In the present study, a porous Ti layer was deposited on the surface of a Co–Cr alloy using the directed energy deposition process, and the effects of the laser power and scan speed on the porosity, coating layer thickness, melt pool depth, contact (bonded) area fraction, and fatigue life of the built components were studied. To fabricate an ideal porous Ti layer on the substrate, a high coating thickness and a high porosity are important for effective bonding between bone tissue and porous structures. Furthermore, a high contact area fraction is desired because as this fraction increases, the resistance to peeling and separation of the porous layer increases, and a high fatigue life is important for long-term reliable use of the components. As the laser power increased, the fatigue life and porosity decreased, but the coating layer thickness and the contact area fraction increased. Therefore, the laser power should be optimized to provide a good balance between the fatigue life/porosity and layer thickness/fraction of contact area. For a given laser power, a decrease in the scan speed increased the coating layer thickness, but it decreased the contact area fraction. Therefore, the scan speed also needs to be optimized. The heat treatment after deposition of the Ti layer greatly increased the fatigue life because it decreased the thickness of the intermetallic compound layer formed at the interfaces and increased the blending of the elements through enhanced atomic diffusion, which reduced the probability of crack nucleation and decreased the crack size upon nucleation during fatigue testing.