inserted into a metallic rotor disk 25 in a manner fixed in terms of rotation the metallic disk 25 is connected to the tie rod 4 and rotates therewith the diameter of the disk 25 is no greater than usual and is also not exposed to the highest temperatures within the hot gas duct 56 and consequently metal can continue to be used as material for the disk 25 in the same way as in a conventional turbine it is also possible to use what are known as hybrid turbine blades which still have a metallic core but this core is surrounded by a ceramic as is known for example from u s pat no 4 563 128 the content of disclosure of this document relating to the structure of the ceramic turbine blade is expressly incorporated in the content of disclosure of the present application further types of hybrid blades are conceivable fig4 shows an example of a hybrid blade 16 a main blade section 28 at its outer surface consists of ceramic 39 in the interior there is a metallic core 31 for example formed from a nickel and or cobalt superalloy the metallic core 31 by way of example also forms a root part 34 of the blade 16 in the radial direction 19 the metallic core 31 does not extend all the way to the radial end 37 of the blade 16 but rather for example only extends over for example 70 of the length of the main blade section 28 in the radial direction 19 since otherwise the loads caused by the centrifugal forces at the intended rotational speed of the turbine would exceed the mechanical strength of the metallic core or of the blade root or of the anchoring in the turbine shaft.