<p>Is it possible to 3D print an axial turbine 2 - 4 inches (50 - 100 mm) in radius, capable withstanding temperatures about 800 - 1000°C and rotation speeds of 100 - 120 x 10<sup>3</sup> rpm?</p>

<p>How expensive is that? Is it cheaper to mill such a turbine from a whole piece of alloy?</p>

<p>What technologies and materials should be used?</p>

<p>Are Inconel alloys suitable for 3D printing?</p>

<p>Are there any titanium alloys suitable for this task? I've read titanium is rarely used in rapidly rotating parts due to its ability to ignite if mechanical failure occurs and rotating blades touch the casing. Do titanium alloys still have this drawback? </p>

<p>Is it possible to make disk of titanium and blades of Inconel, and have them welded (considering heat expansion)?</p>

<p>How blades or blisks can be ceramically coated?</p>

<p>Thank you!</p>

This depends primarily on economics and on desired lifetime.  Rather obviously you need a material whose strengths and melting points exceed the operational specs.  Determining the various break strengths (shear, bending, etc) is an engineering problem, not a manufacturing problem per se.
Next, consider the production time and cost of 3D-printing vs. some typical assembly line process.  Nearly always the 3D approach loses for large quantity builds.
Designing and operating devices like this can be extremely dangerous. Very tight tolerances are required.
This site
describes the difficulties, starting with material choice, moving on to tolerances, and so on.  I don't think you want to go at this in your basement.