MXPA99001159A - MANUFACTURE AND USE OF ZrB2 - Google Patents

Abstract

The invention relates to ZrB2/Cu composites, and more specifically to methods of making ZrB2/Cu composite electrodes and methods of using ZrB2/Cu composite electrodes. ZrB2 powder is contacted with a polymer and shaped to a desired form. The polymer is vaporized and the ZrB2 powder is sintered. The sintered ZrB¿2 ?is contacted with Cu and heated above the melting point of Cu which causes the Cu to infiltrate the ZrB2, forming the ZrB2/Cu composite electrode.

Description

i MANUFACTURE AND USE OF COMPOSITE ELECTRODES OF ZRB, / Cu This research was carried out under the granting of the government of the National Science Foundation Grant No. DMR-94203896, and under a grant of Graduate Research from the National Science Foundation and the government may have some rights in this patent.

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to the manufacture and use of electrodes composed of zirconium / copper diboride (ZrB2 / Cu). More specifically, the invention relates to a method for the manufacture of ZrB2 / Cu compounds which include ZrB2 powder coating with a polymer, using a rapid prototype or cold pressing to form or process the polymer coated powder into a form desired, sintering the desired shape to vaporize the polymer and sinter the ZrB2 powder, and then infiltrate the sintered ZrB2 with copper. The fabrication technique provides ZrB2 / Cu composite electrodes with minimal electrode wear rates to be used in electrode applications where minimal wear is advantageous, including electric shock machining electrodes. 2. Description of Related Art The ZrB2 is a known ceramic or intermetallic cermet. However, due to its low terminal shock resistance and its brittle quality at room temperature ZrB2 is rarely used for industrial purposes.

The ZrB2 / Cu compounds are known but rarely, if ever, used in the industry due to the difficulty involved in making the compound. Generally, its use has been limited to research purposes. The compound ZrB2 / Cu was investigated for possible use as a high strength refractory coating for spacecraft subjected to laser bombardment as well as for protection when re-entering the Earth's atmosphere.

The only known way to be parts of ZrB2 / Cu, particularly of complex and variable topographies, would be to press the hot one a mixture of ZrB2 and Cu into a matrix that is the negative of the desired shape or hot-pressed a mixture and then machine it to the desired shape. Both of these processes involve significant disadvantages, including that they are very energy and time intensive and that the machining of a ZrB2 / Cu compound is known to be very difficult. It is also known that these techniques produce non-homogenous parts of ZrB2 / Cu, leading to reduced performance of the parts.

SYNTHESIS OF THE INVENTION There is a need for composite ZrB2 / Cu electrodes which have minimal electrode wear rates and which are manufactured in an efficient manner of time and cost and provide dimensional accuracy and surface quality to make the electrodes suitable for use. as EDM electrodes.

The invention relates to a method for manufacturing ZrB2 / Cu compounds comprising coating a ZrB2 powder with a polymer using a cold pressing or rapid prototype to shape or process the polymer coated ZrB2 powder in a desired form. The shaped powder form of polymer-coated ZrB2 is sintered to vaporize the polymer and sinter ZrB2. The sintered ZrB2 is then infiltrated with copper.

It is an object of this invention to manufacture composite ZrB2 / Cu electrodes, which have minimal electrode wear rates, in an effective cost and time manner, and in a manner that provides sufficient dimensional accuracy and surface quality. so that the ZrB2 / Cu electrode can be advantageously used as an EDM electrode.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the present invention and the advantages associated therewith will be obtained by referring to the accompanying drawings in which: Figure 1 is a graph showing workpiece removal rates for copper, graphite and ZrB2 / Cu composite electrodes at different times.

Figure 2 is a graph showing the tool removal rates for copper, graphite and ZrB2 / Cu composite electrodes at different times.

Figure 3 is a graph showing the wear ratios for electrodes composed of copper, graphite and ZrB2 / Cu at different times.

DETAIL DESCRIPTION OF THE EXAMPLE INCORPORATIONS I. Electrode Formation ZrB2 / Cu Compounds The electrode production path is generally a four step process. First, unprocessed ZrB2 powders are coated with a polymer coating which is optimized for use in a selective laser sintering machine (SLS) or another forming step. Second, these polymer-coated powders are preferably processed using selective laser sintering to "glue" together the ZrB2 powders by sintering their respective polymer coatings, creating (shaping) a part of ZrB2 in the desired form, ZrB2 Underlying is not thermally affected during this step. Third, a high temperature furnace is used to both vaporize the polymer coating and sinter the ZrB2 powder. Finally, the dense network of 30-70% zirconium diboride is infiltrated with an appropriate copper alloy.

A. Powder of ZrB-, Coated with Polymer First the ZrB2 powder must be obtained appropriately. Generally, the ZrB2 powder having a particle size of about 1 μm to about 10 μm with an average of about 3 μm, is available and is suitable for cold pressing to form the polymer-coated ZrB2 powder. the desired forms as discussed below. However, for the selective laser sintering method as discussed below, a particle size of about 10 μm to about 100 μm is generally preferred. Suitable powders of ZrB2 can be obtained from Advanced Refractory Technology (ART) (from Buffalo, New York). The polymer-coated ZrB2 powder suitable, particularly for selective laser sintering as discussed below, can be obtained from DTM Corporation (of Austin, Texas). The polymer-coated ZrB2 powder suitable for processing by methods other than selective laser sintering can be obtained from ART.

The coating of the ZrB2 powder with the low Tg polymer should be done in such a way that each particle is individually coated, for example, a fluidized bed, spray drying, etc., as is known to those skilled in the art. In the powder coating, consideration must be given to the production of the thinnest possible polymer coating consistent with good coverage and good tack of the powder particles. The thickness of the coating also has an effect on the shrinkage during laser sintering of the polymer coating to glue the ZrB2 particles together and during sintering of the desired shape which vaporizes the coating and sinters ZrB2. A suitable low Tg polymer, particularly for selective laser sintering, is the acrylic-based binder available from DTM Corporation. Polymers suitable for the other prototype manufacturing techniques can be obtained from vendors of the rapid prototype manufacturing technique of interest.

For the "cold pressing" process of forming the ZrB2 as discussed below, the uniformity and thickness of the polymer coating is less critical compared to the selective laser sintering process. Consequently, when cold pressing is used, less advanced techniques can be employed to coat the ZrB2 powder. For cold pressing, suitable polymers include the known press polymers, for example, CERAMER 1608 (see Example 1).

B. Conformation of ZrB, / Polymer to the Desired Form Particularly where a simple mass production of electrodes is desired, the "cold pressing" of the ZrB2 powder with a polymer binder is the preferred method of shaping the ZrB2 / polymer into a desired shape.

Example 1 The ZrB2 powder was sent to ART Co. to be coated with a thin layer of the polymer binder. The polymer binder, CERAMER 1608, was obtained from Petrolyte Corporation (of St. Louis, Missouri). At ART Co., CERAMER 1608 was mixed with acetone to achieve 25% of the CERAMER 1608 binder in acetone. Three percent by weight of the CERAMER 1608 binder of the solution was then added to the ZrB2 powder. This mixture was combined using a stir bar while stirring a small amount of acetone. After the acetone was evaporated from the ZrB2 mixture the material was placed on a shaker to break the dry powder. The dry powder was then screened through a 60 micron sieve to break up the agglomerates.

The ZrB2 coated with the polymer binder particles was then cold-pressed at 10,000 pounds per square inch in a 1-inch by 1-inch square matrix to form a square electrode with a height of approximately 1.4 inches. of lecithin mold was used on the matrix to facilitate the removal of the rectangular electrode.

The rectangular electrode was then placed in the graphite furnace of GROUP 1000 of Thermal Technology, Inc. (of Santa Rosa, California). The furnace was then brought to an increased temperature of about 600 ° C per% hour to vaporize the polymer binder, and then subsequently heated to 1600 ° C for one electrode and 1700 ° C for another electrode for two hours to sinter ZrB2. Argon was used as an inert operating gas. This process resulted in a dense part of approximately 50%. Then, the copper alloy powder (copper and about 3% by weight of boron) was added to the crucible and put on fire at 1200 ° C for 2 hours to infiltrate the copper through the capillary action. This resulted in a dense part of approximately 100%. Each compound was then cut and ground into four 3/8 inch by 3/8 inch electrodes.

A matrix-sinking machine from AGIETRON 1U (from Losone, Switzerland) was used to compare the performance of the ZrB2 / Cu composite electrodes in relation to copper and graphite electrodes at different times.

The materials were tested under a constant current of 24.8A, inactivity time of 100 μs and working times ranging from 560 - 3.2 μs. The dielectric fluid used was British Petroleum's cutting oil, 200 EDM Dielectric Fluid (petroleum-based hydrocarbon, available from an EDM supplier), and drainage was achieved from the vertical movement of the electrode. The material removal rate was calculated as the volumetric removal rate divided by the total time.

The workpiece removal rates are shown in Figure 1 for the copper, graphite and electrodes ZrB2 / Cu at different work times. Figure 1 shows the higher workpiece removal rates of the composite ZrB2 / Cu electrodes compared to those of graphite and copper.

At 180 μs, the workpiece removal rates of the ZrB2 / Cu electrode are 1.7 times better than those of graphite and 1.3 times better than those of copper. The data shows that ZrB2 / Cu has a peak workpiece removal rate of around 5.71E-2 cubic inch / hour.

The tool removal rates for the copper, graphite and ZrB2 / Cu electrodes are shown in figure 2 for variable work times. This figure also shows the superior performance of the ZrB2 / Cu compounds. At a working time of 3.2 μs, ZrB2 / Cu is 4.7 times better than copper and 3.7 times better than graphite. At a working time of 7.5 μs, ZrB2 / Cu is 10 times better than copper and 4.7 times better than graphite. At a working time of 13 μs, ZrB2 / Cu is 20 times better than copper and 6 times better than graphite. Therefore, at low working times where the surface finish is carried out, ZrB2 / Cu is an electrode superior to copper and graphite.

The wear rates for copper, graphite and ZrB2 / Cu for different working times are shown in Figure 3. Again, this demonstrates the superior performance of the ZrB2 / Cu composite electrode. According to the wear ratio at a time of 3.2 μs, ZrB2 / Cu is 7.8 times better than copper and 12.6 times better than graphite.

At a working time of 13 μs, ZrB2 / Cu is 37 times better than copper and 6 times better than graphite.

Modified versions of the "rapid prototype" fabrication are preferred where the electrode to be manufactured is of a complex or variable topography or where limited numbers of electrodes are to be manufactured. The "rapid prototype manufacturing" is a known technology to facilitate the rapid development of the product. Currently, commercial rapid prototyping techniques are generally capable of generally making only polymer or paper solids. These polymer or paper solids are then used to evaluate the product or shape molds for subsequent setting. The modified versions of the rapid prototype fabrication as described herein are suitable for processing or shaping the ZrB2 into a desired form. This is particularly advantageous for complex or variable topographies, since ZrB2 is known to be difficult to machine in the desired forms.

In a rapid prototype fabrication, a 3-D model produced on a computer aided design (CAD) system is mathematically divided into a large number of thin layers, a few thousandths of an inch thick. The different processes for making a rapid prototype usually work on the same basic principle, for example, the desired part is built in small layers, about 0.005 inches thick, one layer at a time, starting from the bottom and working up until the complete part is finished. Therefore, the layers are constructed and consolidated simultaneously to the preceding layer, using the description of that layer of the computer. 1. Selective Laser Sintering The preferred rapid prototype manufacturing technique is "selective laser sintering" ("SLS"). Selective laser sintering uses a C02 laser to sinter polymer-coated powders by scanning in the horizontal plane only as dictated by a current layer description in the CAD model. The three-dimensional solid is constructed by adding layers of material.

The selective laser sintering machine consists of computer components and programs. The device components include the process chamber and the motor, the control cabinet and the atmospheric control unit. The process chamber incorporates the laser, the preheater and the energy management equipment. The control cabinet interprets the CAD drawing and controls and monitors the selective laser sintering process. The atmospheric control unit regulates the temperature and the amount of N2 flowing through the air in the chamber. It also filters the air that flows through the process chamber. The computer program components use a UNIX operating system and other applications owned by DTM Corporation.

The CAD drawing is modified geometrically to horizontally divide the desired shape into thin horizontal layers. These layers can be adjusted in thickness, but are typically around 0.005 inches. The thin layers represent the sintering planes to be drawn by the C02 laser. In operation, a layer of polymer coated ZrB2 extends. When the desired cross section of the layer is drawn by the C02 laser, the temperature of the polymer coated particles will be increased, and the polymer coatings will melt together. The part is then lowered in the selective laser sintering machine in a manner similar to the shape of the solid mass. The selective laser sintering machine accumulates the part of one layer at a time by first creating the lower layer, and then adding layers until the part is finished.

The polymer coated ZrB2 powder was then sintered with laser using the DTM machine SINTERSTATION 2000 which sinters only the polymer coating and not the underlying ZrB2 powder. As described below, further processing is necessary to vaporize.

Sublimate, or "burn" the polymer coating and sinter the ZrB2 powder. After this, the sintered Zrb2 powder is infiltrated with copper. The subsequent selective laser sintering process generally results in a small shrinkage due to the vaporization of the polymer coating and the sintering of the ZrB2 powder. By keeping the processing variables constant, this shrinkage can be compensated in the CAD design of the electrode as for example, the CAD design provides a slightly larger shaped form of ZrB2 / polymer than with the shrinkage, the compound electrode of ZrB2 / Cu It will be the desired size.

Generally, for the conformation of selective laser sintering of the polymer / ZrB2 to the desired shape, the polymer coated powder preferably has a particle size greater than 10 μm because the powder in the selective laser sintering machine is moved by a roller against rotating, and this method of dust transfer does not work well for finer powders.

The C02 laser used in the selective laser sintering machine is generally only capable of producing enough heat to melt the low melting polymers such as nylon or polycarbonate. As such, it is these and the similar low melting point polymers which are used to coat the ZrB2 powder when the selective laser sintering process is employed. Additionally, the polymer or copolymer used must vaporize or sublimate suitably in the vaporization step before sintering the ZrB2 powder. A powder of ZrB2 coated with suitable polymer is available from DTM Corporation (of Austin, Texas). 2. Laminate Object Manufacturing Laminate object fabrication ("LOM") is a rapid prototyping technique wherein the polymer-coated ZrB2 powder tapes are cut and stacked to form the ZrB2 in a desired shape. Such a laminated object manufacturing technique is offered by Helisys Company (of Torrance, California) and by ART (of Buffalo, New York). 3. 3d print There are two general methods that use 3-D printing to form ZrB2 in a desired form. In a first 3-D printing method, a powder layer of ZrB2, without a polymer coating as discussed below, is sprayed with polymer from a spray jet similar to an ink jet printer spray jet. The spray is controlled by computer and is based on the CAD drawing in a similar way as discussed above. The polymer spray agglutinates only the powder in that layer that comes in contact with the polymer. Then, another layer of the ZrB2 powder is placed, the sprayer sprinkles the polymer on the appropriate sections, and the desired shape is built in the layer-by-layer manufacturing technique.

In a second 3-D printing method, a solution of polymer and ZrB2 powder is made so that it has suitable flow characteristics so that it can be sprayed from a spray jet similar to a jet jet spray jet. from ink. The spray of the solution is controlled by computer based on the CAD drawing and the desired shape is built layer by layer.

These 3-D printing techniques are offered by the Department of Mechanical Engineering and the Department of Material Science and Engineering of MIT.

Modeling with Cast Tank ("FDM") Modeling with molten deposit employs a thermoplastic polymer and ZrB2 combined in a formed wire. This polymer wire and ZrB2 is fed through a nozzle which heats and extrudes the polymer and ZrB2 in a thin layer. The thin layers are accumulated, layer by layer, to form the polymer and ZrB2 in a desired form. Molten deposit modeling is generally less preferred than the manufacturing techniques indicated above. However, a molten deposit modeling technique is offered by Stratasys (from Eden Prairie, Minnesota).

After each of the cold pressing or fast prototyping methods, the ZrB2 / polymer can also be formed by machining or milling. Generally, for this to be done, a high Tg polymer must be used or the machining or milling step must be done in a cooled environment.

C. Sintering of the ZrB? / Polymer Shaped After the ZrB2 powder coated with polymer is formed to the desired shape, the desired shape is sintered to vaporize or sublimate the polymer coating and to sinter the ZrB2 powder. The steaming step can be mentioned by those skilled in the art as a "burn"; however, this terminology is somewhat misleading in the sense that it is preferred that there is essentially no oxygen present during the sintering step. As discussed below, oxygen present in the sintering step can lead to reduced wetting in the copper infiltration step or oxidation of ZrB2. The vaporization step is achieved by heating the desired shape to a temperature of about 600 ° C and maintaining that temperature for about 20 minutes. Then, the sintering step ZrB2 is achieved by heating the sintering furnace containing the desired shape at about 1600 ° C to about 1700 ° C and maintaining that temperature for about 2 hours. After the sintering step, the sintered ZrB2 powder conformed to the shape is allowed to cool.

In the sintering step, it is preferred that the polymer coating the ZrB2 powder is vaporized, and that it does not melt, since the melting would lead to a degradation of the shape of the desired contour.

The sintering step produces a sintered shape which is from about 30% volume to about 70% volume occupied by the sintered ZrB2, for example, from about 30% to about 70% dense. The density can advantageously be varied depending on the desired application, for example, to minimize the rate of electrode wear in a particular application. The density or porosity can be altered by varying the size or size distribution of the ZrB2 powder particles used, varying the thickness of the polymer coating, varying the manufacturing technique etc. The density or porosity determines the proportion of ZrB2-copper and can be optimized to meet specific objectives.

It is preferred that the sintering step be essentially free of oxygen, because if oxygen is present, ZrB2 can oxidize Zr02 and B203. B203 is gaseous and will be removed in the sintering process.

After the sintering step, regardless of whether cold pressing or rapid prototyping is used, the sintered ZrB2 can be shaped into a second desired shape, for example by machining or milling. This can be done if it is required that certain dimensions are very accurate or even for the general conformation of the sintered ZrB2 in a second desired form.

D. Infiltration of ZrB, Sintered with Copper Tests indicate that ZrB2 may not be easily moistened by pure copper or that there may be an oxide coating on ZrB2 or a contamination of carbon or ash from ZrB2, perhaps formed during the vaporization of the polymer coating or sintering of ZrB2, as It was discussed above. Therefore, even when pure copper is preferred because of its electrical and thermal conductivity if adequate wetting can be achieved, copper alloys have been developed to make the wetting more thermodynamically favorable. In particular, it has been found that copper which is alloyed with suitable amounts of gold or nickel, for example, up to about 3% by weight of boron or up to about 10% by weight of nickel, provides adequate wetting of the ZrB2. Additionally, this wetting problem may not be solved by providing a suitably inert atmosphere in the sintering furnace. It should be noted that this copper alloy reduces the thermal and electrical conductivity of the copper infiltrate, which in turn reduces the erosion resistance of the electrode. Therefore, attempts must be made to avoid significant reductions in the thermal and electrical conductivity of the copper infiltrate by, for example, using only the minimum amount of boron or nickel that provides adequate wetting.

This wetting problem can be eliminated or alleviated by contacting the ZrB2 with a mixture having an available amount of hydrogen and an inert gas, preferably argon, at an elevated temperature. Hydrogen serves to prevent ZrB2 and any Zr or B2 from being present from oxidation. Contact with the hydrogen in combination with the heating step can be carried out before, during or after the sintering step, preferably during the sintering step, and involves contacting the ZrB2 and the inert gas / hydrogen mixture and heat it to at least about 100 ° C, preferably, between about 1300 ° C / 1800 ° C. The hydrogen is present in an amount of from about 2 volume% to about 20 volume%, preferably, from about 5 volume% to about 15 volume% and more preferably from about 6 volume% to about 8% volume This wetting problem can also be eliminated or alleviated by the acid washing of ZrB2, preferably after the polymer coating has vaporized or sublimated. Preferably, the acid wash was carried out before or after the sintering step of ZrB2. While the acid employed can be any suitable acid, the acid wash is preferably carried out with hydrofluoric acid, boric acid or mixtures thereof. With any acid employed, and particularly with boric acid, it is preferred to carry out the acid wash at an elevated temperature. Also, with any acid, and particularly with boric acid, it is preferred to acid wash ZrB2 just before the sintering step, a thin acid coating is retained on all ZrB2 surfaces, and then sintered as described above. Acid washing, and preferably acid washing at elevated temperatures, promotes the oxides and other contaminants of ZrB2, allowing ZrB2 to be more easily wetted by copper, and can eliminate or reduce the need for copper to be alloyed with boron or nickel as discussed above.

Infiltration is achieved by placing the powder or small pieces of pure copper or the copper alloy discussed above on one side of the shaped ZrB2 form, placing it in an oven and heating above the melting point of copper (108 oc) or of the copper alloy, so that by capillary action, copper or copper alloy infiltrates within the open area of the shaped ZrB2 to produce the ZrB2 / copper compound in the desired form with a density of about 100% . It has been found less preferable to place copper or copper alloy around the shaped ZrB2 form, since this causes lines of imperfection within the composite caused by the capillary fronts of more than one direction.

The copper, before or during the infiltration step, can similarly be contacted with a mixture of hydrogen and an inert gas to remove the copper abdicated to improve the wetting and conductivity of the electrode. Preferably, the copper is contacted with a mixture of inert gas / hydrogen at an elevated temperature of at least about 500 ° C. If it is done during the infiltration step, the hydrogen also serves to prevent the ZrB2 and any Zr or B2 from being present from the oxidation. If this is done during the infiltration step, it is preferred that the infiltration step be carried out around HOOoC at around 1300oC.

Another, but less preferred method of infiltrating the shaped ZrB2 form is by depositing heat of copper or a copper alloy. Generally, vapor deposition is less preferred since it does not completely fill open areas as does the annotated capillary action. However, vapor deposition can alleviate the wetting problem discussed above, thereby allowing pure copper or a purer copper alloy to wet the shaped ZrB2 form.

II. Uses for ZrB / Cu Electrodes Preferred uses for the composite electrode of ZrB2 / Cu of the present invention are listed below. These uses currently use electrodes of copper, graphite or similar and have electrode erosion, so that the electrode should be located, avoiding prolonged and continuous use.

A significant advantage of the present invention is that the ZrB2 / Cu composite electrodes have minimal electrode wear rates. The ZrB2 / Cu composite electrodes of the present invention are suitable for replacing currently used copper, graphite or similar electrodes. This replacement will occur more frequently where the electrode currently used has an electrode wear or erosion and should be replaced. Applications which have the electrode erosion wherein the ZrB2 / Cu composite electrodes are preferred to be used include: A. Electrical Discharge Machining A particularly preferred use of the compound electrodes ZrB2 / Cu of the present invention is for electrodes in electric discharge machining (EDM). Electrical discharge machining allows the "machining" of materials, such as steel tools, which are otherwise very hard to machine using traditional machining methods. The electric discharge machining is an electrical erosion process where the electrode and the work piece (typically the anode and the cathode, respectively) are separated by a liquid dielectric. A voltage is applied to the separation of approximately 40 μm between the electrode and the work piece. This transfer of energy causes the electrode and the work piece to erode. The time by which the current flows between the electrode and the work piece is called the work time. This working time is followed by an appropriate time of inactivity, where the current falls to zero and the dielectric is allowed to drain the eroded material. These working times and non-activity times for the matrix-sunken EDM machines are generally in the order of 10 μs to 200 μs.

However, the use of an electrode as an EDM electrode requires that the electrode is suitably formed with dimensional accuracy and surface quality. Generally, any material with less than 1 ohm-m electrical resistivity, regardless of hardness, can be machined using EDM. The EDM also allows the convenient production of complex shapes in the tool cavity, such as complex topographies that can often be formed more easily on the electrode than inside a cavity. Even certain simple shapes such as rectangular or square cavities are often easier to produce using the EDM than conventional machining.

The most common currently used electrode materials for EDM are graphite and copper. These materials have a combination of electrical and thermal properties that make them very suitable for EDM electrodes. Additionally, these materials are relatively easy to machine to a desired shape. Even with these advantages, however, EDM machining is precluded from many niche markets by the relatively high cost of current electrode production. The cost of the current electrode fabrication is generally 50% higher and sometimes as large as 80% of the total cost of manufacturing a matrix using EDM. In the EDM, the high wear rate of graphite and copper electrodes require the use of multiple electrodes in the production of each cavity because the electrode is worn and loses its initial shape very quickly. Therefore, the replacement of the graphite and copper electrodes with the inventive compound ZrB2 / Cu electrodes, which are more resistant to wear, significantly improve the cost effectiveness of the EDM tool production.

In addition, many molds or other tools having multiple cavities, manufactured with current EDM machining techniques, use a different electrode for each separate cavity because it is more cost effective and easier to machine several electrodes of simple and small shapes than what It is the machining of a complex and large electrode. This requires a greater total sink time in the EDM machine, since multiple electrodes are used sequentially rather than simultaneously.

For EDM electrodes, several variables are used to measure the operation. The most important variables are (1) the wear ratio [(electrode wear rate) -H (workpiece wear rate)]; (2) volumetric removal rate of the work piece (sink rate); (3) dimensional accuracy of the cavity produced; and (4) surface finish of the cavity produced. The first two variables related to the efficiency of the EDM process. Here, the rate of wear is an important variable since it determines how frequently the electrode should be removed and replaced. The volumetric removal rate is a measure of the production speed of a workpiece cavity. The last two variables are related to the cavity of the product produced by the EDM process. The tools and dies produced by EDM for metal stamping and forging are frequently required to have dimensional accuracy, while matrices produced by EDM by injection molding usually require a surface finish of superior quality over the cavity produced.

Generally, the surface finish of the work piece is directly proportional to the working time. At low work times, a superior surface quality finish is obtained. At higher work times, a rougher workpiece surface finish is obtained.

The EDM has the significant advantage of allowing the tool part to be heat treated to its full hardness before a cavity occurs there, which eliminates the need for heat treatment after machining. Therefore, there will be no distortion in the final part due to the heat treatment. Also, the EDM process imparts a minimum work hardening or minimum mechanical stresses since there is no contact between the work piece and the tool. In addition, EDM offers superior dimensional accuracy and ease of production of complex shapes in tool cavity compared to conventional machining.

A particular advantage of the present invention is the use of selective laser sintering to produce an EDM electrode. Selective laser sintering provides the advantage of allowing the production of EDM electrodes in a complex manner. Therefore, with the low wear rate of the composite ZrB2 / Cu electrodes and the ability to make complex shapes, a composite ZrB2 / Cu electrode of complex shape can replace several EDM copper electrodes currently used, leading to a manufacturing of matrix and less expensive and faster tool.

Example 2 The anodes of (1) copper, (2) graphite, and (3) of ZrB2 / Cu were measured with respect to spark erosion when machining the steel in an EDM AGIETRON 1U sinking-matrix machine. The operating conditions of the machine were the same for the three different electrodes: current of 63 amperes; pulse time at 18 μs; pause time at 320 μs. These conditions, for example, high current and short pulse time, were chosen for this test since generally, these conditions provide unusually high electrode erosion rates. The results in Table 1 show that the graphite electrode wear ratio of .150 is 4.3 times more than the electrode wear ratio of ZrB2 / Cu of .0346. Table 1 further shows that the copper electrode is worn 16.6 times more than the ZrB2 / Cu electrode under these conditions.

TABLE 1 ELECTRODE Copper Graphite ZrB, / Cu Steel Erosion Rate 3 .40 4. 84 3. 12 (mmVmin) Electrode Erosion Rate 1. 97 0. 717 0. 108 (mm3 / min) Electrode Wear Ratio / 0 .58 0. 15 0. 035 work piece) Therefore, the ZrB2 / Cu electrodes provide a fast sink rate with significantly lower electrode wear ratios than copper or graphite.

B. Aluminum Recycling In the recycling of aluminum, an electric arc is bombarded from an electrode to melted aluminum in one case. The purified aluminum is then separated from the slag containing paints and other impurities from the recycled aluminum cans. Generally, the electrodes are consumed in the process at a rate so that three parallel production units are commonly used, two operating with the third closed for electrode replacement.

C. Spot Welding In spot welding, the electrodes are consumed and must be replaced periodically. In some cases, contamination of the weld with the eroded electrode material is a problem. This can be eliminated, at least substantially reduced with the ZrB2 / Cu composite electrodes of the present invention.

D. Arc Jet Plasma Reactors Arc jet plasma reactors are used for a variety of applications. The current reactors can now be operated for only about 10-30 hours before the current copper anode (a hole) erodes, causing the anode to disintegrate with small parts of the copper violently expelled from the reactor exhaust. The ZrB2 / Cu composite electrode of the present invention will allow a longer anode life while also reducing the safety hazard.

E. Waste Recycling or Nuclear or Municipal Waste The new waste remedy plants are operating in Norway and France which use plasma arc devices to remedy the waste. The current operation is continuous except for a daily shutdown of 1-2 hours for electrode replacement. The use of the ZrB2 / Cu composite electrodes of the present invention will allow a longer run time before the closure for electrode replacement.

F. Rail guns Used mostly for military applications, arc-driven rail guns are used to accelerate massive projectiles at high speeds.

G. High Current Switches for Pulsed Powder There may be many applications involving electrical switches where the erosion of the switch electrodes is a problem. High-energy switches exhibit a temporary arc when they open or close. Frequently the opening or closing as in the supplies of pulsed energy can lead to an erosion of the electrode and to failure.

H. High Power Ion Impellers Ion beam sources have been developed for space propulsions as well as ion machining and sputtering coating applications.

I. Microelectronics Processing Plasmas are currently used in around % of all microelectronics processing operations. Here, electrode erosion is frequently a problem due to the contamination of the plates.

J. Plasma Spray Coating The plasma spray coating is best known for spraying aircraft surfaces with titanium.

Currently, the electrodes last around 30 hours and must be replaced by disassembling the plasma gun.

The ZrB2 formed by the process of the present invention has excellent material properties such as a high resistance to wear and abrasion, an extreme hardness, a superior melting point and good thermal and electrical conductivity. The addition of copper to the ZrB2 matrix to produce the compound ZrB2 / Cu has a synergistic effect, providing a material far superior to either any ZrB2 or copper. The compound of ZrB2 / Cu has an electrical conductivity close to that of copper with an abrasion and wear resistance superior to that of copper, making it an excellent material for electrodes, particularly for electrodes where the minimum electrode wear rates are advantageous. If the ZrB2 were to be used only as an electrode, the mechanical failure of the electrode will occur, without melting, but by overcoming the resistance of the bonding strength with the thermal force alone. This is called "peeling force" and this occurs when ZrB2 expands and contracts during sudden temperature changes on the electrode surface during erosion. When copper is used by itself, it is eroded by melting. When ZrB2 is combined with copper, the combination allows the copper to melt and resolidify to the higher melting point ZrB2 material, and excess heat is carried out of the surface rapidly due to the high thermal conductivity of the copper. Copper also helps reduce the effects of thermal flaking because it is not brittle and helps reduce internal stresses that cause flaking.

The ZrB2 / Cu composite electrodes of the present invention provide the following advantages: (1) improved wear resistance over known copper and graphite electrodes; (2) the improved sinking rate over known copper and graphite electrodes; (3) control of the dimensional accuracy of an EDM workpiece; and (4) an improved surface finish on an EDM workpiece.

The present invention solves the problems mentioned above by providing electrodes composed of ZrB2 / Cu, and particularly EDM electrodes, which can be manufactured cost-efficiently and time-wise and which provide sufficient dimensional accuracy and surface quality so that the ZrB2 / Cu composite electrode can be used as an EDM electrode.

Although the present invention has been described in detail, it should be understood that various changes, alterations and substitutions can be made to the teachings given herein without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims (88)

R E I V I N D I C A C I O N S

1. An electrode produced by a process comprising the steps of: forming the ZrB2 powder in a desired form by a method selected from the group of shaping methods consisting of selective laser sintering, laminated object fabrication, 3-D printing, molten deposit modeling and cold pressing; sintering the shaped ZrB2 powder; Y contact the ZrB2 powder with the Cu and heat the sintered ZrB2 and Cu above the melting point of the Cu to infiltrate the ZrB2 with the Cu to form the compound electrode of ZrB2 / Cu.

2. The electrode as claimed in clause 1, characterized in that the powder formation of ZrB2 in a desired form comprises a method selected from the group comprising selective laser sintering, laminated object fabrication, 3-D printing, molten deposit modeling, and cold pressing.

3. The electrode as claimed in clause 1, characterized in that the shaping step further comprises contacting the ZrB2 powder with a polymer and using the polymer to maintain the ZrB2 powder in the desired form; and further comprises the step of vaporizing the polymer before sintering the shaped ZrB2 powder.

4. The electrode as claimed in clause 3, characterized in that the polymer is vaporized at a temperature of about 350 ° C to about 700 ° C.

5. The electrode as claimed in clause 1, characterized in that the sintering step is carried out in an essentially oxygen-free environment.

6. The electrode as claimed in clause 1, characterized in that the sintering step produces a sintered shaped form which is from about 30% volume to about 70% volume occupied by the sintered ZrB2.

7. The electrode as claimed in clause 1, characterized in that the sintering step comprises heating the desired shape by from about 1300 ° C to about 1900 ° C.

8. The electrode as claimed in clause 1, characterized in that the step of contacting the sintering ZrB2 with the Cu comprises that the Cu is alloyed with a suitable amount of boron so that the Cu alloy adequately wet the ZrB2 Sintered

9. The electrode as claimed in clause 8, characterized in that the amount of boron is up to about 3% by weight of boron.

10. The electrode as claimed in clause 1, characterized in that the step of contacting the sintered ZrB2 with the Cu comprises that the Cu is alloyed with a suitable amount of nickel so that the Cu alloy adequately moistens the sintered ZrB2. .

11. The electrode as claimed in clause 10, characterized in that the amount of nickel is up to about 10% by weight of nickel.

12. The electrode as claimed in clause 1, characterized in that the composite ZrB2 / Cu electrode has a lower wear ratio than a copper electrode or a graphite electrode in a similar service.

13. The electrode as claimed in clause 1, characterized in that after the step of sintering the shaped ZrB2 powder, the process further comprises the step of shaping the sintered ZrB2 to a second desired shape.

14. The electrode as claimed in clause 1, characterized in that the process further comprises the step of contacting the shaped ZrB2 powder with a mixture of hydrogen and at least one inert gas.

15. The electrode as claimed in clause 1, characterized in that the process further comprises the step of acid washing the shaped ZrB2 powder.

16. The electrode as claimed in clause 15, characterized in that the step of acid washing the shaped ZrB2 powder comprises contacting the powder of ZrB2 formed with an acid selected from the group comprising hydrofluoric acid, boric acid or mixtures thereof .

17. A method for producing an electrode comprising the steps of: forming the ZrB2 powder in a desired form by a method selected from the group of shaping methods consisting of selective laser sintering, laminated object fabrication, 3-D printing, molten deposit modeling and cold pressing; sintering the shaped ZrB2 powder; Y contact the ZrB2 powder with the Cu and heat the sintered ZrB2 and the Cu above the melting point of Cu to infiltrate the ZrB2 with the Cu to form the compound electrode of ZrB2 / Cu.

18. The method as claimed in clause 17, characterized in that the shaping of the ZrB2 powder in a desired form comprises a method selected from the group comprising selective laser sintering, laminated object manufacturing, 3-D printing, Molded tank modeling, and cold pressing.

19. The method as claimed in clause 17, characterized in that the forming step further comprises contacting the ZrB2 powder with a polymer and using the polymer to maintain the ZrB2 powder in the desired form; and further comprises the step of vaporizing the polymer before sintering the shaped ZrB2 powder.

20. The method as claimed in clause 19, characterized in that the polymer is vaporized at a temperature of about 350 ° c to about 700 ° c.

21. The method as claimed in clause 17, characterized in that the sintering step is carried out in an environment essentially free of oxygen.

22. The method as claimed in clause 17, characterized in that the sintering step produces a shaped sintered shape which is from about 30% volume to about 70% volume occupied by the sintered ZrB2.

23. The method as claimed in clause 17, characterized in that the sintering step comprises heating the desired shape by from about 1300 o C to about 1900 o C.

24. The method as claimed in clause 17, characterized in that the step of contacting the sintered ZrB2 with the Cu comprises that the Cu is alloyed with an adequate amount of boron so that the Cu alloy adequately moistens the sintered ZrB2. .

25. The method as claimed in clause 24, characterized in that the amount of gold is up to about 3% by weight of boron.

26. The method as claimed in clause 17, characterized in that the step of contacting the sintered ZrB2 with the Cu comprises that said Cu is in alloy with a suitable amount of nickel for the Cu alloy to adequately wet the sintered ZrB2. .

27. The method as claimed in clause 26, characterized in that the amount of nickel is up to about 10% by weight of nickel.

28. The method as claimed in clause 17, characterized in that the composite electrode ZrB2 / Cu has a lower wear ratio than that of the graphite electrode or that of the copper electrode in a similar service.

29. The method as claimed in clause 17, characterized in that after the step of sintering the shaped ZrB2 powder, the process further comprises the step of shaping the sintered ZrB2 to a second desired shape.

30. The method as claimed in clause 17, characterized in that it also comprises the step of contacting the formed ZrB2 powder with a mixture of hydrogen and at least one inert gas.

31. The method as claimed in clause 17, characterized in that it further comprises the step of acid washing the shaped ZrB2 powder.

32. The method as claimed in clause 31, characterized in that the step of washing with acid to shaped ZrB2 powder comprises contacting the powder of ZrB2 formed with an acid selected from the group comprising hydrofluoric acid, boric acid or mixtures thereof.

33. In a process using an electrode in an application in which the erosion electrode is eroded, the improvement comprising using the compound electrode of ZrB2, the electrode being produced by a process comprising the steps of shaping the ZrB2 powder into a desired shape by a method selected from the group of shaping methods consisting of selective laser sintering, laminated object manufacturing, 3-D printing, molten deposit modeling and cold-printing, sintering the shaped ZrB2 powder, and contacting the ZrB2 powder with the Cu and heating the sintered ZrB2 and the Cu above the melting point of the Cu to infiltrate the ZrB2 with the Cu to form the composite electrode ZrB2 / Cu.

34. The process as claimed in clause 33, characterized in that the process using an electrode in an application in which the electrode has erosion is selected from the group comprising electrical discharge machining, aluminum recycling, spot welding, reactors arc jet plasma, waste remediation, rail guns, high current switches for pulsed power supplies, high power ion impellers, microelectronic processing, and plasma spray coating.

35. The process as claimed in clause 33, characterized in that the electrode composed of ZrB2 / Cu is formed with a process comprising: forming the ZrB2 powder in a desired form; sintering the shaped ZrB2 powder; contact the sintered ZrB2 with the Cu and heat the sintered ZrB2 powder and the Cu above the melting point of the Cu to infiltrate the ZrB2 with the Cu to form the compound electrode of ZrB2 / Cu.

36. The process as claimed in clause 35, characterized in that the powdering of ZrB2 into a desired form comprises a method selected from the group comprising selective laser sintering, laminated object manufacturing, 3-D printing, Molded tank modeling, and cold pressing.

37. The process as claimed in clause 33, characterized in that the forming step further comprises contacting the ZrB2 powder with a polymer using the polymer to maintain the ZrB2 powder in the desired form; and further comprises the step of vaporizing the polymer before sintering to the shaped ZrB2 powder.

38. The process as claimed in clause 37, characterized in that the polymer is vaporized at a temperature of about 350 ° C to about 700 ° C.

39. The process as claimed in clause 35, characterized in that the sintering step is carried out in an environment essentially free of oxygen.

40. The process as claimed in clause 33, characterized in that the sintering step produces a sintered shape which is about 30% volume to about 70% volume occupied by the sintered ZrB2.

41. The process as claimed in clause 33, characterized in that the sintering step comprises heating the desired shape by from about 1300 ° C to about 1900 ° C.

42. The process as claimed in clause 33, characterized in that the step of contacting the sintered ZrB2 with the Cu comprises that said Cu is alloyed with an adequate amount of boron so that the Cu alloy adequately moistens the sintered ZrB2. .

43. The process as claimed in clause 42, characterized in that the amount of boron is up to about 3% by weight of boron.

44. The process as claimed in clause 33, characterized in that the step of contacting the sintered ZrB2 with the Cu comprises that the Cu is alloyed with a suitable amount of nickel so that the Cu alloy adequately moistens the sintered ZrB2. .

45. The process as claimed in clause 44, characterized in that the amount of nickel is up to about 10% by weight of nickel.

46. The process as claimed in clause 33, characterized in that the compound electrode of ZrB2 / Cu has a lower wear ratio than that of the copper electrode or that of the graphite electrode in a similar service.

47. The process as claimed in clause 33, characterized in that after the step of sintering the shaped ZrB2 powder, the process further comprises the step of shaping the ZrB2 to a second desired shape.

48. The process as claimed in clause 33, further characterized in that it comprises the step of contacting the shaped ZrB2 powder with a mixture of hydrogen and at least one inert gas.

49. The process as claimed in clause 33, further characterized in that it comprises the step of acid washing the shaped ZrB2 powder.

50. The process as claimed in clause 49, characterized in that the step of acid washing the shaped ZrB2 powder comprises contacting the shaped ZrB2 powder with an acid selected from the group consisting of hydrofluoric acid, boric acid or mixtures thereof.

51. An electrode produced by a process comprising: obtaining a ZrB2 powder essentially coated with a polymer; using selective laser sintering to shape the ZrB2 powder coated with polymer to a desired shape; vaporizing the polymer in the desired manner; after the vaporization step, sinter the ZrB2 powder into the desired shape; contact the sintered ZrB2 with the Cu and heat the sintered ZrB2 and the Cu above the melting point of the Cu to infiltrate the ZrB2 with the Cu to form the compound electrode of ZrB2 / Cu.

52. The electrode as claimed in clause 51, characterized in that the polymer is vaporized at a temperature of about 350 ° C to about 700 ° C.

53. The electrode as claimed in clause 51, characterized in that the sintering step is carried out in an environment essentially free of oxygen.

54. The electrode as claimed in clause 51, characterized in that the sintering step produces a shaped sintered shape which is from about 30% by volume to about 70% by volume occupied by the sintered ZrB2.

55. The electrode as claimed in clause 51, characterized in that the sintering step comprises heating the desired shape by from about 1300 ° C to about 1900 ° C.

56. The electrode as claimed in clause 51, characterized in that the step of contacting the ZrB2 sintered with Cu comprises that the Cu is in alloy with an adequate amount of boron so that the Cu alloy moistens adequately the sintered ZrB2.

57. The electrode as claimed in clause 56, characterized in that the amount of boron is up to about 3% by weight of boron.

58. The electrode as claimed in clause 51, characterized in that the step of contacting the ZrB2 sintered with Cu understands that the Cu is alloyed with an adequate amount of nickel so that the Cu alloy moistens properly the sintered ZrB2.

59. The electrode as claimed in clause 58, characterized in that the amount of nickel is up to about 10% by weight of nickel.

60. The electrode as claimed in clause 51, characterized in that the electrode composed of ZrB2 / Cu has a lower wear ratio than the copper electrode or the graphite electrode in a similar service.

61. The electrode as claimed in clause 51, characterized in that after the step of sintering the ZrB2 powder, the process further comprises the step of shaping the sintered ZrB2 to a second desired shape.

62. The electrode as claimed in clause 51, characterized in that the process further comprises, after the vaporization step, the step of contacting the ZrB2 with a mixture of hydrogen and at least one inert gas.

63. The electrode as claimed in clause 51, characterized in that the process further comprises, after the vaporization step, the step of acid washing ZrB2.

64. The electrode as claimed in clause 63, characterized in that the step of acid washing ZrB2 comprises contacting ZrB2 with an acid selected from the group comprising hydrofluoric acid, boric acid or mixtures thereof.

65. An electrode produced by a process comprising: shaping the ZrB2 powder in a desired form; sintering the shaped ZrB2 powder; use the copper vapor tank to at least partially infiltrate the sintered ZrB2 with the Cu to form an electrode composed of ZrB2 / Cu.

66. The electrode as claimed in clause 65, characterized in that shaping the ZrB2 powder in a desired form comprises a method selected from the group comprising selective laser sintering, laminated object manufacturing, 3-D printing, fused deposit modeling, and cold pressing.

67. The electrode as claimed in clause 65, characterized in that the shaping step further comprises contacting the ZrB2 powder with a polymer and using the polymer to hold the ZrB2 powder in the desired form; and further comprises the step of vaporizing the polymer before sintering the shaped ZrB2 powder.

68. The electrode as claimed in clause 67, characterized in that the polymer is vaporized at a temperature of 350 ° C to about 700 ° C.

69. The electrode as claimed in clause 65, characterized in that the sintering step is carried out in an environment essentially free of oxygen.

70. The electrode as claimed in clause 65, characterized in that the sintering step produces a sintered shape which is from about 30% volume to about 30% volume occupied by the sintered ZrB2.

71. The electrode as claimed in clause 65, characterized in that the sintering step comprises heating the desired shape from about 1300 o C to about 1900 o C.

72. The electrode as claimed in clause 65, characterized in that the electrode composed of ZrB2 / Cu has a lower wear ratio than that of the copper electrode or that of the graphite electrode in a similar service.

73. The electrode as claimed in clause 65, characterized in that after the step of sintering the shaped ZrB2 powder, the process further comprises the step of shaping the sintered ZrB2 to a second desired shape.

74. A method for producing a composite article comprising the steps of: forming the ZrB2 powder in a desired form by a method selected from the group of shaping methods consisting of selective laser sintering, laminated object fabrication, 3-D printing, fused deposit modeling and cold pressing; sintering the shaped ZrB2 powder; Y contact the ZrB2 powder with the Cu and heat the sintered ZrB2 and the Cu above the melting point of the Cu to infiltrate the put the small formula with the Cu to form an article composed of ZrB2 / Cu.

75. The method as claimed in clause 74, characterized in that the shaping step further comprises contacting the ZrB2 powder with a polymer and using the polymer to maintain the ZrB2 powder in the desired form; and further comprises the step of vaporizing the polymer before sintering the shaped ZrB2 powder.

76. The method as claimed in clause 75, characterized in that the polymer is vaporized at a temperature of about 350 ° C to about 700 ° C.

77. The method as claimed in clause 74, characterized in that the sintering step is carried out in an environment essentially free of oxygen.

78. The method as claimed in clause 74, characterized in that the sintering step produces a shaped or sintered shape which is about 30% volume to about 70% occupied by the sintered ZrB2.

79. The method as claimed in clause 74, characterized in that the sintering step comprises heating the desired shape by from about 1300 ° C to about 1900 ° C.

80. The method as claimed in clause 74, characterized in that the step of bringing into contact when placing the sintered ZrB2 with the Cu comprises that the Cu is alloyed with an adequate amount of boron so that the Cu alloy adequately wet the ZrB2 sintered.

81. The method as claimed in clause 80, characterized in that the amount of boron is up to about 3% by weight of boron.

82. The method as claimed in clause 74, characterized in that the step of bringing into contact when placing the sintered ZrB2 with the Cu comprises that the Cu is alloyed with a suitable amount of nickel so that the Cu alloy adequately moistens the Cu ZrB2 sintered.

83. The method as claimed in clause 82, characterized in that the amount of nickel is up to about 10% by weight of nickel.

84. The method as claimed in clause 74, characterized in that the compound article of ZrB2 / Cu has a lower wear ratio than that of a copper electrode or a graphite electrode in a similar service as an electrode.

85. The method as claimed in clause 74, characterized in that after the step of sintering the shaped ZrB2 powder, the process further comprises the step of shaping the sintered ZrB2 to a second desired shape.

86. The method as claimed in clause 74, further characterized in that it comprises the step of contacting the shaped ZrB2 powder with a mixture of hydrogen and at least one inert gas.

87. The method as claimed in clause 74, further characterized in that it comprises the step of acid washing the shaped ZrB2 powder.

88. The method as claimed in clause 87, characterized in that the step of acid washing the shaped ZrB2 powder comprises contacting the shaped ZrB2 powder with an acid selected from the group comprising hydrofluoric acid, boric acid or mixtures thereof. V '58 R E S UM E N The invention relates to ZrB2 / Cu compounds and more specifically to the methods for making the ZrB2 / Cu compound electrodes and to the methods for using the ZrB2 / Cu composite electrodes. The ZrB2 powder is contacted with a polymer and formed into a desired shape. The polymer vaporizes and the ZrB2 powder sinters. The sintered ZrB2 is brought into contact with the Cu and heated above the melted point of Cu which causes the Cu to infiltrate the ZrB2, forming the compound electrode of ZrB2.