KR101115225B1 - Feedstock composition and method of using same for powder metallurgy forming of reactive metals - Google Patents

Abstract

Methods of forming metal parts using raw material compositions and powder metallurgy techniques include mixing a metal or metal compound with a new aromatic binder system. Compositions of the new raw materials include aromatic binder systems and metal powders. Aromatic binder systems include aromatics and may further include lubricants, surfactants, and polymers as additives. Metal powders include metals, metal compounds, and metal alloys, especially for highly reactive metals. The method of forming a metal part includes feeding and mixing the metal powder and the aromatic binder system to produce new raw materials. The method further includes processing new raw materials into metal parts using powder metallurgy molding techniques such as metal injection molding. Metal parts molded through the present invention each have an increase in oxygen and carbon content of 0.2 wt% or less relative to the metal powder used to make the part.

Description

FEEDSTOCK COMPOSITION AND METHOD OF USING SAME FOR POWDER METALLURGY FORMING OF REACTIVE METALS}

FIELD OF THE INVENTION The present invention generally relates to metal forming techniques, and more particularly to the field of powder metallurgy forming techniques for reactive metals and components made therefrom.

Powder metallurgy involves the use of metal powders to form highly integrity, frequently very dense metal parts. This includes a wide variety of metal fabrication techniques for the economical production of complex net-like shaped parts. Examples of powder metallurgy manufacturing techniques include extrusion, injection molding, compression molding, powder rolling, blow molding, laser molding, isostatic pressing, and spray molding. Powder metallurgy manufacturing techniques facilitate the creation of graded structures, injecting porous preforms, preparing dispersion of second phase particles in a parent matrix, and creating non-equilibrium phases and structures. It provides some desirable features, including the ability to do so. While many materials can be molded using powder metallurgy techniques, highly reactive metals are not suitable for current processing practices. Processing reactive metals in accordance with powder metallurgy techniques known in the art leads to metal parts containing unacceptably high impurity concentrations. The presence of these impurities, in particular carbon, oxygen, and nitrogen, greatly lowers the mechanical properties of the resulting components. Alternative molding methods exist, such as machining and casting, but in many instances, this alternative produces parts that are expensive or have unacceptable properties. Thus, alternative molding methods have little utility outside of certain markets.

Current titanium metal injection molding (MIM) practices provide a good example of the limitations of powder metallurgy. Titanium exhibits a surprising combination of properties; It is very lightweight, exceptionally corrosion resistant, very high in strength and hardness, and resistant to creep and fatigue. Most powder metallurgy techniques, including MIM, include mixing metal powder with a primary-polymeric or -aqueous binder, shaping the shape of the metal part, and heating to remove the binder. And sintering at high temperatures. However, titanium readily reacts with oxygen, carbon, and nitrogen at elevated temperatures, ie, during combustion and sintering of the binder, and loses many of its desirable properties. As a result, titanium is typically unsuitable for current MIM processing in applications requiring the mechanical properties of uncontaminated metals.

The development of binder systems suitable for reactive metals has emerged as a key technical barrier to making powder metallurgy technology valuable and widely applicable across a wide range of materials and markets. Thus, there is a need for both binder systems and methods for forming metal parts for powder metallurgy of highly reactive metals and metal alloys.

In view of the foregoing and other problems, the present invention has studied the limitations and disadvantages of powder metallurgy techniques for highly reactive metals. The present invention exists in a new raw material composition for powder metallurgy molding technology and a method for forming metal parts. Compositions of the new raw materials include aromatic binder systems and metal powders.

The method of forming a metal part includes mixing the metal powder and the aromatic binder system to supply the metal powder and the aromatic binder system and generate new raw materials. The method further includes processing the new raw material into metal parts using powder metallurgy molding technology.

It is an object of the present invention to provide a raw material for the powder metallurgy forming technology which leads to metal parts with little or no increase in impurities compared to the metal powder starting material.

Another object of the present invention is to extend the applicability of the powder metallurgy forming technology to more metals, especially metals with high reactivity.

It is another object to provide a method for forming a metal part that has little or no increase in impurities compared to the metal powder starting material.

It is still another object of the present invention to provide a metal-injection-molded Ti part having an increased carbon and oxygen content of less than 0.2% each for the Ti powder to be processed.

1 is a schematic view of one embodiment of a forming method.

2 is a plot of the torque applied to the mixing blade as a function of time.

3 is a plot of temperature at sintering as a function of time.

The present invention is directed to raw material compositions for powder metallurgy techniques and methods of molding metal parts. Metal parts have a very high purity and, when composed of reactive metals, do not need to burn in an oxidizing environment because the raw material uses a binder system that is easily removed and leaves little carbon and / or nitrogen in the part. . The binder provides relatively high green-part and brown-part strengths, rapid sublimation under moderate vacuum, and / or elevated temperatures, thermoplastic and / or thermosetting polymers, lubricants, and / Or simultaneously serve as a solvent for additional binders such as surfactants.

The present invention includes a raw material comprising an aromatic binder system and a metal powder. Aromatic binder systems include at least one aromatic and can optionally include polymers, lubricants, and / or surfactants. As used herein, metal powder refers to elemental metals, as well as their compounds and alloys, in a finely divided solid state. In addition, the expression aromatic refers to a cyclic organic compound system that satisfies the criterion for aromaticity of Whikel. The present invention is expected to be used in powder metallurgy molding technology after forming a raw material by mixing an aromatic binder system and a metal powder.

These days, commonly used binders include water that oxidizes the metal upon heating, or organic materials that are difficult to remove, such as waxes and oils. In contrast, the present invention uses aromatics as the main binder component of the raw materials. Aromatics may be monocyclic or polycyclic and may include benzene, naphthalene, anthracene, pyrene, phenanthrenequinone and combinations thereof; The list of suitable aromatic compounds is not limited to these materials. Aromatics may comprise less than about 40% by volume of the raw material, in one embodiment, between about 29% and 37%. Preferably, the raw material contains only as much aromatic as necessary to maintain the integrity of the green and brown parts.

Although the present invention is particularly advantageous in forming reactive metal parts, those skilled in the art will appreciate that it is applicable to almost all metal parts. In one embodiment, the metal powder is an elemental metal selected from a group of refractory metals, metals commonly used for gettering, alkaline earth metals, and Group IV metals, as well as alloys and compounds thereof. It includes. Examples of refractory metals include, but are not limited to, Mo, W, Ta, Rh, and Nb. The getter material readily collects free gases by adsorption, absorption, and / or occlusion, and often contains Al, Mg, Th, Ti, U, Ba, Ta, Nb, Zr, And P, but some others also exist. Eventually, Group 4 metals include Ti, Zr, and Hf. Examples of the metal compound include metal hydrides such as TiH ₂ and intermetallics such as TiAl and TiAl ₃ . Specific examples of alloys include Ti-6Al, 4V, among others. TiH ₂ powders are believed to promote higher densities at relatively lower sintering temperatures. It is also believed to contain fewer impurities because hydrogen reacts with impurities to form volatile organics that can be easily removed by heat. In another embodiment, the metal powder comprises at least about 45% by volume of the raw material, and in another, it includes between about 54.6% and 70.0%.

In one embodiment, the aromatic binder system comprises up to approximately 10% by volume of the polymer. The polymer may be a thermoplastic, a thermoset, or a combination thereof. Suitable thermoplastics enhance the strength of green and brown bodies and include, but are not limited to, ethylene vinyl acetate (EVA), polyethylene, and butadiene-based polymers. Among other things, thermosets such as unsaturated polyesters, epoxies, and polymethylmethacrylates ultimately help to retain parts from each other after removal of the aromatic binder. Thermoplastics comprise between approximately 2.1% and 5.3% by volume of the raw material. The thermoset may be approximately 2.3% by volume of the raw material. Preferably, the polymer comprises a mixture of thermosets and thermoplastics, wherein the thermoplastics comprise 2.1% -5.3% of the raw material volume and the thermosets comprise 2.3% of the raw material volume.

In another embodiment, the aromatic binder system further comprises a surfactant. Surfactants reduce the case of raw material agglomeration and allow for higher metal powder loadings. Blisters Nick ^N-100? Hunt is meonsa (Huntsman Corporation) million (four ports chess, Texas (Port Neches, Texas)) not a non-ionic surfactant was obtained which was effective from those skilled in the art can determine the appropriate alternative. The surfactant may comprise up to about 3% by volume of the raw material, preferably up to about 2.3% of the raw material volume.

In another variation of the invention, the aromatic binder system further comprises a lubricant. Examples of lubricants include, among others, solid waxes including microcrystalline waxes and organic fatty acids. Organic fatty acids include stearic acid as well as metallic salts and branched or substituted versions thereof. Examples of solid waxes include paraffin wax and carnuba wax. Adding lubricant to the raw material composition improves homogeneity in the powder compact and flow inside the mold and facilitates the release of the part from the mold. The lubricant may comprise up to approximately 3% of the raw material volume and preferably comprises approximately 1.5%.

In another embodiment, the metal powder may further comprise an alloy powder. Exemplary alloy powders include sintering aids. Sintering aids such as silver can reduce the temperature required for effective sintering of the brown state to the final part. The use of alloy powders is also envisaged as the only way to form metal matrix composite material parts and metal alloys that cannot be obtained through conventional metal forming processes. Conventional processing, such as melt alloying, can frequently lead to heterogeneous products due to segregation of component metals based on different melting points. Mixing metal elements as powders of raw materials, ie metal powders and alloy powders, provides a solid state approach to preparing alloys from metal alloy and metal matrix composite materials and potentially minimizing heterogeneity in these parts. Examples of metal matrix composite materials include Ti-TiB ₂ composites.

Table 1 provides a summary of one embodiment of new raw material compositions. In addition, this shows an example of a Ti-based raw material composition successfully molded into a metal part.

Table 1: Summary of one example of new raw material compositions. Sample compositions of Ti-based raw materials are also summarized.

Raw material composition Acceptable composition
(Volume% of raw materials) Sample Ti-based Raw Material
(Volume% of raw materials) Metal powder
(Eg, powder of reactive metal) At least 45 62.1
(TiH ₂ Powder) Binder (can also act as a solvent)
(For example, aromatic compounds) 15-40 29.3
(naphthalene) Polymer
(Eg, thermoplastics and thermosets) 0-10 2.1 / 2.3
(EVA / epoxy) Surfactants
(For example, Suphonic N-100 ^？ ) 0-3 2.3
(Nick naught yen ^-100?) slush
(E.g., organic acids and solid waxes) 0-3 1.5
(Stearic acid) Sintering aid
(For example, silver) 0-1 0.4
(silver)

Another aspect of the invention is a method of molding a metal part from the raw materials described previously. Referring to FIG. 1, an embodiment of the present invention may include forming a raw material by mixing the metal powder 101 and the aromatic 102; And then processing the raw material into metal parts using powder metallurgy techniques. Although FIG. 1 illustrates a metal injection molding process, the present invention is not limited to just one powder metallurgy technique. Additional techniques include, among others, extrusion molding, compression molding, powder rolling, blow molding, and isostatic pressing; All of these are expected in the present invention. The aromatic binder system of the raw materials used in the molding method may further include additives 103, such as polymers, surfactants, lubricants, and sintering aids, in various combinations and concentrations corresponding to the embodiments described above. The raw material may also include an alloy powder 104 that reaches the metal alloy part after processing the raw material.

Mixing of the raw material components may occur at a particular temperature using a high-shear mixer 105 while measuring the torque applied to the impeller 106. The mixer should be operated at a rotational speed sufficient to disperse the elements constituting the raw material. In one embodiment, the high shear mixer operates at 50 RPM. Referring to the plot of time versus measured torque in FIG. 2, after the amount of torque required to rotate the impeller is reduced to remain constant 21 over time, the raw material is considered well mixed. Typical mixing times for raw materials comprising naphthalene and Ti based powders are approximately 10 minutes.

In order to minimize premature sublimation and prevent premature solidification of the raw materials during mixing, the temperature should be just above the melting temperature of the binder system. In a preferred embodiment in which the aromatic 102 comprises naphthalene and the metal powder 101 is a Ti-based powder, suitable mixing temperatures include approximately 85 ° C. Those skilled in the art will appreciate that the composition of the raw materials and the presence of additives such as surfactants, lubricants, and polymers can reach the melting point of the aromatic binder system. In this example, the actual melting temperature of the binder system can be easily determined empirically by one skilled in the art, for example by constructing a cooling or heating curve.

The molding method may further comprise pelletizing and solidifying the raw material. In one embodiment, these steps include reducing the temperature of the mixer 105 to a value below the freezing temperature of the aromatic binder system while continuing to operate the mixer 105. The reduced temperature causes the mixer blade 106 to solidify the binder system at the point where the raw material is atomized into pellets, granules, or powder. Suitable temperatures for raw materials comprising naphthalene and Ti based powders are approximately 78 ° C.

Mixing and pelletizing may occur differently using an extruder and pelletizer 109. Prior to pelletizing, a large batch mixer 105 premixes the metal powder and the aromatic binder system. The premixed powder is then passed through a single or double screw extruder 107 to melt the aromatic binder system and evenly disperse the metal powder in a heated extruder barrel to a homogeneous raw material. The extruder extrudes a 1/8 to 3/16 inch diameter rod through an extrusion die to solidify upon cooling. The cooled rod 108 is fed into the pelletizer 109 to cut the rod into pellets 1/8 to 1/4 inch long.

In another embodiment of the method, processing of the raw material comprises: molding the green state 112 by injecting the raw material into the mold 111; Debinding the green state to form a brown state; Sintering the brown state to form a very dense metal part; And cooling the resulting metal part. Metal parts formed in accordance with the present invention have an increase in carbon and oxygen content of approximately 0.2 wt% or less relative to the metal powder used to mold the parts. Table 2 shows the results of experiments in which the carbon and oxygen contents of the metal parts according to the examples of the present invention are compared with the carbon and oxygen contents of the Ti-6Al, 4V powder used in the raw materials to form the same parts. Ti-6Al, 4V powder was a high purity alloy containing 4 wt% vanadium and 6 wt% aluminum obtained from Titanium Systems, Inc. (Phoenix, Arizona). Prior to processing, the powder contained 0.08 wt% carbon and 1.46 wt% oxygen. After the powder was mixed with the binder to form a raw material, the carbon and oxygen were increased by approximately 0.2 and 0.07 wt%, respectively.

Table 2: Summary of the carbon and oxygen content present in Ti 6Al, 4V metal powder prior to MIM processing and the resulting Ti metal parts after MIM processing in accordance with an embodiment of the present invention.

The metal part further comprises an increase in nitrogen content of about 0.2 wt% or less relative to the metal powder used to mold the part.

In one embodiment of the method, injection of the raw material into the mold 111 takes place while the raw material is maintained at the temperature higher than its melting point in the injector 113. However, the temperature of the mold 111 must be kept below the melting point of the raw material in order to solidify the injected part. For example, preferred temperatures for raw materials comprising naphthalene and Ti based powders are at least about 85 ° C. For the same raw material, the mold 111 should be kept below about 85 ° C, preferably about 78 ° C. Injection also occurs using an injector 113 having a barrel 114 maintained at a temperature in the range between approximately 120 ° C and 140 ° C. The pressure in the injector 113, ie the injection pressure, can be between 3000 and 20,000 psi and can be generated in a variety of ways such as pneumatic, hydraulic and mechanical.

After the raw material solidifies in the mold 111 to form the green state 112, the degreasing step 115 attempts to remove as much aromatic binder as possible. In one embodiment, the green part 112 is heated to a temperature just below the melting point of the raw material under vacuum. Although a vacuum pressure of approximately 35 Torr is acceptable, lower pressures are also preferred to assist in sublimation of the binder. The duration of the degreasing step may comprise approximately 8 to 48 hours. Instead, the green-state-degreasing step may include drying and washing with a denser fluid, eg, a denser propane. Degreasing with higher density propane involves: i) heating and pressurizing the chamber containing the green part to transfer propane to the higher density phase; Ii) exposing the binder group to a denser fluid; V) decompression of the chamber leading to complete evaporation of propane.

The brown state is the result of degreasing the green state and requires a sintering step 116 to form a coherent mass. Referring to the plot of time versus sintering temperature in FIG. 3, the sintering step involves raising the temperature to the first set point 31 and maintaining that temperature for a certain period of time. After the first heating stage, the rise in temperature continues to the second set point 32 and heating continues for another time. The first set point 31 is approximately 300 ° C to 600 ° C. The first heating period 31 is approximately 60 to 180 minutes. The second heating period 32 may range from 1000 ° C. to 1350 ° C. and may last between one hour and six hours. In a preferred embodiment, the second heating stage has a duration of approximately four hours at 1100 ° C. In both cases the rate of increase may range from 1 to 20 ° C. per minute. Cooling 33 of the part involves using a furnace chiller to complete the sintering step and reduce the temperature as quickly as possible.

As in the degreasing step 115, the sintering step 116 involves heating the brown state without impurities, especially oxygen, carbon, and nitrogen, thereby maintaining the required physical properties of the pure metal or alloy. Thus, the sintering step 116 includes heating the metal part in a hydrogen cover gas. Instead, heating can occur at about 1 × 10 ⁻⁵ Torr or below, under high vacuum. Sintering may include a series of combinations of heating in various environments including hydrogen cover gas and under high vacuum.

The invention also includes metal injection molded parts processed according to the molding method embodiments described above. The part in this case has an increase in carbon and hydrogen content of approximately 0.2% or less relative to the metal powder used to process the part. The same part may further comprise an increase in nitrogen content of about 0.2% or less relative to the metal powder used to process the part.

Numerous embodiments of the invention have been shown and described, and it will be apparent to those skilled in the art that many more modifications and improvements can be made without departing from the invention in its broader aspects. Accordingly, the appended claims are intended to cover all such modifications and improvements while matching the scope and spirit of the invention.

The present invention provides a raw material for powder metallurgy forming technology leading to metal parts that have little or no increase in impurities compared to metal powder starting materials, and the applicability of powder metallurgy technology to more metals, especially high reactivity To provide a method of forming a metal part that extends to the metal having an excitation and has little or no increase in impurities relative to the metal powder starting material, an increased carbon of up to 0.2% each for the Ti powder to which the part is processed, and The invention relates to providing a metal-injection-molded Ti part having an oxygen content.

Claims (95)

As a composition for forming parts by powder metallurgy molding technology, A metal powder, a polymer and an aromatic binder, the metal powder comprises an elemental metal of Al, Mg, Th, Ti, U, Ba, Ta, Nb, Zr and P, and the polymer is ethylene vinyl acetate (EVA) , Polyethylene, or a combination thereof, wherein the aromatic binder is benzene, naphthalene, anthracene, pyrene, phenanthrenequinone, or a combination thereof, and the aromatic binder and the metal powder are mixed and powdered. A raw material for metallurgical forming technology is formed, the raw material comprising from 29% to 37% by volume of the aromatic binder, at least 45% by volume of the metal powder and up to 10% by volume of polymer. The composition of claim 1 further comprising a surfactant. The composition of claim 2, wherein the surfactant comprises a nonionic surfactant. The composition of claim 2, wherein the surfactant comprises less than 3% of the raw material volume. The composition of claim 2, wherein the surfactant comprises 2.3% of the raw material volume. The composition of claim 1 further comprising a lubricant. The composition of claim 6, wherein the lubricant is selected from the group consisting of organic fatty acids, metallic salts, solid waxes, and combinations thereof. The composition of claim 7 wherein the organic fatty acid is selected from the group comprising stearic acid, branched versions of stearic acid, substituted versions of stearic acid, and combinations thereof. The composition of claim 7 wherein the metal salt is selected from the group consisting of sodium stearate, calcium stearate, and combinations thereof. The composition of claim 7, wherein the solid wax is selected from the group consisting of microcrystalline wax, paraffin wax, carnuba wax, and combinations thereof. The composition of claim 6, wherein the lubricant comprises up to 3% of the raw material volume. The composition of claim 6, wherein the lubricant comprises 1.5% of the raw material volume. The composition of claim 1, wherein the metal powder comprises an alloy powder. The composition of claim 13, wherein the alloy powder comprises a sintering aid. The composition of claim 14, wherein the sintering aid comprises silver. The method according to any one of claims 1 to 15, wherein the powder metallurgy molding technology, injection molding, extrusion molding, compression molding, powder rolling, blow molding, laser forming, isostatic pressing, spray molding And combinations thereof. The composition of claim 1, wherein the metal powder comprises 54.6% to 70% by volume of the raw material. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

Images