Plastic and nonmetallic article shaping or treating: processes – Including step of generating heat by friction
Patent
1990-12-18
1993-10-05
Derrington, James
Plastic and nonmetallic article shaping or treating: processes
Including step of generating heat by friction
264 62, 264 67, C04B 4185
Patent
active
052502422
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of producing a ceramic sintered body having a dense ceramic membrane on the surface efficiently.
BACKGROUND ART
Ceramics are superior to metals in heat resistance, corrosion resistance, wear resistance, etc., and are the materials to be hoped. Examples of such ceramics include alumina, silicon nitride, silicon carbide, partially stabilized zirconia, and the like. It is known to impart novel functions in addition to the native properties of the sintered body of the above material by forming the membrane of a foreign ceramic on the surface of the sintered body.
For example, it is known to coat the surface of a silicon nitride sintered body with alumina by CVD. Silicon nitride itself is excellent in strength and toughness, but it tends to react with iron. Therefore, the uses as cutting tools for steel materials are restricted, whereas alumina coating prevents the reaction of silicon nitride with iron resulting to extend the life of the cutting tools.
Besides, it is also known to increase the resistance to the damage during using it by the thermal spraying of zirconia onto the surface of a silicon nitride sintered body (J. L. Schienle and J. Smyth; High Temperature Coating Study to Reduce Contact Stress Damage of Ceramics, Proc. Twenty-Third Automotive Technology Development Contractors' Coordination Meeting, (1985), p.249).
As mentioned above, as the method of forming a membrane of foreign ceramic on the surface of a ceramic, there are the above methods according to CVD or PVD, and furthermore the method of applying the liquid of metal polymer onto the surface of a sintered body followed by sintering, etc. A dense membrane can be formed by coating the surface of a sintered body by CVD. However, there are the problems that the film-forming speed is small, and the coating takes a lot of time. Furthermore, it is difficult to form an uniform membrane on complex-shaped articles, and the application of this method to big articles is also difficult. There are similar problems in PVD.
Another method of forming ceramic membrane is comprised of coating the surface of a sintered body with the suspension of ceramic powder, the solution of hydroxide, the liquid, paste or solution of metal polymer or the like by spraying, brush coating, immersing or the like, drying, pyrolyzing, and then sintering. Besides, the method of thermal spraying of ceramic powder is also known. The restrictions of these methods to the shape and the size are less than CVD, PVD. However, there is a common disadvantage in these methods. That is, the produced membrane contains pores, and in most cases, atmospheric gas contacts the substrate of the sintered body through the pores, and for example, some objects of the coating, such as the improvement in oxidation resistance, are not achieved.
A method of converting a membrane with much pores to a dense membrane with little pores by the hot isostatic pressing (HIP) is proposed in order to solve the above problem (H. Kuribayashi et al; Ceramic Bulletin, vol.65, No.9, (1986), p1306). This method comprises forming a ceramic membrane on the surface of stainless steel by plasma spraying, sealing it with a vessel of pyrex glass, using argon gas as the pressurizing medium, and subjecting it to HIP. Thus, dense alumina, zirconia and titanium carbide membranes were formed on the surface of stainless steel.
A flow sheet of the method of conducting the above HIP treatment is shown in FIG. 4. Respective processes are explained more concretely. First, a known molding method, such as uniaxial pressing, CIP, extrusion, slurry casting or injection molding, is applied to the raw powder of a ceramic sintered body to obtain a molded body, and various sintering methods are applied to the molded body to obtain a sintered body. As the sintering method, for example, the low pressure sintering method wherein the sintering is conducted under vacuum, ordinary pressure or a pressure of less than 10 atm. is known. In this method, since pores usually remain, it is also known to
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Chemical Abstracts, vol. 104, No. 20, abstract 173213R.
American Ceramic Society Bulletin, vol. 65, No. 9, pp. 1306-1311.
World Patent Index, Abstract of JP-A-60039001 (Nippon Tungsten KK).
Nishio Hiroaki
Sato Michitaka
Watanabe Keiji
Derrington James
NKK Corporation
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