Titanium

js

Well-known member
Joined
Aug 2, 2003
Messages
5,793
Location
Upstate New York
So, I've just read some of the sections in the Donachie book on Heat Treatment. The short of it is this: heat treatment is very difficult for the reasons Don already mentioned: it must be done in an inert atmosphere to avoid oxygen and nitrogen infiltration and consequent embrittlement and degradation.

Any heat treatment at temperatures above about 427 °C (800 °F) must provide the titanium or titanium alloy with an atmospheric protection that prevents pickup of oxygen or nitrogen and formation of alpha case. The protection also obviates the possibility of undesirable scale formation. (Contamination during heat treatment is discussed later in this Chapter.)

(The beta transus of Ti-6-4 is 1000C +/- 20 C) (!)

Moreover, it only increase the hardness and strength by a pretty small margin in the case of Ti-6-4. As received from the supplier, grade 5 Ti-6-4 has a yield strength of 141ksi. With further heat treatment, you can increase this to 153ksi. However this will be at the expense of ductility. And, as I just implied, grade 5 Ti-6-4 is already annealed. In fact, all the stock titanium has to be straightened by what is essentially annealing:

Straightening, Sizing, and Flattening. Straightening, sizing, and flattening of titanium alloys are often necessary to meet dimensional requirements because it can be difficult to prevent distortion of close-tolerance thin sections during annealing. Because titanium alloys have excessive springback, the straightening of bar to close tolerances and the flattening of sheet present major problems for titanium producers and fabricators. Straightening, sizing, and flattening can be conducted independently of other related processes or can be combined with annealing (or stress relief) by use of appropriate fixtures.

Unlike aluminum alloys, titanium alloys are not easily straightened when cold, as explained previously. (See the section "Forming" in Chapter 5.) Because of springback and resistance to straightening at room temperature, it is necessary to employ elevated-temperature forming. Therefore, titanium alloys are straightened primarily by creep straightening processes.

Creep straightening uses the concept that at annealing temperatures, many titanium alloys have low creep resistance. The creep resistance can be sufficiently low enough to permit the alloys to be straightened during annealing. With proper fixturing and, in some instances, with judicious weighting, sheet metal fabrications and thin complex forgings have been straightened with satisfactory results. Again, uniform cooling to below 315 °C (600 °F) after straightening can improve results.

Creep flattening consists of heating titanium sheet between two clean, flat sheets of steel in a furnace containing an oxidizing or inert atmosphere. Various jigs and processing techniques have been proposed for annealing titanium in a manner that yields a flat product. Creep flattening and vacuum creep flattening are two such techniques. Vacuum creep flattening is used to produce stress-free flat plate for subsequent machining. The plate is placed on a large, flat, ceramic bed that has integral electric heating elements. Insulation is placed on top of the plate, and a plastic sheet is sealed to the frame. The bed is slowly heated to the annealing temperature while a vacuum is pulled under the plastic. Atmospheric pressure is used to creep flatten the plate.

*****

So I'm guessing that there is no way that heat treatment wouldn't be stupidly expensive, and ultimately more or less just cosmetic for our purposes. Although I am definitely curious to hear what the response to Don's question is!
 

McGizmo

Well-known member
Joined
May 1, 2002
Messages
17,273
Location
Maui
I have a small electric furnace that can go up to 2400F as I recall. I have used it to memory form nitinol which really is an amazing alloy of Ti. I have also thought about sticking some Ti flashlight parts in there and elevating them in temp perhaps with some cloisonne powder or even organic materials (I remember doing raku ceramics in high school) just to see what might result but then again, it might be akin to a kid playing with an adult chemistry set and unwanted accidents resulting. :green:
The Haiku that survived the fire got me thinking about playing with the furnace again but who know what risks might be involved. At the minimum probably a respirator should be worn.

I remember some weld beads I made on titanium joints that I was hardly able to grind off due to contamination probably but if one could get that kind of surface hardening on a titanium light you would really have to go our of your way to scuff it up! But you might drop the light and have it break. :duck:
 

js

Well-known member
Joined
Aug 2, 2003
Messages
5,793
Location
Upstate New York
Don,

Not only have you worked in the coolest places, lived (and live, present tense) in the coolest places, but you also have the coolest TOYS! You have an IS as well as a small electric furnace--and presumably a welder and lathe as well? Not to mention flashlights, dive gear, photography stuff, and who knows what else! . . .

That's too cool for words! LOL!
 

gollum

Well-known member
Joined
Mar 17, 2008
Messages
994
Location
Brisbane
great thread

I have spent a lot of time working titanium mainly in my knives

I was not sure but I love the name for Tungsten...


its called Wolfram (from germany originally)
 
Last edited:

RocketTomato

Well-known member
Joined
Jul 20, 2008
Messages
475
Great post on titanium. Hopefully it will help prevent some of the aluminum versus titanium threads that pop up periodically.
It's great to have all the information collected in one thread to reference. By the way, there is a typo in the oxide section. The oxide has a much lower conductivity then the metal.

One thing though is that I would not call titanium inert or corrosion resistant. As you point out in your welding post, it is very reactive. Titanium dioxide, TiO2, however is extremely stable and inert and forms a highly impervious barrier analogous to Al2O3 on aluminum. Also, people do not have allergies to pure gold and pure platinum. It is their alloys that they are sensitive to, most typically alloys with nickel.
 

Ny0ng1

Well-known member
Joined
Oct 14, 2004
Messages
337
Location
Singapore
I have a small electric furnace that can go up to 2400F as I recall. I have used it to memory form nitinol which really is an amazing alloy of Ti.

my wife is an orthodontist. Some of the wires used in these braces are made of NiTiNOL, pre-made in factory according to specified parabolic curves.
After the patient's jaw size is measured, a correct wire size selected and installed. It would follow the patterns of the patient's current teeth that needs to be corrected to a proper curve.
These NiTiNOL wires are pre-set to typical human mouth temperature, so the slow process of 'correcting' and 'aligning' your teeth started :D

well at least thats how she explained to me heee
 

fyrstormer

Banned
Joined
Jul 24, 2009
Messages
6,620
Location
Maryland, Near DC, USA
They also use special pliers to crimp the wire in various places before installing it, in case they need to modify the curve of the wire to make the patient's teeth fit properly. It aches terribly for the first few days, but after that the nerves give up and go numb.
 

js

Well-known member
Joined
Aug 2, 2003
Messages
5,793
Location
Upstate New York
Great post on titanium. Hopefully it will help prevent some of the aluminum versus titanium threads that pop up periodically.
It's great to have all the information collected in one thread to reference. By the way, there is a typo in the oxide section. The oxide has a much lower conductivity then the metal.

One thing though is that I would not call titanium inert or corrosion resistant. As you point out in your welding post, it is very reactive. Titanium dioxide, TiO2, however is extremely stable and inert and forms a highly impervious barrier analogous to Al2O3 on aluminum. Also, people do not have allergies to pure gold and pure platinum. It is their alloys that they are sensitive to, most typically alloys with nickel.

RocketTomato,

Thanks! I will clarify the inertness-through-passivation issue in my OP.

Do you have a reference for the conductivity of the oxide layer of titanium? I looked high and low on the internet and only found a technical paper about the use of TiO2 as a semi-conductor and it's conductance vs. the partial pressure of oxygen. I also didn't find any info in the Donachie text, which is more oriented towards mechanical properties than electrical ones. So, I would love it if you could post a link to a reference, or the appropriate section of a hard-copy reference!
 

js

Well-known member
Joined
Aug 2, 2003
Messages
5,793
Location
Upstate New York
. . .

Also, people do not have allergies to pure gold and pure platinum. It is their alloys that they are sensitive to, most typically alloys with nickel.

Even if this is true, it isn't relevant as no gold or platinum jewelry item is pure. Pure gold is far too soft, obviously, and platinum jewelry is 90-95 percent pure by weight--if you're lucky. Here's an interesting link to a jeweler talking about his choice of platinum alloy:

Platinum Purity

And one on the rise of the 58 percent pure platinum alloy:

The Platinum Standard: Purity Issue Divides Jewelers

This is why makers of titanium jewelry tout its hypo-allergenic nature.
 

kaichu dento

Well-known member
Joined
Apr 5, 2008
Messages
6,055
Location
現在の世界
... people do not have allergies to pure gold and pure platinum. It is their alloys that they are sensitive to, most typically alloys with nickel.
Even if this is true, it isn't relevant as no gold or platinum jewelry item is pure.
I hesitated to comment earlier as I didn't want to derail the thread, but do think it's worth adding that zinc is one of the worst offenders when it comes to 'gold' allergies. I've made gold rings for customers who had allergy problems with commercial rings and since I alloyed my own gold, it had only gold, silver and copper. No allergy problems.

Nickel is added to white gold, hence it's incredible durability.
 

fyrstormer

Banned
Joined
Jul 24, 2009
Messages
6,620
Location
Maryland, Near DC, USA
I thought white gold was gold and silver? If a hardener were to be added, I think I'd want the hardener to be platinum or rhodium, not nickel. Nickel is good for hardening industrial alloys, not so much for hardening jewelry.
 

kaichu dento

Well-known member
Joined
Apr 5, 2008
Messages
6,055
Location
現在の世界
I thought white gold was gold and silver? If a hardener were to be added, I think I'd want the hardener to be platinum or rhodium, not nickel. Nickel is good for hardening industrial alloys, not so much for hardening jewelry.
Nope. Gold and silver is how green gold is made, red comes from gold and copper. If I remember correctly blue comes from alloying with iron and purple from aluminum.

Another option that one of my friends liked using was palladium white gold; while not as tough as nickel white gold, is better for people allergic to nickel. (Palladium, one of the six platinum group metals is also at times referred to as poor mans platinum.) Rhodium is used for plating white gold, platinum or palladium to give a purely white appearance, but I prefer not to plate because I like the natural appearance as they are.
 

choppedlow

Member
Joined
Nov 22, 2012
Messages
14
This is one thread that you will be smarter when you finish reading it. Great info and it busts many of peoples misconceptions of the metal.
 

archimedes

Moderator,
Staff member
CPF Supporter
Joined
Nov 12, 2010
Messages
15,792
Location
CONUS, top left
Saw some interesting discussion of "SM-100" (or nickel-titanium alloy NiTiNOL 60) ... might be amazing stuff for a flashlight host ???

Probably super-expensive though :eek:
 

McGizmo

Well-known member
Joined
May 1, 2002
Messages
17,273
Location
Maui
Saw some interesting discussion of "SM-100" (or nickel-titanium alloy NiTiNOL 60) ... might be amazing stuff for a flashlight host ???

Probably super-expensive though :eek:

I imagine if they can use it in powder form it might find more applications but NiTiNOL can't be machined like the other metals can. Definitely a cool material though!!
 
Top