JPH0436112B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a novel ceramic-metal composite material. The ceramic-metal composite of the present invention has a dense, polycrystalline microstructure and exhibits significantly greater strength and fracture toughness than conventional ceramics. BACKGROUND OF THE INVENTION AND SUMMARY OF THE INVENTION The method of forming ceramic metal composites of the present invention is based on the discovery of conditions that create a surprising oxidation reaction of ceramic materials. When suitable metals or alloys (as hereinafter described) are exposed to an oxidizing atmosphere at a specified temperature above their melting point, the liquid metal oxidizes from its outer surface and forms an otherwise impermeable oxide. It proceeds in the direction of the oxidizing atmosphere along channels that are formed in place of high-energy grain boundaries in the structure. New oxidation reaction products are continuously formed by the reaction of the liquid metal with the oxidizing vapor, thus growing a connected ceramic oxide structure along the low energy grain boundaries. In the resulting material, some or all of the parent metal or components of the parent metal are dispersed in a fine structure in a connected or separated state, and the extent of their presence differs depending on the reaction conditions. The high fracture toughness of the resulting ceramics is believed to be due to the uniformly dispersed metallic substance and the dense nature of the oxide-metal structure. The materials of the present invention can be grown at substantially uniform rates cross-sectionally to thicknesses unattainable by conventional methods of forming dense ceramic structures. The method for obtaining these materials also eliminates the increased cost associated with the production of uniform fine powder and compaction techniques that are characteristic of conventional ceramic manufacturing methods. In recent years, ceramics have come to be considered as structural materials that can replace metals. The reason for this is that compared to metals, they have superior properties such as corrosion resistance, hardness, elastic modulus, and fire resistance, and that conventional materials have improved the performance of many modern parts and systems in terms of these properties. There are limitations, etc. Examples of such promising replacement fields include engine parts, heat exchangers,
Examples include cutting tools, bearings and wear surfaces, pumps, and machinery. However, the point at which metals and ceramics can be interchanged as structural materials is whether it is cost-effective to develop ceramics with improved strength and fracture toughness that can be reliably used in a given environment, including tensile loads, vibration, and shock. The answer was no. Today, efforts to manufacture high strength, monolithic ceramics have focused on powder processing techniques, but while improvements in ceramic performance have been achieved, these techniques have been complex and generally not cost effective. The importance of these traditional powder processing techniques is twofold: (1) improved methods of manufacturing ultra-fine homogeneous powder materials using sol-gel, plasma, and laser techniques, and (2) sintering. Improved densification and compaction methods including compaction techniques, hot presses and hot isostatic presses. Such efforts aimed at creating dense, fine-grained, defect-free microstructures, and such methods have in fact improved the structural performance of ceramics. However, while improved ceramic structures have been obtained, these developments have dramatically increased the cost of ceramics as engineering materials. Another limitation in ceramic materials that is not only unresolved but has recently become even worse is dimensional diversity. Conventional methods directed at densification (i.e., removal of voids between powder particles) include ceramics in furnace liners,
Large integral structures such as pressure shells, boilers and superheater tubes cannot be applied. This is because as these dimensions increase, the pressure holding time and molding pressure increase dramatically. Similarly, the wall thickness of the pressure chamber (in hot isostatic presses) and the die size (in hot presses) also increase significantly. The present invention uses a mechanism that is simpler and less expensive than the conventional methods described above to achieve the objective of forming a dense, high strength, and high fracture toughness ceramic microstructure. With the present invention, it is possible to manufacture large-sized ceramics and/or ceramics with thick cross-sections, and it is expected that ceramics will be applied to areas that could not be predicted in the past. Traditionally, metal oxidation has been viewed as a conceptually attractive approach to the production of oxide ceramic bodies. As used herein, the term "oxidation reaction product" means any oxidation state of one or more metals, such that the metal donates or loses electrons to any other element or combination of elements. including cases where they covalently form a compound, and, for example, metals and oxygen, nitrogen, halogen, carbon, boron, sulfur,
Compounds with phosphorus, arsenic, selenium, terium and compounds or mixtures thereof, such as methane, ethane, propane, acetylene, propylene, and mixtures such as air, H ₂ /H ₂ O and CO/CO ₂ means. The term "oxidizing agent" used in this specification corresponds to the definition of "oxidation reaction product" above, and is defined as an oxidizing agent in a broad sense, i.e., a compound that performs a redox reaction on a metal, depriving the metal of electrons. means a compound. The basic method of producing the ceramic materials of the present invention begins with the discovery of the necessary and sufficient conditions that create the surprising oxidation behavior of the metal. To appreciate the significance of this discovery, it would be helpful to understand the general oxidation behavior of metals and the limited previous uses of metal oxidation. Traditionally, metals have been oxidized in one of four general ways: first, when exposed to an oxidizing atmosphere, a flake-like, crushed powder-like, or porous oxide is formed; It is something that is continuously exposed to. In this method, an oxide object cannot be obtained in the form of a metal oxide as it is, but oxide flakes, particles, etc. are formed. For example, iron is oxidized in this way. Second, some metals (eg, aluminum, magnesium, chromium, nickel, etc.) oxidize to form a relatively thin protective oxide film that protects the underlying metal from further oxidation. This mechanism does not provide a sufficiently thick oxide structure. Third, certain metals are known to form solid or liquid oxide films that are permeable to oxygen and therefore cannot protect the underlying metal. Oxygen-permeable membranes slow the rate of oxidation of the underlying metal, but do not completely protect it. This type of oxidation occurs, for example, with silicon, forming a glassy film of silicon dioxide that is permeable to oxygen when exposed to air at elevated temperatures. Typically, these methods cannot be performed at a rate fast enough to form ceramic oxides to useful thicknesses. Finally, other metals are vaporized and exposed to continuous oxidizing conditions to form oxides. Tungsten is an example of a metal that is oxidized in this manner. These conventional oxidation methods are not sufficient for forming oxide ceramic materials for the reasons mentioned above.
However, as a variation of the second method, a flux can be added to the metal surface to dissolve or destroy the oxides and cause them to transport oxygen or metal, forming a thicker oxide film than normal. nevertheless,
The formation of oxide structures is limited to thin sections of relatively limited strength. These techniques are used on metal powders to oxidize their surfaces in mixtures with other powders to obtain porous, low-strength ceramics, such as H.
No. 3,255,027 to Talsma and US Pat. No. 3,299,002 to WAHaer. Alternatively, a similar method can be used for thin-walled Al ₂ O ₃ refractory structures (DR
Sowards, US Pat. No. 3,473,987 and REOberlin, US Pat. No. 3,473,938) or thin-walled hollow refractory particles (LESeufert, US Pat. No. 3,298,842). However, a feature of these methods is that the thickness of the oxide formed as a reaction product is limited. This is because the protective film grows slowly. Increasing the flux concentration to promote the growth of thicker oxide films results in products with lower strength, lower refractory properties, and lower hardness. One method that can be used to make ceramics by oxidizing metals is a redox reaction.
It has long been known that certain metals reduce oxides of other metals to form new oxides and reduced products of the original oxides. The use of such redox reactions in the production of ceramic materials is, for example, LE
Seufert, US Pat. No. 3,437,468 and LE Wilson, US Pat. No. 3,973,977. The main drawback of the redox reactions described in both US patents is the difficulty in forming a single, hard, refractory oxide phase; i.e., the products of such redox reactions are composed of multiple oxides. phase, which has inferior hardness, fracture rate, and wear resistance compared to structures containing only the desired single oxide phase. The present invention differs from any prior oxidation methods and involves a novel acid phenomenon that overcomes their difficulties and limitations, as described below. [Specific Disclosure of the Invention] The gist of the present invention is (1) to provide a parent metal that normally forms a passive coating in the presence of a gas-phase oxidizing agent with a method that prevents the formation of such a passive coating and that (2) combining the parent metal with at least one dopant that allows the continuation of the reaction in the reaction involving the parent metal and the gas-phase oxidizing agent; (3) react the parent metal with the gas phase oxidant to produce an oxidation reaction product; (4) the surface of at least a portion of the oxidation reaction product is The state is maintained in contact with the vapor phase oxidant and between the vapor phase oxidant and the molten parent metal, so that the parent metal passes through the oxidation reaction product to the vapor phase oxidant side. transported so that the fresh oxidation reaction product grows on the side of the gas phase oxidant, and (5) continuing the above reaction to obtain a ceramic-metal composite material containing the oxidation reaction product and metal. A method for manufacturing ceramic-metal composite materials. This invention discloses useful ceramic-metal composite materials (which mainly include ceramics and will be hereinafter referred to as "ceramics" and "ceramic products" for simplicity).
Also called. ) is formed by a novel oxidation reaction at the interface between molten metal and a gas-phase oxidizing agent. Under appropriate processing conditions, molten metal is drawn between the oxidation reaction products, causing continuous growth of the oxidation reaction products at the product/atmosphere interface. The resulting ceramic product consists of an oxide phase (i.e., the oxidation reaction product) bound primarily through relatively low-energy grain boundaries and a metallic phase (or voids replacing the metallic phase) at least partially bound. 〓). As used herein, the term "ceramic" or "ceramic product" refers to an object that is primarily ceramic in composition or properties, but is not limited to the typical meaning of ceramic, i.e., consisting entirely of non-metallic and non-organic materials. However, it may contain small or substantial amounts of one or more metals derived from the parent metal of the object, typically from about 1 to 40% by volume, and even more. As used herein, the term "parent metal" refers to a metal that is a precursor of a polycrystalline oxidation reaction product, such as aluminum, and refers to a relatively pure metal, a commercially available metal containing impurities and/or alloying components. , or alloys in which metal precursors are the main component, and where a particular metal, such as aluminum, is mentioned, this should be read with this in mind, unless specified otherwise. As used herein, the terms "oxidizing agent" and "oxidation reaction product" have the broad meaning as previously defined. Under the particular conditions of this invention, molten metal is carried along a portion of the oxidation reaction product crystal contact. This is caused by appropriate wetting phenomena, which result in the formation of channels of liquid metal at grain boundaries where relatively high surface energies of oxidation reaction products are formed. This proper wetting phenomenon is related to two interfacial energy conditions. In other words, (1) the liquid metal must be wetted by the oxidation reaction product, that is, δSL < δSG (δSL means the energy of the oxidation reaction product-molten metal interface, and δSG is the relationship between the oxidation reaction product and the gas atmosphere). (2) The energy of part of the grain boundary, δB, is more than twice as large as the solid-liquid interface energy, that is, δBMAX>2δSL (here, δBMAX is the oxidation reaction (meaning the maximum grain boundary energy in the product). Under such conditions, grain boundaries are not formed, and a molten metal channel between the two oxidation reaction product-metal interfaces is preferentially formed, and the grain boundaries spontaneously decompose. All polycrystalline materials exhibit grain boundary energies that are a function of the degree of angular mismatch between two adjacent grains. For example, grain boundaries with small angle mismatch generally exhibit low surface energy, and conversely, grain boundaries with large angle mismatch exhibit high surface energy. This relationship is usually not so simple that it increases or decreases depending on the angle. This is because at intermediate angles more preferential alignment of atoms often occurs. Under certain appropriate processing conditions, the sites of the oxidation reaction product where large crystallites of large angular mismatch intersect provide paths for the wicking of molten metal. These channels are connected to each other in the same manner as the grain boundaries of the polycrystalline material are connected, so the molten metal passes through the oxidation reaction products to the interface with the oxidizing agent atmosphere, where it is oxidized, so the oxidation reaction products growth will occur continuously. Furthermore, the wicking action along the channel of molten metal is much faster than the ionic conduction mechanism in normal oxidation phenomena.
The growth rate of oxidative organisms in the present invention is significantly faster than in other oxidative phenomena. This also results in the formation of a dense reaction product layer. Since the oxidation reaction products of the present invention are interposed by metals along the high-energy grain boundary sites, the oxidation reaction products themselves are intercalated along grain boundaries with relatively small angles (i.e., which do not meet the condition of δB > 2δSL). connected three-dimensionally. The products of the invention therefore have the desirable properties of pure solid oxides (e.g. hardness,
fire resistance, strength) and also has advantages (especially toughness and fracture strength) due to the presence of a distributed metallic phase. Certain pure metals can naturally satisfy the interfacial energy conditions necessary for the oxidation phenomenon of the present invention by appropriate combinations of temperature and oxidant atmosphere. However, it has been found that the addition of certain elements (promoter dopants) to the metal influences the interfacial energy requirements as described above to be more easily met. For example, dopants or combinations thereof that reduce the solid-liquid interfacial energy help convert the protective polycrystalline oxide film to include channels through which molten metal travels. Another important feature of the invention is that by varying the surface energy, the microstructure and properties of the resulting ceramic product can be controlled.
For example, by creating processing conditions that reduce the solid-liquid interfacial energy in relation to the range of grain boundary energies in the oxidation reaction products, structures with high amounts of metal and low connectivity of the oxide phase can be created. can be created. Furthermore, by changing the correlated surface energy in the opposite direction, it is possible to create an oxide structure with a high degree of connectivity and less metal phase (fewer metal transfer channels). In this way, the properties of the resulting product can be controlled with high precision. In other words, it is possible to create any material with properties that are close to those of pure ceramic, such as those with a metal phase content of 25 to 30%, or even higher, with good toughness and conductivity. Additionally, other types of elements (initiator dopants)
was found to play an important role in initiating the above-mentioned oxidation reaction product growth phenomenon. This acts as a nucleating agent in the formation of stable oxide crystals,
Alternatively, it is thought that the initially passive oxide layer is destroyed by some kind of action. Although this initiator dopant is not essential for producing the oxidation reaction product growth phenomenon in the present invention, for certain parent metal systems, there is no practical problem in the time required to initiate oxidation reaction product growth. This is extremely important in reducing the time to a certain degree. [Preferred embodiment of the present invention] The present invention uses aluminum or its alloy as a parent metal and α as an interconnected oxidation reaction product.
- Although it has also been found in the process of forming alumina (gas phase oxidant is air or oxygen), and the following description is also based on this, the present invention applies to many other parent metals (e.g. zirconium, titanium, silicon, tin, etc.) and oxidizer systems (as described above). The invention is based on the discovery that the oxygen mechanism of conventional metals, such as aluminum, can be altered by adding certain dopants to the metal or alloy, resulting in a completely new oxidation mechanism. This dopant allows the metal to pass through its normally impermeable polycrystalline oxide shell when the metal is heated to a certain temperature range above its melting point. This metal passing through comes into contact with an oxidizing atmosphere and creates an oxidation reaction product, and another molten metal of the oxidation reaction product passes through and is oxidized, and the process is repeated, resulting in the growth of an oxidation reaction product layer. . This oxidation mechanism is in stark contrast to the conventional aluminum mechanism, where once aluminum is oxidized, its oxide protects the substrate from further oxidation. In the case of aluminum, this conventional oxidation mechanism is true; in the case of solid aluminum, sufficient oxidation occurs even at temperatures below zero, and even in liquid aluminum, the shell of aluminum oxide remains until the melting point of the oxide (2050°C) is reached. protected by Note that if the melting point of the oxide is exceeded, the aluminum underneath will ignite. The above mechanism for this transition metal and liquid phase/vapor phase reactions, as well as the materials formed, are quite unique when compared to conventional oxidation mechanisms and ceramic products. The present invention makes it possible to literally grow high-density, high-hardness, non-porous, good fire resistance, and tough ceramic to any desired thickness. Ceramic products obtained through this unique oxidation phenomenon may at first glance be classified as cermets, but their physical properties are far different from those obtained by pressing and sintering conventional metal and ceramic powders. They are different. That is, conventionally, the physical properties of cermets could be predicted as a combination of the properties of the metal binder phase and ceramic particles contained therein. For example, the softening point and conductivity of conventional cermets can be predicted as a reflection of the properties of the metallic phase within the cermet. However, the ceramic-containing body of the present invention does not have such physical properties of conventional cermets. That is, a ceramic-containing body obtained by treating a doped aluminum alloy with the oxidation mechanism of the present invention can be heated to 1500°C.
The modulus of rupture (MOR) at temperatures (approximately 840°C above the melting point of the parent metal) is 60-70% of the MOR value at room temperature.
The aluminum-based ceramic containing body obtained by this invention generally has a room temperature MOR of 30 to 60 kpsi.
Regarding conductivity, dopant, pressing temperature,
Although it varies depending on the processing atmosphere, the electrical conductivity of the metal itself (less than 0.05 ohm/inch for a bar with a 1/2 inch square cross section) to the electrical conductivity of the oxide ceramic itself (more than 10 MΩ/inch for a similar bar) ) (see Example 2, Table 2B). The unique physical properties of the ceramic-containing body of the present invention are believed to be due to the high degree of connectivity of the oxidation reaction product phase of the ceramic body. The metal phase is also at least partially bound in this ceramic-containing body, but unlike conventional cermets, it does not necessarily act as a binder for the bound oxidation reaction product crystallites. By continuing the process to oxidize as much of the metal phase as possible, the bound metal is removed in favor of new oxidation reaction product growth, leaving voids in the oxidation reaction product. It turns out. This fact is consistent with the high temperature strength (MOR value) and various conductivity developments of the materials of the invention. A doping system that creates intergranular metal migration and oxidation reaction product growth has been found to be effective as a two-component doping system when aluminum or aluminum alloys are used as the parent metal and air or oxygen is used as the oxidizing agent. Ta.
One component, the "initiator" dopant, facilitates initiation of the metal migration mechanism, resulting in the growth of oxidation reaction products. The other component, the “accelerator”
Dopants primarily stimulate the migration movement of the metal and therefore the growth rate. The concentration of both dopants was also found to influence growth morphology. It has been found that when aluminum or its alloys are used as the parent metal and alpha-alumina is formed as the oxidation reaction product, magnesium metal and/or zinc metal are effective initiator dopants. It has been found that the concentration of this dopant is important in effecting metal migration and oxidation reaction product growth initiation. Furthermore, the concentration of the initiator dopant also influences the growth morphology of the oxidation reaction product. This magnesium and/or
Alternatively, the zinc initiator dopant is added to the aluminum-based parent metal at a temperature below 900°C. In this case, a concentration of magnesium and zinc dopants of 0.1 to 15% by weight, based on the total product, is particularly effective for the disclosure of ceramic growth. However, in order to obtain the desired growth form and speed,
Preference is given to magnesium and/or zinc in the range 0.1 to 3% by weight. A variety of promoter dopants have been found to enhance reaction rates when using aluminum-based parent metals. For example, metals of group B in the periodic table, such as Si, Ge, Sn, and Pb. Note that carbon is not effective in the present invention because it tends to produce aluminum carbide. These Group B dopants or combinations thereof can be applied by alloying with the aluminum parent metal system. If lead is used, it must be added to the parent metal at a temperature of at least 1000° C. unless other soluble alloying components (such as tin) are added. This is because the solubility of lead in aluminum is low. The amount of accelerator dopant added is based on the weight of the entire aluminum alloy.
It is 0.5 to 15% by weight, more preferably about 1 to 10% by weight in terms of growth rate and morphology. Other examples of useful dopant materials for aluminum parent metals include sodium, lithium, calcium,
Boron, phosphorus, and yttrium can be used alone or in combination with one or more dopants depending on the oxidizing agent and processing conditions. Sodium and lithium are present in very small amounts, approximately 100-200ppm
can be used in low ppm order, and each can be used alone or in combination or with other dopants. Rare earth elements such as cerium, lanthanum, praseodymium, neodymium and samarium are also useful dopants, especially when used in combination with other dopants. When aluminum or an aluminum alloy is used as the parent metal in the present invention, a two-component dopant (initiator and promoter) is added to the parent metal, the parent metal is then placed in a crucible or other refractory container, and the metal surface is coated with an oxidizing agent. Exposure to atmosphere (usually air at atmospheric pressure). This parent metal is then heated in a furnace at typically 850°C to 1450°C, more preferably 900°C.
~1350° C. (if α-alumina is obtained as the oxidation reaction product), which causes the parent metal to break through the oxidation reaction product shell and migrate.
In this way, the parent metal is continuously exposed and the oxidation reaction product gradually becomes thicker, while a fine network structure of the parent metal is formed along the areas that should become the grain boundaries of the formed high-energy oxidation reaction product. be done. This oxide grows at a constant rate (ie, constant rate of thickness increase) as long as sufficient air (or oxidant atmosphere) ventilation is provided and the oxidant source is held constant. Ventilation of this air can be achieved by providing a ventilation hole in the furnace. This oxide growth continues until at least one of the following three conditions is met: (1) If all the parent metal is consumed, (2)
(3) When the oxidizing atmosphere is replaced with a non-oxidizing atmosphere or the oxidizing agent is removed or evacuated; (3) When the temperature inside the furnace is changed and exposed to a temperature outside the reaction temperature range (the reaction temperature is 1450℃). Figure 1 shows the relative performance of an aluminum parent metal system oxidized in air using various concentrations of magnesium as an initiator dopant and doped with 3% silicon as a promoter dopant as a function of furnace set temperature. It shows an increase in weight. FIG. 2 shows the weight gain for various percentages of silicon as promoter dopant as a function of furnace set temperature for the same parent metal oxidant system using a 2% concentration of magnesium as the initiator dopant. The total processing time for the samples in Figures 1 and 2 was 24 hours, and air at standard atmospheric pressure was used as the oxidant. For comparison, samples with an aluminum parent metal system without magnesium initiator dopant and with 0-3% silicon promoter dopant both showed negligible weight increase, thus inhibiting ceramic growth. was negligible. Within the range of operating conditions at which this oxidation reaction product growth occurred, many different and reproducible product microstructures and surface morphologies were observed. Typically, rapidly moving regions exhibit essentially smooth planar growth. FIG. 3 shows the cross-sectional growth of a magnesium/silicon doped aluminum parent metal system. Figure 4 shows that otherwise,
An example of a polycrystalline oxide structure of non-porous aluminum oxide (corundum) with webs of aluminum along such that the structure shown at 400x magnification shows highly angular mismatched grain boundaries. shows. In this regard, Section 9a-9 shows a comparison of the X-ray diffraction patterns of Al ₂ O ₃ (corundum), aluminum, and the ceramic material of the present invention.
It is necessary to pay attention to Figure 9c. FIG. 11 shows details of the microstructure of a sample produced under conditions comparable to those of FIG. Figure 11a is an X-ray diffraction pattern using Laue's back reflection method to show an Al ₂ O ₃ structure in a large area of the sample (the metallic phase of this structure was etched before performing the X-ray analysis). ). 1st
The pattern in Figure 1a is typical of a crystalline material containing numerous grain boundaries that are misoriented by small angles (up to about 5°). Figures 11b-e show details of the microstructure observed using a higher magnification transmission electric microscope. Figures 11b and c show typical low angle grain boundaries commonly observed in this material. These low-angle grain boundaries were clearly visible in each case, and there was no evidence of the existence of any other grain boundaries. High-angle grain boundaries were very rarely observed in this sample. Figures 11c and e are micrographs of two high angle grain boundaries seen therein. In both cases, the interface between the two particles contains a relatively wide groove (i.e. 100-200 μm) of the solidified metal phase. Clearly, the information provided in FIGS. 4 and 11 provides a good indication of the microstructural effects associated with the oxidation mechanism of the present invention. In particular, the ceramic product has been shown to be an oxide structure with interlocking high-angle grain boundaries along which the low-angle grain boundaries are replaced by grooves filled with a metallic phase. Aluminum-based metal inclusions 10 can be seen in FIG. 4, and such inclusions may be more numerous depending on the growth regime of the process, which varies with the two process temperature regimes and dopant type and concentration. or less formed. Rougher, higher surface area growth surfaces give larger, more complex parent metal inclusions. It occurs as the structure develops voids by periodically connecting protrusions on the growth surface. These voids are filled by the movement of metal. (In such a case, such formed voids can no longer have access to the oxidizing atmosphere, and the metal that has migrated there through the grain boundaries of the oxidation reaction products remains unoxidized.) If process conditions are maintained at a point that exceeds the total oxidation reaction product growth conversion of the parent metal, these metal inclusions will be relocated, leaving a favorable void for further oxidation reaction product growth. . An example of the closed cell porous structure formed is the fifth
Shown in the micrograph in Figure. As shown therein, metal inclusions were removed from the cavity 12 by the movement described above. However, the discontinuous inclusions of the parent metal located along the polycrystalline oxide grain boundaries are not removed;
remain in a stable state. Various other microstructures are observable in the ceramic products of the present invention obtained from the aluminum parent metal system, as shown in the 400x photomicrographs of FIGS. 6 and 7. Figure 6 shows the preferred orientation and approximately 25
−35% open cell porosity by volume (number 14 in Figure 6)
) shows a polycrystalline microstructure. 7th
The figure shows extremely small metal inclusions (number 16 in Figure 7).
) exhibits a dense, low-porosity microstructure. FIG. 8 shows the extreme morphology growth variations that are possible for certain portions of the process parameters. A substantial feature of the process of the invention is to obtain a void-free ceramic material, and as long as the growth process is carried out beyond the consumption of the parent metal, a dense, void-free ceramic is obtained. When aluminum parent metal doped with magnesium initiator is oxidized in air or an oxygen atmosphere, the process temperature growth region is e.g.
Before reaching ~950°C, the magnesium is at least partially oxidized. Here, the magnesium forms a magnesium oxide and/or magnesium aluminate spinel phase on the surface of the molten aluminum alloy. During the growth process, such magnesium compounds mainly remain on the initial surface of the parent metal compound (initial surface), while the rest migrates along the growth front (growth surface) of the resulting oxidation reaction product/metallic ceramic structure. do. The various initial surfaces of the ceramic materials of the invention are
Tested by X-ray diffraction using CuKα. The results are shown in Table 1 below, and the data correspond to pure MgAl ₂ O ₄ (spinel). Furthermore, the presence of spinel type in the initial surface corresponds to the magnesium peak in FIG. FIG. 10 shows an X-ray probe (energy scattering X-ray analysis) superimposed with a scanning electron micrograph of the ceramic material of the invention.

[Table] When a specific aluminum alloy is used as the parent metal for the oxide growth mechanism and air or oxygen is used as the oxidant, a structure consisting mainly of aluminum oxidation reaction products is formed (magnesium on the initial surface - apart from a relatively thin layer of aluminate spinel). Typically, inorganic alloying components in the parent metal (particularly metals with low free energies of oxide formation) end up being concentrated in metal grain boundaries and metal-inclusive phases. Small amounts of manganese, iron, copper, boron, zinc, tungsten and other metals do not interfere with the growth mechanism of the aluminum-based parent metal system. It was found to be a compatible alloy diluent. Examples of the present invention will be shown below to specifically explain the present invention. Examples demonstrate (1) the growth of ceramics by novel oxidation mechanisms, and (2) the growth of such ceramics in parent metal/oxidation reaction product systems that do not inherently exhibit surface energy relationships conducive to the growth of ceramics by the mechanisms of the present invention. The use of initiator and accelerator dopants to effect growth. Example 1 0-10% Magnesium (initiator dopant)
Seven aluminum/magnesium/silicon alloys with and 3% silicon (promoter dopant) were tested at temperatures from 1125 to 1400°C to demonstrate that the magnesium initiator and temperature ranged from the aluminum-based parent metal to the present invention. The effect of this on the growth of ceramic materials in air was determined. In all tests, cylindrical aluminum/magnesium ingots 1 inch long and 1 inch diameter were used.
Cast from metal at 850℃ and in a suitable refractory crucible
Embedded in 220 mesh aluminum oxide grains.
The cut side of the ingot was placed approximately flush with the aluminum oxide surface and approximately 1/4 inch below the top of the crucible. The furnace cycle was as follows. Elapsed time temperature (℃) 0 to 5 hours 30 to set temperature 5 to 29 hours Set temperature 29 to 43 hours Set temperature to 600 More than 43 hours Removed from furnace Diagnose various samples and calculate the total weight of crucible and contents I tested the increase. "Weight gain" means the ratio of the total weight change of the crucible/aluminum oxide/ingot before and after the furnace cycle to the original weight of the parent metal, expressed in g/g. If the primary aluminum is converted to Al ₂ O ₃ , this ratio will increase towards the theoretical value of 0.89, the difference from the theoretical value being due to unreacted residual aluminum in the parent metal, plus included metals in the product. Almost 0 to 35-40% of the phase. The weight gain of various aluminum/magnesium/silicon alloys at selected furnace setpoint temperatures, without corrections for phase or moisture removal from the crucible or any experimental errors, is shown in Table 2 and Figure 1. ing. When adopting a parent metal system mainly consisting of aluminum to react with air to grow the aluminum oxide material of the present invention, it can be seen from Table 2 and FIG. 1 that there is no weight increase without the use of an initiator dopant. It can be seen that a ceramic structure was not obtained.

TABLE The above furnace experiment (illustrated in FIG. 1) also involved aluminum ingots without the addition of magnesium and/or silicon as dopants. The weight increase rate of the aluminum ingot was negligible at all specified temperatures, indicating no growth. The results are shown in Table 3.

[Table] Example 2 To investigate the effect of group B elements on the formation of the ceramic material of the present invention, an aluminum alloy containing 2% magnesium and 1-10% silicon was heated at 1125-1400°C in air. Processed at set temperature. The weight gain of samples showing growth of the ceramic material of the present invention is shown in Table 4 and Figure 2, and the hardness (Rockwell A hardness) and electrical conductivity are shown in Tables 5A and 5B, respectively. In each case, the furnace cycle, ingot size, and layer composition and morphology were similar to those used in Example 1.
In the present invention, the Group B element is useful for modifying the surface energy relationship of the metal system mainly consisting of aluminum and α-type aluminum oxide,
It has been found that this enables the ceramic growth mechanism of the present invention. These elements serve as promoter dopants. Table 6 and Figure 2 clearly show that in the absence of silicon promoter dopant in the aluminum/magnesium/silicon parent metal system, no oxidation reaction product growth phenomenon occurs.

【table】

【table】

【table】

【table】

EXAMPLE 3 To investigate the effect of removing or nearly removing the promoter dopant on the production of the ceramic materials of this invention from an aluminum-based parent metal, about 2.4% of the initiator dopant magnesium and 0.4% of the initiator dopant magnesium. Samples of aluminum alloys (2 inches x 9 inches x 0.5
reagent grade alumina refractory particles (90 mesh Norton) in a fireproof container.
It was buried in E1). This sample was heated from room temperature to a treatment set temperature of 1250° C. over a period of 10 hours, and then treated in air at the treatment temperature setting for 48 hours. The sample was then cooled for approximately 10 hours. The weight increase as defined in Example 1 was negligible and was calculated to be 0.05 g/g. Example 4 In order to investigate the effect of the group B element Ge on the production of the ceramic materials of the invention from aluminum-based parent metals, it was alloyed with magnesium as an initiator dopant and with 3% or 5% germanium. Aluminum was cast into ingots as described in Example 1. The samples were treated in exactly the same manner as described in Examples 1 and 2 in air at 1200°C and 1325°C, respectively, to obtain ceramic materials. 1200℃ and 1325℃ for these aluminum/magnesium/germanium alloys.
The weight increase in was as follows. Weight increase Ge content 1200℃ 1325℃ 3% 0.04 0.73 5% 0.71 0.73 Example 5 In order to investigate the influence of group B element tin on the production of the ceramic material of the present invention from aluminum-based parent metal, magnesium 2 % and alloyed with 10%, 5% or 3% tin was cast into a 1 inch diameter ingot and cut into 1 inch long billets exactly as described in Example 1. At 1200℃ and
Processed at 1325°C. The weight increases at 1200°C and 1325°C were as follows. Weight increase Sn content 1200°C 1325°C 10% 0.74 0.71 5% 0.56 0.22 3% 0.69 0.29 Example 6 To investigate the influence of group B element lead on the production of the ceramic material of the present invention from aluminum-based parent metal Aluminum alloyed with 3% magnesium and 1 to 10% lead by weight was prepared. Samples were prepared as follows. 5% by weight lead was added to a 97% aluminum/3% magnesium alloy at 1000°C and the resulting molten alloy was cast into ingots 1 inch in diameter and 1 to 2.5 inches long. To prepare the 10% lead/10% tin/Mg/Al alloy, tin and lead were added to the molten aluminum/magnesium alloy at 1000°C. These ingots were embedded in 90 mesh aluminum oxide refractory particles so that the surface thereof was the same as that of the particles. Therefore, the ingot surface was exposed to the air atmosphere. The treatment was as in Examples 1 and 2.
The furnace temperature schedule was exactly the same as that of 1, except that the temperature was maintained at 1250°C for 48 hours, and the time for cooling to below 600°C was 10 hours. The weight increase was as follows. Dopant weight increase (g/g) 10%Pb/10%Sn/3%Mg 0.46 5%Pb/3%Mg 0.49 1%Pb/3%Mg 0.25 1%Pb/0%Mg 0.03 Example 7 In order to determine the level of diluent that is acceptable as it has a negligible effect on the production of ceramic materials, aluminum alloys containing the following known diluents (initiator magnesium 1
% and containing 0.6% promoter silicon). Diluent Type Diluent Weight % Copper 0.1 Chromium 0.2 Iron 0.3 Manganese 0.1 Titanium 0.2 In a suitable refractory tray, a sample of the above aluminum alloy (2 in.
38), and exposed to the furnace air atmosphere with its 2 inch x 9 inch surface flush with the alumina particles. The samples were heated to a treatment set temperature of 1325° C. over 4 hours, processed at this temperature for 30 hours, and then cooled to room temperature over 10 hours. The weight gain as defined in Example 1 was observed to be unaffected by the diluent and was 0.6 g/g.

[Brief explanation of drawings]

FIG. 1 is a graph showing weight gain as a function of temperature for aluminum parent metal systems doped with 3% silicon and having various magnesium concentrations and oxidized in air. FIG. 2 is a graph showing weight gain as a function of temperature for aluminum parent metal systems oxidized in air with various silicon dopant concentrations and constant magnesium concentration. Figure 3 shows aluminum doped with 10% silicon and 2% magnesium at a temperature of 1300°C.
FIG. 2 is a micrograph of a metallographic structure showing a ceramic structure manufactured according to Example 2. Figure 4 is 1%
1 is a micrograph (400x magnification) of a metallographic structure showing a ceramic structure manufactured according to Example 2 using an aluminum alloy doped with silicon and 2% magnesium at a temperature of 1150°C. Figure 5 is a micrograph (400x magnification) of a metallographic structure showing a closed-cell porous ceramic structure manufactured according to Example 2 at a temperature of 1300°C using an aluminum alloy doped with 3% silicon and 2% magnesium. It is. Figure 6 is a micrograph (400x magnification) of a metallographic structure showing an open-cell porous ceramic structure manufactured according to Example 2 at a temperature of 1300°C using an aluminum alloy doped with 10% silicon and 2% magnesium.
It is. Figure 7 shows an aluminum alloy doped with 5% silicon and 2% magnesium.
FIG. 2 is a micrograph (400x magnification) of a metallographic structure showing a dense, low-porosity ceramic structure produced according to Example 2 at 1350°C. FIG. 8 is a micrograph (1.6x magnification) of a metallographic structure showing a ceramic structure manufactured according to Example 2 at a temperature of 1400° C. using an aluminum alloy doped with 3% silicon and 2% magnesium. Figures 9a-9c are X-ray diffraction patterns of Al ₂ O ₃ , elemental aluminum and a ceramic structure prepared according to Example 2. FIG. 10 is a photograph (80x magnification) of the elemental distribution plot of the metal structure showing the ceramic structure of the present invention, showing the magnesium and aluminum concentration distribution measured by energy dispersive X-ray analysis. Figures 11a to 11e are the fourth
Another microstructure based on an example produced under conditions similar to those used for carrying out the figure; a is a large area of material after removal of the aluminum phase;
X-ray photographs showing the Laue X-ray diffraction pattern; b and c are transmission electron photographs showing the typical low-angle grain boundaries observed for the example; d and e are the presence of a metallic phase between the grain boundaries. This is a transmission electron photograph of a metal structure showing high angle grain boundaries seen in an example.

Claims (1)

[Scope of Claims] 1 (1) A parent metal that normally forms a passive coating in the presence of a gas phase oxidizing agent is provided with a method that prevents the formation of such a passive coating and that allows the parent metal and the gas in the molten state to form a passive coating. (2) heating the dopant-containing parent metal above its melting point in the presence of the gas phase oxidizing agent, and At that temperature, (3) the parent metal and the gas phase oxidant are reacted to form an oxidation reaction product, and (4) the surface of at least a portion of the oxidation reaction product is in contact with the gas phase oxidant. in contact with and maintaining a state between the vapor phase oxidant and the molten parent metal;
Thus, the parent metal is transported through the oxidation reaction product to the gaseous oxidant side, allowing fresh oxidation reaction product to grow on the gaseous oxidant side, and (5) continuing the reaction. A method for producing a ceramic-metal composite material comprising the steps of: obtaining a ceramic-metal composite material containing an oxidation reaction product and a metal. 2. The method of claim 1, wherein the parent metal includes at least two of the dopants. 3. Claim 1, wherein the parent metal is made of aluminum.
Or the method described in 2. 4. Claim 1, wherein the gas phase oxidizing agent comprises air, nitrogen, halogen, carbon, boron, or a mixture thereof.
The method described in 2 or 3. 5. The method of claim 1, wherein the parent metal is aluminum and includes at least one dopant among magnesium, silicon, tin, germanium, and lead. 6. The method according to claim 5, wherein the temperature is 1000 to 1450°C. 7. A method according to any one of claims 1 to 6, wherein the reaction is continued for a period substantially longer than the molten metal is used up to obtain a porous ceramic-metal composite. 8. The method according to any one of claims 1 to 6, wherein the reaction is carried out so that the ceramic metal composite contains metal as inclusions. 9 The parent metal is made of aluminum, the aluminum parent metal is a first dopant made of magnesium in an amount of 0.3 to 10%, silicon, tin in an amount of 0.5 to 10%, based on the weight of the aluminum parent metal. ,
2. The method of claim 1, including a second dopant comprising at least one of germanium and lead. 10. The method according to claim 8, wherein at least some of the metals contained in the ceramic metal composite are three-dimensionally connected. 11. Claim 7: At least a portion of the ceramic metal composite includes three-dimensionally connected pores.
Method described. 12. The method of claim 1, wherein the at least one dopant is alloyed with the parent metal. 13. The method of claim 2, wherein said two dopants are alloyed with said parent metal. 14. The method of claim 1, wherein the parent metal comprises aluminum, the gas phase oxidant comprises air, and the oxidation reaction product is alpha-alumina. 15 The dopant is magnesium, silicon,
4. The method according to claim 3, comprising at least one of tin, germanium, and lead.