DE3744245C1 - Hot pressing process for bonding silicon carbide shaped parts and also silicon carbide intermediary for bonding the shaped parts - Google Patents

Abstract

For the bonding of silicon carbide shaped parts, a 1-3 mu m thick titanium layer is applied to at least one of the contact surfaces, after which the parts are joined by hot pressing at 1200-1600@C, in particular 1450-1500@C, and pressing pressures of 5-100 MPa, in particular 15-30 MPa, in reducing protective gas, (in particular Ar/H2 mixtures) for at least 0.5 hour, in particular about 1 hour. For the joining process, use is particularly advantageously made of a SiC intermediary (in particular a ring for binding sections of pipe) fitted to the shaped parts to be bonded and having a thickness of 1-10 mm, which intermediary is coated on both sides with 1-3 mu m of titanium in each case. Under the specified conditions, a titanium carbosilicide of the composition Ti3SiC2 of sufficient plasticity is formed along the joint seam, which compound contributes to the reduction of internal stresses of the composite after joining.

Description

The invention relates to a method for joining molded silicon carbide parts by hot pressing, in the foregoing at least one of the polished mating surfaces one thin titanium layer as adhesion-promoting intermediate layer is applied.

Silicon carbide is a material for high temperature applications of considerable interest. Because of however, due to its high hardness, there are design difficulties, and especially complicated designed bodies are therefore through Connecting partial bodies created.

For joining molded silicon carbide parts are already different joining techniques known, to which joining process in the hot press belong, where appropriate, adhesion-promoting layers can be provided along the seam.

A method is described in DE-PS 30 03 186 described in which contains free silicon Surfaces by diffusion welding up to approx. 1400 ° C when pressing z. B. 400 bar with each other get connected.  

According to DE-OS 35 18 710 are depressurized sintered SiC or hot pressed SiC Molded parts joined together in the hot press, being on at least one of the polished mating surfaces an activating layer of a Carbide and / or silicide formers of the group Ag, Al, Au, B, Be, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Ni, Pd, Pt, Ti, V, W and Zr in maximum 1 µm layer thickness is applied.

In DE-PS 36 08 559 a method for Joining silicon carbide moldings in the Hot press described in which along the seam an adhesion-promoting layer made of a copper or manganese alloy containing cobalt which is additionally Cr, Ti, Zr, Fe, Ni and / or Ta can have.

Finally, the "progress reports the German Ceramic Society ", Volume 1 (1985), Issue 2, pages 188-198, about investigations for diffusion welding of silicon carbide molded parts reported where as an adhesion promoter along the seam, carbide and silicide formers like Pt, Pd, Cu, Ni, Co, Fe, Mn, Cr, Mo, Zr, Nb, Hf, Al, Ti, V, Ta and W are considered were.

Temperature behavior and strength of the obtained Bodies, especially along the seam, are however not fully satisfactory, and it is therefore the object of the present invention, to provide a joining process for silicon carbide, in which the strength of the body obtained  also essentially along the seam of the basic material.

The invented for this purpose developed Process is essentially characterized by that a titanium layer of 1 to 3 microns Thickness is applied and the hot pressing at 1200-1600 ° C and pressures from 5 to 100 MPa in reducing protective gas over at least 0.5 hours.

In this way emerges among the named Conditions along the seam of a titanium carbosilicide the composition Ti₃SiC₂, with the the internal tensions of the composite after Disassembled due to sufficient plasticity be so that the bending strength of the added products within the standard deviation the strength values of the base material lies, whereas so far only 30-50% the basic strength was achieved.

Optimal joining temperatures are 1450-1500 ° C, and there are pressures between 15 and 30 MPa preferred. As a reducing protective gas to prevent oxidation of the titanium layer Hydrogen-containing ones are particularly suitable Argon mixtures, specifically Ar / 4% H₂ has been used. Other shielding gases can also provided that they are low Ensure oxygen partial pressure over the titanium.

The holding times at the level of the joining temperature depend on the titanium layer thickness. Times  of at least ½ hours are for the above Thickness ranges already sufficient. Joining times of 1 hour gave the best results. Longer Joining times are not necessary, but without Disadvantage applicable.

The required titanium layer thickness is for optimal results (especially taking into account a later deployment of the association under corrosive conditions) between 1 and 3 µm. Below 1 µm titanium layer thickness will also be a composite under the mentioned joining conditions achieved, but the inner Tensions of the composite do not when cooling be broken down so well. Thicker layers out Titan also cause a bond is achieved with high strengths, however the vulnerability of the network in use corrosive conditions is increased.

The joining surfaces of the ceramic partners to be joined should be in a polished condition (Ra: 0.05-0.1 µm). In the case of higher roughness care must be taken that the Titanium layer is at least 1 µm thicker than the surface roughness of the silicon carbide.

In the joining surfaces of the silicon carbide generally after preparing for the Joining process impurities present as sintering aids or through upstream Cleaning or grinding processes or through targeted infiltration into the ceramic material be entered. Such impurities have no negative influence on the strength behavior  of the association.

The connection of Partial SiC bodies with the interposition of a SiC intermediate piece (e.g. an SiC ring for Connection of pipe ends), which on both sides with the desired titanium film is provided. On this way a titanium coating can be larger and possibly unwieldy parts can be avoided.

The invention is illustrated below by means of examples explained in more detail:

Examples 1 to 3

In the examples described below 1 to 3 each became a rectangular plate cut from silicon carbide. The single ones Parts became after coating the parting surfaces with Titan in the press together again connected, under different joining conditions, worked as indicated below has been.

In each case, the SiC plate was divided into three Parts cut, with a middle segment about 3 mm thick. The cut surfaces were ground and polished and the middle segment in a sputtering system with titanium on both sides coated. The brought together again Partial bodies were then in a guided tour provided press that so during the Hot pressing with the action of the press ram maintained their desired position.

After applying a small form on the parts to be joined the press was closed  and the joining room evacuated. After sufficient Pressure reduction (to 1.33 Pa) became protective gas passed through the apparatus, which then on Joining temperature was heated. After expiration the actual joining time was the power supply interrupted and the apparatus of cooling left to room temperature by convection. After cooling, the joined sample taken from the press and tested.

The following table shows the different ones Process conditions in the examples 1 to 3 were observed.

The strength values achieved in all three examples corresponded to the strength of the base material.

Claims (7)

1. A method for connecting silicon carbide moldings by hot pressing in which a thin titanium layer is applied as an adhesion-promoting intermediate layer to at least one of the polished mating surfaces, characterized in that a titanium layer of 1 to 3 µm thick is applied and the hot pressing at 1200-1600 ° C and pressures from 5 to 100 MPa in reducing protective gas over at least 0.5 hours. 2. The method according to claim 1, characterized, that the hot pressing takes place at 1450-1500 ° C. 3. The method according to claim 1 or 2, characterized, that pressures between 15 and 30 MPa applied will. 4. The method according to any one of the preceding claims, characterized, that a joining time of one hour is selected. 5. The method according to any one of the preceding claims, characterized, that as a reducing protective gas containing hydrogen Argon, especially an Ar / 4% H₂ mixture used becomes.   6. Method according to one of the preceding Expectations, characterized, that the connection of the molded parts with interposition one coated on both sides with titanium Intermediate piece made of silicon carbide he follows. 7. The joining surfaces of to be joined SiC adapter matched to silicon carbide moldings of 1-10 mm thick, both sides is coated with 1-3 µm titanium.