Efficient catalytic debinding feedstock design for material extrusion additive manufacturing of low warpage and high-density titanium alloy

Titanium alloy, known for its high strength and excellent biocompatibility, is widely used in aerospace, biomedical, and other fields. Material extrusion-based 3D printing offers a rapid design and effective way to fabricate complex shape part, but suffered from the time-consuming debinding and poor relative density. POM (Polyformaldehyde)-based binder has the fastest removal efficiency to achieve the debinding and sintering of parts with large cross-section. However, both the high viscosity and crystallinity limits its application in extrusion printing. In this paper, we significantly reduced the viscosity of POM-based feedstock by adding the plasticizer DOP (Dioctyl Phthalate). The crystallization properties and printing effects of conventional PP (Polypropylene) and newly developed PS (Polystyrene) as backbone binder were studied. The results showed that high crystallization increased the shrinkage of feedstock, causing warping and reduced mechanical properties of Ti-6Al-4V. With the PS as the backbone binder, the crystallization capacity of the feedstock was decreased and the warping was improved. High-density (98.62 ± 0.25 %) titanium alloy (TC4) was obtained, with an ultimate tensile strength of 948.4 ± 3.7 MPa, an elongation of 5.91 ± 0.9 %. 3D cubic samples with thickness of 30, 35, and 40 mm and a scaled human leg bone model with a thickness of 23 mm were successfully fabricated. This study has reference significance for the application of 3D printing of POM-based binder system and the preparation of titanium alloy with large cross-section.