Three dimensional printing of cermet or cemented carbide

Abstract

The present invention relates to a powder mixture for three-dimensional (3D) printing of a cermet or a cemented carbide body. The powder mixture includes 65-85 wt % of porous cemented carbide or cermet particles of a median particle size (D50) of 10-35 μm, and 15-35 wt % of a dense cemented carbide or cermet particles of a median particle size (D50) of 3-10 μm. The present invention also relates to a method of making a cermet or cemented carbide body, the method including the steps of forming the powder mixture, 3D printing a body using the powder mixture and a printing binder and thereby forming a 3D printed cermet or cemented carbide green body and sintering the green body and to form a cermet or cemented carbide body.

Claims

1. A method of making a cermet or cemented carbide body, said method comprising the steps of: mixing a powder of porous cermet and/or cemented carbide particles having a median particle size (D50) of 5-35 μm with a powder of dense cermet and/or cemented carbide particles having a median particle size of (D50) 3-15 μm, to form a powder mixture, wherein the powder mixture includes 65-85 wt % porous particles and 15-35 wt % dense particles; three-dimensional (3D) printing a body using said powder mixture and a printing binder to form a three-dimensional (3D) printed cermet or cemented carbide green body; and sintering said green body to form a cermet or cemented carbide body.

2. The method in accordance with claim 1, wherein, subsequent to or integrated in the sintering step, further comprising a step of sinter-HIP processing the cermet or cemented carbide body.

3. The method in accordance with claim 1, wherein the three-dimensional printing is a binder jetting.

4. The method in accordance with claim 1, wherein the body is a cutting tool for metallic cutting or a cutting tool for mining application or a wear part.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1. A LOM (light optical microscope) image of a cross section of Sample B. No pores are visible in the image.

(2) FIG. 2. A LOM image of a cross section of Sample B, where the microstructure is visible. The WC grains are grey in color and Co metallic binder phase is white.

(3) FIG. 3. A LOM image of a cross section of porous particles of PP1.

(4) FIG. 4. A LOM image of a cross section of porous particles of PP2.

(5) FIG. 5. A SEM (Scanning Electron Microscope) image of a cross section of dense particles of DP2.

(6) FIG. 6. A SEM image of a cross section of dense particles of DP3.

(7) FIG. 7. A LOM image of a cross section of Sample D. Graphite is visible as dark areas in the image.

(8) FIG. 8. A LOM image of a cross section of Sample E. Pores are visible as dark areas in the image.

(9) FIG. 9. A LOM image of a cross section of Sample F. Pores are visible as dark areas in the image.

(10) FIG. 10. A LOM image of a cross section of Sample G. Pores are visible as dark areas in the image.

(11) FIG. 11. A LOM (light optical microscope) image of a 3D printed and sintered cemented carbide body.

(12) FIG. 12. A LOM (light optical microscope) image of a 3D printed and sintered cemented carbide body.

DEFINITIONS

(13) The term “cermet” is herein intended to denote a material comprising hard constituents in a metallic binder phase, wherein the hard constituents comprise carbides or carbonitrides of one or more of Ta, Ti, Nb, Cr, Hf, V, Mo and Zr, such as TiN, TiC and/or TiCN.

(14) The term “cemented carbide” is herein intended to denote a material comprising hard constituents in a metallic binder phase, wherein the hard constituents comprise WC grains. The hard constituents can also comprise carbides or carbonitrides of one or more of Ta, Ti, Nb, Cr, Hf, V, Mo and Zr, such as TiN, TiC and/or TiCN.

(15) The metallic binder phase in the cermet or in the cemented carbide is a metal or a metallic alloy, and the metal can for example be selected from Cr, Mo, Fe, Co or Ni alone or in any combination. Preferably the metallic binder phase comprises a combination of Co, Ni and Fe, a combination of Co and Ni, or only Co. The metallic binder phase can comprise other suitable metals as known to the skilled person.

(16) The particle sizes distribution is herein presented by D10, D50 and D90 values. The D50, the median, is defined as the particle diameter where half of the population has a size smaller than this value. Similarly, 90 percent of the distribution is smaller than the D90 value, and 10 percent of the population is smaller than the D10 value.

EXAMPLES

(17) Embodiments of the present invention will be disclosed in more detail in connection with the following examples. The examples are to be considered as illustrative and not limiting embodiments.

(18) The dense powder DP1 is a recycled WC-Co powder with product code Grade F (fine) from Tikomet Oy. The dense powder DP2 also a recycled WC-Co powder, produced as Grade F by Tikomet Oy, but milled to a slightly finer grain size. A cross section of the powder DP2 is shown in FIG. 5.

(19) The DP3 is a powder produced by spray drying granules of WC, Co and PEG and sintering of the spray dried granules. The sintering is performed to remove the PEG and also to remove the porosity and thereby provide dense cemented carbide particles of a spherical shape. The method of making the DP3 powder is disclosed in further detail in WO2015/162206. A cross section of the powder DP3 is shown in FIG. 6. The porosity can be adjusted in the sintering step and the particle size distribution can be adapted in a subsequent sieving step or air-classifier step.

(20) DP4 is a cobalt powder that is used to adjust the cobalt content in the final cemented carbide body. The DP4 powder is a R-125 cobalt powder d25/450 of the material 20060 from Freeport Cobalt.

(21) The porous powders PP1 and PP2 are so called “Amperit 519” WC-Co 88/12 from H. C. Starck. PP1 is agglomerated sintered 45/15 μm Amperit 519.074 and PP2 agglomerated sintered 30/5 μm Amperit 519.059. Cross sections of PP1 and PP2 are shown in FIG. 3 and FIG. 4, respectively.

(22) The PP3 is a porous powder produced by spray drying granules of WC, Co and PEG and partial sintering of the spray dried granules. The partial sintering is performed to remove the PEG and thereby provide porous cemented carbide particles of a spherical shape.

(23) The porosity measurement was performed by studying the through-cut and image analysis with ImageJ. (Open source software https://imagej.nih.gov/ij/index.html).

(24) The shape of the particles was studied in SEM (Scanning Electron Microscope) and in LOM (Light Optical Microscope). The particle size distribution (D10, D50 and D90) were analyzed with Sympatec HELOS/BR Particle size analysis with laser diffraction and RHODOS dry dispersing system. The shape that most of the particles have in each powder is presented in Table 1.

(25) The Co content and the Cr content were studied in ICP-MS or XRF. The results are presented in Table 1. The cemented carbide powders also comprise WC in the amount adding up to 100% from the Co and/or Cr values in the table 1.

(26) TABLE-US-00001 TABLE 1 Dense and porous powders Co Cr D10 D50 D90 Porosity Shape of Powder (wt %) (wt %) μm μm μm (%) particles DP1 9.8 0.41 1.3 6.1 11.9 0 crushed DP2 8.2 0.27 1.2 4.7 8.8 0 crushed DP3 12.9 0.56 18.7 28.5 45.8 0 Sperical DP4 100 — 1.6 3.3 6.5 — Rod-like PP1 11.9 0.01 22.7 33.5 47.1 27 Sperical PP2 11.7 — 10.9 18.2 28.2 29 Spherical PP3 12.9 0.57 16.6 28.9 41.8 18 Spherical

(27) Powder mixtures were produced by mixing dense and porous powder into the powder mixtures as shown in table 2.

(28) Printing was performed in a binder jetting printing machine “ExOne X1-lab” with a layer thickness during printing of 100 μm. Saturation during printing was between 80% and 110% as shown in Table 2. The saturation of printing binder is defined as the percent of the void volume that is filled with printing binder at a specified powder packing density (here the powder packing density is set to 60%). A higher saturation is needed when printing with a powder mixture comprising a larger fraction of porous particles as compared to a lower fraction of porous particles. Water based printing ink X1-Lab™ Aqueous Binder (7110001CL) was used as printing binder. During the printing the sequence for each layer was as follows: a layer of the powder mixture was spread over the bed, printing binder was spread in a pattern as defined in a CAD model, followed by drying of the printing binder to remove the solvent of the printing binder. This was repeated until the full height of the body was printed. Thereafter curing was done for 8 hours at 195° C. in argon atmosphere. Depowdering was done manually using a small brush and pressurized air.

(29) The printed and cured green bodies were subsequently sintered to provide sintered cemented carbide bodies. The sintering was done at Y-coated graphite trays in a DMK80 sintering furnace. In a first sintering process the bodies were subjected to a debinding step where the temperature was increased from room temperature up to 480° C. in a sintering chamber with a H.sub.2 flow of 500 l/hour. This was followed by a vacuum step where the temperature was increased from 480° C. to 1380° C. where it was hold for 30 minutes. Thereafter the temperature was increased to 1410° C. where it was hold for one hour. Thereafter the chamber was cooled down and the sintered bodies removed from the chamber.

(30) The sintered bodies (sample A-F, not sample G) were then subjected to a HIP-sintering process including a step of holding the temperature at 1410° C. for 30 minutes followed by a pressurized step where Ar was introduced into the chamber during approximately 13 minutes to reach the pressure 55 bar, and thereafter holding this pressure for 15 minutes. The chamber was thereafter cooled down and the sintered and HIP-sintered bodies removed from the chamber

(31) The linear shrinkage of each sample was about 25-30% from green body to the sintered and HIP-sintered body. A cross section of each sintered and HIP-sintered sample was studied and comments are listed in table 2. Porosity was investigated both by cemented carbide ABC-judgment according to ISO4505-1978 and image analysis with ImageJ.

(32) TABLE-US-00002 TABLE 2 Powder mixtures and printed samples Saturation Printed Powder mixture during Co sample ref. Powder Porous printing content no. mixture powder Dense powder (%) (wt %) Comment Sample A PM1 70 wt % PP1 29 wt % DP2 80 12 A00B00C00 1 wt % DP4 Sample B PM2 70 wt % PP2 29 wt % DP2 80 12 A00B00C00 1 wt % DP4 See FIG. 1 and 2. Sample D PM4 100% wt % PP1 no 90 12 A00B00C06-08 Poor green strength. See FIG. 7. Sample E PM5 90 wt % PP3 10 wt % DP3 110 13 About 6 vol % porosity. Open porosity. See FIG. 8. Sample F PM6 no 20% DP1 80 12.3 About 4 vol % 80% DP3 porosity. Open porosity. See FIG. 9. Sample G* PM7 100 wt % PP1 no 90 9.8 Open porosity and very inhomogeneous microstructure. See FIG. 10. *not subjected to sinter-HIP process

(33) Examples of three dimensional printed cemented carbide bodies are shown in FIG. 11 and FIG. 12.

(34) While the invention has been described in connection with the various exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments; on the contrary, it is intended to cover various modifications and equivalent arrangements within the scope of the appended claims.