Tensile strength of Superalloys

[Caster]

Hi guys ..have'nt been on for a year or so, glad to see you're all still here.
My problem is Ni superalloy castings which are failing the ultimate on the tensile strength test.My question is this .In general for mechanical properties of Ni alloysis it better to cast at a higher melt temperature or lower ?
If you could provide a brief explanation it would be great.
Many thanks

 

[EdStainless]

Which alloy? How large of a part?
In many cases you need to consider the heat treat sequence also. You will form a bunch of primary MC and gamma on soldification. You need to disolve most of this before you can end up with the structure that you really want. And you hope that the grain size comes out OK too.

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Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[Caster]

Thanks Ed

The parts range from 30mm to 60mm in Diameter.No heat treatment.Average weight is about 120 grams.The alloy is an Inconel.I am trying to help someone else out here so i am not as familiar with all the parameters as i'd like to be but these are the basics anyway.It's a vacuum assisted investment casting furnace.
Thanks

 

[EdStainless]

Which specific alloy? This is critical because they have different strengthening mechanisms.
Have you tried heat treating any in order to see if you can 'recover' the properties?

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Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[Caster]

As far as i know the alloy is 713c,From what i understand heat treatment is not an option.

 

[EdStainless]

As I recall, the higher the casting temp the more critical is the cooling rate. Strength at intermediate temp (1200-1400F) is favored by slow cooling. Strength at high temp (1600-1800F) often requires more rapid cooling.
If the melt temp and mold temp were off, changing your cooling rate, there isn't much that you can do.

What poperties are you trying to meet? What are you getting?

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[Caster]

Passing UTS but failing on yield....so i would imagine it is brittle ?
Melting is carried out at approx 1250 c and metal is superheated to approx 1450 -1550 c

 

[EdStainless]

Maybe they went to the top end of the superheat and the molds were at their top end also? I suppose that you have tested multiple parts and get the same results.
Your Yield fails low? What about the elongation and RA?
What does the microstructure look like? Very coarse? Is it the strengthening phases that are coarse?
It might be worth playing with heat treating a few pieces. Give a couple of them an aging treatment, maybe some at 1750F and some at 1950F. You might get enough secondary pahses to boost you strength. At least you would have a better picture.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[Caster]

Thanks Ed
I appreciate it.

 

[bobdz]

The lower the pouring temp the better chance you have for a finer grain structure and hence better properties.
If in a real bind, HIP the castings, will increase yield and ductility and close any porosity.

Bob Dzugan

http://www.buyCASTINGS.com