Your question looks as if you wouldn’t know very much on the issue, but I doubt it otherwise you wouldn’t have been given the reponsibility to define a protocol for creep tests on such specific alloys.

So could you be more accurate on what you really want to know : for instance, do you have the kind of information that follows :

Are the turbine blades manufactured as single crystals or cast polycrystalline superalloys or wrought, or another structure, … ?

Are the test pieces coming from new material for blades or from actual service aged blades ?

As a corollary, what do you want to assess : the quality/conformity of new material at delivery or the residual life of service aged blades (service aged at which temperature ?) ?

What does the temperature range of t° 760° – 980° C given in the question exactly cover ? Are these possible constant creep temperatures in operation for your alloy or are they fluctuations or anything else ?

Do you know the materials standards for the Ni-based superalloy concerned giving the tables of values (rupture times and / or times for 1%-deformation in function of stress and different temperatures) ?

Do you know the design codes for manufacturing blades in Ni-based superalloys for use at high temperatures including rules for creep-fatigue interaction, corrosion, etc.. ? Do you know the safety factors vs minimum or mean stress – time to rupture (or time to 1 % strain) imposed by the code ? 

Have you heard of accelerated creep tests and do you know whether such accelerated tests have already been performed on your superalloy either by increasing the stress or by increasing the temperature (as compared to the service conditions of the turbine blades) ? If yes, do you have access to the test results ?

You write that you would like to conduct high temperature creep tests on your alloy, so one would assume that you are speaking of accelerated creep tests. Otherwise, you certainly know that performing creep tests under stress and temperature conditions close to the service conditions are very difficult : indeed the expected safe service life is of the order of magnitude of 100,000 hours to 200,000 hours. So, you must be able to perform the tests non-stop during 12 to 24 years with perfect control of stress, temperature and environmental parameters in the laboratory all the time. Is this what you are planning to do ?

Concerning the relationship of stress vs temperature you can deduce them yourself just from the above mentioned tables of values as given by materials standards and as resulting from accelerated creep tests. There exist (I have developed some) equations for low-alloy Cr-Mo steels. I wouldn’t be surprised that such kind of equations also exist for your Ni-based superalloy or that they can be deduced with a shape analogous to what exists for low-alloy Cr-Mo steels.

Your question looks as if you wouldn’t know very much on the issue, but I doubt it otherwise you wouldn’t have been given the reponsibility to define a protocol for creep tests on such specific alloys.

So could you be more accurate on what you really want to know : for instance, do you have the kind of information that follows :

Are the turbine blades manufactured as single crystals or cast polycrystalline superalloys or wrought, or another structure, … ?

Are the test pieces coming from new material for blades or from actual service aged blades ?

As a corollary, what do you want to assess : the quality/conformity of new material at delivery or the residual life of service aged blades (service aged at which temperature ?) ?

What does the temperature range of t° 760° – 980° C given in the question exactly cover ? Are these possible constant creep temperatures in operation for your alloy or are they fluctuations or anything else ?

Do you know the materials standards for the Ni-based superalloy concerned giving the tables of values (rupture times and / or times for 1%-deformation in function of stress and different temperatures) ?

Do you know the design codes for manufacturing blades in Ni-based superalloys for use at high temperatures including rules for creep-fatigue interaction, corrosion, etc.. ? Do you know the safety factors vs minimum or mean stress – time to rupture (or time to 1 % strain) imposed by the code ? 

Have you heard of accelerated creep tests and do you know whether such accelerated tests have already been performed on your superalloy either by increasing the stress or by increasing the temperature (as compared to the service conditions of the turbine blades) ? If yes, do you have access to the test results ?

You write that you would like to conduct high temperature creep tests on your alloy, so one would assume that you are speaking of accelerated creep tests. Otherwise, you certainly know that performing creep tests under stress and temperature conditions close to the service conditions are very difficult : indeed the expected safe service life is of the order of magnitude of 100,000 hours to 200,000 hours. So, you must be able to perform the tests non-stop during 12 to 24 years with perfect control of stress, temperature and environmental parameters in the laboratory all the time. Is this what you are planning to do ?

Concerning the relationship of stress vs temperature you can deduce them yourself just from the above mentioned tables of values as given by materials standards and as resulting from accelerated creep tests. There exist (I have developed some) equations for low-alloy Cr-Mo steels. I wouldn’t be surprised that such kind of equations also exist for your Ni-based superalloy or that they can be deduced with a shape analogous to what exists for low-alloy Cr-Mo steels.