Troubleshooting Cracks in NiTiHf Alloy Produced Through VIM Process

In summary: increase the cooling rate after the transition. increase the cooling rate after the transition. try to avoid right angle transitions, its most preferred to use polynomial transitions in order to avoid uneven cooling tension. increase the cooling rate after the transition.
  • #1
mah65
24
0
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
 
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  • #2
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?
 
  • #3
mah65 said:
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.
 

1. What is NiTiHf alloy and what is the VIM process?

NiTiHf alloy is a shape memory alloy composed of nickel, titanium, and hafnium. The VIM process, or Vacuum Induction Melting process, is a method of melting and refining metals under vacuum conditions to produce high-quality alloys.

2. What are some common causes of cracks in NiTiHf alloy produced through the VIM process?

Some common causes of cracks in NiTiHf alloy produced through the VIM process include improper melting and casting conditions, contamination of the alloy, and the presence of impurities or inclusions in the alloy.

3. How can cracks in NiTiHf alloy be prevented during the VIM process?

To prevent cracks in NiTiHf alloy during the VIM process, it is important to carefully control the melting and casting conditions, use high-quality raw materials, and ensure a clean and controlled environment to avoid contamination.

4. Can cracks in NiTiHf alloy be repaired?

In some cases, cracks in NiTiHf alloy can be repaired through methods such as welding or heat treatment. However, the success of these repairs depends on the severity and location of the cracks.

5. Are there any other factors that can affect the occurrence of cracks in NiTiHf alloy produced through the VIM process?

Yes, factors such as the composition of the alloy, cooling rate during solidification, and post-processing treatments can also affect the occurrence of cracks in NiTiHf alloy produced through the VIM process.

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