Infiltrated molded articles of spherical non-refractory metal powders

• US 4,431,449 A
• Filed: 06/01/1983
• Issued: 02/14/1984
• Est. Priority Date: 09/26/1977
• Status: Expired due to Term

• Current Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Original Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Inventors: Dillon, Kenneth R., Terchek, Richard L.
• Primary Examiner(s): Hunt, Brooks H.
• Application Number:
  US06/499,412
• Time in Patent Office: 258 Days
• Field of Search: 419/26, 419/27, 419/36, 419/38, 419/48, 75/246, 75/247, 428/567
• US Class Current: 75/246
• CPC Class Codes: A61F 2002/30968 Sintering
• CPC Class Codes: B22F 1/065 Spherical particles
• CPC Class Codes: B22F 2998/00 Supplementary information concerning processes or compositions relating to powder metallurgy
• CPC Class Codes: B22F 2998/10 Processes characterised by the sequence of their steps
• CPC Class Codes: B22F 3/1021 Removal of binder or filler removal of binder from ceramics C04B35/638
• CPC Class Codes: B22F 3/1275 by coating a model and eliminating the model before consolidation
• CPC Class Codes: B22F 3/26 Impregnating making ferrous alloys by impregnation C22C33/0242
• CPC Class Codes: B22F 5/007 of moulds
• CPC Class Codes: Y10T 428/1216 Continuous interengaged phases of plural metals, or oriented fiber containing

Abstract

A molded, non-refractory metal article is made by molding in a flexible mold a plastic mixture of non-refractory, spherical metal powders and a heat-fugitive binder comprising thermoplastic material to form a green article of predetermined shape and dimensions, heating the green article to remove said binder and consolidate the non-refractory spherical powders in the form of a porous, monolithic skeleton of necked particles of non-refractory metal, infiltrating the skeleton with a molten metal having a melting point that is at least 25° C. less than the melting point of the lowest melting of said spherical, non-refractory metal particles, and cooling the infiltrated skeleton thereby forming a homogeneous, void-free, non-refractory metal article of two intermeshed metal matrices.

Claims

1. A shaped, homogeneous, monolithic, metal article comprising at least 60 percent by volume of a first continuous phase of spherical non-refractory metal particles comprising cobalt or cobalt alloy, which particles are metallurgically integral at their contiguous points of contact in the form of a skeleton with perceptible necking, when viewed by a light microscope, between the largest contiguous particles thereof, and as a minor portion a second continuous phase of metal which has a melting point of at least 25°

Kelvin lower than the melting point of the lowest melting of said spherical non-refractory particles and which occupies the volume of said article not occupied by said skeleton, said article thereby comprising two intermeshed matrices and being substantially void free.

2. The metal article of claim 1 wherein said non-refractory spherical metal particles comprise a distribution of diameters in the range of about 1 to 200 μ

m.

3. The metal article of claim 2 wherein said non-refractory spherical metal particles are less than 45 μ

m in diameter.

4. The metal article of claim 3 wherein said non-refractory spherical metal particles have a calculated surface area in the range of about 1.8×

10^-2 m² /g to 14.2×

10^-2 m² /g.

5. The article of claim 1 wherein the ratio of the melting temperature of said second continuous phase to the melting temperature of said first continuous phase is less than about 0.98 when both temperatures are expressed on the Kelvin scale.

6. The metal article of claim 5 wherein said ratio is less than about 0.95.

7. The metal article of claim 5 wherein said ratio is greater than about 0.5.

8. The metal article of claim 5 wherein said ratio is greater than about 0.6.

9. The metal article of claim 1 wherein said first continuous phase has a melting temperature in the range of 1273°

Kelvin to 2073°

Kelvin and said second continuous phase has a melting temperature in the range of 700°

Kelvin to 2048°

Kelvin.

10. The article of claim 1 wherein said first continuous phase or said second continuous phase or both said first continuous phase and said second continuous phase are hardenable metals or alloys.

11. The metal article of claim 1 wherein said second continuous phase comprises metal selected from the group consisting of copper, silver, gold and alloys containing one or more of copper, silver and gold.

12. The article of claim 1 wherein said first continuous phase is an alloy containing cobalt and said second continuous phase is an alloy containing copper.

13. The article of claim 1 wherein said first continuous phase is an alloy containing cobalt and said second continuous phase is gold or an alloy containing gold.

15. The metal article of claim 1 wherein said molded metal article is a dental prostheses.

16. A metal article of claim 1 wherein said non-refractory article is an injection molding die cavity.

17. The metal article of claim 1 wherein said molded article is a metal die casting cavity.

18. The metal article of claim 1 wherein said second continuous phase wets said first continuous phase.

14. A shaped, homogeneous, monolithic, metal article having a working surface, said article comprising at least 60 percent by volume and not more than 80 percent by volume, of a first continuous phase of spherical, non-refractory metal particles comprising cobalt or cobalt alloy, said particles having a distribution of diameters in the range of about 1 to 45 m, and a surface area in the range of about 1.8×

10^-2 m² /g to 14.2×

10^-2 m² /g, said particles being metallurgically integral at their contiguous points of contact in the form of a skeleton with perceptible necking, when viewed by a light microscope, between the largest contiguous particles thereof, and a second continuous phase of a metal which has a melting point of at least 25°

Kelvin lower than the melting point of the lowest melting of said spherical non-refractory particles and which occupies the volume of said article not occupied by said metallurgically integral spherical particles, said article thereby comprising two intermeshed matrices and being substantially void free.

19. A process for forming a shaped, monolithic, metal article comprising the steps of:

heating a mixture of non-refractory spherical metal powder comprising cobalt or cobalt alloy and fugitive organic binder comprising a thermoplastic material above the softening temperature of said binder;

molding the resulting plastic mass in a heated flexible mold to form an essentially void-free green molded article having the shape and size of the mold;

supporting the resulting green molded article in a non-reactive refractory powder;

heating the said green molded article to volatilize the organic binder and to lightly sinter said non-refractory spherical metal powder and thereby form a coherent monolithic metal skeleton;

cooling the resulting monolithic metal skeleton and infiltrating said monolithic metal skeleton with a second metal with a melting point that is at least 25°

K. lower than the melting point of the lowest melting said spherical metal powder, to form an infiltrated molded metal article.

20. A process for forming a molded, monolithic, non-refractory metal article comprising the steps of:

mixing a non-refractory, spherical metal powder comprising cobalt or cobalt alloy with a fugitive organic binder comprising a thermoplastic material;

heating the resulting powder-binder mixture above the softening temperature of said organic binder to form a plastic mass;

feeding the plastic mass mixture into a warmed, elastic mold;

vibrating the mold and its warm contents at reduced pressure;

maintaining the mold and its warm contents without vibrating at a temperature above the softening temperature of the organic binder for 1 to 24 hours;

vibrating the mold and its contents;

cooling the mold and its contents;

demolding said contents by applying a vacuum to the outside of said elastic mold, thereby forming a green molded article;

packing the green molded article in a non-reactive refractory powder;

heating said green molded article to volatilize the organic binder and to lightly sinter the non-refractory powder, thereby forming a metallurgically integral, monolithic skeleton;

placing solid infiltrant metal contiguous to, but not touching, said skeleton such that upon melting the melted infiltrant will, under the influence of gravity, flow toward and contact the surface of said skeleton;

heating said skeleton and infiltrant metal above the melting point of said infiltrant metal, whereby said infiltrant melts and flows toward said skeleton surface and infiltrates into the skelton through the surface of said skeleton;

cooling the resulting infiltrated skeleton to form a molded, non-refractory spherical powder metal article.

21. The process in accordance with claim 20 wherein said plastic mass is cooled into a solid, the resulting solid powder-binder mixture is milled to a granular consistency, and the granular powder-binder mixture is heated above the softening temperature of said binder prior to further processing.

22. The process in accordance with claim 20 wherein said non-refractory skeleton is placed in direct contact with solid infiltrant metal.

25. The process of claim 20 wherein said organic binder is a mixture of a thermoplastic material and a thermosetting material.

26. The process of claim 20 wherein said organic binder comprises organic carboxy compound selected from the group consisting of mixtures of stearic acid and oleic acid, oleic acid, stearic acid, lower alkyl esters of oleic acid, lower alkyl esters of stearic acid, polyethylene glycol esters of oleic acid, polyethylene glycol esters of stearic acid, and mixtures thereof.

27. The process of claim 26 wherein said organic binder is polyethylene glycol distearate.

23. A process for forming a molded, monolithic, non-refractory metal article comprising the steps of:

mixing a non-refractory, spherical metal powder with a fugitive organic binder comprising a thermoplastic material;

heating the resulting powder-binder mixture above the softening temperature of said organic binder to form a plastic mass;

feeding the plastic mass mixture into a warmed, elastic mold;

vibrating the mold and its warm contents at reduced pressure;

maintaining the mold and its warm contents without vibrating at a temperature above the softening temperature of the organic binder for 1 to 24 hours;

vibrating the mold and its contents;

cooling the mold and its contents;

demolding said contents by applying a vacuum to the outside of said elastic mold, thereby forming a green molded article;

packing the green molded article in a non-reactive refractory powder;

heating said green molded article to volatilize the organic binder and to lightly sinter the non-refractory powder, thereby forming a metallurgically integral, monolithic skeleton;

coating a portion of the surface of said metallurgically integral, monolithic skeleton with zirconia powder leaving a portion of said skeleton surface free of zirconia powder;

placing solid infiltrant metal contiguous to, but not touching said skeleton such that upon melting the melted infiltrant will, under the influence of gravity, flow toward and contact said uncoated portion of said skeleton;

heating said non-refractory skeleton and said infiltrant metal above the melting point of said infiltrant metal whereby said infiltrant flows toward said skeleton surface portion free of zirconia powder and infiltrates into the non-refractory skeleton through the said skeleton surface portion free of zirconia powder; and

cooling and resulting infiltrated skeleton to form a molded, spherical powder metal article.

24. A process for forming a molded, monolithic, non-refractory metal article comprising the steps of:

mixing a non-refractory, spherical metal powder with a fugitive organic binder comprising a theremoplastic material;

heating the resulting powder-binder mixture above the softening temperature of said organic binder to form a plastic mass;

feeding the plastic mass mixture into a warmed, elastic mold;

vibrating the mold and its warm contents at reduced pressure;

maintaining the mold and its warm contents without vibrating at a temperature above the softening temperature of the organic binder for 1 to 24 hours;

vibrating the mold and its contents;

cooling the mold and its contents;

demolding said contents by applying a vacuum to the outside of said elastic mold, thereby forming a green molded article;

packing the green molded article in a non-reactive refractory powder;

heating said green molded article to volatilize the organic binder and to lightly sinter the non-refractory powder, thereby forming a metallurgically integral, monolithic skeleton;

coating a portion of the surface of said metallurgically integral, monolithic skeleton with zirconia powder leaving a portion of said skeleton surface free of zirconia powder;

placing said non-refractory skeleton in direct contact with solid infiltrant metal;

heating said non-refractory skeleton and said infiltrant metal above the melting point of said infiltrant metal whereby said infiltrant flows toward said skeleton surface portion free of zirconia powder and infiltrates into the non-refractory skeleton through the said skeleton surface portion free of zirconia powder; and

cooling the resulting infiltrated skeleton to form a molded, spherical powder metal article.

28. A shaped, homogeneous, monolithic, uniformly, porous metal article comprising non-refractory spherical metal particles which are metallurgically integral at their contiguous points of contact in the form of a skeleton with perceptible necking, when viewed by light microscope, between the largest contiguous particles thereof, a portion of the surface of said metal article being coated with a layer of a material that inhibits surface blooming on said metal article.

29. A metal article in accordance with claim 28 wherein said surface blooming inhibitor is zirconia powder.