SINTERED CEMENTED CARBIDE GRANULATE AND ITS USE

Abstract

The invention is concerned with the fields of cemented carbide materials and ceramic and/or powder-metallurgical process engineering and relates to a sintered cemented carbide granulate such as that which can, for example, be used for the production of wear parts or tools with cemented carbides, and to its use.

The object of the present invention is to specify a cemented carbide granulate with which cemented carbide green bodies and cemented carbide sintered bodies that exhibit a high green density and high green strength can be produced, and to specify the use thereof.

The object is attained with a sintered cemented carbide granulate which, for the majority of granules, has an inhomogeneous distribution of hard material and metallic binder in the individual granule, wherein the concentration of the metallic binder at the surface of the individual granule is, in total, at least 25% greater than in the interior of the granule.

Claims

1. A sintered cemented carbide granulate which, for the majority of granules, has an inhomogeneous distribution of hard material and metallic hinder in the individual granule, wherein the concentration of the metallic binder at the surface of the individual granule is, in total, at least 25% greater than in the interior of the granule.

2. The sintered cemented carbide granulate according to claim 1 in which WC, TiC, TiCN, NbC, TaC, Cr.sub.3C.sub.2, VC, and/or Mo.sub.2C, and/or mixtures thereof are present as hard materials.

3. The sintered cemented carbide granulate according to claim 1 in which Co, Fe, and/or Ni, and/or mixtures thereof are present as metallic binders.

4. The sintered cemented carbide granulate according to claim 1 in which additives of Cr.sub.3C.sub.2, VC, and/or TaC are present in the granules as grain growth inhibitor.

5. The sintered cemented carbide granulate according to claim 1 in which the hard material is present with an average grain size of 0.05 to 7 m in the cemented carbide granules.

6. The sintered cemented carbide granulate according to claim 1 in which the concentration of the metallic binder at the surface of the individual granule is, in total, 25% to 2000% greater than in the interior of the granule.

7. The sintered cemented carbide granulate according to claim 1 in which the distribution of the metallic binder at the surface is as uniform as possible across the entire surface of the individual granule.

8. The sintered cemented carbide granulate according to claim 7 in which the metallic binder is present in the form of a most complete possible surface layer on the individual granules.

9. A use of sintered cemented carbide granulate according to claim 1 for additive manufacturing methods and/or for thermal spraying.

10. The use according to claim 9 for powder bed-based additive manufacturing methods, such as 3D powder printing (binder jetting) or selective laser sintering/melting or electron beam melting.

Description

EXAMPLE 1

[0051] Sintered cemented carbide granulate was produced by a milling and mixing of WC, Co, Cr.sub.3C.sub.2, and 2 mass % organic binder, in this case paraffin, in heptane, a subsequent spray granulation, and a sintering at 1200 C. The granules were then deagglomerated and screened into the fraction 90 m. The fraction 10 m and 32 m was then obtained by means of conventional separating technology.

[0052] The cemented carbide granulate presintered in such a manner comprised 19 vol % Co and WC distributed homogeneously in the granules, with an initial grain size of 0.75 m d.sub.FSSS.

[0053] The presintered and separated cemented carbide granulate was, in a further sintering, briefly heated to 1345 C. and then cooled to 1200 C. at a cooling rate of 0.5 K/min. After a cooling to room temperature (approx. 20 C.), the granulate was once again deagglomerated and separated.

[0054] Following production, the surface of the granules was 50% covered with cobalt, wherein the concentration of cobalt at the surface was, in total, then 263% greater than the original cobalt content in the interior of the granules.

EXAMPLE 2

[0055] Sintered cemented carbide granulate was produced by a milling and mixing of WC, 16 vol % (equal to 10 mass %) Co, and 2 mass % organic binder, in this case paraffin, in heptane, a subsequent spray granulation, and a sintering at 1200 C. in a sinter-HIP furnace. The granules were then deagglomerated and screened into the fraction 90 m. The fraction 10 m and 32 m was then obtained by means of conventional separating technology.

[0056] The granulate presintered in this manner was then transferred to a PVD coating system and kept in motion by means of a vibrating table adapted for the powder coating. The coating took place at 5*10.sup.3 mbar with an adapted power output (DC voltage) at room temperature. The cobalt target had a surface structuring specifically suited to magnetic materials.

[0057] Following coating, the surface of the granules was 90% covered with cobalt, wherein the cobalt content at the surface in the coated state was, in total, 565% higher than the cobalt content in the interior of the granules.

EXAMPLE 3

[0058] Sintered cemented carbide granulate was produced by a milling and mixing of WC, 16 vol % (equal to 10 mass %) Co, 0.5 mass % Cr.sub.3C.sub.2, and 2 mass % organic binder, in this case paraffin, in heptane, a subsequent spray granulation, screening to <90 m, and a sintering in very thin bulk in a vacuum sinter furnace at approx. 1320 C. with a very slow cooling rate of 0.5 K/min to 1150 C., wherein metallic binder was pressed to the surface.

[0059] Following production, the surface of the granules was 75% covered with cobalt, wherein the cobalt content at the surface was, in total, then 468% greater than the original cobalt content in the interior of the granules.

EXAMPLE 4

[0060] Sintered cemented carbide granulate was produced by a milling and mixing of WC, 16 vol % (equal to 10 mass %) Co, 0.5 mass % Cr.sub.3C.sub.2, and 2 mass % organic binder, in this case paraffin, in heptane, a subsequent spray granulation, screening to <90 m, and a debinding with a subsequent sintering to 1290 C. For the debinding in an N2Ar mixture, a very high heating rate of 20 K/min to 800 C. without a holding time was thereby used, so that the organic binder present was only removed in the edge region of the granules and the carbon content in the interior thus increased as a result of the decomposition of the organic binder, which caused a diffusion of the metallic binder to surface during the sintering.

[0061] Following production, the surface of the granules was 80% covered with cobalt, wherein the cobalt content at the surface was, in total, then 500% greater than the original cobalt content in the interior of the granules.