Metallurgical process

• US 4,591,481 A
• Filed: 01/14/1985
• Issued: 05/27/1986
• Est. Priority Date: 05/06/1982
• Status: Expired due to Term

• Current Assignee: Ultra-Tec Corporation
• Original Assignee: Ultra-Tec Corporation
• Inventors: Lueth, Roy C.
• Primary Examiner(s): Lechert, Jr., Stephen J.
• Application Number:
  US06/690,935
• Time in Patent Office: 498 Days
• Field of Search: 419/26, 419/28, 419/36, 419/37, 419/47, 419/48, 419/57, 419/60, 75/228, 75/236
• US Class Current: 419/26
• CPC Class Codes: B22F 2999/00 Aspects linked to processes or compositions used in powder metallurgy
• CPC Class Codes: B22F 3/1035 Liquid phase sintering
• CPC Class Codes: B22F 3/15 Hot isostatic pressing
• CPC Class Codes: B22F 3/16 in successive or repeated steps

Abstract

The present invention discloses a method for densifying previously sintered parts constructed of powdered metals, ceramics or the like to nearly 100% theoretical density. The method of the present invention comprises heating the parts containing binder and hard phase above their liquid phase temperature and then applying a pressure in a predetermined range to the parts for a predetermined period of time and simultaneously maintaining the parts at or above their liquid phase temperature. This pressure range is set so that the pressure is below the pressure necessary to overcome the capillary force acting on the binder to keep the binder from entering the voids but above the pressure necessary to physically move or collapse the microstructure inwardly, thus filling the voids with a homogenous mixture of binder and hard phase. The method of the present invention achieves complete closure of even large voids and the elimination of substantially all porosity within the part.

Claims

1. A method for densifying previously liquid phase sintered parts which may contain voids or porosity and constructed of cemented carbides, powdered metals, ceramics or the like comprising the steps of:

heating said parts in a vacuum to a temperature such that they are substantially in the two phase field of hard phase plus liquid and that an equilibrium or nearly equilibrium amount of hard phase has dissolved in the liquid phase, and

applying a pressure in an amount below that which overcomes the capillary forces imposed on the molten binder in a direction away from the part voids and above the pressure necessary to physically collapse the part structure inwardly to said parts for a predetermined period of time while maintaining said parts above said temperature.

2. The method as defined in claim 1 wherein said pressure applying step comprises applying pressure to said parts in the range of 50 to 500 psi.

3. The method as defined in claim 1 wherein said pressure applying said step comprises applying pressure to said parts in the range of 50 to 300 psi.

4. The method as defined in claim 1 wherein said pressure applying step comprises the steps of placing said parts in a pressurizable chamber, and introducing a sufficient amount of gas to said chamber to create said pressure.

5. The method as defined in claim 4 wherein gas is argon.

6. The method as defined in claim 1 wherein said predetermined period of time is in the range of 5-500 minutes.