High pressure isostatic densification process

• US 5,151,247 A
• Filed: 11/01/1991
• Issued: 09/29/1992
• Est. Priority Date: 11/05/1990
• Status: Expired due to Term

• Current Assignee: Sandvik AB
• Original Assignee: Sandvik AB
• Inventors: Haglund, Bengt O., During, Bengt N.
• Primary Examiner(s): JENKINS, DANIEL J
• Application Number:
  US07/786,608
• Time in Patent Office: 333 Days
• Field of Search: 419/13, 419/14, 419/15, 419/16, 419/17, 419/18, 419/47, 419/57, 419/60
• US Class Current: 419/13
• CPC Class Codes: B22F 3/14 simultaneously
• CPC Class Codes: C22C 1/051 Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor

Abstract

The present invention is a method for densifying powder metallurgical parts to 100% theoretical density. The method comprises applying a high pressure of 0.1-100 MPa during sintering in a high pressure furnace at a temperature before which the liquid phase is formed and maintaining this pressure during the rest of the sintering cycle until the furnace has cooled to almost room temperature. The method achieves rapid, complete closure of the porosity which results in parts with close dimensional tolerances and practically no warpage.

Claims

1. A method of liquid phase sintering of powder metallurgical parts in a high pressure furnace comprising applying a pressure to the part of from about 0.1-100 MPa at a temperature below the formation of eutectic liquid phase, T_liq, and maintaining this pressure during the remainder of the sintering cycle until the part has been subjected to substantial cooling.

2. The method of claim 1 wherein the said pressure is applied at a temperature in the range T_liq -50 to T_liq -2°

C.

3. The method of claim 1 wherein T_liq occurs at a temperature of from about 1200°

C.-1600°

C.

4. The method of claim 3 wherein the said pressure is maintained during the sintering cycle until the furnace has been cooled to at least 800°

C.

5. The method of claim 4 wherein the pressure is maintained until the furnace has been cooled to an ambient temperature.

6. The method of claim 1 wherein said powder metallurgical part comprises at least one hard constituent of a carbide, nitride and/or carbonitride of at least one metal of groups IVB, VB and/or VIB of the Periodic System and a binder metal based on Co, Ni and/or Fe, said high pressure is 0.3-30 MPa and the sintering is performed in an inert atmosphere.

7. The method of claim 1 wherein the atmosphere during sintering is a vacuum, inert gas or reducing gas.

8. The method of claim 1 wherein said powder metallurgical part consists of a grade of tungsten carbide and cobalt and the T_liq (°

C.) is calculated from the formula

space="preserve" listing-type="equation">T.sub.liq =(1314-456Δ

C)(Wt%Co).sup.(0.0015+0.0938Δ

C)

where Δ

C is the difference between actual and stoichiometric carbon for the grade in weight-%.

9. The method of claim 1 wherein the powder metallurgical part is maintained at the temperature before pressurizing the furnace for a period of time, t, in minutes calculated by the formula