Porous metal based composite material

Abstract: A porous composite material includes a metal material for forming a matrix, and at least two kinds of fine particle materials having different wettabilities with respect to the metal material. The porous composite material is provided by melting and impregnating the metal material for forming a matrix with the mixture of at least two kinds of fine particle materials. The porous composite material has excellent characteristics in shock absorbency, acoustics, non-combustibility, lightness, rigidity, and so forth.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous metal based composite material which requires no pressuring mechanism during manufacture due to the spontaneous penetration of a metal which will become a matrix. 2. Description of the Related Art Known methods of manufacturing porous materials include: (1) powder metallurgy to sinter metal powder or short fibers; (2) method to foam by directly adding a foam material to molten metal; (3) method to remove plastic after plating on foam plastic; (4) method to compound a material having a small density, such as a foam material, with a metal; (5) method to blow gas into molten metal under zero gravity; and so forth. However, in consideration of these methods, including the aspect of making a metal-based composite material porous, the method (1) is powder metallurgy and is thus uneconomical although the manufacture of Ti or Ti alloy stainless steel has been attempted. As an example of the method (2), Al alloy is foamed by using hydride such as Ti and Zr. In this method, it is difficult to select a foam material for a steel material. It is also difficult to provide an even structure in this method by foaming a composite material of metal and non-metal or the like. In the method (3), plastic as an organic material is partially used, so that the application thereof is limited, which is troublesome. As an example of the method (4), Al alloy and Shirasu balloon-pumice are compounded. However, since hot molten metal has to be pressured and injected into an inorganic material having a small density, there are restrictions on a manufacturing facility. The method (5) has a difficulty in mass-production. On the other hand, the present inventors discovered the application of a hard brazing material for a base which has little restriction on the types, shapes and the like of joining members and which can be joined in various ways. By adding a fine particle material to the hard brazing material to lower thermal stress, an appropriate bonding strength is kept between different members. Joining strength around a joining interface is not lowered even by thermal stress during cooling after joining at high temperature, and also no cracks are formed at weak members by thermal stress during cooling, so that it was found that two or more different members can be joined. In other words, the present inventors found that the above-noted properties can be obtained by an adhesive composition for bonding two or more different members. The adhesive composition consists of at least two types of fine particle materials having different wettabilities with respect to the hard brazing material, and the hard brazing material. The present inventors thus applied Japanese Patent Application No. 11-300184 as of October 21, 1999. However, since this invention focuses on joining, there was not enough examination concerning the specific thickness of the adhesive composition or the application of the adhesive composition as a member itself at the time of the application. EP 1093882, published 25 May 2001, describes a process in which a mixture of alumina particles plated with Ni and alumina particles subjected to no surface treatment are impregnated with a hard solder A5005 (Al-0.8mg) under application of pressure. JP-A-4-110440 describes a process in which ceramic particles having good wettability (SiC) together with 2 wt% hBN as ceramic particles having less wettability are mixed, and impregnated with an Al alloy which is poured when molten onto the mixed powder in a dye, which is pressurised to infiltrate the molten metal. Thereafter the composite is stirred to uniformly disperse the ceramic particles into the matrix alloy. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide method of making a porous composite material which has, e.g., an excellent coefficient of thermal expansion, Young's modulus, proof stress and so forth, and in particular, to provide a porous composite material that preferably is simple for industrial applications and can be economically manufactured. It is effective to make a material porous by controlling mechanical properties and physical properties. A porous material has excellent characteristics as a functional material, including shock absorbency, acoustic characteristics, non-combustibility, lightweight, rigidity and so forth, and a wide range of applications is expected. For instance, the material may be a shock absorbing material for the interior and exterior of a vehicle. As a building material, the sound-absorbing property, in addition to being non-combustible and lightweight, can also be expected. Then, the applicability of the adhesive composition was examined not only as an adhesive composition to fill in the gaps of joining materials but also as a large member product and as a porous material of the member. When molten metal permeates into the mixture of fine particle materials having different wettabilities with respect to the molten metal, it is necessary to provide a fixed or higher level of penetration force by choosing the conditions of a matrix metal, fine particle material and so forth. Additionally, the powder having different wettabilities is mixed to provide an evenly porous material. Thus, it was found that a member having a desirable size can be manufactured and an effective porous composite material can be obtained. While focusing on this fact, the present inventors carried out various tests in order to address the above-noted problems. In one aspect, the present invention provides method of making a porous composite material as set out in claim 1. In another aspect, the present invention provides a porous composite material as set out in claim 8. Accordingly, a porous metal material includes a metal material for forming a matrix and at least two fine particle materials having different wettabilities with respect to the metal material, and is provided by melting and impregnating the metal material into the mixture of at least two fine particle materials. The inventors found that the porous metal material is a composite material having an excellent balance of mechanical and physical characteristics that are different from those of the matrix metal, for instance, a characteristic balance between a low expansion coefficient and low proof stress, and so forth, thus completing the present invention. In other words, it was found that a porous metal material can be provided by using a specific metal material as a matrix and by melting and impregnating the metal material to fine particle materials which can lower thermal stress, thus forming a composite. The porous metal material can achieve the above-noted properties as a material having excellent physical and mechanical characteristics because of the metal material as a matrix, the fine particle material that has superior wettability with respect to the metal material and can lower thermal stress, and holes that are formed by particles having inferior wettability with respect to the metal material, thereby achieving the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an optical microscopic photograph, showing the microstructure of a composite material in which aluminum alloy A5005 penetrated and solidified in a plated fine particle material (alumina having the average particle size of 50 µm); FIG. 2 is an optical microscopic photograph, showing the microstructure of a composite material in which aluminum alloy A5005 penetrated and solidified in particles where a plated fine particle material (alumina having the average particle size of 50 µm) and a non-plated fine particle material (alumina having the average particle size of 50 µm) were mixed at 2:1; and FIG. 3 is an optical microscopic photograph, showing the microstructure of a composite material in which aluminum alloy A5005 penetrated and solidified in particles where a plated fine particle material (alumina having the average particle size of 50 µm) and a non-plated fine particle material (alumina having the average particle size of 50 µm) were mixed at 1:2. DESCRIPTION OF THE PREFERRED EMBODIMENT According to a first aspect of the present invention, there is provided a method of forming a melt-inpregnated porous composite material according to claim 1. The invention provides in a second aspect a melt-impregnated porous composite as set out in claim 8. It is preferable that the metal material for forming a matrix is Au, Ag, Cu, Pd, Al, Fe, Cr, Co or Ni, or an alloy containing these metals as a main component. Furthermore, it is preferable that the mixture of at least two kinds of fine particle materials having different wettabilities with respect to the metal material contains the surface untreated fine particle material and the surface treated fine particle material at the volume ratio of 80:20 to 5:95. Additionally, a second aspect of the present invention relates to the application of the above-noted porous metal based composite material as a shock-absorbing material, a vibration-absorbing material or a sound-absorbing material. Combinations of a material having superior wettability with respect to the metal material and a material having inferior wettability with respect to the metal material, for example, include ceramic fine particles that are surface treated by such as plating and ceramic fine particles that are not surface treated. There is no particular limitation on a plating method. However, electroless plating is preferable. Wettabilities with respect to the metal material can be kept even without metal plating by mixing an additive such as Ti to the metal material or to the fine particle materials as fine particles, and thus by forming a reaction layer of active materials such as nitride, oxide and carbide on a ceramic surface when the matrix material is melted and impregnated. In this case, the above-mentioned effects can be obtained by combining materials having different wettabilites with respect to the metal material containing the additive. The effects can be preferably obtained by the combination of dispersion materials, for instance, nitride and oxide or nitride and carbide. The amount of the active materials is preferably around 0.5 to 5% in a weight ratio relative to the amount of the metal material for forming a matrix. Moreover, each average particle size of at least two kinds of fine particle materials having different wettabilities with respect to the metal material may be similar to each other or different from each other. Particle sizes can also be selected over a wider range than the sizes when the materials are used as an adhesive composition. In other words, the mixture of at least two kinds of fine particle materials having different wettabilities with respect to the metal material can be easily prepared by mixing, for instance, alumina particles that are Ni-plated at about 0.3 µm and have a desirable grain size such as the average particle size of 50 µm as particles that are surface treated at a desirable thickness, and, for example, alumina particles that have a desirable grain size such as the average particle size of 50 µm as surface untreated particles. Or alternatively, the mixture can be easily prepared by mixing, for instance, alumina particles that are Ni-plated at about 0.5 µm and have a desirable grain size such as the average particle size of 50 µm as particles that are surface treated at a desirable thickness, and, for example, Shirasu balloon particles that have a desirable grain size such as the average particle size of 100 µm as surface untreated particles. The mixture of at least two kinds of fine particles having different wettabilities with respect to the metal material containing Ti or the like as an additive at a fixed amount can be easily prepared by mixing, for instance, aluminum nitride having a desirable grain size such as the average particle size of 50 µm and, for example, alumina particles having a desirable grain size such as the average particle size of 50 µm. A mixing ratio between the surface untreated fine particle material and the surface treated fine particle material is more preferably 1:9. In other words, the mixing ratio of the surface untreated fine particle material in all particles is about 10% to 3:1, in other words, around 75%. When the mixing ratio of the surface untreated material is higher than 3:1, the metal material cannot easily penetrate without pressure and pressurization or the like is often required, which is not preferable. Moreover, when the mixing ratio of the surface untreated material is lower than 1:9, the mechanical property of a composite material becomes similar to that of compact filler, which is not preferable. The composite material relating to the present invention may be generally manufactured in accordance with the conditions described in Japanese Patent Application No. 11-180902. The surface treated fine particle material does not have to be the same as the surface untreated fine particle material. The material is good as long as it is the combination of the surface treated fine particle material and the surface untreated fine particle material. In other words, it is unnecessary to use the same material for plated and non-plated materials. The metal material for forming a matrix for use in the composite material relating to the present invention includes pure metal such as Au, Ag, Cu, Pd, Al, Fe, Cr, Co or Ni, or an alloy having these metals as a main component. For the alloy containing these metals as a main component, at least one kind of the above-noted metals may be contained as the main component. Of course, metals other than the metals mentioned above may be contained. Appropriate metals or an alloy may be selected for use based on reactivity to the particles of a dispersion material or temperature under which the composite material is used. Al alloy, for instance, BA4004 (Al-10Si-1.5Mg), A5005 (Al-0.8Mg) and so forth is preferably used since a light composite member can be obtained, and manufacturing temperature can be low. In melting and impregnating the pure metal or alloy material into the particle materials, it is important to improve wettability between the particles having superior wettability and molten metal in order to improve the penetration force of the molten metal and to enlarge a composite material to a desirable level. Generally, the wettability of molten metal or the like is expressed by the following Young-Dupre equation in which a drop is placed on the surface of a solid (sessile drop method) and in which each surface energy is in balance at solid/liquid/gas interfaces under the following condition: γ SV = γ S1 + γ 1V × cos wherein  is a contact angle; γ SV is solid-gas surface energy; γ 1V is gas-liquid surface energy; and γ S1 is solid-liquid surface energy. In general, a system having good wettability is  < 90°, and a system having poor wettability is  > 90°. In order to improve wettability ( < 90°) based on the equation mentioned above, it is necessary to set the solid-gas surface energy γ SV high and the gas-liquid surface energy γ 1V and the solid-liquid surface energy γ S1 low. Thus , although an oxide film is formed on the surface of a metal which is coated on the fine particle material having superior wettability with respect to the molten metal during heating before melting and impregnating the metal, the oxide has small surface energy (solid-gas surface energy γ SV ) and is stable, so that the wettability of the material coated with the oxide film thereon is poor. Therefore, when the oxide is removed in a reduction atmosphere or the like, the surface becomes active, having large surface energy (solid-gas surface energy γ SV ), and wettability increases. It is desirable to prevent oxidation under high vacuum. It is also possible to lower the solid-gas surface energy γ SV to improve wettability by changing the components of molten liquid with an added element or the like. Joining strength between a dispersion material dispersed in the metal material and the metal material is positively partially reduced, or fine holes are positively formed in the composite material. Thus, a porous metal based composite material provided by reducing Young's modulus and proof stress, in addition to coefficient of thermal expansion, can provide a cushioning effect when the material is joined to another member having low coefficient of thermal expansion and low fracture toughness. Additionally, a composite material having excellent heat resistance can be provided. More specifically, the effects can be achieved by mixing the dispersion material dispersed in the metal material with the particles having superior wettability with respect to the metal material, and the particles having inferior wettability with respect to the metal material. When the ratio of the particles having superior wettability with respect to the metal material is high, the microstructure of the optically observed porous metal based composite material is not so different from that of a composite material formed only of surface treated particles. However, the coefficient of thermal expansion and Young's modulus of the porous material are reduced by as much as those of a composite material formed only of particles having superior wettability. The proof stress of the porous material is reduced by more than that of a composite material formed only of surface treated particles. This is because joining strength between the particles having inferior wettability and the metal material is reduced in comparison with the particles having superior wettability. Thus, parts with the particles having inferior wettability essentially function as holes, and it is considered that the characteristics of a composite material could be controlled in a desirable direction. As the ratio of the particles having inferior wettability with respect to the metal material increases, optically observable holes are formed in a porous metal based composite material, and the coefficient of thermal expansion declines by as much as that of a composite material formed only of particles having superior wettability. Additionally, Young's modulus and proof stress decrease further in comparison with a composite material having less particles with inferior wettability with respect to the metal material. This is because the cross section of a composite material visually decreases because of holes, in addition to the decrease in joining strength between a dispersion material and the metal material, in the composite material with more particles having inferior wettability with respect to the metal material. Accordingly, Young's modulus decreases, and proof stress decreases since parts adjacent to the holes or the like become crack generating points during loading. The effects of the porous metal based composite material relating to the present invention were explained in accordance with the amount of particles that are not surface treated such as by plating to keep wettability, for the sake of convenience. However, the object, method and effects are all the same, and it is almost unnecessary to strictly distinguish whether or not they can be recognized as optical holes. For the characteristic control of the composite material, it is necessary to arrange the kinds of fine particle materials and adjust the packing density relative to the metal material. The packing density of fine particle materials relative to the metal material is 30 to 90%, preferably 40 to 70%, in volume ratios when only particles having superior wettability with respect to the metal material are dispersed. The packing densities are effective in controlling the coefficient of thermal expansion of a formed material in particular. When the particles having superior wettability to the metal material and the particles having inferior wettability to the metal material are dispersed, the volume ratio of the particles is similarly set at 30 to 90%, preferably 40 to 70%, based on the assumption that the composite material has no holes. It is also advantageous to increase the packing density of the particle materials in order to lower the coefficient of thermal expansion. However, if the packing density is increased too much, it would be often difficult to melt and penetrate matrix metal, which is not preferable. When the packing density is low and the coefficient of thermal expansion is lower than a desirable level, particles cluster on one side during manufacture and a homogeneous material is not often provided, so that attention is required. In other words, the coefficient of thermal expansion is adjusted by selecting the kinds of fine particle materials, or by appropriately selecting the particle size distribution of the fine particle materials. Examples The present invention will be explained in further detail by referring to examples. However, the present invention is not limited to these examples. Example 1 Alumina that was Ni-plated at the thickness of 0.3 µm on the surface of particles and had the average particle size of 50 µm, and alumina that was not surface treated and had the average particle size of 50 µm, were mixed at each ratio of 1:0, 2:1, 1:1 and 1:2. Dispersion particles mixed at the ratio were filled in a graphite jig. Subsequently, pure aluminum A1050 (Al > 99.5%) or aluminum alloy A5005 (Al-0.8Mg) arranged on the particles melted, penetrated without pressure, and solidified, thus providing a composite material as a sample. The mechanical and physical characteristics of the sample are shown in Table 1. In Table 1, the degree of penetration was determined by whether or not molten metal penetrated evenly to thickness of the layer of the dispersion particles filled in the jig. FIG. 1, FIG. 2 and FIG. 3 are optical microscopic photographs, showing typical microstructures. FIG. 1 is an optical microscopic photograph, showing the microstructure of a composite material in which aluminum alloy A5005 penetrated and solidified in a plated fine particle material (alumina having the average particle size of 50 µm). FIG. 2 is an optical microscopic photograph, showing the microstructure of a composite material relating to the present invention in which aluminum alloy A5005 penetrated and solidified in particles where a plated fine particle material (alumina having the average particle size of 50 µm) and a non-plated fine particle material (alumina having the average particle size of 50 µm) were mixed at 2:1. FIG. 3 is an optical microscopic photograph, showing the microstructure of a composite material relating to the present invention in which aluminum alloy A5005 penetrated and solidified in particles where a plated fine particle material (alumina having the average particle size of 50 µm) and a non-plated fine particle material (alumina having the average particle size of 50 µm) were mixed at 1:2. Matrix alloy Plating thickness (µm) Mixing ratio of plated particles (%) Coefficient of thermal expansion (×10 -6 ) Young's modulus (GPa) Yield strength (MPa) Penetration A1050 0.3 100 13.4 54 33 Partially difficult to penetrate A1050 0.3 67 13.5 - - Partially difficult to penetrate A1050 0.3 50 - - - Difficult to penetrate A1050 0.3 33 - - - Difficult to penetrate A5005 0.3 100 13.3 110 72 Good A5005 0.3 67 13.2 95 69 Good A5005 0.3 50 13.5 55 44 Good A5005 0.3 33 13.4 45 39 Good Note: In the table, - indicates no measurement or unmeasurable. Example 2 Alumina that was Ni-plated at the thickness of 0.3 µm on the surface of particles and had the average particle size of 50 µm, and alumina that was not surface treated and had the average particle size of 50 µm, were mixed at the ratio of 2:1. Dispersion particles mixed at the ratio were filled in a graphite jig. Subsequently, pure aluminum A1050 (Al > 99.5%) or aluminum-magnesium alloy (Al-0.18 to 2.308Mg) arranged on the particles melted, penetrated without pressure, and solidified, thus providing a composite material as a sample. The mechanical and physical characteristics of the sample are shown in Table 2. In Table 2, the degree of penetration was determined by whether or not molten metal penetrated evenly to the degree of penetration was determined by whether or not molten metal penetrated evenly to thickness of the layer of the dispersion particles filled in the jig. Matrix alloy Plating thickness (µm) Mixing ratio of plated particles (%) Penetration Young's modulus (GPa) Yield strength (MPa) Al (>99.5) 0.3 67 Difficult to penetrate - - Al - 0.18 Mg 0.3 67 Difficult to penetrate - - Al - 0.41 Mg 0.3 67 Good 83 63 Al - 0.62 Mg 0.3 67 Good 89 66 Al - 0.81 Mg 0.3 67 Good 95 69 Al - 1.08 Mg 0.3 67 Good 104 72 Al - 2.30 Mg 0.3 67 Good 122 84 Note: In the table, - indicates no measurement or unmeasurable. Clearly shown in the above-noted results, impregnation characteristics improve with the increase in the amount of added Mg. This is because Mg effectively reduces solid-liquid surface energy as shown above. The porous metal based composite material relating to the present invention is a superior composite material that can be manufactured while mechanical and physical characteristics such as coefficients of thermal expansion, Young's modulus and proof stress are effectively controlled at preferable levels by a simple control. Moreover, the porous metal based composite material relating to the present invention is reliable, with no damage, since stress among materials is reduced, so that an excellent composite material can be provided.

Claims: Method of forming a melt-impregnated porous composite material having a metal matrix, including the step of melting the metal of the metal matrix and impregnating it due to the spontaneous penetration of the metal, without application of pressure, into a mixture of first and second fine particle materials having respectively different wettabilities with respect to the metal, wherein the first fine particle material is ceramic particles which are surface-treated by plating and the second fine particle material is ceramic particles which are not surface-treated. Method according to claim 1, wherein the metal matrix is Au, Ag, Cu, Pd, Al, Fe, Cr, Co or Ni or an alloy having one of these metals as a main component. Method according to claim 2, wherein the metal matrix is an aluminium or aluminium alloy matrix. Method according to claim 3, wherein the metal matrix is an aluminium alloy containing at least 0.41 wt% and not more than 2.30 wt% Mg. Method according to any one of claims 1 to 4, wherein the first fine particle material is plated alumina particles and the second fine particle material is alumina particles which are not surface-treated. Method according to claim 5, wherein the first fine particle material is nickel-plated alumina particles. Method according to any one of claims 1 to 6, wherein the ratio in said mixture of said first and second fine particle materials is in the range 20:80 to 95:5. A melt-impregnated porous composite having a metal matrix and a mixture of first and second fine particle materials in said matrix; wherein said metal of said metal matrix is an aluminium alloy containing at least 0.41 wt% and not more than 2.30 wt% Mg, said first fine particle material is nickel-plated alumina particles and said second fine particle material is alumina particles which are not surface treated; and said composite is obtainable by melting the metal of the matrix and impregnating it due to the spontaneous penetration of the metal, without application of pressure, into said mixture of the first and second fine particle materials; excluding such a composite wherein the Mg content of the aluminium alloy is 0.8 wt%.

Inventors: KIDA MASAHIRO, SHINKAI MASAYUKI, KIDA, MASAHIRO, SHINKAI, MASAYUKI, Kida, Masahiro, c/o NGK Insulators, Ltd., Shinkai, Masayuki, c/o NGK Insulators, Ltd.
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 2001
Main classification: C22C1
IPC codes: B22F3, C22C1, B22F1, B22D19