Patent Application
20070282068
It has now surprisingly been found that a spray dried cemented carbide or cermet powder having well developed agglomerates with good flow properties and good plasticity can be obtained by using a baroplastic polymer as a binder. The hard property of the binder is used at normal pressures, during handling of the spray-dried powder and in the green body, whereas the blended, softer properties are used at higher pressures during the pressing of the material when the pressure exceeds 10 MPa.
The baroplastic material is a block copolymer composition of a core-shell polymer consisting of particles with a core of a polymer with soft properties, and a shell of a polymer with hard properties with the size of the particles in the range of from about 50 to about 200 nm.
Preferably, the hard component of the polymer is polystyrene, poly(butyl methacrylate), poly(caprolactone), poly(ethyl methacrylate), poly(methyl methacrylate) or poly(hexyl methacrylate) and the soft component poly(butyl acrylate), poly(methyl acrylate), poly(ethyl acrylate), poly(ethylhexyl acrylate) or poly(caprolactone).
One aspect of the invention relates to a method of making an agglomerated ready-to-press powder mixture by wet milling a powder mixture containing the baroplastic binder and spray drying said slurry to form an agglomerated powder.
Preferably, the powder mixture is a cemented carbide, cermet or ceramic powder mixture and the pressure induced transformation from hard to soft takes place within a pressure range of from about 10 to about 50 MPa.
More preferably, the powder mixture contains hard constituent powder(s) based on carbides, nitrides and/or carbonitrides of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and/or W and from about 5 to about 15 wt-% metal binder phase powder(s) of Co and/or Ni as well as an agglomerating binder of a baroplastic polymer.
Another aspect of the invention relates to a an agglomerated powder containing hard constituent powder(s) based on carbides, nitrides and/or carbonitrides of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and/or W and metal binder phase powder(s) of Co and/or Ni. According to the invention, the agglomeration binder is a baroplastic polymer.
In another aspect, the invention relates to a slurry containing hard constituent powder(s) based on carbides, nitrides and/or carbonitrides of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and/or W and metal binder phase powder(s) of Co and/or Ni as well as binders. According to the invention, the agglomeration binder is a baroplastic polymer.
The invention has been described with reference to bodies of cemented carbide or cermets. It is obvious that the invention can generally be applied to the manufacture of bodies by powder metallurgical methods such as ceramics.
The invention is additionally illustrated in connection with the following examples, which are to be considered as illustrative of the present invention. It should be understood, however, that the invention is not limited to the specific details of the examples.
A cemented carbide ready to press powder was produced. First a slurry was produced based on 93 wt % WC, 5 wt % Co, 2 wt % baroplastic polymer as binder and 0.3 l/kg milling liquid. The baroplastic polymer was added as an emulsion of about 100 nm large particles which had a shell of polystyrene and a core of poly(2-ethylhexyl acrylate). The powder was milled to an average particle size of 3 μm. The slurry was dried according to standard practice resulting in an agglomerated powder mixture with well developed agglomerates shown in
Example 1 was repeated with PEG 4000 as binder. The appearance of the agglomerates is shown in
Example 1 was repeated with a mixture of 60% PEG 4000 and 40% PEG 300 as binder. The appearance of the agglomerates is shown in
The powders from Examples 1, 2, and 3 were subjected to measurements of flow time according to ISO 4490. Porosity according to ISO 4505 was evaluated on polished cross sections of the sintered bodies. The following results were obtained.
Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without department from the spirit and scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0601195-1 | May 2006 | SE | national |
