This invention relates to a ceramic-metal friction welding member and a ceramic cast-in bonded piston made thereof which are useful for heat-resistant and wear-resistant parts to be used in engines and other industrial machines.
Recently, for example, with a piston for an internal combustion engine, in order to improve heat-resistance and wear-resistance, as well as decrease the weight of the engine itself, a piston made of a ceramic material and a metal integrally joined by cast-in bonding has been proposed and is actually being used.
Ceramic joined pistons made of integrally joined ceramic and metal members by cast-in bonding have been known as disclosed in, for example, Japanese Patent Laid-open No. 59-101,566 and Japanese Utility Model Laid-open No. 62-200,147.
The ceramic joined piston disclosed in the Japanese Patent Laid-open No. 59-101,566 is made of a ceramic member and a metal member being integrally joined by cast-in bonding through a metallized layer coated on a surface of the ceramic member and a cushioning material joined to the metallized layer.
Moreover, the ceramic joined piston disclosed in the Japanese Utility Model Laid-open No. 62-200,147 includes a ceramic member provided in a piston cavity and having an outer circumference which is formed with a groove or taper diverging from an upper end to a bottom end of a piston, thereby preventing any dislodgment of the ceramic member. In order to improve the bonding to an aluminum alloy, moreover, this publication discloses a feature of metallizing the outer circumference of the ceramic member.
With the ceramic joined piston disclosed in the Japanese Patent Laid-open No. 59-101,566, however, the joining force between the piston main body and the ceramic member is enhanced by a bond force of the metallized layer. Therefore, the metallized layers are formed in wide areas in order to endure stresses due to inertia forces, thermal deformations, and the like, of the piston. However, it is technically difficult to form the metallized layers uniformly in the wide areas, and as such tends to increase the manufacturing cost. Moreover, as the inertia forces and the thermal deformations are supported only by the metallized layers, reliability in strength is insufficient. In fact, joined surfaces often peel in operation of the piston so that burnt gases enter the peeled portions, with the result that the combustion efficiency of the engine will be lowered and fuel consumption will be increased. Moreover, such an entrance of the burnt gases would cause damage to the piston material and accumulation of carbon particles therein.
On the other hand, the ceramic joined piston disclosed in the Japanese Utility Model Laid-open No. 62-200,147 includes a ceramic member having an outer circumference formed with a groove or taper to prevent dislodgment of the ceramic member. Any sealing for preventing burnt gases from entering the joining surfaces is not considered. This is clear from the fact that in the embodiment of FIG. 5 in the Japanese Utility Model Laid-open No. 62-200,147, surfaces of the piston to be joined to the ceramic member are not subjected to any treatment.