AT393121B - METHOD FOR JOINING SILICON CARBIDE MOLDED PARTS - Google Patents

Description

AT 393 121B

The invention relates to a method for connecting silicon carbide moldings, in which the polished, free element-fitting surfaces are brought together and heated to high temperature in a first or reducing atmosphere under pressure.

According to the invention, connections between molded parts made of pressure-sintered silicon carbide (SSiC) and / or hot-pressed silicon carbide (HPSiC) are produced in particular. Silicon carbide construction parts are essentially manufactured by three different processes, which lead to different materials, namely: 1) infiltrated or reaction-bonded silicon carbide (SiSiQ 10 2) pressure-free sintered silicon catbide and 3) hot-pressed silicon carbide.

Molded parts made of infiltrated or reaction-bonded silicon carbide, which are obtained by siliconizing corresponding green bodies made of carbon or carbon and silicon carbide, contain 5-30% by weight of free silicon, which can be used to bond molded parts.

According to DE-OS 3003186, individual parts made of SiSiC are fitted together to form a workpiece and are diffused by free silicon at temperatures < 1300 ° C with simultaneous pressure loading of the connecting surface by so-called diffusion welding. According to EPOS 3139270, ground and polished connecting surfaces of SiSiC molded parts are fitted together and connected to one another by heating to 1500 ° -1800 ° C. 20 (i.e. above the melting point of silicon). Both processes produce dense, up to approx. 1400 ° C mechanically stable, temperature change-resistant, corrosion and oxidation-resistant connections with a silicon seam that is approx. 1 pm narrow, possibly with very fine silicon carbide precipitates.

Regardless of the presence of free silicon in the material, silicon carbide components can be joined together by means of cementing materials containing carbon or carbon / silicon carbide containing 25 organic binders, coking them and infiltration of silicon to convert the carbon into silicon carbide. Different variants of this method are e.g. B. described in US-PS 2,319,323 and DE-OS 29 22 953. According to DE-OS 33 11553 of the applicant, the cement or carbon is not brought between the connecting surfaces but into the roughened surface thereof for this purpose. According to US Pat. No. 4,156,051 30, ceramic molded parts are joined together without any binder by first presintering them individually in a first stage to a density of at least 65% of the theoretical value, then joining them together and finally to a density of approx. 98 % of theory are hot pressed again. This process is complex since not only the mating surfaces have to be loaded in the second stage.

Finally, extremely often attempts have been made to combine hot-pressed silicon carbide with metals or over 35 metal layers. Attempts have always been made to bridge the difference in the coefficient of thermal expansion between silicon carbide and metal either by intermediate phases formed (silicides and / or caibids) or by means of SiC-metal powder mixtures with a gradually increased metal content towards the metal. The report BMFT-FB T 79-124 reports, for example, on the connection of hot-pressed SiC using likewise thin, compact layers (100 - 500 μm) of hot-pressed tungsten-40 and molybdenum powder. Characteristic of such composites are the cracks running from the transition zone formed into the SiC and the high porosity in the hot-pressed material.

The object of this invention is to permanently connect pressurized sintered and / or hot pressed silicon carbide molded parts by means of a gas-tight, corrosion and oxidation resistant, temperature change resistant, mechanically stable joining seam up to approx. 2200 ° C. 45 This object is achieved according to the invention by a method of the type mentioned, which is characterized in that silicon carbide molded parts made of pressure-sintered SiC (SSiQ or hot-pressed SiC (HPSiC) are connected to each other by a maximum of at least one dm polished fitting surfaces 1 μm thick activation layer of at least one carbide- and / or silicide-forming element from the group Ag, Al, Au, B, Be, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Ni, Pd, Pt , Ta, Ti, V, W and Zr is applied and the 50 assembled parts in an inert or reducing atmosphere in the range from 10 '* to 10 ^ Pa at temperatures in the range from 800 to 2200 ° C under a pressure in the range from 1 to 100 MPa are welded together.

In this method, a very thin " activating " covering layer made of a carbide- and / or silicide-forming material, which practically disappears during the subsequent joining treatment under increased use of temperature and pressure and is no longer detectable as such in the joining surface. The method according to the invention differs significantly from known methods, who work with adhesive layers containing foreign material.

The activating layer of the above-mentioned carbide and / or silicide formers or mixtures or alloys thereof is preferably applied with a thickness of 0.1 to 1 μm by any suitable method to at least one mating surface, advantageously z. B. evaporated or sputtered

The applied joining temperature depends on the applied activation layer: for Ag, Al, Au and -2-

AT 393 121B

Mg is chosen between 800 and 1200 ° C; for Be, Cu, Ge and Mn between 1200 and 1600 ° C; for Co, Cr, Fe, Ni, Pd, Pt and V between 1600 and 2000 ° C and for B, Mo, Nb, Ni, Ti, V, W and Zr between 2000 and 2200 ° C.

Cr, Cu, Ni, Pt and / or Pd or alloys thereof have proven particularly useful as materials for the activating layer, in particular copper and copper alloys.

The joining treatment is carried out in an inert or reducing atmosphere, in particular in argon and / or

Hydrogen. It is particularly expedient to work in argon from 10 ^ to 10 ^ Pa. The heating-up time is about 1 to 2 hours under constant pressure until the joining temperature is reached, which is maintained for at least 10 minutes, depending on the activation material and the pressure used, followed by cooling of the furnace

The joining temperature is chosen especially above the melting point of the material of the thin layer and the temperature, pressing pressure and treatment time are coordinated with one another taking into account the material of the applied layer, the thickness of which is less than 1 pm.The duration of the high temperature pressing pressure must be chosen the shorter the higher the joining temperature In an analogous manner, the contact pressure can be set lower, the higher the joining temperature is intended. A relatively low temperature together with a relatively high pressure or a combination of high temperature, relatively low pressing pressure and shortened pressing time appear to be favorable.

Temperatures in the range from 1500 to 1800 ° C., in particular 1550 to 1750 ° C. and pressures from 15 to 45 MPa, in particular around 25 MPa and joining times between 15 and 120 minutes, in particular in the range from 30 to 60 minutes, are preferred.

The invention is described below by way of examples with reference to the attached drawings; show it:

Figure a micrograph of the seam (1000 x) and

Figures 2 and 3, the distribution plan of the body according to Examples 2 and 3.

Example 1:

The polished surface of an SSiC disk with a diameter of 20 mm and a height of 3 mm was provided with a 0.5 μm thick copper layer by sputtering. Another disc, also with a polished surface, was placed on it and housed in a graphite die with a die and stamp. This arrangement was then inserted under the hot press die. The press room was evacuated several times and aerated with welding argon. Finally an Ar / H2 * pressure of 1 KPa was set and the

Sample heated to 1700 ° C under a pressure of 30 MPa. After a holding time of 30 minutes, the heating was slowly turned down (average 20 ° C / min). Fig. 1 shows the quality of the weld area after polishing and etching. With a thickness of approx. 0.1 pm, the weld seam lies in the thickness range of the etched grain boundary.

Example 2:

An approximately 03 pm thick palladium layer was applied on both sides to a 3 mm thick SSiC disk of 25 x 10 mm, polished, on both sides, analogously to a printing process using a roller. After the dispersant had been evaporated, the pane was placed between the polished end faces of two SSiC cuboids, each measuring 25 × 25 × 10 mm, and, as described in Example 1, hot-pressed. Test specimens were cut from the assembled sample in accordance with the plan shown in FIG Grinding and polishing tested in a 4-point bending testing machine. The flexural strength values of the individual samples were in the same range as that of the starting material (at 270 ± 20 MPa).

Example 3:

A 3 mm thick, plane-parallel pipe section was cut from an HPSiC pipe with an outer diameter of 40 mm and an inner diameter of 30 mm, and the polished cut surfaces were vacuum-coated on both sides with a 0.2 pm thick Cr / Ni alloy. This " ring washer " was then placed between the polished base surfaces of two 28 mm long pieces of pipe of the same material and hot-pressed in an analogous manner as described in Example 1 at 1800 ° C. and a pressing pressure of 50 MPa. The welded pipe was then tested for leaks in a vacuum testing system; the leak rate was 10 ~ ^ pals ’*. The tube was then cut into tube segments, as shown in FIG. 3, and rectangular bending rods were produced therefrom by grinding. After polishing, the bending strength of the samples was measured. It was 500 ± 30 MPa and was only 4% below that of seamless samples.

Further results that were aimed at connecting pressureless sintered SiC (surface ground, lapped, cleaned in an ethyl acetate ultrasound bath) using thin (<, 1 pm) sputter layers made of copper, copper alloys or palladium are summarized in the table below - 3-

Claims (10)

AT 393 121B test no. &Lt; 1 mm from temp. T time min pressing pressure MPa pressing atmosphere Pa bending strength MPa 98 Cu 1550 60 * 15.0 4.0104 240 ± 87 96 Cu 1750 60 15.0 4.0104 200 ± 44 75 Cu 1750 60 24.5 2.7 103 211 ± 36 97 Cu 1750 30 15.0 4.0104 233 ± 66 74 Pd 1750 60 24.5 2.7103 102 ± 20 99 Cu / Si 1550 60 24.5 4.0104 149 ± 19 101 Cu / Pd 1550 60 24.5 4.0 104 148 ± 32 The heating rate was 10 - IS ° C / min. As the table shows, the results achieved with copper are particularly good and are significantly higher than the 20 values that can be achieved with activating Si quantities: the bending strength at room temperature reaches up to 80% of the bending strength of the base material. 25 PATENT CLAIMS 30 1. A process for connecting silicon carbide moldings, in which the polished, free element-fitting surfaces are brought together and heated in an inert or reducing atmosphere under high pressure to a high temperature, characterized in that silicon carbide moldings made of drucldos sintered SiC (SSiC) or hot-pressed SiC (HPSiC) are connected to one another by activating at least one μm-thick activation layer of at least one carbide- and / or silicide-forming element from the group Ag, Al, Au, B, Be on at least one of the polished mating surfaces , Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Ni, Pd, Pt, Ta, Ti, V, W and Zr is applied and the joined parts in an inert or reducing atmosphere in the range of 10 * 1 to 10 ^ Pa at temperatures in the range of 800 to 2200 ° C under a pressure in the range of 1 to 100 MPa are welded together. 2. The method according to claim 1, characterized in that a 0.1 to 1 pm thick activation layer is applied to at least one of the mating surfaces. 45 3. The method according to claim 1 or 2, characterized in that the carbide- and / or silicide-forming material is evaporated, sputtered or applied with the roller. 4. The method according to claim 1, characterized in that 50 Cr, Cu, Ni, Pt and / or Pd or alloys thereof are applied as the carbide- and / or silicide-forming material. 5. The method according to claim 1, characterized in that copper or copper alloys are used for the thin layer. 6. The method according to claim 1, characterized in that the joining temperature is chosen above the melting temperature of the material of the thin layer. 7. The method according to claim 1 or 6, characterized in that the temperature, pressing pressure and treatment time taking into account the material of the applied 1 mm thick layer to each other -4- AT 393 121B are coordinated. 8. The method according to claim 7, characterized in that the pressing pressure at IS to 45 MPa, in particular around 25 MPa, the temperature between 1500 and 1800 ° C and the duration of the pressure action between 15 and 5 120 min., In particular in the range of 30 up to 60 min. chosen to graze. 9. The method according to any one of the preceding claims, characterized in that the joining treatment is carried out in argon at a pressure in the range from 10 ^ to 10 ^ Pa. 10 For this 1 sheet drawing -5-