Manufacture of complex shaped Cr.sub.3 C.sub.2 /Al.sub.2 O.sub.3 components by injection molding technique

• US 5,993,726 A
• Filed: 04/22/1997
• Issued: 11/30/1999
• Est. Priority Date: 04/22/1997
• Status: Expired due to Term

• Current Assignee: National Science Council
• Original Assignee: National Science Council
• Inventors: Twu, Kuo-Chi, Huang, Jiunn-Jye, Huang, Jow-Lay
• Primary Examiner(s): Fiorilla, Christopher A.
• Application Number:
  US08/839,160
• Time in Patent Office: 952 Days
• Field of Search: 264/642, 264/645
• US Class Current: 264/642
• CPC Class Codes: B28B 1/24 by injection moulding injection moulding of ceramic slips B28B1/265; of tubular articles B28B21/38
• CPC Class Codes: B28B 11/243 Setting, e.g. drying, dehydrating or firing ceramic articles B28B11/242 takes precedence
• CPC Class Codes: C04B 35/117 Composites

Abstract

The purpose of this invention is to manufacture complex shaped Cr₃ C₂ /Al₂ O₃ components efficiently with effective cost. Chromium carbide, which is quite chemically inert at elevated temperature, is added into an alumina matrix for toughening purposes. Chromium carbide and alumina ceramic powders are mixed with binders to form a solidified suspension. The suspension is then crushed, heated, and injected into green products. Controlled solvent and thermal debinding processes are followed before performing pressureless sintering. Samples are sintered in pre-treated argon gas with minimum oxygen partial pressure, or in vacuum for controlling the phase stability and microstructure for tailoring mechanical properties. The processing parameters for injection molding, the composition design of binders and ceramic composites, and the techniques for controlling the phase transformation of chromium carbide are developed. A near-net shape complex component with minimum after machining can be manufactured. The injection molding and pressureless sintering process make the mass production possible. Optimized properties of 97.8% in the theoretical density, 500 Mpa in strength, and 5.85 MPam^1/2, are obtained. These properties are greater, in comparison, than the properties of conventional alumina ceramics.

Claims

1. A process for manufacturing a sintered Cr₃ C₂ /Al₂ O₃ product comprising:

mixing chromium carbide powder and alumina powder in a ratio of 10;

90 to 40;

60 respectively to form a mixture;

mixing at least one binder with said mixture to form a solidified suspension;

heating said solidified suspension to render it fluid;

injection molding said heated suspension to form an injection molded product;

degreasing said injection molded product to form a degreased injection molded product by solvent degreasing followed by thermal degreasing;

cold isostatic pressing said degreased injection molded product; and

vacuum sintering or pressureless sintering said degreased injection molded product subjected to cold isostatic pressing to form said sintered product.

2. The process defined in claim 1,

wherein said at least one binder is a member selected from the group consisting of polypropylene, paraffin, and stearate in a quantity of 55-60 volume % based on said chromium carbide powder and alumina powder.

3. The process defined in claim 1, further comprising

forming complex-shaped components,

wherein an injection molding machine used in said injection molding step is heated to a temperature of 155-150-150 C.,

wherein an injection nozzle is heated to a temperature to 160°

C., and

wherein an injection pressure is 500kg/cm², and

wherein an injection speed is 40cc/sec to form complex-shaped components.

4. The process defined in claim 1, wherein said degreasing step further comprises

degreasing with a solvent selected from the group consisting of normal ethane, normal heptane, normal hexane, and normal octane at a temperature of approximately 60°

C.

5. The process defined in claim 1, wherein said thermal degreasing step further comprises

degreasing at a temperature of 500-600 C.,

wherein said binder is removed from said injection molded product during sintering forming an even pore distribution in said injection molded product.

6. The process defined in claim 1,

wherein said cold isostatic pressing is performed at 100MPa, and

wherein internal voids in said injection molded products are minimized and a density of said injection molded products is increased.