SE463818B - PROCEDURES FOR COMBINING SILICONE CARBID FORM - Google Patents

Description

463,818 10 15 20 25 30 35 bituminous putty with organic binder, coking of these and infiltration of silicon to convert the carbon to silicon carbide. Different variants of this method are described e.g. in US-PS 2 319 323 and DE-OS 29 22 953. According to DE-OS 33 11 553, the putty resp. the carbon not between the joint surfaces but in their roughened surface for this purpose. Without any adhesive, ceramic moldings are bonded together according to U.S. Pat. No. 4,156,051 by pre-sintering them in a first step to a density of at least 65% of the theoretical value, then joining them together and finally hot-pressing them again to a density. of about 98% of the theoretical value. This method is cumbersome since in the second step not only the fitting surfaces have to be loaded.

Extremely often, attempts have finally been made to connect hot-pressed silicon carbide to metals or over metal layers. Attempts have always been made to bridge the difference in coefficient of thermal expansion between silicon carbide and metal either by means of intermediate phases (silicides and / or carbides) or by means of SiC metal powder mixtures with a gradually increasing proportion of metal against the metal. The report BMFT-FB T 79-124 describes, for example, the connection of hot-pressed SiC by means of similarly thin layers (100 - 500 μm) of hot-pressed tungsten or molybdenum powder. Characteristic of such joints are the cracks extending from the formed transition zone into the SiC as well as the high porosity of the hot-pressed material.

The object of the invention is to permanently connect pressure-free sintered and / or hot-pressed silicon carbide molded parts by means of a gas-tight, corrosion- and oxidation-resistant, resistant to temperature fluctuations, up to about 220,000 mechanically stable joints.

This object is solved according to the invention by means of a process of the kind indicated in the introduction, which is characterized in that silicon carbide molded parts of pressure sintered SiC (SSiC) or hot-pressed SiC (VPSiC) are connected to each other by that at least one of the polished pass surfaces has a maximum activation layer of at least one carbide and / or silicide-forming element in the group Ag, Al, Au, B, Be, Co, Cr, Cu, Fe, Mg, Mn, Mo , Nb, Ni, Pd, Pt, Ta, Ti, V, W and Zr are applied and the joined parts are welded together in an inert or reducing atmosphere in the range from 10'1 to 105 Pa at temperatures in the range from 800 to 2200OC under a press pressure in the range from 1 to 100 MPa.

In this process, a very thin "activating" covering layer of a carbide and / or silicide-forming material is applied to one or both high-quality joint surfaces, which during the subsequent joint treatment under high temperature and pressure application practically disappears and is no longer detectable as such in the joint surface. . Therein, the method according to the invention is clearly different from known methods, which work with adhesive layers containing foreign material.

The activating layer of the above-mentioned carbide and / or silicide formers or mixtures or the alloys thereof are preferably applied with a thickness of 0.1 to 1 μm according to any suitable method on at least one pass surface, suitably t. ex. by steaming or sputtering.

The joint temperature used depends on the applied activation layer: for Ag, Al, Au and Mg it is chosen between 800 and 1200 ° C; for Be, Cu, Ge and Mn between 1200 and 1600 ° C; for co, cr, Fe, Ni, Pa, P: ooh v between 1600 ooh 2000 ° c ooh for B, Mo, Nb, Ni, Ti, v, W and Zr between 2000 and 2200 ° C.

Particularly suitable are Cr, Cu, Ni, Pt and / or Pd or alloys thereof as materials for the activating layer, in particular copper and copper alloys. 463 818 4 10 15 20 25 30 35 The joint treatment takes place in an inert or reducing atmosphere, especially in argon and / or hydrogen. Particularly suitable is a work 1 of 103 to 105 Pa.

The heating time is about 1 to 2 hours under constant pressure load until the joint temperature is reached, which, depending on the activating material and the pressure used, is maintained for at least 10 minutes, after which a cooling in the oven is connected.

The joint temperature is chosen in particular over the melting point of the material in the thin layer and the temperature, press pressure and treatment time are matched to each other, taking into account the material in the applied 3 1 μm thick layer. In this case, the time for the effect of the compressive pressure at high temperature must be chosen the shorter the higher the joint temperature. In an analogous way, the press pressure can be set the lower the higher the joint temperature is selected.

A relatively low temperature together with a relatively high pressure or a combination of high temperature, relatively low press pressure and short press time seems to be favorable.

Preferably temperatures are used in the range 1soo - 1soo ° c, especially 1550 - 17so ° c, a pressure of 15 - 45 MPa, especially about 25 MPa, and joint times between 15 and 120 minutes, especially in the range from 30 to 60 minutes.

The invention is described below in connection with examples with reference to the accompanying drawings.

Figure 1 shows a grinding image of the joint (1000x) and Figures 2 and 3 show the division plan for the body according to examples 2 and 3.

Example 1 The polished surface of an SSiC board with a diameter of 20 mm and a height of 3 mm was provided by sputtering with a 0.5 μm thick copper layer. Another disc, also with a polished surface, was then placed * x 10 15 20 25 30 35 5 463 and applied to a graphite matrix with sinker and stamp. This device was then inserted under the plunger into the hot press. The press room was evacuated several times and filled with welding argon. Finally, an Ar / H 2 pressure of 1 kPa was set and the sample was heated under a compression pressure of 30 MPa to 1700 ° C. After a residence time of 30 minutes, the heating was regulated slowly downwards (average 20oC / min). Figure 1 shows the quality of the weld joint area after polishing and etching. With a thickness of about 0.1 μm, the weld is in the thickness range of the etched grain boundaries.

Example 2 On a double-sided polished 3 mm thick SSiC board of 25 x 10 mm, an approximately 0.3 μm thick palladium layer was applied on both sides analogously to a printing process by means of a roller. After evaporation of the dispersant, the wafer was placed between the polished end surfaces of two SSiC blocks of 25 x 25 x 10 mm each and hot pressed as described in Example 1. Samples were cut from the joined sample according to the plan shown in Figure 2 and tested after grinding and polishing in a 4-point bending test machine. The flexural strength values for the individual samples were in the same spreading range as for the starting material (at 270 120 MPa).

Example 3 From a VPSiC pipe with an outer diameter of 40 mm and an inner diameter of 30 mm, a 3 mm thick flat-parallel pipe section was cut off and the polished cut surfaces were vacuum-evaporated with a 0.2 μm thick Cr / Ni alloy. This "ring plate" was then placed between the polished base surfaces of two 28 mm long pipe pieces of the same material and hot-pressed in an analogous manner to that described in Example 1, at 1800 ° C and a press pressure of 50 MPa. then in a vacuum test facility at tightness; the leakage was 10 "'Pals'1. The pipe was then cut into pipe segments as shown in Figure 3,818,463,818 and the rectangular bending rods were made therefrom by grinding. After polishing, the flexural strength of the samples was measured. It was 500 130 MPa and was thus only 4% below the joint-free samples.

Additional results obtained by bonding pressureless sintered SiC (surface ground, lipped, purified in ethyl acetate-ultrasonic bath) using thin (3 μm) sputtering layers of copper, copper alloys or palladium are summarized as follows Chart.

För- 31 um Temp. Time Press- Press- and Flexural strength search of C min pressure atmosphere hot no MPa Pa MPa 98 cu 1550 60 15.0 4.0 10 * 280 587 96 cu 1750 60 15.0 4.0 10 ”200 544 75 cu 1750 60 24.5 2.7 10 * 211 536 97 cu 1750 30 15.0 4.0 10 ”233 566 74 Pa 1750 50 24.5 2.7 103 102 120 99 Cu / Si 1550 60 24.5 4.0 10 "149 t19 101 Cu / Pd 1550 60 24.5 4.0 10" 148 t32 The heating rate was at 10 - 15 ° C / min.

As the table shows, the results obtained with copper are extremely good and are clearly above the values that can be obtained with activating Si amounts.

The flexural strength at room temperature is up to 80% of the flexural strength of the base material.

Claims (9)

10 15 20 25 30 35 463 818 PATENT CLAIMS A method for connecting silicon carbide molded parts, in which the polished, free element-showing mating surfaces are brought against each other and in an inert or reducing atmosphere heated to a high temperature under press pressure, characterized in that silicon carbide molded parts of pressureless sintered SiC (SSiC) or hot-pressed SiC (VPSiC) are connected to each other by placing on at least one of the polished pass surfaces a maximum activation layer of at least one carbide and / or silicide-forming element in the group Ag, Al, Au , B, Be, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Ni, Pd, Pt, Ta, Ti, V, W and Zr are applied and the joined parts are welded together in inert or reducing atmosphere. sphere in the range from 10'1 to 105 Pa at temperatures in the range from 800 to 2200 ° C under a press pressure in the range from 1 to 100 MPa. A method according to claim 1, in that a 0.1 to 1 μm thick actinic coating layer is applied to at least one of the fitting surfaces. 3. A method according to claim 1 or 2, characterized in that the carbide and / or silicide-forming material is vaporized, sputtered or rolled. A method according to claim 1, in that Cr, Cu, Ni, Pt and / or Pd or alloys thereof are applied as carbide and / or silicide nuclei. A method according to claim 1, in that copper or copper alloys can be used for the thin layer. 6. A method according to claim 1, wherein the melting temperature of the material in the thin layer. feel that the joint temperature is selected above 463 818 p 10 7. A method according to claim 1 or 6, characterized in that the temperature, press pressure and treatment time are matched to each other taking into account the material in the applied 1 μm thick layer. Process according to Claim 7, characterized in that the compression pressure is chosen at 15 to 45 MPa, in particular about 25 MPa, the temperature between 1500 and 1800 ° C and the time for the action of pressure between 15 and 120 minutes, in particular in the range from 30 to 60 minutes. Process according to one of the preceding claims, characterized in that the joint treatment is carried out in argon at a pressure in the range from 103 to 105 Pa.