Three dimensional printing of cermet or cemented carbide

Abstract

The present invention relates to a powder for three-dimensional printing of a cermet or a cemented carbide body. The powder has 30-70 vol % of the particles that are <10 μm in diameter. The present invention also relates to a method of making a cermet or cemented carbide body. The method includes the steps of forming the powder, 3D printing a body using the powder together with a printing binder to form a 3D printed cermet or cemented carbide green body and subsequently sintering the green body to form a cermet or cemented carbide body.

Claims

1. A method of making a 3D printed cermet or cemented carbide body, said method comprising the steps of: mixing a cermet or cemented carbide raw powder and organic binder; spray drying said raw powder and thereby forming a granulated raw powder; pre-sintering said spray dried raw powder, removing said organic binder and thereby forming a pre-sintered granulated powder with an average porosity of the cermet and/or cemented carbide particles with a diameter of ≥20 μm is 10-40 vol %; milling said pre-sintered granulated powder until 30-70 vol % of the cermet and/or cemented carbide particles are <10 μm in diameter to thereby form a powder; 3D printing a body using said powder together with a printing binder to thereby form a 3D printed cermet or cemented carbide green body; and sintering said green body to form a 3D printed cermet or cemented carbide body.

2. The method in accordance with claim 1, further comprising, subsequent to 3D printing and before sintering, the steps of: curing the 3D printed body in inert atmosphere at 150-230° C.; and depowdering the 3D printed body to remove loose particles from surfaces of the body.

3. The method in accordance with claim 1, wherein the sintering step includes a debinding step, where printing binder is burned off.

4. The method in accordance with claim 1, wherein the spray dried powder is sieved before the pre-sintering to remove particles larger than 42 μm in diameter.

5. 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.

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

7. The method in accordance with claim 1, wherein the body is a cutting tool for metal 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 B4SH. The periodicity is visible as horizontal lighter and darker layers.

(2) FIG. 2. A plot of the intensity of Co in relation to depth into the body for sample A2SSH as measured by WDS in a micro probe analysis. The measurement is made as disclosed in the example below and perpendicular to the printed layers.

(3) FIG. 3. The cake of pre-sintered powder was breakable by hand.

(4) FIG. 4. A LOM image of a through cut of pre sintered particles of powder B4.

(5) FIG. 5. An SEM (scanning electron microscope) image of a cross section of sample A1S.

DEFINITIONS

(6) 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.

(7) 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.

(8) 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.

(9) 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

(10) 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.

(11) Powders of Co, Cr and WC were mixed to form a cemented carbide raw powder. Also PEG was added to this raw powder.

(12) As a next step spray drying of said raw powder was performed forming spherical granules of WC, Co, Cr and PEG. The powder of spray dried granules was sieved to remove granules larger than 42 μm in diameter.

(13) The spray dried granules were then pre-sintered to remove the PEG but keep a residual porosity in the pre-sintered granules. The pre-sintering was performed at 1230° C. for 1 hour. The pre-sintering resulted in a fragile cake of pre-sintered granules, i.e. of porous cemented carbide particles. The cake was breakable by hand, see FIG. 3.

(14) The porosity of the particles was analyzed by studying a through-cut of several particles. Particles were embedded in bakelite and polished and an image analysis was made using ImageJ at 1000× magnification. An example, powder B4, is shown in FIG. 4.

(15) The powder of porous cemented carbide particles was then milled in a 30 liter ball mill for 4 hours. 50-100 kg cemented carbide cylpebs were used. In this milling step a relatively high fraction of particles which are <10 μm in diameter was formed. The amount of small fraction can for example be adjusted by tuning in the milling time.

(16) The particle size distribution (D10, D50 and D90) and the fraction of the particles with a diameter<10 μm were analyzed with Sympatec HELOS/BR Particle size analysis with laser diffraction and RHODOS dry dispersing system. The results are presented in Table 1.

(17) 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 Cr values in the Table 1.

(18) TABLE-US-00001 TABLE 1 Powders Co Powder (wt Cr D10 D50 D90 Vol % <10 μm porosity Powder %) (wt %) (μm) (μm) (μm) (vol %) (vol %) A1 12.79 0.58 2.2 13 29 41 15 A2 12.79 0.58 3.2 14 25.5 32 15 A3 12.79 0.58 5.5 20 35 20 15 A4 12.59 0.57 2.0 11.3 23 44.5 20 B1 9.76 0.44 1.5 7.6 17 65 19 B2 9.76 0.44 2.2 11 24 43 19 B3 9.76 0.44 2.2 12 24.5 41 19 B4 9.76 0.44 1.6 10.3 22.4 49 22

(19) Printing was performed in a binder jetting printing machine with a layer thickness during printing of 100 μm. “ExOne X1-lab” was used for samples A1S, A2S, A3S, A1SSH, A2SSH, A3SSH, B1SSH, B2SSH, B1S, B2S and “ExOne Innovent” for samples B3S, A4SH, B3SSH, B4SH. Saturation during printing was between 90-97%. 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 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 100 μm layer of the powder 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 green 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.

(20) The printed and cured green bodies were subsequently sintered to provide sintered cemented carbide samples (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 550° 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 550° 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 samples removed from the chamber. Samples treated with this process are named *S, for example A1S. The results are presented in Table 2.

(21) Some of the sintered samples were then subjected to a sinter-HIP process including a step of holding the temperature at 1410° C. for 1 hour 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 sinter-HIP processed samples removed from the chamber. Samples treated with this process are named *SSH, for example A1SSH. The results are presented in Table 3.

(22) In an alternative process samples were sintered and sinter-HIP processed in one single process, i.e directly after two hours in 1410° C. an increase in pressure to 55 bar was applied and this increased pressure was hold for 15 minutes. Samples treated with this process are named *SH, for example A4SH. The results are presented in Table 3.

(23) The linear shrinkage of each sample was about 25-30% from green body to the sintered and/or sinter-HIP processed body (sample). A cross section of each sintered and sinter-HIP processed sample was studied. Porosity was investigated both by cemented carbide ABC-classification according to ISO4505-1978 and image analysis with ImageJ.

(24) TABLE-US-00002 TABLE 2 Sintered samples Sample Sintering porosity Sample Powder temperature (° C.) Density (g/cm.sup.3) (vol %) A1S A1 1410 13.86 3-4 A2S A2 1410 13.73 4-5 A3S A3 1410 13.37  8 B1S B1 1410 13.92 8-9 B2S B2 1410 13.42 13 B3S B3 1410 13.67 11

(25) TABLE-US-00003 TABLE 3 Samples treated by sinter-HIP process Density Porosity Sample Powder Sintering cycle (g/cm.sup.3) classification A1SSH A1 1410° C. at 55 bar 14.18 A00B00C00 A2SSH A2 1410° C. at 55 bar 14.15 A02B00C00 A3SSH A3 1410° C. at 55 bar 14.11 A02B02C00 A4SH A4 1410° C. at 55 bar 14.31 A00B00C00 B1SSH B1 1410° C. at 55 bar 14.42 A00B00C00 B2SSH B2 1410° C. at 55 bar 14.51 A02B00C00 B3SSH B3 1410° C. at 55 bar 14.47 A02B00C00 B4SH B4 1410° C. at 55 bar 14.57 A02B00C00

(26) Samples A1SSH, A4SH and B1SSH was classified A00B00C00. As can be noticed from the examples both the porosity and the amount of <10 μm particles is important to achieve a dense and pore free 3D printed cemented carbide.

(27) The binder phase content did vary periodically in the 3D printed bodies. This was studied in detail with EDS and WDS line scans with a JEOL JXA-8530F microprobe. The lines were measured perpendicular to the direction of the printed layers. The instrument settings and WDS crystals used for each analyzed element can be seen in Table 4 and 5.

(28) TABLE-US-00004 TABLE 4 EPMA setting for line analysis Line length 1400 μm Line width 200 μm Acceleration voltage 15 keV Probe current 50 nA Dwell time 500 ms Step width 3.5 μm Scan type Stage scan

(29) TABLE-US-00005 TABLE 5 Measured elements and WDS-crystals used Element Crystal W PETJ Co LIFH C LDE6H Cr LIFH

(30) An example of a typical Co variation is shown in FIG. 1 (sample B4S) and FIG. 2 (sample A2SSH). The average binder phase content, as an average of 15 adjacent periods, showed a difference of 17%, 17% and 16% from the average binder phase content in the body for samples A1SSH, A2SSH and B2SSH, respectively. FIG. 5 shows a through cut of the sample A1S.

(31) 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.