US20160325354A1 - Compressive Sintering Apparatus Comprising Protected Opposing Rams - Google Patents
Compressive Sintering Apparatus Comprising Protected Opposing Rams Download PDFInfo
- Publication number
- US20160325354A1 US20160325354A1 US15/147,077 US201615147077A US2016325354A1 US 20160325354 A1 US20160325354 A1 US 20160325354A1 US 201615147077 A US201615147077 A US 201615147077A US 2016325354 A1 US2016325354 A1 US 2016325354A1
- Authority
- US
- United States
- Prior art keywords
- sintering apparatus
- protection layer
- surface protection
- compressive
- die
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000005245 sintering Methods 0.000 title claims abstract description 56
- 239000000463 material Substances 0.000 claims abstract description 47
- 238000000034 method Methods 0.000 claims description 19
- 239000002131 composite material Substances 0.000 claims description 14
- 238000002490 spark plasma sintering Methods 0.000 claims description 12
- CREMABGTGYGIQB-UHFFFAOYSA-N carbon carbon Chemical compound C.C CREMABGTGYGIQB-UHFFFAOYSA-N 0.000 claims description 11
- 239000011203 carbon fibre reinforced carbon Substances 0.000 claims description 11
- 239000011248 coating agent Substances 0.000 claims description 3
- 238000000576 coating method Methods 0.000 claims description 3
- 229910000831 Steel Inorganic materials 0.000 claims description 2
- 239000010959 steel Substances 0.000 claims description 2
- 239000010410 layer Substances 0.000 description 21
- 239000000843 powder Substances 0.000 description 11
- 238000010438 heat treatment Methods 0.000 description 10
- 238000009792 diffusion process Methods 0.000 description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 5
- 239000002245 particle Substances 0.000 description 5
- 239000002184 metal Substances 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 238000003825 pressing Methods 0.000 description 4
- 230000004888 barrier function Effects 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 239000000919 ceramic Substances 0.000 description 3
- 230000006835 compression Effects 0.000 description 3
- 238000007906 compression Methods 0.000 description 3
- 238000013461 design Methods 0.000 description 3
- 238000007731 hot pressing Methods 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 229910001220 stainless steel Inorganic materials 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 230000015556 catabolic process Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 238000000280 densification Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- 229910001055 inconels 600 Inorganic materials 0.000 description 2
- 238000009413 insulation Methods 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- 239000011241 protective layer Substances 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- QYEXBYZXHDUPRC-UHFFFAOYSA-N B#[Ti]#B Chemical compound B#[Ti]#B QYEXBYZXHDUPRC-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910033181 TiB2 Inorganic materials 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000009529 body temperature measurement Methods 0.000 description 1
- 238000002144 chemical decomposition reaction Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000007596 consolidation process Methods 0.000 description 1
- 238000009770 conventional sintering Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000003116 impacting effect Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229910001026 inconel Inorganic materials 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000009766 low-temperature sintering Methods 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 239000012811 non-conductive material Substances 0.000 description 1
- 238000010943 off-gassing Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 229910000601 superalloy Inorganic materials 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/003—Apparatus, e.g. furnaces
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/10—Sintering only
- B22F3/105—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/12—Both compacting and sintering
- B22F3/14—Both compacting and sintering simultaneously
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B30—PRESSES
- B30B—PRESSES IN GENERAL
- B30B1/00—Presses, using a press ram, characterised by the features of the drive therefor, pressure being transmitted directly, or through simple thrust or tension members only, to the press ram or platen
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B30—PRESSES
- B30B—PRESSES IN GENERAL
- B30B11/00—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses
- B30B11/007—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses using a plurality of pressing members working in different directions
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B30—PRESSES
- B30B—PRESSES IN GENERAL
- B30B11/00—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses
- B30B11/02—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses using a ram exerting pressure on the material in a moulding space
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2201/00—Treatment under specific atmosphere
- B22F2201/20—Use of vacuum
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2202/00—Treatment under specific physical conditions
- B22F2202/06—Use of electric fields
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2202/00—Treatment under specific physical conditions
- B22F2202/13—Use of plasma
Definitions
- the present invention relates to methods and systems for compressive sintering having protected opposing rams.
- SPS Spark plasma sintering
- DCS direct current sintering
- FAS field assisted sintering
- HP hot-pressing
- an ON-OFF DC pulse typically referred to as SPS
- a constant direct current is applied to a sample contained within a tooling material composed of graphite, metal, ceramic, or a composite to generate joule heat.
- the heat is transferred to the sample by conduction, and, if the sample is conductive, electrical current can flow through it directly generating joule heat within the sample itself.
- DCS's operational or “monitored” temperatures are commonly 200° C. to 500° C. lower than with conventional sintering, classifying DCS as a low temperature sintering technology.
- Material processing pressure and temperature rise and hold time
- the relatively low temperatures combined with fast processing times ensure tight control over grain growth and microstructure, enhancing material properties directly related to microstructure, such as strength, toughness, and electrical, thermal, and optical properties.
- DCS systems involve the use opposing rams to contact and compress a sinterable material contained within a die cavity.
- current DCS, SPS and HP furnaces show significant wear on the pressing faces of the rams due to constant carbide reaction between graphite tooling and metal ram bodies in addition to overheating due to low pressure conditions, which increases contact resistance. Removal of the worn rams for refinishing or replacement is a labor intensive process, especially for larger pressing systems.
- the damage layer (carbide reaction zone) on the surface typically has a depth of from about 0.03-0.04′′, which limits the number of times the rams can be turned down to create a fresh surface without impacting performance.
- the present invention relates to an apparatus for compressively sintering a material and forming a sintered product.
- the compressive sintering apparatus comprises a die set and a vacuum chamber into which the die set is placed.
- the die set comprises a die casing and opposing rams forming a die cavity loaded with material to be sintered and is configured to compress the material during sintering.
- At least one of the opposing rams comprises a surface protection layer in contact with the material to be sintered.
- the present invention further relates to the die set and to a method of compressively sintering.
- FIG. 1-3 show various embodiments of the method and apparatus of the present invention while FIG. 4 shows a slug design used for measuring component performance.
- the present invention relates to a method and system/apparatus for sintering materials under compression.
- the compressive sintering apparatus of the present invention which can be, for example, a hot press, a spark plasma sintering (SPS) system, or a direct current sintering (DCS) system, involves the use of pressure and high temperature to convert a material to be sintered, especially in particulate or powder (fine particulate) form, to a higher density product.
- SPS and DCS processes are similar, with SPS using a pulsed direct current to generate heat and DCS using a non-pulsed direct current.
- Hot pressing and DCS differ in how and where the heat is generated.
- DCS is a pressure assisted direct current heated sintering process that utilizes uniaxial force and direct current to consolidate powder material.
- the application of DC voltage and current between powder material particles creates localized heating within a conductive powder compact and within the conductive die assembly (die set). Due to heat being generated within the die set and potentially within the powder, high heating rates are achievable, in contrast to conventional hot pressing where heat must be transferred into the die set from the exterior by radiant heating elements.
- direct current sintering heat is generated in and around the sample, rapidly heating it and limiting particle/grain growth due to the speed of the process.
- the same apparatus can be applied to diffusion bonding, and a heat treating type process where no sintering takes place.
- the electrical current flowing between particles can assist in removing fine impurities and gases on and between the surfaces of the particles due to dielectric breakdown of surface oxides and local heating.
- the higher heating rates achievable allow the fine powders to be heated to high temperatures before grain coarsening can occur, allowing the powder to retain a high surface area to contribute to the sintering process, which progresses quickly.
- Force also plays an important and predictable role in curbing particulate growth and influencing overall densities in SPS and DCS systems. For example, force multiplies diffusion throughout the sample as the material moves under pressure, especially during early sintering stages. Both too much and too little pressure can negatively influence the process. In large samples where high density is required, force is commonly increased in stages to enhance out-gassing at low temperatures and sintering diffusion at higher temperatures. Accordingly, accurate manipulation of force can enhance the process.
- the compressive sintering systems of the present invention use opposing rams, particularly a pair of rams, that compress material contained within a die during sintering.
- Any ram design or type known in the art can be used, including, for example, a liquid cooled metallic pressing ram, and the rams can be made of any material capable of withstanding conditions of compressive sintering, including, for example, steel, stainless-steel, a copper-based, a super alloy or a composite.
- the opposing rams have at least one surface in contact with the material in the die during sintering.
- a protective layer is provided on the contacting surface of at least one of the rams, and preferably, on both opposing rams.
- This layer can be, for example, metallic, carbon, ceramic or a composite thereof and creates a barrier from the sintering material at high temperature, thereby preventing damage or wear to the metallic ram.
- the surface protection layer can vary in thickness and geometry depending, for example, on the size of the ram, the material to be sintered, and the sintering conditions.
- the layer may have a thickness of from about 0.1 inches to about 2 inches, including about 0.2 inches to about 1 inch and 0.25 inches to about 0.75 inches.
- the surface protection layer may cover the entire ram surface in contact with the material in the die or can cover a portion of the surface, particularly the center portion which typically experiences higher temperatures.
- the protective layer may also be of a segmented design allowing large faces to be covered using multiple fitted pieces.
- the surface protection layer can be a coating applied to the ram surface or can be a separate layer of material attached or bonded to the ram surface, such as a faceplate or end cap.
- the surface protection layer is replaceable and can be removed as necessary with another one put in its place with minimal labor and machine downtime.
- Additional optional layers may also be included.
- an optional intermediate layer can be used at the interface of the surface protection layer and the ram to provide a diffusion barrier to prevent, for example, carbon diffusion into the ram material.
- This diffusion barrier can be a thin metallic or ceramic layer resistant to carbon diffusion formation, such as, for example, Ni, Cu, Nb, Mo, Ti, TiN, TiB 2 , or Ta.
- the optional intermediate layer is preferably thin compared to the surface protection layer and can be applied as a separate sheet or as coating.
- the compression sintering apparatus of the present invention comprises opposing rams, wherein at least one of the rams comprises a surface protection layer, such as an attached faceplate, in contact with the material to be sintered.
- a surface protection layer such as an attached faceplate
- sintering apparatus 100 includes vacuum chamber 102 located within load frame 104 and further includes observation window 106 and temperature measurement device 108 , both of which are incorporated into vacuum chamber 102 .
- the material to be sintered (typically a powder material), is loaded into die set 111 and is placed within vacuum chamber 102 of sintering apparatus 100 wherein the SPS process is performed.
- die set 111 includes die casing 112 and two opposing rams, lower ram 120 and upper ram 122 , forming die cavity 110 in which the material to be sintered is placed.
- Sintering apparatus 100 further includes hydraulic power unit 116 and hydraulic press cylinder 118 .
- the hydraulic power unit provides power to the hydraulic press cylinder, which in turn is used to move the lower ram and the upper ram up and down to manipulate the mechanical force (or pressure) applied, thereby compressing the sinterable material during the process.
- the force may be measured and monitored, such as with a load cell.
- a DC power supply 114 provides the necessary electric current within vacuum chamber 102 during the compression.
- sintering apparatus 100 also includes vacuum pump 124 , which allows the apparatus to operate under negative atmospheric pressure. Gas 126 can also be injected into vacuum chamber 102 if desired during the process.
- Central control system 128 can be used to control the different aspects of the sintering apparatus during use.
- the control system can be used to control the DC power supply, the hydraulic power unit, the vacuum pump, as well as to control the amount of any inert gas introduced to the vacuum chamber during use.
- both of the opposing rams comprise surface protection layers.
- lower ram 120 comprises lower faceplate 140 and upper ram 122 comprises upper faceplate 142 .
- upper faceplate 142 is attached to upper ram 122 using a plurality of fasteners, bolts or screws.
- FIG. 3 shows a detailed view of upper faceplate 142 .
- a faceplate was prepared from a carbon-carbon composite material, which was found to have a significantly higher electrical resistivity compared to metallic based systems but improved high temperature strength.
- an 80 mm slug with no thermal insulation was used to achieve high peak current levels ( ⁇ 7,800 A).
- the slug assembly, shown in FIG. 4 was heated to 1450° C. at 50° C./min and held for 5 min at temperature.
- the operational temperature for the faceplate was measured.
- the carbon-carbon composite faceplate was found to reach a peak temperature of 720° C. and generated a peak ram temperature of 415° C., due to its higher electrical resistivity resulting in more joule heating.
- this carbon-carbon composite does not have a yield point in a classical sense, and it can be used up to these temperatures and higher without consequence.
- the performance of the carbon-carbon composite faceplates was tested under true operational conditions using a standard 40 mm die assembly.
- the test conditions included a heating rate of 100° C./min to 2000° C. for a 5 min hold under 200 MPa of pressure.
- 4 layers of radial felt and 1 layer of felt on top and bottom was used for insulation.
- the results showed that a carbon-carbon composite faceplate used as a surface protection layer for a ram assembly had excellent operational characteristics under standard operational conditions.
- the peak ram temperature reached was ⁇ 300° C., well below the 450° C. operational limit for the material, and the carbon-carbon composite faceplate temperatures did not exceed 600° C.
- testing was also conducted with a 316 SS faceplate, using the same set up and conditions shown in FIG. 4 .
- the stress in the faceplate quickly exceeded the yield strength of the material. This resulted in warping of the faceplate, with the edges of the plate bowing towards the sintering material and forming a dish in the center with a depth on the order of 0.020-0.030′′.
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Powder Metallurgy (AREA)
Abstract
A compressive sintering system is described that comprises a die set and a vacuum chamber into which the die set is placed. The die set comprises a die casing and opposing rams forming a die cavity loaded with material to be sintered and is configured to compress the material during sintering. At least one of the opposing rams comprises a surface protection layer, such as a faceplate, in contact with the material to be sintered.
Description
- This application claims priority to U.S. Provisional Patent Application Ser. No. 62/158,326, filed May 7, 2015, the entire contents of which are incorporated herein by reference.
- 1. Field of the Invention
- The present invention relates to methods and systems for compressive sintering having protected opposing rams.
- 2. Description of the Related Art
- Spark plasma sintering (“SPS”), also referred to as direct current sintering (“DCS”) and field assisted sintering (“FAS”), is a pressure assisted high-speed powder consolidation/sintering technology related to hot-pressing (“HP”) capable of processing conductive and nonconductive materials. The mechanisms of DCS that provide rapid densification and material property enhancement are still under investigation. However the most commonly accepted mechanisms are rapid heating rates, joule heating of conductive powders and an electric field influence on densification.
- During a typical DCS process, either an ON-OFF DC pulse (typically referred to as SPS) or a constant direct current is applied to a sample contained within a tooling material composed of graphite, metal, ceramic, or a composite to generate joule heat. The heat is transferred to the sample by conduction, and, if the sample is conductive, electrical current can flow through it directly generating joule heat within the sample itself.
- DCS's operational or “monitored” temperatures (200° C.-2400° C.) are commonly 200° C. to 500° C. lower than with conventional sintering, classifying DCS as a low temperature sintering technology. Material processing (pressure and temperature rise and hold time) is typically completed in short periods of approximately five to twenty-five minutes. The relatively low temperatures combined with fast processing times ensure tight control over grain growth and microstructure, enhancing material properties directly related to microstructure, such as strength, toughness, and electrical, thermal, and optical properties.
- Typically, DCS systems involve the use opposing rams to contact and compress a sinterable material contained within a die cavity. However, current DCS, SPS and HP furnaces show significant wear on the pressing faces of the rams due to constant carbide reaction between graphite tooling and metal ram bodies in addition to overheating due to low pressure conditions, which increases contact resistance. Removal of the worn rams for refinishing or replacement is a labor intensive process, especially for larger pressing systems. In addition, the damage layer (carbide reaction zone) on the surface typically has a depth of from about 0.03-0.04″, which limits the number of times the rams can be turned down to create a fresh surface without impacting performance.
- Thus, while DCS, SPS and HP methods and systems are known, there is a need to provide a compressive sintering apparatus comprising components that are resistant to wear and damage without significant cost or complexity. This is a significant challenge particularly for DCS and SPS systems since high electric currents must pass through the parts with minimal impact on the component and operation of the system as a whole.
- The present invention relates to an apparatus for compressively sintering a material and forming a sintered product. The compressive sintering apparatus comprises a die set and a vacuum chamber into which the die set is placed. The die set comprises a die casing and opposing rams forming a die cavity loaded with material to be sintered and is configured to compress the material during sintering. At least one of the opposing rams comprises a surface protection layer in contact with the material to be sintered. The present invention further relates to the die set and to a method of compressively sintering.
- It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present invention, as claimed.
-
FIG. 1-3 show various embodiments of the method and apparatus of the present invention whileFIG. 4 shows a slug design used for measuring component performance. - The present invention relates to a method and system/apparatus for sintering materials under compression.
- The compressive sintering apparatus of the present invention, which can be, for example, a hot press, a spark plasma sintering (SPS) system, or a direct current sintering (DCS) system, involves the use of pressure and high temperature to convert a material to be sintered, especially in particulate or powder (fine particulate) form, to a higher density product. SPS and DCS processes are similar, with SPS using a pulsed direct current to generate heat and DCS using a non-pulsed direct current. Hot pressing and DCS differ in how and where the heat is generated. For example, DCS is a pressure assisted direct current heated sintering process that utilizes uniaxial force and direct current to consolidate powder material. Specifically, the application of DC voltage and current between powder material particles creates localized heating within a conductive powder compact and within the conductive die assembly (die set). Due to heat being generated within the die set and potentially within the powder, high heating rates are achievable, in contrast to conventional hot pressing where heat must be transferred into the die set from the exterior by radiant heating elements. During direct current sintering, heat is generated in and around the sample, rapidly heating it and limiting particle/grain growth due to the speed of the process. The entire process—from powder to finished bulk sample—is completed quickly, with high uniformity and without changing the particles' characteristics, specifically grain size and microstructure. In addition to sintering the same apparatus can be applied to diffusion bonding, and a heat treating type process where no sintering takes place.
- In a DCS process, it is believed that the electrical current flowing between particles can assist in removing fine impurities and gases on and between the surfaces of the particles due to dielectric breakdown of surface oxides and local heating. In addition, the higher heating rates achievable allow the fine powders to be heated to high temperatures before grain coarsening can occur, allowing the powder to retain a high surface area to contribute to the sintering process, which progresses quickly.
- Force (pressure) also plays an important and predictable role in curbing particulate growth and influencing overall densities in SPS and DCS systems. For example, force multiplies diffusion throughout the sample as the material moves under pressure, especially during early sintering stages. Both too much and too little pressure can negatively influence the process. In large samples where high density is required, force is commonly increased in stages to enhance out-gassing at low temperatures and sintering diffusion at higher temperatures. Accordingly, accurate manipulation of force can enhance the process.
- In order to provide the proper pressure during sintering, the compressive sintering systems of the present invention use opposing rams, particularly a pair of rams, that compress material contained within a die during sintering. Any ram design or type known in the art can be used, including, for example, a liquid cooled metallic pressing ram, and the rams can be made of any material capable of withstanding conditions of compressive sintering, including, for example, steel, stainless-steel, a copper-based, a super alloy or a composite. The opposing rams have at least one surface in contact with the material in the die during sintering.
- In the present invention, in order to prevent thermal and/or chemical degradation and damage of the rams over time, a protective layer is provided on the contacting surface of at least one of the rams, and preferably, on both opposing rams. This layer can be, for example, metallic, carbon, ceramic or a composite thereof and creates a barrier from the sintering material at high temperature, thereby preventing damage or wear to the metallic ram.
- The surface protection layer can vary in thickness and geometry depending, for example, on the size of the ram, the material to be sintered, and the sintering conditions. For example, the layer may have a thickness of from about 0.1 inches to about 2 inches, including about 0.2 inches to about 1 inch and 0.25 inches to about 0.75 inches. In addition, the surface protection layer may cover the entire ram surface in contact with the material in the die or can cover a portion of the surface, particularly the center portion which typically experiences higher temperatures. The protective layer may also be of a segmented design allowing large faces to be covered using multiple fitted pieces. Furthermore, the surface protection layer can be a coating applied to the ram surface or can be a separate layer of material attached or bonded to the ram surface, such as a faceplate or end cap. Preferably the surface protection layer is replaceable and can be removed as necessary with another one put in its place with minimal labor and machine downtime. Additional optional layers may also be included. For example, an optional intermediate layer can be used at the interface of the surface protection layer and the ram to provide a diffusion barrier to prevent, for example, carbon diffusion into the ram material. This diffusion barrier can be a thin metallic or ceramic layer resistant to carbon diffusion formation, such as, for example, Ni, Cu, Nb, Mo, Ti, TiN, TiB2, or Ta. The optional intermediate layer is preferably thin compared to the surface protection layer and can be applied as a separate sheet or as coating.
- Thus, the compression sintering apparatus of the present invention comprises opposing rams, wherein at least one of the rams comprises a surface protection layer, such as an attached faceplate, in contact with the material to be sintered. Specific embodiments are shown in
FIG. 1 ,FIG. 2 , andFIG. 3 . However, it should be apparent to those skilled in the art that this is merely illustrative in nature and not limiting, being presented by way of example only. Numerous modifications and other embodiments are within the scope of one of ordinary skill in the art and are contemplated as falling within the scope of the present invention. In addition, those skilled in the art should appreciate that the specific conditions and configurations are exemplary and that actual conditions and configurations will depend on the specific system. Those skilled in the art will also be able to recognize and identify equivalents to the specific elements shown, using no more than routine experimentation. - As shown in
FIG. 1 ,sintering apparatus 100 includesvacuum chamber 102 located withinload frame 104 and further includesobservation window 106 andtemperature measurement device 108, both of which are incorporated intovacuum chamber 102. The material to be sintered (typically a powder material), is loaded into die set 111 and is placed withinvacuum chamber 102 ofsintering apparatus 100 wherein the SPS process is performed. More specifically, as shown, die set 111 includesdie casing 112 and two opposing rams,lower ram 120 andupper ram 122, formingdie cavity 110 in which the material to be sintered is placed.Sintering apparatus 100 further includeshydraulic power unit 116 andhydraulic press cylinder 118. The hydraulic power unit provides power to the hydraulic press cylinder, which in turn is used to move the lower ram and the upper ram up and down to manipulate the mechanical force (or pressure) applied, thereby compressing the sinterable material during the process. The force may be measured and monitored, such as with a load cell. In addition, aDC power supply 114 provides the necessary electric current withinvacuum chamber 102 during the compression. As shown,sintering apparatus 100 also includesvacuum pump 124, which allows the apparatus to operate under negative atmospheric pressure. Gas 126 can also be injected intovacuum chamber 102 if desired during the process.Central control system 128 can be used to control the different aspects of the sintering apparatus during use. For example, the control system can be used to control the DC power supply, the hydraulic power unit, the vacuum pump, as well as to control the amount of any inert gas introduced to the vacuum chamber during use. - As shown in
FIG. 1 , both of the opposing rams comprise surface protection layers. In particular,lower ram 120 compriseslower faceplate 140 andupper ram 122 comprisesupper faceplate 142. A more detailed view ofupper ram 122 is specifically shown inFIG. 2 . Thus,upper faceplate 142 is attached toupper ram 122 using a plurality of fasteners, bolts or screws.FIG. 3 shows a detailed view ofupper faceplate 142. - As a specific example, a faceplate was prepared from a carbon-carbon composite material, which was found to have a significantly higher electrical resistivity compared to metallic based systems but improved high temperature strength. To test the suitability of such a faceplate material, an 80 mm slug with no thermal insulation was used to achieve high peak current levels (˜7,800 A). The slug assembly, shown in
FIG. 4 , was heated to 1450° C. at 50° C./min and held for 5 min at temperature. - The operational temperature for the faceplate was measured. The carbon-carbon composite faceplate was found to reach a peak temperature of 720° C. and generated a peak ram temperature of 415° C., due to its higher electrical resistivity resulting in more joule heating. However this carbon-carbon composite does not have a yield point in a classical sense, and it can be used up to these temperatures and higher without consequence.
- Experiments were also run using 347 stainless steel and Iconel 600 as the faceplate material. Both of these metal plates performed similarly to the carbon-carbon composite, with plate temperatures of ˜575° C. The Inconel 600 plate was found to have a slightly higher temperature due to a lower thermal conductivity and higher electrical resistivity.
- Current usage was also measured and found to be identical for the three materials studied, taking ˜7800 A to heat the slug to 1450° C. However, the voltage differed significantly for the metal based materials compared to the carbon-carbon composite plate, with the metal systems having lower voltage than the carbon-carbon composite faceplate system. Power off free cooling of the sample was found to be nearly identical for all of the faceplate systems studied.
- The performance of the carbon-carbon composite faceplates was tested under true operational conditions using a standard 40 mm die assembly. The test conditions included a heating rate of 100° C./min to 2000° C. for a 5 min hold under 200 MPa of pressure. In addition, 4 layers of radial felt and 1 layer of felt on top and bottom was used for insulation. The results showed that a carbon-carbon composite faceplate used as a surface protection layer for a ram assembly had excellent operational characteristics under standard operational conditions. The peak ram temperature reached was ˜300° C., well below the 450° C. operational limit for the material, and the carbon-carbon composite faceplate temperatures did not exceed 600° C.
- As a comparative example, testing was also conducted with a 316 SS faceplate, using the same set up and conditions shown in
FIG. 4 . However, it was found that, after the faceplate temperatures reached >300° C., the stress in the faceplate quickly exceeded the yield strength of the material. This resulted in warping of the faceplate, with the edges of the plate bowing towards the sintering material and forming a dish in the center with a depth on the order of 0.020-0.030″. Similar results were found with a 321H SS and 347 SS faceplate, showing similar warping occurring with the central dish depth in the 0.080″ range, as well as with a higher grade material (Inconel 600), also resulting in similar warping at the same temperature ranges as the stainless steels. Thus, while these materials may be useful for different sintering conditions, a carbon-carbon composite surface protection layer is preferred. Degradation of the ram pressing face would be minimized, especially during long term use, which would be expected to allow for easy end user replacement in the event of catastrophic damage to the ram faceplate. - The foregoing description of preferred embodiments of the present invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings, or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.
Claims (14)
1. A compressive sintering apparatus comprising
a) a die set comprising a die casing and opposing rams forming a die cavity loaded with material to be sintered, the die set configured to compress the material during sintering; and
b) a vacuum chamber into which the die set is placed,
wherein at least one of the opposing rams comprises a surface protection layer in contact with the material to be sintered.
2. The compressive sintering apparatus of claim 1 , wherein the die set comprises an outer die casing, an upper ram, and a lower ram, and wherein both the upper ram and the lower ram comprise the surface protection layer.
3. The compressive sintering apparatus of claim 1 , wherein the surface protection layer has a thickness of from about 0.1 inches to about 2 inches.
4. The compressive sintering apparatus of claim 3 , wherein the thickness of the surface protection layer is from about 0.2 inches to about 1 inch.
5. The compressive sintering apparatus of claim 4 , wherein the thickness of the surface protection layer is from about 0.25 inches to about 0.75 inches.
6. The compressive sintering apparatus of claim 1 , wherein the surface protection layer is a coating applied to the ram.
7. The compressive sintering apparatus of claim 1 , wherein the surface protection layer is a faceplate attachable to the ram.
8. The compressive sintering apparatus of claim 1 , wherein the surface protection layer is an end cap attachable to the ram.
9. The compressive sintering apparatus of claim 1 , wherein the surface protection layer is replaceable.
10. The compressive sintering apparatus of claim 1 , wherein the surface protection layer comprises a carbon-carbon composite.
11. The compressive sintering apparatus of claim 11 , wherein the opposing rams comprise a steel.
12. The compressive sintering apparatus of claim 1 , wherein the compressive sintering apparatus is a spark plasma sintering apparatus or a direct current sintering apparatus.
13. A die set for a compressive sintering apparatus, the die set comprising a die casing and opposing rams forming a die cavity, wherein the die set is configured to compress material to be sintered within the die cavity during sintering and wherein at least one of the opposing rams comprises a surface protection layer in contact with the material to be sintered.
14. A method of forming a sintered product comprising, in any order, the steps:
i) loading a material to be sintered into a die cavity of a die set comprising a die casing and opposing rams configured to compress the material;
ii) placing the die set into a vacuum chamber of a sintering apparatus; and
iii) compressively sintering the material in the die cavity to form the sintered product, wherein at least one of the opposing rams comprises a surface protection layer in contact with the material to be sintered.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US15/147,077 US20160325354A1 (en) | 2015-05-07 | 2016-05-05 | Compressive Sintering Apparatus Comprising Protected Opposing Rams |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US201562158326P | 2015-05-07 | 2015-05-07 | |
US15/147,077 US20160325354A1 (en) | 2015-05-07 | 2016-05-05 | Compressive Sintering Apparatus Comprising Protected Opposing Rams |
Publications (1)
Publication Number | Publication Date |
---|---|
US20160325354A1 true US20160325354A1 (en) | 2016-11-10 |
Family
ID=57218343
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US15/147,077 Abandoned US20160325354A1 (en) | 2015-05-07 | 2016-05-05 | Compressive Sintering Apparatus Comprising Protected Opposing Rams |
Country Status (5)
Country | Link |
---|---|
US (1) | US20160325354A1 (en) |
EP (1) | EP3291935A4 (en) |
HK (1) | HK1252361A1 (en) |
MA (1) | MA42058A (en) |
WO (1) | WO2016179352A1 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN108559867A (en) * | 2018-05-15 | 2018-09-21 | 北京科技大学 | A kind of high conductivity CuCr30 contact materials and preparation method thereof |
CN109373761A (en) * | 2018-11-27 | 2019-02-22 | 成都易飞得材料科技有限公司 | A kind of multi- scenarios method material handling system |
EP3924980A4 (en) * | 2019-02-12 | 2022-10-26 | Westinghouse Electric Company Llc | Sintering with sps/fast uranium fuel with or without burnable absorbers |
Family Cites Families (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE10010671C2 (en) * | 2000-03-04 | 2002-03-14 | Fette Wilhelm Gmbh | Process for producing pressed parts by pressing metal powder and then sintering the compact |
WO2008085947A1 (en) * | 2007-01-05 | 2008-07-17 | The University Of Houston System | Minimizing heat losses and leakage currents in spark plasma sintering |
CN101505557A (en) * | 2009-03-02 | 2009-08-12 | 深圳大学 | Composite electrode crimp and discharging plasma sintering equipment |
TWI651395B (en) * | 2012-04-18 | 2019-02-21 | 日東電工股份有限公司 | Phosphor ceramics and methods of making the same |
US10790065B2 (en) * | 2012-08-15 | 2020-09-29 | University Of Florida Research Foundation, Inc. | High density UO2 and high thermal conductivity UO2 composites by spark plasma sintering (SPS) |
CN103093921B (en) * | 2013-01-29 | 2016-08-24 | 烟台首钢磁性材料股份有限公司 | A kind of R-T-B-M-C system sintered magnet and manufacture method thereof and special purpose device |
-
2016
- 2016-05-05 US US15/147,077 patent/US20160325354A1/en not_active Abandoned
- 2016-05-05 EP EP16790063.8A patent/EP3291935A4/en not_active Withdrawn
- 2016-05-05 MA MA042058A patent/MA42058A/en unknown
- 2016-05-05 WO PCT/US2016/030896 patent/WO2016179352A1/en active Application Filing
-
2018
- 2018-09-11 HK HK18111647.4A patent/HK1252361A1/en unknown
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN108559867A (en) * | 2018-05-15 | 2018-09-21 | 北京科技大学 | A kind of high conductivity CuCr30 contact materials and preparation method thereof |
CN109373761A (en) * | 2018-11-27 | 2019-02-22 | 成都易飞得材料科技有限公司 | A kind of multi- scenarios method material handling system |
EP3924980A4 (en) * | 2019-02-12 | 2022-10-26 | Westinghouse Electric Company Llc | Sintering with sps/fast uranium fuel with or without burnable absorbers |
Also Published As
Publication number | Publication date |
---|---|
WO2016179352A1 (en) | 2016-11-10 |
HK1252361A1 (en) | 2019-05-24 |
EP3291935A4 (en) | 2018-11-07 |
MA42058A (en) | 2018-03-14 |
EP3291935A1 (en) | 2018-03-14 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
Cavaliere et al. | Spark plasma sintering: process fundamentals | |
Grasso et al. | Electric current activated/assisted sintering (ECAS): a review of patents 1906–2008 | |
Zadra et al. | Spark plasma sintering of pure aluminium powder: mechanical properties and fracture analysis | |
Ageev et al. | Fabrication and investigation of carbide billets from powders prepared by electroerosive dispersion of tungsten-containing wastes | |
McKinnon et al. | Flash spark plasma sintering of cold-Pressed TiB2-hBN | |
US20160325354A1 (en) | Compressive Sintering Apparatus Comprising Protected Opposing Rams | |
JP5876050B2 (en) | Sintering of metal and alloy powders by microwave or millimeter wave heating. | |
Montes et al. | Consolidation by electrical resistance sintering of Ti powder | |
Ghasali et al. | Low temperature sintering of aluminum-zircon metal matrix composite prepared by spark plasma sintering | |
Tao et al. | Properties and microstructure of Cu/diamond composites prepared by spark plasma sintering method | |
JP6403421B2 (en) | Sintering apparatus and sintering method | |
Ling et al. | Fabrication and evaluation of SiC/Cu functionally graded material used for plasma facing components in a fusion reactor | |
Zhang et al. | Field activated sintering techniques: a comparison and contrast | |
US20160325353A1 (en) | Automated Pyrometer Tracking in a Spark Plasma Sintering Apparatus and Method | |
KR100960732B1 (en) | method of manufacturing tantalum sintering for sputtering target | |
Yao et al. | Fabrication of ultra-fine grain tungsten by combining spark plasma sintering with resistance sintering under ultra high pressure | |
Kellogg et al. | Effect of current pathways during spark plasma sintering of an aluminum alloy powder | |
KR101122307B1 (en) | method of manufacturing aluminium compacts for sputtering target | |
Tünçay et al. | Evaluation of the particle bonding for aluminum sample produced by spark plasma sintering | |
Nakayama et al. | Carbon-Dispersed WC–FeAl Hard Material Fabricated by Mechanical Milling and Subsequent Pulsed Current Sintering | |
RU2820688C1 (en) | Method of making diamond-hard-alloy plates | |
JP6678434B2 (en) | Spark plasma sintering apparatus and continuous discharge plasma sintering apparatus | |
Sglavo et al. | Flash sintering of metal-like ceramics: a short overview | |
Meilakh et al. | Two-layer copper-based powder electrocontact | |
Behrens et al. | Investigation on temperature control in the SPS process with titanium aluminides |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |