3D Printing TC4 Titanium Alloy: How Powder Particle Size Changes Density and Performance

TC4 (Ti-6Al-4V) is hard to machine. It work-hardens, it holds heat at the cutting edge, and a deep pocket in titanium can eat a small end mill in one pass. That is the reason additive routes get attention. The catch is that a printed part is only as good as the powder that goes into it.

The study behind this page used three TC4 powder batches with different particle size distributions, all printed on the same machine at a 40 μm layer thickness. After printing and sintering, the team measured powder morphology, sintered density, grain size, tensile strength, hardness and elongation. One variable changed. Everything else held still.

Density is the first thing to watch, because porosity drives nearly every other property. A part at 95% density has voids that act as crack starters. Push the density to 98% and the same geometry behaves differently in fatigue. Powder size is one of the strongest levers you have on that number.

Small particles pack better and sinter faster. That is the short version. The longer version involves surface energy, grain growth and what happens to your elongation when the grain structure gets too fine or too coarse. Both directions have a cost.

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  Packing densityFiner powder fills voids between larger particles, so green density starts higher.
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  Sintering driving forceSmall particles carry more surface energy, which accelerates neck growth.
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  Grain size after sinterFiner starting powder usually gives finer grains, up to a point.
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  FlowabilityVery fine powder can bridge in the hopper and spread unevenly across the bed.

Each batch was defined by its D10, D50 and D90 values. The finest batch, labeled TC4-3, had a D50 of 8.49 μm. The middle batch, TC4-2, started at D10 = 6.45 μm. The coarsest batch ran up to a D90 of 22.10 μm. Those three numbers cover most of the practical span you will see from a titanium powder supplier.

Printing conditions were fixed: 40 μm layer thickness, same binder, same spreader settings. Sintering followed the same thermal profile for all three batches. That matters, because a change in hold time or peak temperature would confound the powder comparison. The team wanted to isolate particle size, nothing else.

Density came from Archimedes measurements. Grain structure came from etched cross sections under optical and electron microscopy. Mechanical data came from tensile bars cut from sintered coupons. Hardness was taken on polished surfaces. This is a standard package, and it is the same set of checks we ask for when a customer wants a printed TC4 part qualified.

The result table below is the core of the study. Read it left to right: as D50 drops, density and tensile strength climb, hardness climbs, and elongation falls. There is no free lunch in the fine-powder direction.

Density scales inversely with particle size here. TC4-3 hit 98.2%, the top number in the study. Smaller particles sinter to a denser body because the driving force for neck growth is surface energy per unit volume, and that term grows fast as diameter shrinks. A dense part resists fatigue crack initiation, which is why aerospace and medical buyers chase the last two percent.

Strength and hardness follow density, but grain size also moves. Finer powder gave finer grains after sintering. Hall-Petch behavior then pushes yield and tensile strength up. The same refinement removes some room for dislocations to travel, so elongation drops. If your part is a bracket loaded in tension, that lost ductility may be the deciding factor, not the strength gain.

The practical window from this work is a D10–D90 span of 6.45 μm to 22.10 μm. Below that range, spreading gets difficult and the risk of loose powder clumps rises. Above it, you lose density and the sintered body stays porous even with a long hold. A supplier who ships you a wide distribution outside this band is asking for inconsistent results.

One caution on the numbers. Sintered density, tensile strength and elongation all depend on the sinter profile, the binder burn-out schedule and the atmosphere. Change the furnace and the ranking can shift. Treat the study as a direction, not a fixed recipe, and qualify your own powder and furnace combination before releasing a production print.

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  Pick fine powderWhen density and fatigue life matter more than ductility.
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  Pick coarser powderWhen you need elongation, or the spreader struggles with fines.
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  Stay inside the bandD10–D90 of 6.45–22.10 μm keeps spreading and sintering predictable.
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  Qualify locallyRe-run density and tensile checks on your own furnace before production.

Binder jet plus sintering wins on geometry freedom and material use. Internal channels, lattice cores and consolidated assemblies are cheap to print and expensive to machine. If your part has features a cutter cannot reach, printing earns its place even with the density trade-off.

CNC wins on density and tolerances. A wrought or billet TC4 part is fully dense by definition, holds ±0.005 mm, and takes a surface finish down to Ra 0.2–0.8 μm. Printed and sintered parts usually need a finishing pass on critical faces anyway, so the two processes often end up in the same workflow.

A common split is to print the near-net shape, then machine the sealing faces, bores and threads. That keeps the hard titanium cutting to a minimum. It also puts the tight tolerances on surfaces where they matter, instead of asking the furnace to hold them.

If your part is a simple prismatic block in TC4 with a few holes, printing adds steps without adding value. Machine it from bar. If it is a manifold with curved internal passages, print the body and finish the ports. The decision is about feature access, not about which process is newer.