Method for producing hard metal powder, and hard metal powder

Abstract

A method for producing hard metal powder suitable for manufacturing hard metal products including metal carbides and a binder is provided. An easy to carry out method that provides high quality hard metal powder includes: a) dissolving in water, water soluble raw materials and a binder source to form an aqueous solution, b) drying the aqueous solution to form a precursor powder having the raw materials homogenously distributed throughout the precursor powder, c) decomposing the precursor powder by heating the powder in an inert atmosphere to remove gas evolved in the decomposition of the raw materials, d) grinding the precursor powder and mixing it with a liquid media to produce a suspension, e) spray drying the suspension to agglomerate the precursor powder, and f) heat treating the agglomerated precursor powder to form a hard metal powder containing agglomerates of carbides evenly distributed and bonded to a metallic matrix.

Claims

1. A method for producing hard metal powder suitable for manufacturing hard metal products comprising metal carbides and a metallic binder, the method comprising: a) dissolving water soluble raw materials in water comprising a hard particle source, comprising a carbon source, and a metallic binder source to form an aqueous solution, b) drying in a drying process the aqueous solution to form a precursor powder having the water soluble raw materials homogenously distributed throughout the precursor powder, c) decomposing the precursor powder in a first heat treatment by heating it in a temperature of 370° C. to 430° C. in an inert atmosphere to remove gas evolved in the decomposition of the water soluble raw materials, d) grinding the precursor powder and mixing it with a liquid media to produce a suspension, e) spray drying the suspension to agglomerate the precursor powder, and f) heat treating the agglomerated precursor powder in a second heat treatment at 900° C. to 1150° C. in an inert atmosphere to form a hard metal powder containing agglomerates of carbides evenly distributed and bonded to a metallic matrix, wherein (f) is carried out immediately after (e).

2. The method according to claim 1, wherein the hard particle source in (a) comprises, in addition to C, one or more of the chemical elements W, Cr, V, Ti, Zr, Mo, Ta, and Nb.

3. The method of claim 1, wherein the hard particle source in (a) comprises ammonium meta tungstate forming a W (wolfram) source.

4. The method of claim 1, wherein the metallic binder source in (a) comprises one or more of chemical elements Co, Cr, Ni, and Fe.

5. The method of claim 1, wherein the hard particle source in (a) comprises glycine forming a C (carbon) source.

6. The method of claim 1, wherein the metallic binder source in (a) comprises cobalt acetate forming a Co (cobalt) source.

7. The method of claim 1, wherein the drying process in (b) is a spray drying process carried out in a hot gas.

8. The method of claim 1, wherein the gas removed in (c) comprises NH.sub.3 and H.sub.2O.

9. The method of claim 1, wherein the precursor powder is grinded in (d) in a ball mill.

10. The method of claim 9, wherein the liquid media in (d) is water.

11. The method of claim 9, wherein the liquid media in (d) is ethanol.

12. The method of claim 1, wherein the liquid media in (d) is water.

13. The method of claim 1, wherein the liquid media in (d) is ethanol.

14. The method of claim 1, wherein the spray drying in (e) is carried out in hot gas without a reducing agent.

15. The method of claim 14, wherein the hot gas in (e) is air.

16. The method of claim 1, wherein the inert atmosphere in (f) is argon.

17. The method of claim 1, wherein the agglomerates of carbides in (f) have a size of 5 μm to 50 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following the invention will be described in greater detail by means of a preferred embodiment with reference to the attached drawing, where the main steps of the invention have been presented in a general form.

DETAILED DESCRIPTION OF THE INVENTION

(2) The attached FIGURE shows the main steps of the method of the invention for producing hard metal powder. The expression “hard metal powder” refers here to a powder comprising fine hard particles of carbide and a binder metal. Typically, the hard particles of carbide are WC, and the binder metal is typically Co. As the FIGURE tells, the steps for producing hard metal powder are: a) dissolving in water water soluble raw materials comprising a hard particle source and a metallic binder source to form an aqueous solution, b) drying in a drying process the aqueous solution to form a precursor powder having the raw materials homogenously distributed throughout the precursor powder, c) decomposing the precursor powder in a first step by heating it in a temperature of 370° C. to 430° C. in an inert atmosphere to remove gas evolved in the decomposition of the raw materials, d) grinding the precursor powder and mixing it with a liquid media to produce a suspension, e) spray drying the suspension to agglomerate the precursor powder, and f) heat treating the agglomerated precursor powder at 900° C. to 1150° C. in an inert atmosphere to form a hard metal powder containing agglomerates of carbides evenly distributed and bonded to a metallic matrix.

(3) The hard particle source in step a) above comprises in addition to carbon (C) one or more of the chemical elements W, Cr, V, Ti, Zr, Mo, Ta, and Nb. Glycine, C.sub.2H.sub.5NO.sub.2, is preferably chosen as the carbon source. If the hard particle source comprises wolfram (W), ammonium meta tungstate, (NH.sub.4).sub.6H.sub.2W.sub.12O.sub.40.H.sub.2O, is preferably chosen as the W source.

(4) The binder source in step a) above preferably comprises one or more of the chemical elements Co, Cr, Ni and Fe. If the binder source comprises Co, cobalt acetate, Co(C.sub.2H.sub.3O.sub.2).sub.2.H.sub.2O, (or C.sub.4H.sub.6CoO.sub.4), is preferably chosen as the binder source.

(5) The drying process of the aqueous solution in step b) is preferably carried out by spray drying in hot gas, preferably in hot air having a temperature preferably above 100° C. Spray drying is an efficient process for producing a homogenous solution.

(6) The gas removed in the decomposing of the precursor powder in step c) is preferably NH.sub.3 and H.sub.2O, and removing these gases will reduce 30% of the mass of the precursor powder.

(7) A ball mill is preferably used for grinding the precursor powder in step d). Preferably, the precursor powder is grinded when being mixed with the liquid media.

(8) The liquid media used in step d) to produce a suspension, is preferably water or ethanol.

(9) The spray drying of the suspension in step e) is preferably carried out with a hot gas without the use of a reducing agent and preferably using a hot air dryer. A reducing agent is not needed in the present invention, because the substances of the suspension are in a state which does not react with oxygen. Thus, air can be used as the hot gas in the dryer.

(10) Nano carbide synthesis takes place in step f). The inert atmosphere for heat treating the agglomerated powder in step f) is preferably argon. Preferably, the inert gas can alternatively be i) a mixture of argon and hydrogen, preferably 96-98% Ar, the rest (2-4%) Hz; ii) nitrogen; or iii) a mixture of nitrogen and hydrogen, preferably 96-98% N.sub.2, the rest (2-4%) H.sub.2. Gas evolved in decomposition reactions in the step f) is small enough to prevent agglomerates to break up. The powder formed can, as such safely be handled and used for various applications.

(11) The total weight loss is roughly 70%, typically 60% to 80%, when the nano carbide synthesis is made with water soluble raw materials. The size of the agglomerates in step f) is preferably 5 μm to 50 μm, more preferably 10 μm to 40 μm and even more preferably 20 μm to 30 μm. A size of 20 μm to 30 μm is applicable for most applications. The distribution of the binder in the nanoparticles is homogenous in the hard metal powder produced by the method of the invention. The size of the carbides (typically WC) defines the hard metal powder produced by the method of the invention to be a nanomaterial.

(12) It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The detailed description does not limit the invention. The invention may in its details vary within the scope of the claims.