Titanium alloys
Titanium alloys
(OP)
I have a question regarding Titanium alloys. We have a tube component made of Ti 6Al-4V, and we nitride the tube at 1450F. After nitriding we are seeing a 0.003”-0.004” expansion in the diameter of the tube, which is not suitable for our application. Can anyone please suggest another Titanium alloy which would not produce such growth? We were thinking of pure alpha Titanium, and see if it grows the same. Please advise. Any suggestion is greatly appreciated.





RE: Titanium alloys
Relief of residual stresses from prior operations such as welding, hardening, machining, and so forth
Stress introduced during nitriding due to inadequate support in the furnace, or too rapid or nonuniform heating or cooling.
Stress is introduced by the increase in volume that occurs in the case. This change causes a stretching of the core, which results in tensile stresses that are balanced by compressive stresses in the case after the parts have cooled to room temperature. The magnitude of the permanent set in the core and case is affected by yield strength of the material, thickness of the case, and by the amount and nature of the nitrides formed.
Have you allowed for the above effects?
Did you try a stress relief for the Ti-6Al-4V- some list a temperature of 1000F?
RE: Titanium alloys
RE: Titanium alloys
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Plymouth Tube
RE: Titanium alloys
RE: Titanium alloys
RE: Titanium alloys
RE: Titanium alloys
RE: Titanium alloys
RE: Titanium alloys
The grade 6 you are looking for is a pretty unusual grade. While there are some uses for it, grade 2,5,and 9 are far more common. The last time we did any grade 6 manufacturing the mills required us to buy 500kilos at a time before they would produce the alloy billets for us. If you would be using this amount then it wouldn't be that hard to source.
The other option is to design to the growth of the tubing. Just have a Grade5 tubeing manufactured that is .007" smaller than your finished product, and let the nitriding growth allow it to expand to the finished tolerances you would need. For this type of specialized production a typical run of 50kilos would be pretty standard.
My other question, is why were you speccing grade5 when grade2 might work? We typically recommend people stick with 2 unless they need the strength of 5 since the manufacturing cost is lower, and it is easier to work with in the field. Obviously where needed you should use 5, but if 2 will work it is typically a less expensive option.
RE: Titanium alloys
RE: Titanium alloys
Are these anywhere close to standard size tubes? You have mentioned four different alloys, and they may all have slightly different growth patterns. (CP2, Grade 5, Grade 6, and Grade 23.
My thought is if you are considering this many different alloys, you may want to do some testing on each of them individually to determine the growth pattern of them. It is absolutely possible that they may all exhibit slightly different growth tolerances. It wouldn't cost much to track down some cut offs in a few different alloys then process them all, long before worrying about exacally which alloy to use.
I am also a little curious about using grade 6 (5al2.5sn) for medical uses. Not that it couldn't be done, but I am not familure with anyone using a tin containing alloy in the medical field, at least not for implants. We don't do a lot of medical work, so I wouldn't state it can't/wouldn't be used, but it is pretty atypical.