As shown in FIG. 3, conventional joints joining ceramic shafts and metal sleeves include a ceramic shaft 31 that is fitted into a metal sleeve 32 and is joined thereto by means of a brazing filler material 33. It has also been known to form a joint by shrink-fitting a ceramic shaft into a metal sleeve.
In each type of conventional joints described above, the thermal expansion mismatch between the metal sleeve or brazing filler material and the ceramic shaft exerts a shear stress on the ceramic shaft in the vicinity of the area where it is fitted into the metal sleeve. This causes either failure of the ceramic shaft as it is being joined to the metal sleeve or deterioration of its thermal or mechanical durability after joining is completed. In order to avoid these troubles, it is necessary to use a brazing filler material having the appropriate strength and Young's modulus, or to control closely the dimensional precision of the area where the ceramic shaft is shrink-fitted into the metal sleeve. The former approach has the disadvantage of limited flexibility in the choice of suitable brazing filler materials, while the second solution is not economical.
USPTO Backgrounds
USPTO Backgrounds