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Titanium Densification using Thermal Cycling

3D printing of titanium can optimize part designs, and produce parts without tooling, but it is very expensive. Titanium powders can run between 150 and 400 dollars per pound and the time to fabricate a component can be measured in hours if not days. Why is the powdered titanium used for 3D printing so expensive? Because during the fabrication process of the powders anywhere between 60 to 85% of the raw titanium material that is used to produce the powder is rejected as being either too large or too small of a particle size. And to reprocess the rejected powder costs more than just using new feed stock.

Temper has developed a process called TiPAD, that can reduce the costs of producing titanium parts dramatically. How? By using this left-over powder and densifying in a mold using mix match plasticity. Let me explain: Allotropic materials such as titanium and aluminide superalloys exhibit allotropic transformations; meaning they undergo solid-to-solid phase transformation that is triggered at certain temperatures. For example, commercially pure titanium is in a hexagonal close pack structure, the alpha (α) phase, below 882 °C and in a body centered cubic structure, the beta (β) phase, above 882 °C. During the atomic restructuring, there is an associated volume change as well.

The volume change can be exploited by using a powdered material contained in a mold while a press applies a constant pressure. When the contained crystal lattice restructures, its easiest path for expansion to fill the voids between grains of powder. Repeating this process joins the grains of powder together and creates a non-porous, near-net shape component.

With the TiPaD DOE program, two milestones were reached. The first was to compressed powdered material into a preform and, using an electron beam, fuse the outside skin to create a durable surface that seals the powdered metal in a vacuum. This creates a puck that can be easily handled via bowl feeding or other high-volume production methods. The second milestone proved the thermal cycling process can make 99.99% dense, void free, components in a production type environment.

To summarize, Temper can purchase titanium powder at $8.00 per pound and densify it in a TiPAD mold in 3 hours. For a one pound part, this can reflect a order of magnitude cost decrease.

Figure 1: Illustrates the atomic structure of the α and β phases.
Figure 2: Thermal cycling of Titanium 6Al-4V
Figure 3: Void free part produced using thermal cycling
Figure 4:Three step process (1) weigh powder and compress into a blank, (2) melt surface of blank in a vacuum using an electron beam, (3) densify blank in a TiPAD tool using thermal cycling

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