TW201507792A - Slip and pressure casting of refractory metal bodies - Google Patents

Abstract

In various embodiments, powders with engineered particle-size distributions are slip or pressure casted to produce homogeneous parts without the need for additives such as flocculating or deflocculating agents.

Description

Mud casting and pressure casting of refractory metal body [Related application]

The present application claims the benefit of priority to U.S. Provisional Patent Application Serial No. 61/830,892, filed on Jun. 4, 2013, the entire disclosure of which is hereby incorporated by reference.

In various embodiments, the present invention relates to mud casting with or without applied pressure, particularly with respect to mud casting or pressure casting of metal bodies.

Powder metallurgy technology has been applied to the manufacture of various types of finished metal parts. For example, the flexible bag can be filled with metal powder and placed in a mold that approximates the final pressed shape and size of the part. The bag and the mold were sealed, and the pressed "green body" of the metal powder was formed by a cold equalizing method. The green body can then be sintered to increase its density and then machined to its final desired size. While these powder metallurgy techniques are suitable for a particular application, the utility of such techniques is limited if the final part has a more complex shape. The more complex the shape, the more excess powder must be placed in the bag and mold to prevent cracking during the pressing process. Thus, the ratio of the weight of the sintered part to the new weight of the part in its final machined form can be greater than 4: 1, resulting in a large amount of machined material and labor costs. Moreover, parts made by such powder metallurgy techniques are difficult to achieve a final sintered density exceeding 94% of their theoretical density. These parts may also have unfavorable large grain sizes (eg, greater than 40 microns).

Another powder metallurgy technique for producing complex shapes is mud casting, in which "mud" (that is, a suspension of fine metal powder in water) and a dispersant (used to stabilize the powder from the influence of colloidal forces) ), one or more solvents (used to control mud viscosity and help casting) and adhesives used to strengthen the cast shape are placed in the mold, the liquid is removed, and the resulting green body is sintered to densify and increase its strength . Disadvantageously, mud casting typically requires the use of de-flocculating or suspending aids to prevent powder settling and cohesion and maintain the desired mud viscosity. Such deflocculating agents include, for example, alcohols, other organic liquids or alginate (e.g., ammonium and sodium salts of alginic acid). The use of such additives increases the cost, complexity, environmental impact and material handling requirements of the mud casting process.

In view of the foregoing, there is a need for a powder metallurgy-based simplification technique for manufacturing complex metal parts that does not use foreign additives and enables high part density and smaller final grain size.

According to various embodiments of the present invention, metal parts (or "body") are produced using mud or pressure casting of metal powders, wherein the metal powders have a specific powder size distribution so that no added organic matter is required during the casting process. Or inorganic suspension aids. The metal powder is suspended in a liquid comprising or consisting essentially of water, such as deionized (DI) water, and poured into a mold for casting. As mentioned above, the liquid does not include any flocculation or deflocculating additives. Moreover, the preferred embodiment uses a powder consisting essentially of only one or more metals and free of solid or powdered agents such as binders or plasticizers. The mold is porous (and may comprise or consist essentially of, for example, gypsum) and the liquid in which the powder is suspended via capillary action is introduced into the mold. The resulting green body is sintered to increase its density and subjected to final machining (required and/or necessary) to shape the final part. The metal powder may comprise or consist essentially of, for example, one or more refractory metals. For example, the metal powder may comprise or consist essentially of tungsten (W), tantalum (Ta), niobium (Nb), zirconium (Zr), molybdenum (Mo), and/or titanium (Ti).

Generally, the mud does not exhibit an expansion flow or a rocking viscous flow, such as when the mud is poured into a mold; in fact, the viscosity of the slurry preferably varies slightly with the shear rate applied to the mud (ie, with shear rate) And change the constant). Moreover, in a preferred embodiment of the invention, the mixing or settling of the metal powder in the slurry is not facilitated by agitation (e.g., agitation, shaking, rotation, and/or vibration) of the slurry and/or mold; in fact, within the slurry The designed particle size distribution of the powder particles prevents sedimentation of the powder in the mud prior to casting and during casting (i.e., in the preferred embodiment, the slurry is colloidally stable rather than, for example, colloidally unstable or even Stable) also contributes to the low resistance castability of the mud itself in the absence of agitation. Similarly, in a preferred embodiment of the invention, no voltage or current is applied to the mold or slurry during the casting process to affect the settling behavior. In addition, green and molded parts (before and after sintering) are generally not functionally or mechanically graded, ie the composition, microstructure, mechanical properties, porosity, residual stress, grain size, The particle size and the like exhibit a small gradient (if any). In fact, the mechanical and functional properties of the blanks and parts produced in accordance with embodiments of the present invention (e.g., the grain size of unsintered or sintered parts, and/or the particle size of the slurry and/or green body) are various ( Or even all) is substantially uniform in direction. Moreover, embodiments of the present invention provide muds that are substantially free of acidic or alkaline pH modifiers; such modifiers may have adverse effects on the metal powder particles used in the preferred embodiments (eg, corrosion and/or Chemical reactions), and are generally not necessary for designing the colloidal stability of the muds described herein.

As used herein, the terms "body", "part" and "object" refer to a massive three-dimensional object (as opposed to a powder crystal only) that has the same simple shape as a plate, but also has more complexities. Shapes, such as domes and other volumes having protrusions and/or depressions. For complex shapes, the final shape (regardless of any process-related shrinkage) is typically formed by casting (as opposed to bulk compression) and sintering and then by machining.

In one aspect, embodiments of the present invention provide a method of making a shaped part. The powder is suspended in a liquid comprising or consisting essentially of water, thereby forming a slurry. The powder There is a particle size distribution d10 of 0.15 micrometers to 0.5 micrometers, a d50 of 0.6 micrometers to 1 micrometer, and a d90 of 2.4 micrometers to 3 micrometers, wherein the particle size distribution dX of Y indicates that X% of the particles have a size smaller than Y. The slurry is introduced into a mold having a shape substantially the same as the desired shape of the formed part. The particle size distribution of the powder (i) substantially prevents the powder from separating from the liquid by cohesion and/or settling, and (ii) maintaining a substantially uniform distribution of the powder particles within the liquid. Thereafter, at least a portion of the liquid is discharged from the slurry to produce a green body comprising or consisting essentially of powder, and the green body is sintered to produce a shaped part.

Embodiments of the invention may include one or more of the following in any of a variety of different combinations. The particle size distribution of the powder can be d10 of about 0.3 microns, d50 of about 0.8 microns, and d90 of about 2.7 microns. After sintering, the shaped part can have a density of from about 95% to about 99% of the theoretical density, or even 97% to 99% of the theoretical density. After sintering, the shaped part can have a grain size (e.g., average grain size) of from about 10 microns to about 20 microns. The powder may comprise or consist essentially of one or more metals, such as one or more refractory metals. The powder may comprise or consist essentially of tungsten, tantalum, niobium, zirconium, molybdenum and/or titanium. The green body can be sintered in hydrogen. The green body can be sintered at a temperature of from about 3000 °F to about 5000 °F.

One portion of the initial powder may be deagglomerated by blending an initial powder having a particle size distribution d10 of about 0.42 microns, a d50 of about 1.8 microns, and a d90 of about 3.8 microns, and blending the deagglomerated portion of the initial powder. A second portion of the initial powder is used to produce the powder. A portion of the initial powder can be deagglomerated by ball milling. The density of the green body can range from about 30% to about 40% of the theoretical density. The liquid can consist essentially of deionized water. The mold can be porous. Essentially all of the liquid from the mud can flow into the mold to form a green body. The slurry or mold is not agitated (e.g., oscillated, agitated, vibrated, and/or rotated) after the slurry is introduced into the mold and before the green body is produced. Super atmospheric pressure (which may be hydrostatic pressure) may be applied to the mold and/or mud during and/or after the slurry is introduced into the mold. The powder may be substantially evenly distributed within the green body (i.e., the particles or grain sizes formed within the green body may have no appreciable gradients or intervals). The mold may contain substantially only mud. Formed parts can be mechanically added The required size and / or shape.

In another aspect, embodiments of the present invention provide a method of producing a shaped part. The powder is suspended in water in the presence of a flocculation-free or deflocculating additive, thereby forming a slurry. Introducing the slurry into a mold that is substantially complementary in shape (i.e., the space into which the slurry is introduced is closed to substantially equal) the desired shape of the shaped part without the need to separate the powder from the water during the process (and/or sedimentation in water) Or deposit powder). Thereafter, at least a portion of the liquid is allowed to drain from the slurry to produce a green body comprising or consisting essentially of powder, and the green body is sintered to produce a shaped part.

Embodiments of the invention may include one or more of the following in any of a variety of different combinations. The particle size distribution (i) of the powder substantially prevents the powder from being separated from the water by at least one of cohesion or sedimentation, and (ii) maintains a substantially uniform distribution of the powder particles within the liquid. The particle size distribution may be d10 of 0.15 micrometer to 0.5 micrometer, d50 of 0.6 micrometer to 1 micrometer, and d90 of 2.4 micrometer to 3 micrometer, and the particle size distribution dX of Y indicates that X% of the particles have a size smaller than Y. The powder may comprise or consist essentially of one or more metals such as refractory metals such as tungsten. Superatmospheric pressure can be applied to the mold and/or mud during and/or after the slurry is introduced into the mold. The mold may contain substantially only mud.

These and other objects, together with the advantages and features of the invention disclosed herein, will become more apparent. In addition, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and may be in various combinations and arrangements. As used herein, the terms "about" and "substantially" mean ±10%, and in some embodiments, ±5%. The term "consisting essentially of" means excluding other materials that contribute to the function, unless otherwise defined herein. However, such other materials may be present in minor amounts, either collectively or individually. As used herein, "consisting essentially of at least one metal" refers to a metal or a mixture of two or more metals, rather than a compound of a metal with a non-metallic element or a chemical such as oxygen or nitrogen (eg, Metal nitrides or metal oxides; these non-metallic elements or chemicals may be present in trace amounts, either collectively or individually (eg in the form of impurities).

100‧‧‧ mud

110‧‧‧Mold

200‧‧‧green

300‧‧‧Sintered parts

500‧‧‧Pressure casting equipment

510‧‧‧pressure jacket

510-1‧‧‧pressure jacket section

510-2‧‧‧pressure jacket section

520‧‧‧ mud feed line

530‧‧‧ pipeline

540‧‧‧ pipeline

In the drawings, similar reference characters generally refer to the same parts in different views. The drawings are also not necessarily to scale, and are in fact In the following description, various embodiments of the invention are described with reference to the following drawings in which: FIG. 1 is a schematic cross-sectional view of a slurry introduced into a mold according to various embodiments of the present invention; FIG. 2 is a schematic view of a mold according to various embodiments of the present invention. FIG. 3 is a schematic cross-sectional view of an article after casting according to various embodiments of the present invention; and FIG. 4 is a micrograph depicting a microstructure of a cast article according to various embodiments of the present invention; 5A-5C are schematic cross-sectional views of the manufacture of articles via pressure casting in accordance with various embodiments of the present invention.

In order to achieve mud and pressure casting without the addition of a suspending aid, the metal powder used in accordance with an embodiment of the present invention has a particle size distribution (PSD) that maintains a favorable ratio between the powder deposition rate and the mud viscosity. In various embodiments, the metal powder has a PSD d10 (eg, 0.3 microns) from 0.15 microns to 0.5 microns, a PSD d50 (eg, 0.8 microns) from 0.6 microns to 1 micron, and a PSD d90 (eg, 2.7 microns) from 2.4 microns to 3 microns. . (As is known to those skilled in the art, a PSD d10 value of X indicates that 10% of the powder particles have a size less than X.) Powders having the desired PSD can be prepared, for example, by de-agglomeration and blending commercially available powders. . In various embodiments, the viscosity of the slurry is from 0.7 to 1.3 Pa-s, and preferably from 0.9 to 1.1 Pa-s. In contrast, the use of powders with conventional PSD and no suspending aid typically produces high deposition rates and low viscosities (eg, below 0.5 Pa-s) that are not suitable for mud casting.

For example, in one embodiment, a tungsten powder having a smaller Fischer sub-sieve sizer (FSSS) particle size is identified. (As known to those skilled in the art, FSSS The particle diameter represents an average particle diameter determined according to gas permeability, wherein it is assumed that the powder particles are completely spherical. In one embodiment, the starting powder has a FSSS particle size of from 0.5 microns to 1 micron (eg, 0.7 microns). For example, the initial powder can be HC70S tungsten powder having a FSSS particle size of 0.7 microns, which is commercially available from H. C. Starck GmbH (Goslar, Germany). The powder may have the following PSD: d10 of 0.42 microns, d50 of 1.8 microns, and d90 of 3.8 microns. The initial powder can be reduced by, for example, ball milling using a tungsten carbide grinding ball to reduce cohesion of the powder, or by ultrasonic processing (ie, applying ultrasonic energy) and for a time sufficient to reduce or substantially eliminate powder cohesion. All or part of it is stuck.

In one embodiment, the powder blend can then be produced by blending the unmilled portion of the initial powder with the portion that has been deagglomerated to form a powder having the desired particle size distribution. Exemplary powder blends can include, for example, from 60% to 80% (e.g., 70%) by weight of the unground powder and from 20% to 40% by weight (e.g., 30%) by weight of the de-agglomerated powder. In one embodiment using HC70S tungsten powder as the initial powder, the resulting powder blend can have the following PSD: d10 of 0.3 microns, d50 of 0.8 microns, and d90 of 2.7 microns.

After producing a powder having a designed particle size distribution, the powder is suspended in a liquid comprising or consisting essentially of water (e.g., DI water). The resulting slurry preferably contains from 30% to 40% by volume (e.g., about 35%) by volume of solid particles. As shown in Figure 1, the slurry 100 is poured into a porous mold 110 (e.g., a mold comprising or consisting essentially of gypsum, resin, one or more polymeric materials (e.g., polystyrene) and/or plaster of Paris), the porous mold 110 has the shape and dimensions required for the pre-sintered part (i.e., after sintering, the part is substantially shaped and dimensioned to the final desired shape and size). In various embodiments of the invention, as described in more detail below, when the mold 110 is filled with the mud 100, external pressure is applied. For example, the slurry 100 can be pumped into the mold 110 at a pressure above atmospheric pressure. The density of the foundry slurry 100 can be, for example, 30% to 40% (e.g., about 34%) as determined by gravimetric analysis. Next, as shown in FIG. 2, the liquid of the suspended powder is absorbed into the mold 110, thereby producing the green body 200 formed by the mold 110. As shown in Figure 3, the green body 200 is removed from the mold 110 and substantially Sintering is performed to densify it, thereby producing a sintered part 300. High pressure air and/or vacuum may be applied (either together or sequentially) via lines 530, 540 to aid in the removal of green body 200 from mold 110. In an exemplary embodiment, the green body 200 is sintered in a hydrogen atmosphere. Sintering can be carried out at a temperature of from about 3000 °F to about 5000 °F (eg, about 4000 °F) for a period of from about 2 hours to about 7 hours (eg, about 5 hours).

After sintering, the grain size of the part 300 can be less than about 30 microns, such as from about 10 microns to about 20 microns. The density of the part 300 can range from about 95% to about 99% (e.g., about 97%) of its theoretical density. The part may be used in the form of casting and sintering, or may be machined into a desired shape, such as a braid, a heat shield, a seamless tubular or other hollow or conical shape. 4 is an optical micrograph of the microstructure of a part 300 made of W powder, in accordance with an embodiment of the present invention. As shown in FIG. 4, the grain size of the part 300 is in the range of from about 10 microns to about 20 microns. In FIG. 4, the grain of the part 300 has been exposed by etching using a Murakami's etchant, which is known to those skilled in the art as potassium ferricyanide (K ₃ Fe(CN) ₆ ), a mixture of potassium hydroxide (KOH) and water.

Embodiments of the invention use pressure casting with a powder of a designed PSD to form a metal part. FIG. 5A depicts a pressure casting apparatus 500 that can be used in embodiments of the present invention. As shown, apparatus 500 provides a mold 110 that is partially or substantially embedded within pressure jacket 510, which may include or consist essentially of one or more materials of mechanical strength and hardness, such The material resists the pressure applied to the mud while preventing the mold 110 from deforming or breaking. As shown, the pressure jacket 510 (and mold 110) can be comprised of a plurality of different parts that can be separated (see Figure 5C) to aid in the removal of the cast parts from the mold 110. The pressure jacket 510 of Figures 5A-5C is depicted as being comprised of pressure jacket portions 510-1, 510-2. Mud 100 is introduced into mold 110 via mud feed line 520, and mud 100 can be drawn through the mud feed line 520 under applied pressure. Apparatus 500 also includes pressure lines 530, 540 for introducing, for example, high pressure air (or other gases, such as inert gases), Pressure is applied to the mud 100 during the casting process. For example, air having a first superatmospheric pressure (i.e., having a pressure above atmospheric pressure) can be introduced into pressure line 530 to apply pressure to mold 110 and mud 100, and can be applied via pressure line 540 to have a lower than first The second pressure of super atmospheric pressure or the application of vacuum. The applied pressure may be substantially hydrostatic pressure, and it may advantageously reduce the amount of time required for the casting process (due to, for example, increasing the outflow of water from the mud 100 during the casting process) and/or increasing the resulting The density of the billet (and / or improve other mechanical properties). According to various embodiments of the invention, a pressure of greater than about 10 bars, about 20 bars, or even greater than about 40 bars may be applied during the casting process.

FIG. 5B depicts the apparatus 500 after the mud 100 is introduced into the mold 110 via the mud feed line 520. After the introduction of the slurry 100, pressure is applied to the slurry 100 within the mold 110 (as described in detail above with respect to FIG. 5A) to produce a green body 200 formed by the mold 110. As shown in FIG. 5C, the pressure jacket 510 and/or the mold 110 can be separated into a plurality of sections to assist in the removal of the green body 200 from the mold 110. After the pressure casting, the green body 200 can be sintered to densify it, thereby producing the sintered part 300. In an exemplary embodiment, the green body 200 is sintered in a hydrogen atmosphere. Sintering can be carried out at a temperature of from about 3000 °F to about 5000 °F (eg, about 4000 °F) for a period of from about 2 hours to about 7 hours (eg, about 5 hours).

The terms and expressions used herein are used as an illustrative and non-limiting term and expression, and are not intended to exclude any feature or part of the features shown and described. Effect. In addition, it is apparent to those skilled in the art that other embodiments incorporating the concepts disclosed herein may be practiced without departing from the invention. Use in the case of spirit and scope. Therefore, the described embodiments are to be considered in all respects as illustrative and not limiting.

Claims (24)

A method of producing a shaped part, the method comprising: suspending a powder having a particle size distribution d10 of 0.15 micrometers to 0.5 micrometers, a d50 of 0.6 micrometers to 1 micrometer, and a d90 of 2.4 micrometers to 3 micrometers in a liquid consisting essentially of water Wherein, a slurry is formed whereby the particle size distribution dX of Y indicates that X% of the particles have a size smaller than Y; and the slurry is introduced into a mold having a shape substantially the same as a desired shape of the shaped part, the particle size distribution of the powder (i) substantially preventing the powder from being separated from the liquid by at least one of cohesion or sedimentation, and (ii) maintaining a substantially uniform distribution of the powder particles within the liquid; thereafter, allowing at least the liquid A portion is discharged from the slurry to produce a green body comprising the powder; and the green body is sintered to produce the shaped part. The method of claim 1, wherein the powder has a particle size distribution of d10 of about 0.3 microns, a d50 of about 0.8 microns, and a d90 of about 2.7 microns. The method of claim 1, wherein the shaped part has a density of from about 95% to about 99% of the theoretical density after sintering. The method of claim 1, wherein the shaped part has a grain size of from about 10 microns to about 20 microns after sintering. The method of claim 1, wherein the powder comprises one or more metals. The method of claim 1, wherein the powder comprises one or more refractory metals. The method of claim 1, wherein the powder comprises at least one of tungsten, ruthenium, osmium, zirconium, molybdenum or titanium. The method of claim 1, wherein the powder comprises tungsten. The method of claim 1, wherein the green body is sintered in hydrogen. The method of claim 1, wherein the green body is sintered at a temperature of from about 3000 °F to 5000 °F. The method of claim 1, further comprising producing the powder by a process comprising: providing an initial powder having a particle size distribution d10 of about 0.42 microns, a d50 of about 1.8 microns, and a d90 of about 3.8 microns; Part of the deagglomeration; and blending the deagglomerated portion of the initial powder with the second portion of the initial powder. The method of claim 11, wherein the portion of the initial powder is deagglomerated by ball milling. The method of claim 1, wherein the green body has a density of from about 30% to about 40% of the theoretical density. The method of claim 1, wherein the liquid consists essentially of deionized water. The method of claim 1 wherein (i) the mold is porous and (ii) substantially all of the liquid from the slurry flows into the mold to form the green body. The method of claim 1, wherein the slurry and the mold are not stirred after the slurry is introduced into the mold. The method of claim 1, further comprising applying superatmospheric pressure to at least one of the mold or the slurry during or after the slurry is introduced into the mold. The method of claim 1, wherein the powder is substantially evenly distributed within the green body. The method of claim 1 further comprising machining the shaped part to a desired size and/or shape. A method of producing a shaped part, the method comprising: suspending a powder in water in the presence of a flocculation-free or deflocculating additive, thereby forming a slurry; and substantially not separating the powder from the water during the process The mud The slurry is introduced into a mold having a shape substantially complementary to the desired shape of the shaped part; thereafter, at least a portion of the liquid is discharged from the slurry to produce a green body comprising the powder; and the green body is sintered to produce the shaped part. The method of claim 20, wherein the particle size distribution (i) substantially prevents the powder from being separated from the water by at least one of cohesion or sedimentation, and (ii) maintaining the powder particles in the liquid A substantially uniform distribution. The method of claim 21, wherein the particle size distribution is d10 of 0.15 micrometer to 0.5 micrometer, d50 of 0.6 micrometer to 1 micrometer, and d90 of 2.4 micrometer to 3 micrometer, and the particle size distribution dX of Y indicates that X% of the particles have a smaller diameter. The size of Y. The method of claim 20, wherein the powder comprises one or more metals. The method of claim 20, further comprising applying superatmospheric pressure to at least one of the mold or the slurry during or after the slurry is introduced into the mold.