Titanium and oxidation

[kingnero]

In this thread I read:

You acid etch the white layer off of these parts much like you etch the brittle oxide layer off of heat-treated Ti parts.

I have had problems in the past with bend test on Ti butt welds (both CP as Ti-Al-V alloy). ISO standards and AWS mentioned different bend radii (ISO being much smaller thus harder to achieve), which put me from the start in a difficult position.
I have had contact with a Ti producer, which has led to some interesting tidbits that ultimately resolved the bend test difficulties, but I still have some questions regarding oxidation/embrittling. I was under the impression that any oxigen would embrittle the base material rather deep. The above quote (which I don't doubt!) indicates that the brittle layer is superficial. Heat treatment doesn't rise to the same temperatures as welding clearly, so that might have something to do with it.
Welds were done using high-purity argon in a purge chamber with continuous monitoring of impurities/O2, in the order of 0 - 20 ppm. Everything cleaned, filed, degreased using pure alcohol, filler rods wiped, ... so the only adverse situation was that the parts were small and heat up a lot. Large grains, very brittle welds.
Can anybody suggest some litterature where this metallurgical phenomenon is discussed in detail? I'm not in a hurry to know all the details, but it might come handy for a next time...

I'm also not looking for a specific solution, I'm more interesting in gaining some general knowledge about Ti (and Ti welding).
Thanks!

 

[EdStainless]

If there is oxygen in welding then you will get oxides in the grain boundaries and brittle welds.
If you having issues with weld bend test perhaps you should bend some pieces of the starting material and see if it will pass.
I have seen pieces of CP that were 0.050" thick and only two grains. The L and T strengths were 35% different from each other.
When you HT Ti it is a solid and the diffusion rate of oxygen is rather limited.
I am thinking of the high temp stress relief of Ti6-4 in open air as an example.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[kingnero]

EdS, thanks for your feedback. Base material bent just fine. Cross section showed grains 1 - 3 mm in size, which is in the same order of magnitude as your example, probably even a bit bigger.

Any ideas about some relevant literature? Is there something as the Nickel Development Institute for Titanium? Any "must-have" books? ...

 

[EdStainless]

Many of the old TiMet publications are still go-to for Ti
I don't have a very extensive Ti library, just what I need to get by.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[kingnero]

TiMet, as in the producer/foundry/rolling mill?
I've had extensive contacts with them during last project, they have indeed been extremely helpful.
Thanks! I'll see if I can get my hands on those old publications.

 

[DekDee]

kingnero,
Welding Titanium - A Designers & Users Handbook by the TITANIUM INFORMATION GROUP (part of TWI) 1999
Not sure if it is any use to you but it has certainly helped me over the years,
Cheers,
Shane

 

[kingnero]

Thx DekDee, I'll have a look at it!

 

[DekDee]

Kingnero,
Edited my post to show the true authors.
If you cannot locate send me a PM and I will send you a copy,
Cheers,
Shane

 

[kingnero]

Thanks Shane,

The document was the second hit from a google search. I looked at it, but it seems rather general/broad. It sure is interesting but I'm looking for a more in-depth knowledge. I was armed with this kind of knowledge when I went to TiMet, but they had another concept of "basic or tacit knowledge"... I learned a lot from them during four meetings and a visit to their facilities in France and UK.
I am still looking for something that discusses the impact of heat input and "foreign" particles on the mechanical and corrosion properties, ... but I'm not in a hurry. Last time was for a "going to mars" mission, those are exceptional projects that don't present themselves regularly.
I have contacted TiMet again for those older publications, I'm eagerly awaiting their reply.

 

[WKTaylor]

Hydrogen is also a 'bad actor'... as found in moisture when it breaks down water to H & O ions under the intense energy of a welding arc.

AND NEVER expose Ti alloys to silver, cadmium and [DANG-IT... I forgot the other plating metal]... liquid-metal embrittlement can occur at moderately high temperatures.

And never forget most titanium & Ti-alloys are poor-to-terrible conductors of heat and electrical energy...

Also, just-for-giggles...

ASM book>> Titanium: A Technical Guide

AWS G2.4 Guide for the Fusion Welding of Titanium and Titanium Alloys

AWS D1.9 Structural Welding Code — Titanium

AWS D17.1 Specification for Fusion Welding for Aerospace Applications

AWS PRGT The Practical Reference Guide for Welding Titanium

AMS2689 Fusion Welding Titanium and Titanium Alloys

SAE AS1814 Terminology for Titanium Microstructures

And for more fun... done by a high school student in her father's USAF HT shop on a weekend for a science fair...

Ti-6AL-4V sheet metal coupons exposed to oxidizing-air heat, for 15-minutes at various temperatures... in a small furnace is a USAF HT shop ~1997. Take my word for it chocolate brown is bad: 'crunchy-brittle'

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]

 

[kingnero]

Thanks, I have some reading to do now...

 

[mrfailure]

Take my word for it chocolate brown is bad: 'crunchy-brittle'

A Timet Crunch Bar?

 

[btrueblood]

"AND NEVER expose Ti alloys to silver, cadmium and [DANG-IT... I forgot the other plating metal]... liquid-metal embrittlement can occur at moderately high temperatures."

Would it be zinc, Wil?

 

[kingnero]

Apart from some of the AWS documents WK Taylor suggested I ordered, I have also bought the next 2 books:

Titanium and Titanium Alloys,
by Wiley - edited by Christoph Leyens and Manfred Peters,

Titanium (2nd Ed.),
by Gerd Lutjering and James C. Williams


And I have found online:
Welding Procedures for Titanium and Titanium Alloys,
By Vagi, Monroe, Evans and Martin from the George C Marshall Space Flight Center, Alabama

Looking forward to do some reading!

 

[WKTaylor]

Btrueblood…

1. Regarding.. metal embrittlement of Ti alloys...

Yes, zinc/zinc alloys... to a somewhat lesser extent than cadmium Cd or silver Ag.

Also, oddly, to a lesser extent still, there is literature which expresses caution about prolonged exposure to copper Cu.

Also avoid the 'universal bad actor' metal... mercury Hg.

And there are certain common environments and chemicals that must be avoided that will induce SCC... Chlorine/Chlorides, Fluorine/Fluorides, etc.

2. Some fairly good references for corrosion and welding titanium [and other reactive metals, etc] are...

MIL-HDBK-729 Corrosion and Corrosion Prevention Metals

MIL-HDBK-735 Material Deterioration Prevention and Control Guide for Army Materiel, Part One, Metals

MIL-STD-1568 Materials and Processes for Corrosion Prevention and Control in Aerospace Weapons Systems

MIL-STD-1587 Materials and Process Requirements for Air Force Weapon Systems

ASTM F945 Standard Test Method for Stress-Corrosion of Titanium Alloys by Aircraft Engine Cleaning Materials

SAE ARP982 Minimizing Stress-Corrosion Cracking in Wrought Titanium Alloy Products

SAE ARP1317 Electron Beam Welding

SAE ARP1795 Stress-Corrosion OF Titanium Alloys - Effect of Cleaning Agents on Aircraft Engine Materials

3 Also... never forget... weld cool-down in an inert gas atmosphere [all sides of welds], or vacuum W/WO inert gas purge, will ensure oxygen and hydrogen are excluded until the solidification and surface oxidation/scale is no-longer an issue [typically less than 500F/260C]


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]