Guides / Materials

Titanium, 316L and PEEK: Choosing a Material for a Machined Medical Part

September 23, 2026

Material choice on a machined medical part is usually made by the regulatory file rather than by the machinist, and that is correct. But the way it is written on the drawing decides what you pay, and a surprising number of drawings leave money on the table by being imprecise in one specific way.

Start from the requirement, not the alloy

Five questions rule material in and out before anyone thinks about machining.

1. Patient contact, and for how long? Transient, prolonged or permanent contact puts you in very different biocompatibility territory.
2. Load, and is it cyclic? A cyclically loaded implant cares about fatigue and fracture toughness in a way a static part does not.
3. Imaging. Metal artefact in CT or MRI can be the reason a polymer wins.
4. Sterilisation method. Autoclave cycles are brutal on some stainless grades and on some polymers.
5. Service life. A single use instrument and a twenty year implant are different problems.

Answer those and the material list is usually two items long. Then the question becomes what to write down.

Titanium

Ti-6Al-4V ELI, Grade 23, to ASTM F136. The workhorse for load bearing implants: trauma plates, bone screws, spinal rods, stems. ELI means extra low interstitials, and in practice it means tighter limits on oxygen and iron than standard Grade 5. That buys better fracture toughness and better fatigue crack growth resistance, which is the whole point on a part that will be cycled for years.

Here is the part worth knowing. Grade 23 and Grade 5 machine essentially identically. Same speeds, same feeds, same tooling, same coolant. The premium on ELI is the bar and the certificate, not the cutting.

So when a quote comes back with a large machining uplift for ELI, that is a fair question to ask. The material line should move. The hours line should not move much.

CP titanium, Grade 2 and Grade 4, to ASTM F67. Commercially pure. Grade 2 is soft and formable and shows up in dental abutments, housings and cranial mesh. It is gummier than Grade 23 on the machine: it smears and builds up on the cutting edge rather than breaking the chip, so finish and burr control take the time rather than the roughing.

Titanium of any grade has low thermal conductivity, which means the heat that would leave in the chip stays in the tool instead. That is why surface speeds look slow to anyone used to aluminium, and why tooling is a real line in a titanium quote.

Stainless

316L and 316LVM to ASTM F138. The LVM is vacuum remelted and the F138 designation is the implant bar with a certificate behind it. General 316L from a stockist is a different purchase. It work hardens fast, which has a practical consequence: a tool that rubs once makes the next pass harder, so a shop that is guessing at feeds will fight the material and pass the cost to you. It needs passivation after machining and it shows every scratch on a polished face.

17-4 PH, condition H900 or H1150. Reusable instrument bodies, jaws, drivers. Not an implant grade. The heat treat condition changes the part substantially and must be on the drawing. “17-4 PH” on its own is an incomplete specification and different shops will make you different parts in good faith.

Martensitic grades for cutting edges that have to survive several hundred autoclave cycles without pitting.

Cobalt chrome

CoCrMo to ASTM F75 cast or F1537 wrought, and ISO 5832-12. Knee femoral components, hip heads, dental frameworks. It wins on wear where titanium does not.

On the machine it is the hardest of the group on a tool, and the cost driver is tool life rather than machine time. Much of the finishing is ground or polished rather than cut. If you have a CoCr part with a mirror bearing surface, most of your quote is the surface, not the geometry.

Polymers

Implant grade PEEK to ASTM F2026. Spinal interbody cages, trials, instrument handles. It cuts easily, which is exactly how it catches people out. The risks are heat and clamping stress causing crazing, and contamination from a machine that has been running steel. A shop that runs implant PEEK properly treats it as a segregated job with its own tooling, and that is what you are paying for rather than the cycle time.

UHMWPE to ASTM F648 and ISO 5834-2. Knee inserts and acetabular liners. Very low melting point, springs back off the tool, needs sharp tooling and light cuts. Measuring it accurately is its own discipline because the part moves while you gauge it.

Nitinol

ASTM F2063. Guide wires, stents, staples, flexible instruments. Superelastic, so it moves away from the tool and springs back. The honest answer is often that it is ground, laser cut or EDM cut rather than milled. Ask before you assume a mill will do it, because a shop that has not run it before will find out on your part.

The comparison

Material	Standard	Where it goes	The cost driver in machining
Ti-6Al-4V ELI, Gr 23	ASTM F136, ISO 5832-3	Load bearing implants, trauma	Tooling, heat in the cutting edge
CP Ti, Gr 2 and 4	ASTM F67, ISO 5832-2	Dental, housings, mesh	Burr control and finish, not roughing
316L / 316LVM	ASTM F138, F139	Instruments, fluidics, temporary fixation	Work hardening, then passivation
17-4 PH	ASTM A564, AMS 5643	Reusable instrument bodies	Heat treat condition, hardness at cut
CoCrMo	ASTM F75, F1537	Knee, hip, dental frameworks	Tool life and the polishing route
PEEK, implant grade	ASTM F2026	Spinal cages, trials, handles	Segregation, contamination control
UHMWPE	ASTM F648, ISO 5834-2	Knee inserts, liners	Sharp tooling, and metrology
Nitinol	ASTM F2063	Wires, stents, staples	Often not milled at all

What to write on the drawing

Four things, and the second one is the one people skip.

1. The material and its standard. Ti-6Al-4V ELI to ASTM F136, not “titanium”.
2. The condition, where it applies. 17-4 PH H900 is a different part from 17-4 PH H1150.
3. The surface treatment and its standard. Passivate to ASTM A967, electropolish to ASTM B912, and say which method where the standard offers several.
4. The acceptance criterion. How you will judge it, so the shop knows what it is being measured against before it quotes rather than after it ships.

And one thing worth doing before you send anything out: go down the material callouts and ask which were chosen for this part and which were copied from the last drawing. On non-implant parts, inherited implant grade specifications are one of the most common places a programme pays a premium for nothing.

If you want the quote side of this, what drives the cost of a machined medical component covers the other five drivers.

Sources

• ASTM F136, wrought Ti-6Al-4V ELI alloy for surgical implant applications
• ASTM F138, wrought 18Cr-14Ni-2.5Mo stainless steel bar and wire for surgical implants
• ASTM F2026, polyetheretherketone (PEEK) polymers for surgical implant applications

Standards and regulations change. Check the current text at the source before you rely on it in a submission.

Frequently asked questions

Keep reading

• UHMWPE Machining for Bearing Surfaces and Liners
• Ti-6Al-4V ELI vs CP Titanium Grade 4: Which One Goes on a Medical Part Drawing