I would say that casting porosity in superalloys has much the same effect as in any other sort of alloy. It all comes down to size, shape and distribution of the porosity within the casting.

Are you saying that you want to control porosity of the casting by changing the alloy chemistry? This may be possible, but take a look at your metal treatment procedures, the way you handle the molten metal, and the design of the casting. For example,is there a route for gas to exit as the metal solidifies?

Thank you Bruv.I also want to know what is the effect of eta phase on Ni-base super alloys? is it detrimental or beneficial to the mechanical properties of the alloy? what are the mechanical properties of eta itself?

Rafi12,

Can you explain what you mean by handling porosity "analytically"?  There are numerous ways to identify porosity based on amount, size, distribution, etc.  Based on the size and distribution, you can assume an equivalent flaw size, and then use fracture mechanics to calculate the stress at which your component will fail.  I have even seen techniques where a flaw (round porosity or thin crack) is modeled in FEA, and the resultant stress intensity used as a predictor of failure, rather than the nominal stress at various portions of the casting.