3-D printing of a ceramic component

Abstract

A method for producing the component, and to the use of the component. The method for producing a three-dimensional, ceramic component containing silicon carbide, by a) providing a powdery composition having a grain size (d50) between 3 microns and 500 microns and comprising at least 50 wt % of coke, b) providing a liquid binder, c) depositing a layer of the material provided in a) in a planar manner and locally depositing drops of the material provided in b) onto said layer and repeating step c), the local depositing of the drops in the subsequent repetitions of the step is adapted in accordance with the desired shape of the component to be produced, d) at least partially curing or drying the binder and obtaining a green body having the desired shape of the component, e) carbonising the green body, and f) siliconising the carbonised green body by infiltration with liquid silicon.

Claims

1. A method for producing a three-dimensional, ceramic component containing silicon carbide, comprising: a) providing a powdered composition having particles of a grain size (d50) of between 3 μm and 500 μm and a shape factor (width/length) of at least 0.5 on average, the powdered composition comprising at least 80 wt. % coke, b) providing a liquid binder, c) three dimensionally printing by a step of planarly depositing a layer of the powdered composition provided in a) and followed by a step of locally depositing droplets of the binder provided in b) to said layer, and subsequently repeating the step of planarly depositing of a layer of the powdered composition provided in a) followed by the step of locally depositing of droplets of the binder to said layer to obtain a printed material, wherein the step of locally depositing the droplets in subsequent repetitions of said step is adjusted according to a desired shape of the three-dimensional, ceramic component to be produced from the printed material, d) at least partially curing or drying the binder of the printed material obtained from step c) to obtain a green body formed of the powdered composition and cured or dried binder, the green body being surrounded by a powder bed consisting of loose particles of the powdered composition, and unpacking the green body from the loose particles, thereby obtaining a green body having the desired shape of the three-dimensional, ceramic component, e) carbonising the green body obtained from step d) of the desired shape of the three-dimensional, ceramic component, and f) siliconising the carbonised green body obtained from step e) by means of infiltration with liquid silicon to obtain the three-dimensional, ceramic component, wherein the green body, while above the melting temperature of silicon and substantially above the surface of a silicon bath, becomes saturated with silicon by means of capillary forces.

2. The method according to claim 1, wherein the coke is selected from the group consisting of acetylene coke, flexi coke, fluid coke, shot coke and carbonised ion-exchange resin beads.

3. The method according to claim 1, wherein the powdered composition according to step a) is a granulate.

4. The method according to claim 1, wherein the binder in step b) comprises phenol resin, furan resin, polyimides or mixtures thereof.

5. The method according to claim 1, wherein the binder in step b) comprises cellulose, starch, sugar or mixtures thereof.

6. The method according to claim 1, wherein the binder in step b) comprises silicates, silicon-containing polymers or mixtures thereof.

7. The method according to claim 1, wherein the siliconising of the carbonised green body takes place in a vacuum.

8. A three-dimensional, ceramic component produced according to the method of claim 1, wherein the three-dimensional, ceramic component contains 20-75 wt. % SiC, 10-45 wt. % free silicon and 10-60 wt. % free carbon.

9. The three-dimensional, ceramic component according to claim 8, wherein the free carbon contained in the three-dimensional, ceramic component is completely surrounded by SiC.

10. The three-dimensional, ceramic component according to claim 9, wherein the carbon is in particulate form.

11. The three-dimensional, ceramic component according to claim 8, wherein the three-dimensional, ceramic component has a work of fracture of at least 150 Nmm.

12. The three-dimensional, ceramic component according to claim 8, wherein the three-dimensional, ceramic component has a three-point flexural strength of at least 40 MPa.

13. The three-dimensional, ceramic component according to claim 8, wherein the three-dimensional, ceramic component comprises cavities, cooling channels or undercuts and consists overall of a microstructure, which is uniform or which gradually changes according to desired material properties of the three-dimensional, ceramic component.

14. Chemical industry equipment comprising the three-dimensional, ceramic component according to claim 8, wherein the industry equipment is selected from the group consisting of a pump, a microreactor, a macroreactor, pipe lining and a branched pipe.

15. A high-temperature furnace comprising the three-dimensional, ceramic component according to claim 8 as at least one element selected from the group consisting of a burner nozzle, a burner insert, a lining of burner walls, an electrical heating element, and a load-bearing structure.

16. A separator wheel comprising the three-dimensional, ceramic component according to claim 8.

17. A heat exchanger or an element of a heat exchanger comprising the three-dimensional, ceramic component according to claim 8.

18. A mechanically loaded component comprising the three- dimensional, ceramic component according to claim 8, wherein the mechanically loaded component is a sliding bearing, a rotary seal, a gear, a piston or a piston sleeve.

19. A mould and crucible comprising the three-dimensional, ceramic component according to claim 8.

20. A ballistic structure comprising the three-dimensional, ceramic component according to claim 8.

21. A frictional body having cooling comprising the three-dimensional, ceramic component according to claim 8.

22. A precision component comprising the three-dimensional, ceramic component according to claim 8.

Description

DETAILED DESCRIPTION

(1) The present invention will be illustrated below on the basis of examples. Unless explicitly indicated below, any of the features mentioned in the examples can be combined with the subjects of the general description of the present application.

EXAMPLE 1

(2) Calcined hard coal tar pitch coke was ground and, following grinding and sieving, had a grain size distribution of d10=130 μm, d50=230 μm and d90=390 μm and a shape factor of 0.69. 1 wt. % of a liquid sulfuric acid activator for phenol resin, based on the total weight of coke and activator, was first added to the coke, which was then processed by a 3D printing powder bed machine. In this process, a doctor blade unit deposits a thin layer of coke powder (approximately 0.3 mm in height) on a flat powder bed, and a type of inkjet printing unit prints an alcoholic phenol resin solution onto the coke bed according to the desired component geometry. The printing table is subsequently lowered by a degree equal to the layer thickness, a layer of coke is re-applied, and phenol resin is locally printed on again. By means of the repeated procedure, rectangular test specimens having the dimensions 168 mm (length)×22 mm (width)×22 mm (height) were constructed in this process. Once the complete “component” had been printed, the powder bed was introduced into a furnace that had been pre-heated to 140° C., and was kept there for approximately six hours. Even though reference is made to “component” even at this stage, it goes without saying that this is not yet intended to mean the finished component according to the invention. In this process, the phenol resin cures and forms a dimensionally stable green body. Following cooling, the excess coke powder was sucked away, and the green body of the component was removed.

(3) Once the binder had cured, the density of the green body was 0.88 g/cm3. The density was determined geometrically (by weighing and determining the geometry). The green body had a proportion of resin of 5.5 wt. %, which was determined by carbonisation treatment. This process proceeded such that the carbon yield of the used cured resin constituent was determined in advance to be 58 wt. % by means of thermogravimetric analysis (TGA). On the basis of the loss in mass of the green body following the subsequent carbonisation at 900° C. in a protective gas atmosphere for one hour, it was possible to calculate the original proportion of resin in the green body.

(4) The carbonised green body was subsequently impregnated with phenol resin and carbonised again at 900° C. This increased the density to 1.1 g/cm.sup.3. Within the scope of the present invention, this procedure is referred to as supplementary densification.

(5) The carbonised green body (example 1.1) having undergone supplementary densification and the carbonised green body not having undergone supplementary densification (example 1.2) were carbonised at 900° C. in a protective gas atmosphere for one hour and then placed in a siliconisation furnace, said green bodies being placed on wicks. The wicks are positioned in a Si powder bed. The bed itself is in a coated graphite crucible. The furnace is heated to approximately 1,600° C. in a vacuum. In the process, the silicon powder turns to a liquid, and the liquid silicon rises, by means of capillary forces alone, via the wicks into the 3D-printed green bodies, without additional gas or liquid pressure being applied. A portion of the carbon reacts with the liquid silicon and forms SiC. Once the furnace has cooled, the components are removed, and the wicks are mechanically removed. The components are not porous.

EXAMPLE 2

(6) 0.35 wt. % of the liquid activator according to example 1 was added to unground calcined acetylene coke having a particle size distribution of d10=117 μm, d50=190 μm and d90=285 μm and a shape factor of 0.82, which coke was then processed so as to form a green body in a similar manner to example 1.

(7) The green body had a proportion of resin of 3.0 wt. %. The density of the green body was 0.98 g/cm.sup.3 and was thus significantly higher than for the ground hard coal tar pitch coke from example 1. Furthermore, said green body had higher strength than the green body from example 1, and this made it easier to handle. It is therefore possible to dispense with the supplementary densification of said green body, thus reducing production costs.

(8) Said green body was placed directly (without separate carbonisation beforehand) into a siliconisation furnace and siliconised as per example 1. The binder was therefore carbonised and siliconized in one step.

(9) Analysis

(10) The following table displays a number of physical and chemical properties of the produced ceramic test specimens:

(11) TABLE-US-00001 Example Example 1.1 1.2 Example 2 (averages) (averages) (averages) AD (g/cm.sup.3) 2.3 2.5 2.3 ER (Ohmμm) 26 16 19 YM 3p (GPa) 30 31 35 FS 3p (MPa) 58 62 65 ε.sub.max (%) 0.16 0.16 0.25 W.sub.Bruch (Nmm) 170 220 340 CTE RT/200° C. 2.8 3.0 3.2 (μm/(m * K)) TC (W/(m * K)) 52 60 51 OP (%) 0 0 0 C (%) 38 24 41 Si (%) 26 38 34 SiC (%) 36 38 25 AD (g/cm.sup.3): density (geometric) with reference to ISO 12985-1 ER (Ohmμm): electrical resistance with reference to DIN 51911 YM 3p (GPa): modulus of elasticity (stiffness), determined from the three-point bending test FS 3p (MPa): three-point bending strength with reference to DIN 51902 ε.sub.max (%): elongation at break W.sub.Bruch (Nmm): work of fracture, determined from the area of the bending deformation curve from the three-point bending method CTE RT/200° C. (μm/(m*K)): coefficient of thermal expansion, measured between room temperature and 200° C. with reference to DIN 51909 TC (W/(m*K)): heat conductivity with reference to DIN 51908 OP (%): open porosity with reference to DIN 51918

(12) Example 1.1: hard coal tar pitch coke, green body additionally impregnated with phenol resin, carbonised at 900° C., siliconised.

(13) Example 1.2: hard coal tar pitch coke, green body not impregnated with phenol resin, but directly carbonised at 900° C., siliconised.

(14) Example 2: acetylene coke, green body not impregnated with phenol resin, carbonised and siliconised in one step.

(15) As shown by all the examples, the method according to the invention makes it possible to obtain ceramic components which are comparable to known C/Si/SiC materials in terms of strength (three-point bending strength). The strength and also the modulus of elasticity are, for example, comparable to those of carbon fibre-reinforced ceramic brake discs.

(16) Furthermore, the modulus of elasticity is less than that of conventional SiC ceramics by a factor of 10, which results in significantly improved thermal shock resistance.

(17) Furthermore, the coefficient of thermal expansion of approximately 3×10.sup.−6 K.sup.−1 is extremely low, which favours in particular thermal shock resistance and ensures high dimensional stability.

(18) The heat conductivities of more than 50 W/mK are also comparable to a range of metal materials, and are thus high enough for heat exchanger applications. This also favours thermal shock resistance.

(19) Furthermore, the components according to the invention have a relatively low density in comparison with conventional SiC ceramics and metals, which results in overall lighter components.

(20) It is also surprising that the specific electrical resistance is in a value range which is typical for heating elements.

(21) It is also surprising that the components according to the invention do not have an open porosity. They are therefore highly suitable for applications in oxidative atmospheres and for applications in chemical apparatus construction.

(22) What the examples also surprisingly indicate is that the acetylene coke in example 2 leads to components having a lower SiC content, or a higher carbon content, than in examples 1.1 and 1.2, and this brings about a lower density. Micrographs of the components have shown that the cause of this is that a protective SiC layer forms around the coke spheres during siliconisation.

(23) Furthermore, the strengths from example 2 are considerably higher than those from examples 1.1 and 1.2, because the rounder coke grain presumably has less of a crack-initiating function than less round coke grains. This property also has a positive effect on the comparably high work of fracture and high elongation at break.

(24) Furthermore, the free Si content can be lowered by additionally impregnating the green body (example 1.1). This is advantageous as the silicon is the only constituent in the component that can still turn to a liquid, and this limits the use of the component at very high temperatures (>1,400° C.).