DE-102018102616-B4 - Process for the production of hard metal bodies

Abstract

A method for producing cemented carbide bodies with a cemented carbide microstructure at room temperature, free of tungsten dicarbide and eta phase, using LPBF, SLM, DMLS or SLS as a laser-based additive manufacturing process with energy input via laser powers of 20 W to 55 W and scan speeds of 20 mm/s to 75 mm/s and track spacings of 30 µm to 205 µm and layer thicknesses of 20 µm to 45 µm at each point of energy input to achieve a temperature of 800 °C to a maximum of < 1800 °C, from cemented carbide granules as starting materials, made of WC as a ceramic hard material with Co as a metallic binder phase and an additive of Cr 3 C 2 , and the cemented carbide granules having a porosity of > 0 vol.% to 40 vol.%, resulting in a cemented carbide green body with a density of at least 50% and at most 70% of the theoretical density of the hard metal body, and which is subsequently subjected to sintering at temperatures up to a maximum of 1600 °C, by means of vacuum sintering at temperatures of 1200 to 1600 °C and at partial pressures of 100 to 90000 Pa or gas pressure sintering at temperatures of 1380 to 1600 °C and pressures of 5 to 10 MPa until a density of the hard metal body of ≥ 98 % to 99.9 % of the theoretical density.

Inventors

• Johannes Pötschke

Assignees

• Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.

Dates

Publication Date

20260513

Application Date

20180206

Claims (5)

1. A method for producing cemented carbide bodies with a cemented carbide microstructure at room temperature, free of tungsten dicarbide and eta phase, using LPBF, SLM, DMLS or SLS as a laser-based additive manufacturing process with energy input via laser powers of 20 W to 55 W and scan speeds of 20 mm/s to 75 mm/s and track spacings of 30 µm to 205 µm and layer thicknesses of 20 µm to 45 µm at each point of energy input to achieve a temperature of 800 °C to a maximum of < 1800 °C, from cemented carbide granules as starting materials, made of WC as a ceramic hard material with Co as a metallic binder phase and an additive of Cr 3 C 2 , and the cemented carbide granules having a porosity of > 0 vol.% to 40 vol.%, resulting in a cemented carbide green body with a density of at least 50% and at most 70% of the theoretical density of the hard metal body, and which is subsequently subjected to sintering at temperatures up to a maximum of 1600 °C, by means of vacuum sintering at temperatures of 1200 to 1600 °C and at partial pressures of 100 to 90000 Pa or gas pressure sintering at temperatures of 1380 to 1600 °C and pressures of 5 to 10 MPa until a density of the hard metal body of ≥ 98 % to 99.9 % of the theoretical density.
2. Procedure according to Claim 1 , in which vacuum sintering is carried out at pressures of 200 to 90000 Pa.
3. Procedure according to Claim 1 , in which hard metal granules are used as starting materials for the laser-based additive manufacturing process with granule sizes from 2 µm to 90 µm.
4. Procedure according to Claim 1 , in which partially compacted and/or fully compacted pre-sintered hard metal granules are used as starting materials for the laser-based additive manufacturing process.
5. Procedure according to Claim 1 , in which partially compacted hard metal granules are used as starting materials for the laser-based additive manufacturing process, which have a bulk density of 25 to 55% of the theoretical density and both monomodal and bimodal or multimodal particle size distributions.

Description

The invention relates to the fields of hard metal materials and ceramic and/or powder metallurgical process engineering and concerns a method for the production of hard metal bodies, such as can be used for the production of wear parts or tools with hard metals. The production of cemented carbide bodies, which in their green state contain cemented carbide starting powders in addition to organic binders, by means of pressing, extrusion, or MIM/CIM followed by sintering, is known according to the prior art. Cemented carbide components with various compositions can be produced in this way. Binder metal contents (e.g., cobalt, iron, and/or nickel) of 0 to ≤ 32 vol.% are achievable. These known manufacturing processes have limitations regarding the geometry of the components to be produced, which cannot be eliminated with these technologies. For design freedom in the production of complex hard metal components, the use of additive manufacturing processes is necessary. In such manufacturing processes, the components are produced according to a 3D model generated by a computer, in which the 3D model is essentially sliced into thin sheets, and then the component is manufactured sheet by sheet. One such additive process is laser sintering, in which a higher strength of the green body can be achieved with a local direct energy input ( Y. Xiong et al: Powder Metallurgy Vol. 53, Iss. 1, 2010 ; T. Gläser, Investigations on the laser sintering of tungsten carbide-cobalt, Dissertation 2010 ; Generative manufacturing of extrusion tools made of hard metal - GENIAL (BMBF)). Also well-known is the additive manufacturing of tungsten carbide-cobalt hard metals using the Laser Powder Bed Fusion (LPBF) process, which enables the production of shaped parts with a high degree of design freedom and the integration of functional properties into hard metal tools. Resources and production times can also be significantly reduced. In this process, hard metal powder is introduced into a fixture in the form of a powder bed, and the desired areas of the hard metal powder are compacted by very short exposure times of a laser beam. During this very short exposure time, a liquid phase is created in the area of the laser beam through local melting, during which significantly higher temperatures are reached during sintering. Because the finished workpiece is completely described in three dimensions beforehand, the laser beam is guided by computer, so that only the areas of the final finished workpiece are melted and compacted. T. Schubert et al: 35th Hagen Symposium on Powder Metallurgy, H. Kolaska, H. Danninger, D. Biermann (Eds.), Heimdall Verlag, Dortmund, 163 - 176, (2016 ).). Pre-sintered and partially compacted hard metal granules can be used as hard metal powder ( Faisal, NH et al: J. Therm. Spray Tech. (2011) 20, 1071 ; SM Nahvi et al: Surface and Coatings Techn., (2016) 286, 95-102 ; G. Bolelli et al: Surface and Coatings Techn. (2012) 206, 4079-4094 ). Regarding the microstructure formation in the production of hard metals, for example from WC-Co, conventional production ideally results in a hard metal microstructure consisting of WC grains in a cobalt-rich matrix with dissolved tungsten and carbon. Since higher temperatures are reached locally during the LPBF process, it must be noted that WC decomposes at temperatures > 2735 °C. Likewise, the process must counteract evaporation of the liquid phase and decarburization through higher cobalt contents in order to prevent embrittlement of the hard metal structure due to the formation of the η-phase ( T. Schubert et al: 35th Hagen Symposium on Powder Metallurgy, H. Kolaska, H. Danninger, D. Biermann (Eds.), Heimdall Verlag, Dortmund, 163 - 176, (2016 ).). It is also known from other publications that WC-Co hard metals are very difficult to produce using laser-based additive manufacturing processes such as Selective Laser Melting (SLM), and only with very high laser powers and high Co contents with sufficient compaction. This in turn leads to WC decomposition, which is undesirable ( E. Uhlmann et al: Procedia CIRP 35 (2015) 8-15 ; T. Gläser, Dissertation RTH Aachen, 2010 , Summary). Next is after Gläser, T. et al: Brilliant. Joint report on the BMBF collaborative project, grant number 02PU2220, September 1, 2009, page 2 (http://publica.fraunhofer.de/documents/N-162064.html ) the production of hard metal bodies using laser sintering or 3D printing is known. From the US 2016 / 0 375 493 A1 A process for the production of sintered products is known in which a hard metal body is produced by means of isostatic pressing, isostatic hot pressing, binder jetting, vacuum sintering or sintering under a hydrogen or argon atmosphere. According to the AT 015 102 U1 is a method for producing a hard metal body layer by layer by alternately applying a hard metal powder layer by layer and selectively, locally hardening the applied hard metal powder by the action of a directed energy beam, wherein the hard me