A SINTERING DEVICE HAVING A DIE LINING OF INCREASED THICKNESS

Abstract

The invention relates in general to sintering under pressure and with electrical current, often termed spark plasma sintering (SPS). Particular aspects of the invention are directed to a sintering device, a sintering process, a ceramic body product, an assembly comprising the ceramic body and the use of a graphite layer in a sintering process. The invention relates to a device having a sintering chamber, the sintering chamber being bordered by the following device parts: i. a first punch surface of a first punch; ii. a second punch surface of a second punch; and iii. an interior surface of a die; wherein: the punches are adapted and arranged to apply a pressure of at least 1 MPa along a compression axis to a target in the sintering chamber; the first punch and the second punch are connected to an electrical power source.

Claims

1. A device having a sintering chamber, the sintering chamber being bordered by the following device parts: i. a first punch surface of a first punch; ii. a second punch surface of a second punch; and iii. an interior surface of a die; wherein the punches are adapted and arranged to apply a pressure of at least 1 MPa along a compression axis to a target in the sintering chamber; the first punch and the second punch are connected to an electrical power source adapted and arranged to provide a current of at least 5 kA; the first and second punches comprise at least 50 wt. % carbon, based on the total weight of the punch; the sintering chamber has a cross-sectional width W perpendicular to the compression axis of at least 300 mm; wherein a layer of a carbon material C.sub. is present at at least part of the interior surface of the die, the having a mean thickness D.sub. determined over the interior surface of the die, wherein D.sub. is in the range from 1.1 to 8 mm.

2. The device according to claim 1, wherein the layer has a standard deviation of thickness D.sub. in the range from 0.01 to 0.08 mm determined over the interior surface of the die.

3. The device according to claim 1, wherein the layer is made up of 2 or more stacked sub-layers.

4. The device according to claim 1, wherein both punches and the die are at least partially present in a vacuum chamber or in a non-oxidising atmosphere or both.

5. The device according to claim 1, wherein the sintering chamber has a diameter D.sub.c and the ratio D.sub.c:D.sub. of the diameter De and the mean thickness of the layer D.sub. is in the range from 100:1 to 350:1.

6. The device according to claim 1, wherein one or both of the following are satisfied: a. a layer of a carbon material C.sub. is present at least part of the first punch surface (004); b. a layer of a carbon material C.sub. is present at least part of the second punch surface.

7. The device according to claim 1, wherein one or more of the following are satisfied: a. The first punch is at least 99% wt. % carbon, based on the total weight of carbon atoms in any chemical form and the total weight of the first punch; b. the second punch is at least 99% wt. % carbon, based on the total weight of carbon atoms in any chemical form and the total weight of the second punch; c. The die is at least 99% wt. % carbon, based on the total weight of carbon atoms in any chemical form and the total weight of the die; d. The is at least 99% wt. % carbon, based on the total weight of carbon atoms in any chemical form and the total weight of the .

8. The device according to claim 1, wherein the die is of a carbon material C.sub.y and one or more of the following are satisfied: a. C.sub. and C.sub.y have a different anisotropy value, b. C.sub. and C.sub. have a different specific conductivity, determined in a direction parallel to the compression axis, c. C.sub. and C.sub. have a different specific conductivity, determined in a direction perpendicular to the interior surface, d. C.sub. and C.sub. have a different specific thermal expansivity, determined in a direction parallel to the compression axis, e. C.sub. and C.sub. have a different specific thermal expansivity, determined in a direction perpendicular to the interior surface, f. The first carbon material and the second carbon material have a different ash content as determined by ASTM C-561].

9. A process for the preparation of a ceramic body, comprising the steps: a. providing a plurality of particles; b. providing a device according to claim 1; c. introducing the particles into the sintering chamber of the device; d. applying a pressure P in the range from 1 MPa to 80 MPa and an electrical current I in the range from 1 kA to 100 kA to obtain the ceramic body.

10. The process according to claim 9, wherein the particles contain at least 30 wt. % yttrium in any chemical form, based on the total mass of yttrium atoms and the total mass of the particles.

11. A ceramic body obtainable by a process according to claim 9.

12. The ceramic body according to claim 11, wherein at least one or all of the following are satisfied: a. A value for density divided by theoretical density that is less than 1.0; b. An average grain size of less than 5 m; c. A standard deviation for the average grain size distribution that is in the range of 1.82 m to 2.22 m.

13. An assembly comprising a ceramic body according to claim 11.

14. The assembly according to claim 13, the assembly being selected from the group consisting of: a. A plasma etcher, b. Plasma processing chamber (etch or deposition processes), c. A wear plate for a bearing, d. A mill liner of a grinding mill.

15. A use of a graphite layer of thickness in the range from 1.1 to 8 mm for preparing a ceramic body having an extension of at least 300 mm by spark plasma sintering.

Description

FIGURES

[0125] The invention is now further elucidated with the aid of the following figures.

[0126] FIG. 1 is a cross sectional side-view of a device according to the invention.

[0127] FIG. 2 is a cross sectional side-view of the device of FIG. 1 with the chamber loaded and ready for sintering.

[0128] FIG. 3 shows the steps of a preparation process for the ceramic body.

[0129] FIG. 4 shows a cutaway cross-section of the sinter chamber.

[0130] FIGS. 5a and 5b show the core test employed herein.

FIGURE DESCRIPTIONS

[0131] FIG. 1 is a cross sectional side-view of a device according to the invention. The device has a first punch 003 having a first punch surface 004 and a second punch 008 having a second punch surface 007. The punches 003 & 008 are made of solid graphite. The punch surfaces 004 & 007 are also of graphite. The first punch 003 is positioned above the second punch 008. The first punch 003 is oriented with the first punch surface 004 being horizontal and facing downwards. The first punch 003 can be moved in a vertical direction by a first pushing means 001 connected via a first piston 002. The second punch 008 is oriented with the second punch surface 007 horizontal and facing upwards. The second punch 008 can be moved in a vertical direction by a second pushing means 010 connected via a second piston 009. The first 004 and second 007 punch surfaces can thus be moved towards each other along the direction of a compression axis 011. The device has a die 006 shaped as a hollow graphite cylinder with an interior surface 005. The device has an electrical power source 012 adapted and arrange to supply up to 20 kA DC current and is connected to the first 003 and second 008 punches. The sintering chamber of the invention is formed as a cavity bordered by the first punch surface 004 from above, the second punch surface 007 from below, and the interior surface 005 to the sides. In this case, both punch surfaces 004 & 007 are circular and the interior surface 005 is cylindrical and the sintering chamber is thus cylindrical. The graphite layer at the interior surface 005 has not yet been positioned in FIG. 1.

[0132] FIG. 2 is a cross sectional side-view of the device of FIG. 1 with the sintering chamber 013 loaded and ready for sintering. The sintering chamber 013 is defined by the first punch surface 004 from above, the second punch surface 007 from below and the interior surface 005 of the die 006 to the sides. The sintering chamber 013 thus has a cylindrical shape. The sintering chamber 013 is filled with a plurality of particles for sintering. The plurality of particles may be tamped after introduction into the sintering chamber to compact it. A layer of carbon material 014 is present at the interior surface 005 of the die 006. The layer 014 in this example thus constitutes a hollow cylindrical layer. In this case, further layers 016 and 015 also of a carbon material are present at the second 007 and first 004 punch surfaces respectively. The further layers 016 and 015 are optional. In practice, the lower layer 016 and the layer 014 at the interior of the die 006 are introduced first to produce a recess into which the plurality of particles can be filled. The particles are then tamped and the optional top layer 015 is lain atop. The punch surfaces (004, 007) are then moved inwards to abut against the compacted disc of particles coated with the graphite layer. For sintering, the punch surfaces (004, 007) are moved inwards along the compression axis 011 as shown by the arrows. The punch surfaces (004, 007) apply a force to the particles thus creating a pressure in the chamber. An electrical current is applied across the sintering chamber 013 (between the first punch surface 004 and the second punch surface 007) from the electrical power source 012.

[0133] FIG. 3 shows the steps of a preparation process 200 for the ceramic body. In a first step a. 201, a plurality of particles is provided. The particle size d.sub.50 may be for example 3 m. An example material for the particles is yttrium aluminium garnet (YAG). In a second step b. 202, a device as described in this disclosure is provided. The sintering chamber of the device may for example have a diameter of 500 mm. In a third step c. 203, the plurality of particles is introduced into the sintering chamber of the device. The graphite layer at the interior surface of the die is introduced prior to the particles. Optionally, a graphite layer at the second punch surface can also be introduced prior to the particles. The plurality of particles can be tamped to compact the particles into a cylinder. Optionally, a graphite layer for the first punch surface can be lain atop the particles before below the first punch surface. In a fourth step d. 204, a pressure of for example 50 MPa is applied to the sintering chamber and a current of for example 80 kA is passed through the chamber to convert the particles into the product ceramic body.

[0134] FIG. 4 shows a cutaway cross-section 300 of the sintering chamber 013. The cut is vertical, along a diameter of the sintering chamber 013, passing through the compression axis 011, to show the sintering chamber 013 from the side. The die 006 is a hollow cylinder with a wall thickness 302. The graphite layer 014 is applied to the interior surface 005 of the die 006 to form a concentric hollow cylinder with a thickness 301, for example 2 mm. The die thickness 302, the layer thickness 301 and the diameter 303 of the sintering chamber 013 are each measured in a radial direction, perpendicular to the compression axis 011.

[0135] FIGS. 5a and 5b show the core test 400 employed herein. FIG. 5a shows a perspective view prior to commencement of the test. A coring tool 401 is positioned above a first flat surface 402 of a flat-form ceramic sample 406. In this case, the flat-form ceramic sample 406 is in the form of a cylindrical disc. The tool 401 is oriented along an axis perpendicular to the first flat surface 402. The arrow 408 shows the direction of the travel of the tool 401 along the axis towards the flat-form ceramic sample 406. Once in contact with the flat-form ceramic sample 406, the coring tool 401 moves in a circular motion inside a coring region 407 that has a diameter that is larger than a diameter of a tip 409 of the coring tool 401. The circular motion is parallel to the first flat surface 402, and leads to the removal of a cylindrical region from the flat-form ceramic sample 406. Furthermore, a geometric centre 405 of the first flat surface 402 is also the geometric centre 405 of the coring region 407. FIG. 5b shows a cutaway view from the side during the core test. The tool 401 has advanced a distance 403 into the flat-form ceramic sample 406, which has a sample thickness 404. FIG. 5b shows that the coring tool 401 has removed a cylindrical section 410 from the flat-form ceramic sample 406. The distance 403 is determined between the first flat surface 402 and the end of the tool 401. The test finishes at the first observation of cracks in the flat-form ceramic sample 406. The success level is determined as the ratio of the distance cored 403 to the total thickness of the flat-form ceramic sample 404 at the end of the test, expressed as a percentage.

Test Methods

C Test

[0136] A flat-form sample ceramic having a first flat face and a thickness perpendicular to the first flat face, obtained in the examples, is cored to determine if there is excess internal stress. The coring tool 401 is a 10 mm diamond coring tool commercially available, for example from Schott Diamantwerkzeuge GmbH of Stadtoldendorf, Germany. The tool is used in commercially available CNC machines to cut a core in in the part under test. The hole formed in the part by cutting the core is from 56 mm to 60 mm, having a nominal diameter of 58 mm. The core is cut by passing the tool 401 over the surface of the part in a helical pattern to bore a hole in the part. Suitable CNC machines that can be used for this test are available, for example, from DMG Mori Company Limited of Los Angeles, California, USA, such as its Ultrasonic 60 eVo linear model. Another provider of suitable CNC machines is Fair Friend Ent. Co. Ltd. Of Taiwan, such as the Feeler HV-1650 model. The test concludes either when the core extends all the way through the sample ceramic or when the sample ceramic is observed to crack, whichever occurs first. The success score is given as the percentage of the thickness of the core cut in the sample under test. 100% success rating indicates low internal stress if any; above 75% but below 100% success rating indicates low internal stress; 25% to 75% success rating indicates corresponds to medium stress; lower than 25% success rating indicates high internal stress.

Particle Size

[0137] Particle size of ceramic particles was determined using a Laser Scattering Particle Size Distribution Analyzer, Model LA-960, from Horiba Scientific of Piscataway, New Jersey in the United States.

Layer Thickness

[0138] The thickness of the graphite layer may be measured by physical measurement devices, such as calipers.

Density and Theoretical Density

[0139] The density of the ceramic body is measured according to the standard ASTM B962-17. The theoretical density is calculated from x-ray diffraction (XRD) data. From the XRD data, the unit cell parameters a, b and c are obtained. Using the unit cell parameters, the unit cell volume is calculated. Based on the crystal structure of the material, the number of molecular units present in every unit cell is determined. The molecular weight of the ceramic body is known as its chemical structure is known. Using the foregoing data, the theoretical density is calculated as follows:

[00001]$\mathrm{Theoretical}\mathrm{density}=\left(\mathrm{Molecular}\mathrm{weight}\mathrm{No}.\mathrm{of}\mathrm{molecules}\mathrm{per}\mathrm{unit}\mathrm{cell}\right)/\left(\mathrm{Volume}\mathrm{of}\mathrm{unit}\mathrm{of}\mathrm{cell}\mathrm{Avogardo}\text{'}s\mathrm{number}\right).$

Average Grain Size

[0140] The average grain size of the ceramic body is measured according to the standard ASTM E112-13 (2021).

EXAMPLES

[0141] The working of the invention is now further elucidated with the aid of specific examples. The invention is not limited by the features of the examples, which are intended to provide a specific concrete realisation of the invention.

Example A

[0142] A device is provided according to the schematic shown in FIG. 1. The die has a height of 1 m and the punches each have a circular punch surface of diameter 650 mm. The sintering chamber correspondingly had cylindrical shape of cross-sectional diameter 650 mm. The graphite layer on the interior surface of the die was a 1.9 mm total thickness of GRAFOIL GTA flexible graphite available from Neograf Solutions, of Lakewood, Ohio. Neograf Solutions provides flexible graphite in sheets having thicknesses of 0.13 mm, 0.25 mm, 0.38 mm, 0.51 mm, 0.64 mm and 0.76 mm. In this example, two sheets of 0.76 mm were used, and one sheet of 0.38 mm, for a total thickness of 1.9 mm.

[0143] Commercially available yttrium oxide and aluminium oxide powders having a particle size d.sub.50 of 3 m were mixed together and 5 kg of the mixture introduced into the sintering chamber, spread to an approximately level height and compacted with a force of about 40 tons to a compacted height of 20 mm. After sintering, this powder mixture forms yttrium aluminium garnet (YAG). Next, a mixture of commercially available powders were introduced into the sintering chamber for producing zirconia toughened alumina (ZTA) when sintered, in amount of 27 kg and spread to an approximately even height of about 100 mm. Finally, a mixture of the powders for forming YAG and ZTA were introduced into the sintering chamber in an amount of 7 kg and spread to an approximately even height of about 30 mm.

[0144] The punches were moved inwards to arrive at a position as shown in FIG. 2. Force was applied to the powder in the sintering chamber by the first and second punches to arrive at a sintering chamber pressure of around 15 MPa. 40 to 70 kA supplied via the punches was passed through the sintering chamber for a total of 9 to 10 hours. The product was a flat form cylindrical ceramic disc with a diameter of approximately 650 mm and thickness of approximately 26 mm. The example was repeated with the following thicknesses for the graphite layer on the interior surface of the die: 0.5 mm, 1 mm, 1.3 mm, 1.5 mm, 2.5 mm, 5 mm, 10 mm and 20 mm.

[0145] While the foregoing examples were of a cylindrical ceramic disc of three layers, the method disclosed herein is also suitable for such discs of single and two layer forms.

Example B

[0146] Examples A was repeated but with a 100 mm circular diameter for the punch surfaces.

Example C

[0147] Examples A was repeated but with the circular diameter for the punch surfaces being 200 mm, 350 mm and 800 mm respectively.

Results

[0148] The results of the example A are shown in table 1

TABLE-US-00001 TABLE 1 Layer Sintering thick- chamber Drill EX ness diameter test Heating # [mm] [mm] success Current Comments 1 0.5 650 0% High Ceramic body exhibited cracks even prior to the drill test 2 1 650 10% High Ceramic body shattered during drill test 3 1.3 650 60% Fair Some moderate cracks appeared during drill test, but no shattering 4 1.5 650 90% Fair Very minor cracks appeared during drill test 5 1.9 650 100% Fair 100% success means a core was cut completely through the ceramic body with no cracking 6 2.5 650 100% Low 7 5 650 NA NA Insufficient heating current 8 10 650 NA NA Insufficient heating current 9 20 650 NA NA Insufficient heating current

[0149] Results of Example B are shown in Table 2

TABLE-US-00002 TABLE 2 Sintering Layer chamber Drill thickness diameter test Heating EX # [mm] [mm] success Current Comments 1 0.5 100 100% High 2 1 100 100% High 3 1.3 100 100% High 4 1.5 100 100% High 5 1.9 100 100% High 6 2.5 100 100% High 7 5 100 NA Insufficient Heating Current 8 10 100 NA Insufficient Heating Current 9 20 100 NA Insufficient . Heating Current

[0150] When considering the results of Table 2, the following can be seen: when considering scaling up from producing a 100 mm ceramic body to producing a 650 mm ceramic body, there is no indication from the results of Table 2 that the layer thickness should be varied in order to produce a 650 mm ceramic body with sufficient quality.

[0151] The examples with diameter 200 mm were similar to those for diameter 100 mm, namely that 100% success was achieved across the board in the core test and the energy consumption was uniform up to and including a layer thickness of 2.5 mm. The results for diameter 350 mm were similar to those for diameter 650 mm except that the core test at 1.5 mm was 100% successful. The results for diameter 800 mm were similar to those for diameter 650 mm except that shattering was observed in the core test at 1 mm thickness and the power supply was insufficient to sinter the product in the 5 and 10 mm thickness tests.

REFERENCE MIST

[0152] 001 First Pushing Means [0153] 002 First Piston [0154] 003 First Punch [0155] 004 First Punch Surface [0156] 005 Interior Surface [0157] 006 Die [0158] 007 Second Punch Surface [0159] 008 Second Punch [0160] 009 Second Piston [0161] 010 Second Pushing Means [0162] 011 Compression Axis [0163] 012 Electrical Power Source [0164] 013 Sintering Chamber [0165] 014 Layer [0166] 015, 016 Further layers [0167] 200 Preparation process for ceramic body [0168] 201 Step a. [0169] 202 Step b. [0170] 203 Step c. [0171] 204 Step d. [0172] 300 Cross-section of sinter chamber [0173] 301 Layer thickness [0174] 302 Die thickness [0175] 303 Sinter chamber diameter [0176] 400 Core test setup [0177] 401 Coring Tool [0178] 402 First flat surface [0179] 403 Drill depth [0180] 404 Sample thickness [0181] 405 Geometric centre [0182] 406 Plat-form ceramic sample [0183] 407 Coring region [0184] 408 Direction of motion perpendicular to flat-form ceramic sample [0185] 409 Tip of coring tool [0186] 410 Cylindrical section removed from flat-form ceramic sample