ES2353704B1 - METHOD OF OBTAINING A NANO-STRUCTURED COMPOSITE MATERIAL OF CERAMIC AND MECHANIZABLE MATRIX BY ELECTROEROSION, AND OBTAINABLE PRODUCT PORDICHO METHOD - Google Patents

Abstract

Method of obtaining a nanostructured composite material of ceramic matrix and machinable by EDM, and product obtainable by said method. # It allows to obtain a composite ceramic material / semiconductor / metal nanostructured and machinable by EDM. The starting materials are: a nanometric particle size ceramic material, a nanometric particle size semiconductor material, and a metal salt, used as a precursor to the corresponding metal. The method comprises the steps of: a) preparation of a ceramic powder / metal oxide material by calcining a dry powder obtained from a homogeneous suspension of the ceramic material and the metal precursor metal salt; b) addition to the powder resulting from the previous stage of the semiconductor material; c) grinding, homogenization, drying and sieving of the powder resulting from the previous stage; d) heat treatment in a reducing atmosphere of the powder resulting from the previous stage, and e) forming and sintering of the powder from the previous stage.

Description

Method of obtaining a nanostructured composite material of ceramic matrix and machinable by EDM, and product obtainable by said method.

Object of the invention

The present invention can be included within the technical field of ceramic matrix composite materials, in particular nanostructured ceramic matrix materials.

The object of the invention is a process for obtaining a nanostructured composite material of ceramic matrix that is machinable by the EDM method. The object of the invention is also the composite material obtainable by said method.

The invention has its application in various fields, among which are electrodes, tools (cutting, extrusion, pressing, ultra-precision machining, etc.), high wear resistance brakes, electronic components, watch parts, etc.

Background of the invention

Ceramic materials currently find technical applications in multiple sectors thanks to their particular physical and chemical properties, such as hardness, toughness, resistance to thermal shock, low coefficient of thermal expansion, high wear resistance, high thermal conductivity, acid resistance , etc.

A common strategy to obtain materials with superior mechanical properties with respect to monolithic ceramic matrices is the incorporation of reinforcing agents (particles, fibers, etc.), giving rise to composite materials of ceramic matrix. Also, in the event that the particles possess functional properties (magnetic, electrical, etc.), the corresponding composite materials can also acquire these new functional properties, becoming multifunctional materials. Specifically, the addition of conductive and / or semiconductor particles (carbides, nitrides, borides, etc.) to insulating ceramic matrices confers, on the one hand, high electrical conductivity, which allows the composite material to replace metallic components in conventional electronic devices, and, on the other, it can reinforce the ceramic matrix by different mechanisms (micro-cracking, crack fl exion, residual tensions, crack bridging, etc.), reaching tenacity values much higher than those obtained for monolithic ceramics [JS Moya, S. Lopez-Esteban, C. Pecharroman "The challenge of ceramic / metal microcomposites and nanocomposites", Progress in Materials Science, 52 (2007) 1017-1090].

However, the exceptional mechanical properties of ceramic materials in general, and nanostructured ceramic matrix materials in particular, can present serious problems that can significantly increase their production costs. Such is the case of materials with high hardness, for which the difficulty of machining by traditional methods increases considerably and, consequently, also increases the cost of the process and the final product. Likewise, finishing with intricate shapes in these materials requires tolerances that are often difficult to achieve with traditional machining techniques.

This situation has favored the development of more sophisticated methods for the machining of parts with complex shapes that avoid mechanical tool / part contact, as is the case of electro-erosion or electrical discharge machining (Electrical Discharge Machining, EDM) [W. König, D.F. Dauw, G. Levy, U. Panten. "EDM-future steps towards the machining of ceramics". Ann. CIRP 1988; 37: 623]. This technique successfully overcomes most of the difficulties posed by these materials, avoiding the high costs of traditional techniques.

The EDM process basically consists in the establishment of a discharge arc between the conductive wire, which propitiates the machining itself, and the piece to be machined, above the breaking voltage of the dielectric in which the part is submerged ( oil or water) Once the discharge begins, a plasma is formed on the machining front which, when cooled, is deposited on the fresh surface produced by the cut, forming a vitreous magma consisting of the corresponding oxides. In the particular case of a ceramic / semiconductor composite material, the deposit formed is constituted by an oxidic glassy phase characterized by having a breaking voltage higher than the initial one. However, in the case of ceramic / semiconductor / metal composite materials, the role of the metal nanoparticles is to induce a drop in the breakdown voltage in the newly deposited layer during discharge, allowing the EDM process to develop. Continuous form. No references have been found in the literature of ceramic / metal nanostructured powders with the addition of semiconductor electroconductive nanoparticles.

The EDM technique can be successfully applied to both oxidic and non-oxidic ceramic materials, provided that they satisfy a series of requirements, among which it is mainly found that the electrical resistivity is less than 100-300 Ω · cm. It may be the case of a ceramic / semiconductor composite material that is not electromechanizable despite complying with the aforementioned low resistivity requirement. This is especially relevant in ceramic matrix composite materials with semiconductor particles that have low electrical resistance and very high hardness values. The technical problem that arises is to confer on the nanostructured material

ceramic / semiconductor that is not electromechanizable the property of being without prejudice to its high mechanical properties.

Description of the invention

The present invention solves the technical problem posed by a method of obtaining a nanostructured ceramic matrix material, of ceramic / semiconductor / metal composition, by sintering, which is machinable by EDM.

As has just been advanced, an object of the invention is a process for manufacturing a ceramic / semiconductor / metal nanostructured ceramic material, which turns out to be machinable by EDM.

A second object of the invention is the composite material itself obtainable by means of the above procedure.

Next, the process of the invention is described:

The starting materials are:

-

a powder ceramic material of nanometric particle size, called ceramic matrix;

-

a semiconductor material of nanometric particle size, and

-

a metal salt, used as a precursor of the corresponding metal.

It is theoretically reasonable to assume that the results of the invention are generally extrapolar regardless of the ceramic matrix employed. However, preferred examples of ceramic materials are Al2O3 (alumina), Al6Si2O13 (mullite), ZrO2 (zirconia), MgAl2O4 (alumina and magnesium spinel) and YAG (aluminum and yttrium garnet). This preferred selection is justified because it includes several different types of high performance technical ceramics, of wide diffusion and varied applications, and which have very high hardness values, so they are especially interesting for the purposes of the invention.

Likewise, the invention is applicable independently of the semiconductor material used. However, semiconductors such as carbides, nitrides and metal borides are preferred, since they confer high values of mechanical properties (hardness, essentially). As particular examples of semiconductors, SiC, TiC, TiN, TiB2 are selected.

As for metals, identical considerations are reasonable. The invention is applicable independently of the metal used. However, metals with a melting point greater than 1400 ° C are preferably selected, such as W, Ni, Mo, Co.

Applying theoretical knowledge related to the concept of percolation, a maximum value of 16% by volume of metal can be considered, since it is the value at which the composite material would acquire a conductive character. However, due to practical considerations, a maximum metal proportion value of 10% is taken, since certain mechanical properties - such as hardness - are negatively affected by higher metal proportions. The minimum proportion of metal used has been 1.9% by volume, although there are no reasons to assume that the invention cannot yield positive results for any non-zero value of metal presence. Therefore, metal concentrations higher than 0% can be considered valid, not being necessary to exceed 16% by volume. However, although it is assumed that the invention has a positive effect for arbitrarily small proportions of metal, it is necessary to choose a preferred minimum value of said proportions from 1% by volume, since for lower values the theoretical knowledge allows to reasonably assume that the Interesting mechanical properties would be negatively affected.

The first stage of the process of the invention deals with the preparation of a ceramic powder / metal oxide material. First, the metal salt dissolves in liquid medium until homogenization is achieved. Then, the ceramic powder is added, obtaining a suspension of ceramic material and metal precursor salt, while stirring until total homogenization. Then, the homogeneous suspension is dried, then calcined, whereby a ceramic / metal oxide powder material is obtained.

Through the second and final stage of the process of the invention, the ceramic / metal oxide material is transformed into a ceramic / semiconductor / metal material. To do this, the nanometric particle size semiconductor material is first added to the ceramic powder / metal oxide mixture and ground and homogenized. It is then allowed to dry and sieved, after which the resulting product is subjected to a heat treatment in a reducing atmosphere, obtaining the final ceramic / semiconductor / metal powder compound. The metal and the semiconductor are in such a proportion that the percolation point of the final compound is exceeded.

Preferably, the reduction occurs at a temperature between 300 ° C and 1000 ° C and for a period between 30 minutes and 2 hours.

Forming and sintering can be performed by any of the usual methods in the advanced ceramic industry, such as pressureless sintering, hot isostatic pressing, hot pressing, spark plama sintering (SPS), etc.

Description of the drawings

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical realization thereof, a set of drawings is accompanied as an integral part of said description. where, for illustrative and non-limiting purposes, the following has been represented:

Figure 1.- Represents a micrograph obtained by scanning electron microscopy of polished surface of sample 3Y-TZP / nTiC / nNi and x-ray diffractogram.

Figure 2.-Samples of 3Y-TZP / nTiC / nNi sintered by HP and machined by EDM in the form of prisms of rectangular section (5 mm x 3 mm) and cutting surface by EDM of said material.

Figure 3.- Represents a micrograph obtained by optical microscopy of polished surface of sample Al2O3 / nTiC / nNi and x-ray diffractogram.

Figure 4.- Represents a sample of Al2O3 / nTiC / nNi sintered by SPS and machined by EDM (25 mm x 25 mm x 8 mm).

Preferred embodiments of the invention

First realization

Nanostructured zirconia / titanium carbide / nickel composite

The starting raw materials have been: As a ceramic material, polygrystalline tetragonal zirconia (3Y-TZP, 3% mol. Y2O3; TZ-3YE, Tosoh Corp., Japan), with average particle size d50 = 260 ± 50 nm; as a metal precursor salt, nickel (II) nitrate hexahydrate (Ni (NO3) 2 · 6H2O, Merck, Germany, 99.0% purity), hereinafter nNi; and as a semiconductor, nanometric titanium carbide (Hubei Minmetals, China) with an average particle size below 50 nm, hereinafter, nTiC.

Two types of compounds have been prepared:

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(a) ceramic / semiconductor / metal, according to proportions of 72% vol. 3Y-TZP, 20% vol. nTiC and 8% vol. nNi, and

-

(b) ceramic / semiconductor, according to the proportions of 72% vol. 3Y-TZP and 28% vol. nTiC.

Both compounds have been formed and sintered by hot pressing (Hot Press, HP, at 1400 ° C, 10 ° C / min, 25 MPa, for 1 hour). 50 mm diameter discs were obtained, with a 98% density of the theoretical one, consisting of a continuous zirconia matrix, a titanium carbide nanoparticles phase and, in the case of a), a dispersed nickel nanoparticles phase. The phase distribution is homogeneous with small agglomerates of the second phases, with no chemical reactions occurring between the components, as shown in Figure 1.

The mechanical properties of the zirconia / nTiC / nNi compounds have improved or, at least, are maintained with respect to the sintered monolithic zirconia under the same conditions. Vickers hardness values (11.5 ± 0.2 GPa) with respect to monolithic zirconia (11.0 ± 0.2 GPa) are maintained. The resistance to flexion values are improved (804 ± 32 MPa for the new material and 752 ± 16 MPa for the monolithic zirconia). The toughness increases markedly with respect to zirconia (6.0 ± 0.2 MPa · m1 / 2 and 4.9 ± 0.2 MPa · m1 / 2, respectively).

The metal-free compound (zirconia / nTiC) has a resistivity of 14.0 · 10−4 ± 1.0 · 10−4 Ω · cm, well below the maximum limit of 100-300 Ω · cm required to apply the EDM technique, without However, it was not possible to perform the machining. The metal composite material (zirconia / nTiC / nNi) has an electrical resistivity of 7.2 · 10−4 ± 1.0 · 10−4 Ω · cm, also below the required maximum, and it could be machined by EDM. The addition, therefore, of a small amount of metal decreases the resistivity of the material by about 50% and allows it to be machined by EDM. Figure 2 shows the material of 3Y-TZP / nTiC / nNi sintered by HP and subsequently machined by EDM in the form of prisms of rectangular section (5x3 mm).

Second embodiment

Nanostructured alumina / titanium carbide / nickel composite

The starting raw materials have been: As ceramic material, alumina (α-Al2O3, Taimei TM-DAR, with average particle size d50 = 150 ± 50 nm; as metal precursor salt, nickel nitrate (II) hexahydrate (Ni (NO3) 2 · 6H2O, Merck, Germany, 99.0% purity), hereinafter nNi; and, as a semiconductor, nanometric titanium carbide (Hubei Minmetals, China) with average particle size below 50 nm, hereinafter, nTiC .

Two types of compounds were prepared:

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(a) ceramic / semiconductor / metal according to the proportions 73.1% vol. Al2O3, 25% vol. nTiC and 1.9% vol. nNi; Y

-

(b) ceramic / semiconductor, according to the proportions 75% vol. Al2O3, 25% vol. nTiC.

The material has been sintered by Spark Plasma Sintering (SPS), at 1375 ° C, 100 MPa for 3 minutes in the form of 40 mm diameter discs. In this way, dense materials (theoretical density 99.5%) consisting of a continuous alumina matrix, a dispersed phase of titanium carbide nanoparticles and, in case a), another of nickel nanoparticles were obtained. With the exception of small agglomerates of Al2O3 / nNi, it is a dense and homogeneous compact, with no chemical reactions occurring between the components, as shown in Figure 3.

The mechanical properties have been improved with respect to sintered monolithic alumina under the same conditions. Vickers hardness values (25.6 ± 0.7 GPa) with respect to monolithic alumina (19.9 ± 0.9 GPa) are improved. The values of resistance to flexion are improved (537 ± 88 MPa for the new nanocomposite material and 395 ± 36 MPa for monolithic alumina). The tenacity values obtained are very similar for the composite and alumina, being 3.7 ± 0.1 MPa · m1 / 2 and 3.5 ± 0.1 MPa · m1 / 2, respectively.

The value of the electrical resistivity obtained at room temperature for Al2O3 / nTiC / nNi materials has been 31.5 · 10−4 ± 1.0-10−4 Ω · cm, and for Al2O3 / nTiC it has been 462.6 · 10−4 ± 36.0 · 10−4 Ω · cm, enough to be machined by EDM. Prisms of 25x25x8 mm square section were machined, as shown in Figure 4.

Claims (13)

one.

Method of obtaining a nanostructured composite material of ceramic matrix and machinable by EDM, characterized in that it comprises the steps of: -preparation of a ceramic / metal oxide powder material, by calcining a homogeneous dry suspension of a ceramic powder of size of nanometric particle and a metal precursor metal salt; -addition to the product of the previous stage of a semiconductor material of nanometric particle size; - grinding and homogenization of the product resulting from the previous stage; - drying and sieving of the product resulting from the previous stage; - heat treatment in a reducing atmosphere of the product resulting from the previous stage, obtaining a ceramic / semiconductor / metal powder

Y -formed and sintered the product of the previous stage.

2.

Method of obtaining a composite material, nanostructured, ceramic matrix and machinable by EDM according to claim 1, characterized in that the heat reduction treatment occurs at a temperature between 300 ° C and 1000 ° C.

3.

Method of obtaining a composite material, nanostructured, ceramic matrix and machinable by EDM according to claim 1, characterized in that the ceramic matrix is selected from:

-

Al2O3 (alumina),

-Al6Si2O13 (mullita), -ZrO2 (zirconia), -MgAl2O4 (alumina and magnesia spinel), -YAG (aluminum garnet and yttrium).

Four.

Method of obtaining a composite material, nanostructured, ceramic matrix and machinable by EDM according to claim 1, characterized in that the semiconductor is selected from carbides, nitrides and borides.

5.

Method of obtaining a composite material, nanostructured, ceramic matrix and machinable by EDM according to claim 4, characterized in that the semiconductor is selected from SiC, TiC, TiN, and TiB2.

6.

Method of obtaining a composite material, nanostructured, ceramic matrix and machinable by EDM according to claim 1, characterized in that the metal has a melting point higher than 1400 ° C.

7.

Method of obtaining a composite material, nanostructured, ceramic matrix 5 and machinable by EDM according to claim 6, characterized in that the metal is W, Ni, Mo or Co.

8. Product directly obtainable by means of the method described in any one of claims 1 to 7.

9.

Product according to claim 8, characterized in that the metal and the semiconductor are in a proportion such that the percolation point of the final compound is exceeded.

10.

Product according to claim 9, characterized in that the proportion of metal is less than 16% by volume.

11. Product according to claim 10, characterized in that the proportion of metal is less than 10% 12. Product according to claim 8, characterized in that the proportion of metal is between 1% and 16% by volume. 6 7 8 SPANISH PATENTS AND BRANDS OFFICE Application no .: 200930551 SPAIN Date of submission of the application: 31.07.2009

REPORT ON THE STATE OF THE TECHNIQUE

Priority Date: 00-00-0000 00-00-0000 00-00-0000

51 Int. Cl.:

See additional sheet

 RELEVANT DOCUMENTS  

Category

56 Documents cited Claims Affected

X

TAICHIU LEE; JIANXIN DENG. " Mechanical surface treatments of electro-discharge machined (EDMed) ceramic composite for improved strength and reliability " Journal of the European Ceramic Society. 2002. Vol. 22 pages 545-550; Section 2.1, Table 1. 8-12

X

DENG, J. et al. " Wear of ceramic nozzles by dry sand blasting " Tribology International 03.03.2005 [online] Vol. 39 pages 274-280; Section 2.1, Table 1. 8-12

TO

BONNY, K. et al. " Influence of secondary electro-conductive phases on the electrical discharge machinability and frictional behavior of ZrO2-based ceramic composites " JOURNAL OF MATERIALS PROCESSING TECHNOLOGY. 21.01.2008. vol. 208, pages 423-430; section 2.1. 1-12

Category of the documents cited X: of particular relevance Y: of particular relevance combined with other / s of the same category A: reflects the state of the art O: refers to unwritten disclosure P: published between the priority date and the date of priority submission of the application E: previous document, but published after the date of submission of the application

This report has been prepared • for all claims • for claims no:

Date of realization of the report 13.09.2010

Examiner V. Balmaseda Valencia Page 1/4

Application number: 200930551 REPORT ON THE STATE OF THE TECHNIQUE CLASSIFICATION OBJECT OF THE APPLICATION C04B 35/119 (2006.01) C04B 35/48 (2006.01) C04B 35/58 (2006.01) Minimum documentation sought (classification system followed by classification symbols) C04B Electronic databases consulted during the search (name of the database and, if possible, search terms used) INVENES, EPODOC, WPI, NPL, XPESP, HCAPLUS  WRITTEN OPINION Application number: 200930551 Date of Completion of Written Opinion: 13.09.2010

Statement

Novelty (Art. 6.1 LP 11/1986)

Claims 1-7 Claims 8-12 IF NOT

Inventive activity

Claims 1-7 YES

(Art. 8.1 LP11 / 1986)

Claims 8-12 NO

The application is considered to comply with the industrial application requirement. This requirement was evaluated during the formal and technical examination phase of the application (Article 31.2 Law 11/1986).  Opinion Base.- This opinion has been made on the basis of the patent application as published.  WRITTEN OPINION Application number: 200930551 1. Documents considered.- The documents belonging to the state of the art taken into consideration for the realization of this opinion are listed below.

Document

Publication or Identification Number publication date

D01

Journal of the European Ceramic Society. Vol. 22 pages 545550 2002

D02

Tribology International Vol. 39 pages 274-280. 03.03.2005

2. Statement motivated according to articles 29.6 and 29.7 of the Regulations for the execution of Law 11/1986, of March 20, on Patents on novelty and inventive activity; quotes and explanations in support of this statement The object of the present invention is a method of obtaining a nano-saturated composite material of ceramic matrix and machinable by EDM. As well as the material resulting from said method. Document D01 describes a method of obtaining a nano-saturated composite material of ceramic matrix and machinable by EDM (Al2O3 / TiC / Mo / Ni) comprising the mixture of Al2O3 (average particle size 500 nm), 55% of TiC (average particle size 800nm) and 5% by volume of Ni and Mo. The resulting mixture is milled and dried and finally shaped and sintered by hot pressing under an argon atmosphere at 35MPa and temperatures between 1600-1800 ° C. The resulting material has a hardness of 20.5 GPa, a resistivity between 2-6 ohm per cm and a toughness of 5.04 MPa m1 / 2 (section 2.1, Table 1). Document D02 describes a ceramic composite consisting of Al2O3 / TiC / Mo / Ni that is obtained from the mixture of Al2O3 with 55% TiC, 0.5% Mo and 4.5% Ni (the particle size being less than 1 micrometer), its ground dried and shaped and sintered by pressing at 1700º C, 36MPa for 1 hour. The resulting material has a hardness of 20.5 GPa, a resistivity comprised between 2-6 ohm per cm, a flexural strength value of 950MPa and a toughness of 5.2 MPa m1 / 2 (section 2.1, Table 1). Claims 8-12 refer to a product defined in terms of its preparation process. The applicant is reminded that such claims would only be admissible if the product, as such, meets the patentability requirements, that is, it is new and has inventive activity. However, such requirements are not met in this case since said product has been disclosed identically in documents D01-D02. Consequently, it is considered that the object of these claims is novel in view of the state of the art (articles 6.1 and 8.1 of the L.P.) The difference between the object of claims 1-7 is that none of documents D01-D02 describes a method of obtaining a nanostructured ceramic matrix composite material, of ceramic / semiconductor / metal composition comprising the preparation of a powder mixture of ceramic / metal oxide (by calcining a powder / metal suspension and a precursor salt of metal metal oxide) and that, subsequently, the conversion of the oxide to the metal is carried out at a stage prior to forming and sintering by a heat treatment in atmosphere ceramic powder reduction / semiconductor / metal oxide. In addition, it would not be obvious to a person skilled in the art said method of obtaining from the cited documents. Consequently, the object of claims 1-7 is considered to be new and implies inventive activity in accordance with Articles 6.1 and 8.1 of the L.P. Report on the State of the Art (Written Opinion) Page 4/4