Preventing Alpha Case

Date 03-26-2008 17:56

Hello. I have some welded titanium 6-4 that went through a heat treat cycle and came back with alpha case. Basically, we burned out the tool in the furnace, wrapped the part in stainless steel foil and sent the part through the heat treat. I'm trying to figure out what we can do differently the 2nd time around to minimize this alpha case problem. I know that our furnaces are not the best, but it's not something I can control. What things can I do to minimize the chance of this alpha case? Will using titanium foil instead of stainless help out at all? Any advice? Thanks.

By Lawrence (*****)

Date 03-26-2008 18:11

Zeek

The alpha case is a byproduct of oxygen and nitrogen making oxide and nitride layers that increase in thickness with temperatures over 800F and also are related to dwell times at temperature.

You need to tell us a bit more about your furnace cycle.

Vacuume?

Argon?

Air?

If you are wrapping in foil and cooking the thing in air you will have alpha case no matter what you wrap with... You will need to focus on the best methods to remove the alpha case.

Here is a good link to some data on stress relief of 6-4 Ti
http://www.timet.com/6-4thermaltreat.html

For more detailed information consult ASM Materials Properties Handbook Vol 4 'Titanium Alloys'