Help! How to discern between grade 2 and Ti6Al4V? 2

[spiridij]

I have a few lots of small parts that were meant to have been machined from grade 2 Ti. I have since learned that some amount of them are likely grade 5 (Ti6Al4V). They have already gone through part of the manufacturing process for 55 of them and they're too expensive to just throw out. Is there a simple, non-destructive (and clean, these are medical devices) method that can be used to determine if they are grade 2 or grade 5?

Any help would be greatly appreciated.

 

[metengr]

Contact a local materials testing lab that offers positive material identification (PMI) testing services. PMI should be able to sort between Grade 2 and Grade 5 Ti alloys.

 

[spiridij]

I'll give that a shot, thank you!

 

[moltenmetal]

Vanadium should be visible to an X-ray fluorescence "gun" which people use for spot PMI.

 

[WKTaylor]

Chemical spot-test for aluminum per DOD-HDBK-249?

Also, I think alloyed Ti-6Al-4V [Gr5 ] is mildly magnetic, relative to commercially pure [CP, Gr2] titanium which is essentially non-magnetic.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

WKTaylor,
Every good metallurgist carries a magnet!


"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

It is so weakly magnetic that I don't think you could tell.
But electrical resistivity may be useful as the difference is about 2x between unalloyed and Ti and 6-4.
This should be enough to allow Eddy Current testing to sort them.

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P.E. Metallurgy, Plymouth Tube

 

PMI is simple and cheap, and there will be one in your neighbourhood.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[spiridij]

I just got some data using a Broker handheld XRF. It was easily able to pick up two known grade 2s, but one of the two units that I was convinced was grade 5 came up as grade 2 and the other was definitely grade 5. When it read the grade 5, it was extremely accurate in seeing 6% Al and 4% V. I'm still wondering how accurate the readings on the grade 2 were and if it's possible for the equipment to be "fooled". The mfg of the equipment is obviously telling me that the equipment is accurate.

The problem is, I have a crimp feature in my part. I received a batch of parts in the past where the tabs were breaking off when crimped and when I inquired with the shop, they confirmed that their material supplier shipped them grade 5 instead of grade 2. I now am seeing cracks again and assumed the same problem, but the XRF is telling me that all of the parts I received in this recent shipment are grade 2. I'm concerned because they're cracking when they shouldn't be.

So do I believe the XRF and commence to addressing the cracking of grade 2?

 

[metengr]

The only way to get to the bottom of your confusing tale is to send one of the known (you think) Grade 2 components (failed tab) and the other known (you think) Grade 5 tab failures to a local materials testing lab for chemical analysis. This sounds like a sorting problem that was never fully investigated other than what the supplier has told you.

 

[EdStainless]

Believe the XRF and look into the processing.
Just because it is Gr2 does not mean that it has good ductility.
The CP grades have a wide range of composition (oxygen) and properties.
And Ti properties can very a lot based on processing.

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P.E. Metallurgy, Plymouth Tube

 

I fully concur with EdStainless.
PMI is good at seeing large, discrete chunks of alloy such as are found in Ti6Al4V. Something else is going on.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

Are these machined from bar or plate?
Do you see the original mill MTRs?

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P.E. Metallurgy, Plymouth Tube

 

[spiridij]

I believe they were milled from a plate. They were machined in China and I've had problems with their supplier giving them the wrong material in the past, even supplying certs that were false. This is why I've been skeptical and after the XRF I've confirmed that it's the right grade, now I need to determine if it's annealed (which the CNC shop have confirmed that it is, again I'm skeptical), and dig into the whether it's a design issue or a machining issue by pulling a larger sample size to test.

 

[EdStainless]

Do you know the thickness of the plate used and which direction the parts are oriented? CP Ti is notorious for having significantly different properties in different directions (L, T, ST). They could just be changing orientation and messing it up that way.

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P.E. Metallurgy, Plymouth Tube

 

Be careful, XRF cannot confirm you have Grade 2. What it can do is rule out Ti6Al4V. Grades 1, 2 and 3 will look identical to a PMI gun. Be aware that PMI is at best a QC or sorting tool; it is NOT equivalent to chemical analysis, in spite of what inspection companies will tell you (PMI is typically their best moneymaker).

Suggest your company seriously reconsider sourcing such a sensitive material from offshore. Take the time to read all of this

http://www.eng-tips.com/viewthread.cfm?qid=172967

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[ornerynorsk]

I source a considerable amount of components from China, but I would never buy titanium there. Way too sketchy. Poorly controlled metallurgy and substitution are rampant, as the opportunity to increase profits through bait and switch are astronomical with titanium compared to other metals. Not to say that you can't get what you specify and pay for, your verification just needs to be much more robust, both on the China side and your side.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.