integral assembly specifically the invention provides that the slits are furnished at least on the axial level of the trailing edges 7 of the vanes 2 on the cover rings 3 and 4 that is the axial extent of the slits include axial position values corresponding to the trailing edge 7 of the vanes 2 the zone of the vane leading edges 6 on the other hand is not as critical with respect to the thermal stresses occurring during operation in the embodiments shown in fig1 to 4 the radially outer cylindrical cover ring 4 is provided with axially extending grooves 9 in the zone of the junctions of the ring 4 and the vanes 2 on its radially outer peripheral surface these grooves 9 may have straight walls as illustrated in fig3 or as shown in fig4 may have contoured walls 13 14 conforming to the contours of the surfaces of vane 2 the width of the grooves in the circumferential direction is approximately 40 to 60 of the vane separation i e the center to center distance of two adjacent vanes from each other fig2 shows the zone of transition from the vane 2 to the outer cover ring 4 on an.