DE102018205893B3 - A material consisting of a three-dimensional framework formed with SiC or SiC and Si3N4 and a noble metal alloy containing silicon, and a process for its production - Google Patents

Abstract

The invention relates to a material consisting of a three-dimensional framework, which is formed with SiC and / or Si ₃ N ₄ , and three-dimensionally connected spaces with an alloy formed with gold and / or silver and silicon. It is a proportion of the scaffold formed with SiC and / or Si ₃ N ₄ in the material at 30 vol .-% to 80 vol .-% and a proportion of the interstitial alloy at 20 vol .-% to 70 vol. -% complied. During production, a semi-finished product with an alloy formed with gold and / or silver and silicon is infiltrated above the melting temperature of the alloy.

Description

The invention relates to a material consisting of a three-dimensional framework, which is formed with SiC or SiC and Si ₃ N ₄ , and a method for its preparation. The material is formed in addition to the framework and a noble metal alloy containing silicon.

As is known, precious metals, and in particular gold and silver, have low hardness, strength and abrasion resistance in comparison to other metals, so that they are not suitable for many applications or the disadvantages, for example increased wear or undesired deformations (in particular scratches) during use must be accepted. Thus, increased wear on electrical contact elements leads to a reduction in useful life. High quality goods, such as Luxury watches can not be offered without these disadvantages from these precious metals and the common alloys that can be produced with them.

That's how it is EP 3 093 355 A1 a material which consists of Si3N4 and a metal, in particular gold, platinum, palladium or an alloy thereof.

It is therefore an object of the invention to provide materials that are formed with gold and / or silver and their life and aesthetic overall impression can be maintained at least over a longer period of use.

According to the invention, this object is achieved with a material having the features of claim 1. It can be produced by a method according to claim 8. Advantageous embodiments can be realized with features described in the subordinate claims.

The material according to the invention consists of a three-dimensional framework which is formed with SiC or SiC and Si ₃ N ₄ . The interstices within the framework are filled with an alloy formed with gold and / or silver and silicon. The material thus consists of two intertwined three-dimensional frameworks, the ceramic framework of SiC and additionally Si ₃ N ₄ or diamond and the metallic alloy of gold and / or silver and silicon. The silicon and the noble metals crystallize in separate grains, since the solubility of the noble metals in Si and Si in the noble metals in the solid phase is low.

In this case, a proportion of the scaffold formed with SiC or SiC and Si ₃ N ₄ in the material at 30 vol .-% to 80 vol .-% and a proportion of the alloy contained in the pores at 20 vol .-% to 70 vol. -% complied.

Suitable alloy compositions can be found for gold-silicon, silver-silicon, and gold-silver-silicon alloys of pertinent known phase diagrams. One can focus on a suitable low melting temperature with selection of a eutectic or on an increased strength and hardness of the material. In the latter case, one can increase the silicon content in the alloy composition. With the silicon content selected in each case, it is also possible to positively influence the wetting behavior of the alloy on the framework material.

The particular alloy should have a melting temperature in the range 350 ° C to 1400 ° C, preferably up to 900 ° C.

The alloy should contain at least 10 at% and maximum 90 at% silicon. Preferably, silicon contents range from 20 at% to 40 at% for gold as the second alloying element and 10 at% to 40 at% for silver as the second alloying element. An alloy consisting of equal parts (at%) of gold and silver should preferably contain 15 at% of Si.

With the appropriate proportion of silicon, the wetting behavior can be improved in addition to the mechanical properties. It has been shown that an infiltration of pure gold or silver into a corresponding ceramic framework made of SiC and or Si ₃ N _{4 is} not possible.

The infiltration capability of a semifinished product formed with a corresponding framework additionally depends on the amount of silicon dioxide or free carbon in the semifinished material which is formed with the framework. Silica can react with free silicon to form gaseous silicon monoxide, which can lead to the degradation of oxide layers on surfaces of the framework-forming semifinished material. Free silicon can react with carbon and thereby form additional SiC. The required amount of silicon should be taken into account when calculating the starting alloy. This should be considered, otherwise the Si content of the melt can be reduced too much and thus the wetting behavior is impaired. This promotes the reproducibility and technical controllability of the manufacturing process. Carbon from an organic binder should preferably be reacted to SiC prior to infiltration or even during infiltration with an Si-containing gas phase. A Si-containing atmosphere can be effectively generated by a chemical reaction of Si + SiO ₂ to gaseous SiO ₂ . SiO has a higher pressure than Si, especially at low temperatures, and may thereby contribute to faster infiltration if there is free carbon in the sample. However, it is also possible to evaporate elemental Si during infiltration.

If one chooses a eutectic alloy composition, such as a gold-silicon alloy with a eutectic temperature of 362 ° C thermal stresses of the material can be kept low. Because of the different coefficients of thermal expansion, for example, that of gold with 14.2 * 10 ^-6 1 / K and SiC with 4 * 10 ^-6 1 / K, it comes to tensions. Until the eutectic temperature is reached during cooling, relaxation of the stresses can occur and therefore the stresses can be reduced.

In a scaffold formed with SiC and Si ₃ N ₄ , a content ratio SiC / (SiC + Si ₃ N ₄ ) of> 20% by weight, preferably greater than 50% by mass, better still greater than 70% by mass should be maintained, because then the infiltration is kinetically favored.

The properties of the material can be further positively influenced, in which the framework is formed with SiC or SiC and Si ₃ N ₄ and diamond particles, wherein a proportion of diamond particles with which the framework is formed, from 0.0 Vol .-% to 98 Vol .-% should be maintained.

Also in such a material may be contained in the alloy silicon in a proportion preferably in a proportion in the range of 20 at% to 40 at%. Since the silicon partially react with the diamond to SiC and thus the framework can be solidified, preferably higher silicon contents are favorable.

In order to avoid further disadvantageous properties of the material, the proportion of a silicide-forming metal contained in the material should be less than 5 at%, preferably less than 1 at% and particularly preferably less than 0.01 at%. This also applies to other additional metals or chemical compounds contaminating the material.

A certain small proportion of silicide contained in the framework material can positively influence the wetting behavior during infiltration. However, this proportion should be less than 20% by volume, preferably less than 5% by volume and more preferably 1% by mass to 10% by mass, of silicide added during the infiltration.
Diamond particles should be contained with an average particle size d ₅₀ in the range 1 μm to 500 μm, preferably in the range 5 μm to 200 μm in the framework, which is formed with the SiC or SiC and Si ₃ N ₄ .

It should be a mean grain size of SiC or Si ₃ N ₄ in the range 0.1 microns to 200 microns, preferably less than 100 microns, more preferably less than 50 microns and most preferably less than 20 microns. This can be achieved by selecting appropriate starting powders with appropriately adapted mean particle sizes in the production of the framework as a semi-finished product.

The framework should have a porosity of at least 20% to a maximum of 70% and / or an average pore size in the range of 0.5 μm to 200 μm, in order to create good conditions for the production and in particular to take up the molten alloy during the production of the material.

The porosity of the framework material should preferably be 1 μm to 60 μm, preferably 5 μm to 40 μm. The porosity can also be influenced by the choice of the starting powder, the shaping technology (eg pressing pressure) and / or the parameters of the thermal treatment during the production of the framework.

The framework can be made with recrystallized SiC (RSiC), solid phase sintered SiC (SSiC), liquid-phase sintered SiC (LPSSiC), silicon-bonded SiC, RBSN (reaction-bonded Si ₃ N) or sintered Si ₃ N ₄ / sialon with the aid of be formed by typical sintering additives. If possible, the sintering additives should have a content of <2% by volume in order not to negatively influence the infiltration.

The framework of SiC or SiC and Si ₃ N ₄ may also be mixed with silicide during the production. As a result, the wetting by the melt can be additionally improved.

The material forming the framework should have a strength determined with a four-point measurement greater than 20 MPa, preferably greater than 30 MPa and particularly preferably greater than 50 MPa.

In the production of a material according to the invention, a semifinished product formed with a three-dimensional framework formed with SiC or SiC and Si ₃ N ₄ at a pressure less than the ambient pressure and / or in an inert atmosphere with an alloy containing gold and / or silver and silicon is formed, above the melting temperature of the alloy infiltrated. For this purpose, the alloy can be brought into contact with the material on at least one surface of the semifinished product and then a heating up to above the melting temperature can be carried out. The improved wetting behavior with the silicon contained in the alloy makes it possible to achieve at least almost complete filling of the pores present in the framework.

Inert atmospheres can be obtained with argon, hydrogen or mixtures thereof.

When infiltration a pressure of less than 10 ^-1 mbar, preferably less than 10 ^-3 mbar should be maintained. For the infiltration, a temperature in the range 850 ° C to 1600 ° C, preferably in the range 1250 ° C to 1450 ° C should be maintained.

The semi-finished product can be made by chemical reaction of diamond particles and an organic binder (previously pyrolyzed under inert conditions or vacuum at temperatures> 600 ° C) with a Si-containing gas phase or with a chemical reaction of silicon or silica with carbon. The SiC bond can also be obtained by admixing Si or / and SiO ₂ under the diamond powder or the carbon-containing SiC powder and subsequent heat treatment in vacuum or under inert gas conditions in the temperature range 1200 ° C - 1600 ° C, preferably 1400 ° C - 1550 ° C done.

During infiltration, a skeleton formed with SiC and diamond particles can be obtained by the chemical reaction of silicon contained in the alloy with carbon. In this case, carbon can be used from an organic binder (which was previously pyrolyzed under inert conditions or vacuum) and / or the diamond particles as a carbon source for the chemical reaction. This carbon can react with the Si from the alloy and form a layer of SiC around the diamond particles or grow on the SiC grains present in the framework material. As a result, a three-dimensional skeleton of SiC or SiC and diamond can be formed.

The invention will be explained in more detail by way of example in the following.

example 1

A three-dimensional open-porous semi-finished product made of RSiC was infiltrated with an alloy formed with 80 at% gold and 20 at% silicon, or with 88 at% silver and 12 at% silicon.

In the table below, parameters can be obtained in comparison with the infiltration of these alloys in a high-temperature microscope with an attempt to infiltrate pure gold and pure silver into the semifinished product. Table 1: Results of the measurements in the heating microscope document metal the atmosphere T max Result RSiC Au-Si high vacuum 1450 ° C Infiltration; Wetting angle <30-40 ° RSiC Au high vacuum 1285 ° C no wetting; Wetting angle> 130 ° LPS SIC Au-Si high vacuum 1450 ° C Infiltration; Wetting angle <30-40 ° RSiC Ag-Si high vacuum 1450 ° C Infiltration; Wetting angle <30-40 ° RSiC Ag high vacuum 1285 ° C no wetting; Wetting angle> 130 ° RBSN Au-Si high vacuum 1450 ° C Superficial infiltration; RBSN Au high vacuum 1450 ° C no wetting; Wetting angle> 130 °

It has therefore been found that the pure noble metals Ag and Au can not be infiltrated into either SiC or Si ₃ N ₄ . The use of a eutectic composition Si-Au or Si-Ag or Si-Au-Ag or a composition that is richer in Si is an alternative that allows good infiltration into SiC or SiC and Si ₃ N ₄ .

In addition, a preform made of LPS SiC prepared with 4 vol .-% Y ₂ O ₃ / Al ₂ O ₃ and additives of an average pore size of 10 microns. This sample could also be infiltrated in a heating microscope. The entire volume of the gold alloy was absorbed by the preform. So there was an infiltration.

Infiltration of compact RSiC samples was done in vacuo at 1360 ° C. The results are shown in Table 2 below. The three-dimensional open-porous semi-finished product formed with RSiC had a porosity of 26% and an average pore channel diameter and average pore size of 37 μm, respectively. The mean SiC grain size was 100 μm. The mean four-point bending strength measurement (4 point bending strength) was 60 MPa.

Infiltration of the alloy produced dense materials containing an Au-Si alloy. The alloy was formed with 20 at% silicon and 80 at% gold.

The gold alloy and the RSiC sample were placed on a BN plate. The gold lay on the RSiC sample and the furnace was heated under vacuum at 5 K / min. The mass intake is listed in Table 2. The samples thus consist after infiltration to 59.2 vol .-% and 60.9 vol .-% of the gold alloy. Table 2: Results of infiltration of compact samples No conditions Mass SiC, g Mass infiltrated, g Δm,% Density, gcm ³ 1 1,360 ° C 10 ^-5 mbar 7:05 17:26 245 5.94 2 1360 ° C 10 ^-2 mbar 7.12 18:22 256 5.88

Diamond powder with a particle size of 50 microns was mixed with 5% by mass of phenolic resin and pressed at a pressure of 70 MPa into tablets of 1 mm thickness. The tablets were pyrolyzed at 800 ° C in Ar atmosphere and then annealed at 1550 ° C in Si vapor in a silicided graphite crucible. The Si vapor was generated by a separately arranged crucible with Si powder.

After the process, the tablets treated as a body had a porosity of about 50%. The carbon of the diamond had been superficially reacted in SiC.

This tablet-shaped molded article was then infiltrated in an analogous manner in a vacuum oven at a temperature of 1360 ° C., a pressure of 10 ^-2 mbar over the course of 20 minutes with an alloy of 30 at.% Si and 70 at.% Au. The supplied alloy was absorbed by the preform. In the finished body, X-ray gold, Si, SiC and diamond could be detected.

Claims (13)

A material consisting of a three-dimensional framework formed with SiC or SiC and Si ₃ N ₄ , and three-dimensionally connected spaces with an alloy formed with gold and / or silver and silicon and a portion of SiC or SiC and Si ₃ N ₄ scaffold formed in the material at 30 vol .-% to 80 vol .-% and a content of the information contained in the interstices of the alloy at 20 vol .-% to 70 vol .-% and a material with SiC and Si ₃ N _{4 is} formed, a content ratio SiC / (SiC + Si ₃ N ₄ )> 20 mass% is maintained. Material after Claim 1 , characterized in that the skeleton with SiC or SiC and Si ₃ N ₄ and diamond particles is formed, wherein a proportion of diamond particles with which the skeleton is formed, from 0 vol .-% to 98 vol .-% is maintained. Material according to one of the preceding claims, characterized in that in the alloy silicon in a proportion in the range 10 at% to 90 at%, preferably in a proportion in the range 20 at% to 40 at% is included. Material according to one of the preceding claims, characterized in that the alloy, which is formed with gold and / or silver and silicon, has a melting temperature in the range 350 ° C to 1400 ° C, preferably up to 900 ° C, Material according to one of the preceding claims, characterized in that a mean grain size of SiC or Si ₃ N ₄ in the range 0.1 microns to 200 microns, preferably less than 100 microns, more preferably less than 50 microns and most preferably less than 20 microns is maintained , Material according to one of the preceding claims, characterized in that diamond particles are contained with an average particle size d ₅₀ in the range 1 micron to 500 microns, preferably in the range 5 microns to 200 microns. Material according to one of the preceding claims, characterized in that the framework with recrystallized SiC (RSiC), by solid phase sintered SiC (SSiC), with liquid-phase sintered SiC (LPSSiC), silicon-bonded SiC, or reaction-bonded Si ₃ N ₄ (RBSN) or is also formed with sintered Si ₃ N ₄ / sialon with the aid of typical sintering additives. A method for producing a material according to any one of the preceding claims, characterized in that a semifinished product with a three-dimensional open-porous framework, which is formed of SiC or SiC_und-Si ₃ N ₄ , at a pressure less than the ambient pressure and / or in a inert atmosphere with an alloy formed with gold and / or silver and silicon infiltrated above the melting temperature of the alloy. Method according to one of the two preceding claims, characterized in that in the infiltration a pressure of less than 10 ^-1 mbar, preferably less than 10 ^-3 mbar and a temperature in the range 850 ° C to 1600 ° C, preferably in the range 1250 ° C to 1450 ° C is respected. Method according to one of the three preceding claims, characterized in that the semifinished product is produced by chemical reaction of diamond particles and the carbon from an organic binder with a Si-containing gas phase. Method according to one of the three preceding claims, characterized in that during the infiltration by chemical reaction of silicon contained in the alloy with carbon, a skeleton formed with SiC and diamond particles, and thereby the organic binder and / or diamond particles as a carbon source used for the chemical reaction. Method according to one of the four preceding claims, characterized in that a framework is used which has a porosity of at least 20% to a maximum of 70% and / or an average pore size in the range 0.1μm to 100 microns Method according to one of the five preceding claims, characterized in that a framework is used which has a strength determined by a four-point bending strength measurement greater than 20 MPa, preferably greater than 30 MPa and more preferably greater than 50 MPa.