Troubleshooting Cracks in NiTiHf Alloy Produced Through VIM Process

[mah65]

Hi guys

I have produced an ingot of NiTiHf alloy through Vacuum Induction Melting (VIM) process and by using pure materials of Ni, Ti and Hf. Casting was done in a Y2O3-coated steel mold, and the crucible was made of graphite.

The problem is that, when I homogenize the ingot at 1000 ^oC and then quench it in water, some cracks happen in it. I have done this process several times before, but no crack was visible. These cracks are deep inside the ingot, which may hinder the rolling process.

What may be the reason for such cracks in this alloy ?

thanx

 

[mah65]

one possible reason for this problem may be the design of the mold, in which the melt is cast. That is, these cracks may happen during the casting & solidification due to inappropriate and non-proportional heat loss, and not during the homogenization. Thus, the design of my new mold for casting may be the cause of the cracks.
What considerations should I give when I want to design a new mold? I mean what should I do to reduce the stresses that give rise to cracks during solidification? What are the characteristics of an appropriate mold?

 

[spanky489]

one possible reason for this problem may be the design of the mold, in which the melt is cast. That is, these cracks may happen during the casting & solidification due to inappropriate and non-proportional heat loss, and not during the homogenization. Thus, the design of my new mold for casting may be the cause of the cracks.
What considerations should I give when I want to design a new mold? I mean what should I do to reduce the stresses that give rise to cracks during solidification? What are the characteristics of an appropriate mold?

try to avoid right angle transitions, its most preferred to use polynomial transitions in order to avoid uneven cooling tension.