Additive manufacturing functionally graded titanium structures with selective closed cell layout and controlled morphology

This article presents the results of deploying a new approach for additive manufacturing (AM) functionally graded titanium (Ti) cellular structures with selectively built closed cells, which tailor the mechanical behavior of structures to mimic the similar properties of bones. A hybrid AM system, which combines two methods of binder jetting and material extrusion, was applied. Ti parts were fabricated from powder-bed AM (binder jetting) with encapsulated sacrificial polymeric droplets within the layers and at designated locations to form a periodic pattern. After a heat treatment step, which resulted in the polymer decomposition, the measurement of porosity among the specimens demonstrated the range of 6 to 16% enhancement in these parameters in samples with periodic cells compared to others. Additionally, micro-computerized tomography was performed on the candidate samples to determine the pore morphology and layout within the specimens. The measurement of stiffness and yield stress suggested a range of 2.48 +/- 0.37 to 3.55 +/- 0.49 GPa and 107.65 +/- 18.14 to 145.75 +/- 13.85 MPa, respectively. These results suggested that the statistical significance occurred in the batches with periodic cells.