JPS61186271A - Method of joining ceramic and metal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method of joining ceramics and metals.

BACKGROUND OF THE INVENTION Ceramics, particularly non-oxide ceramics, are expected to be used as mechanical structural members. One of the issues when using it as a structural member is how to bond it to metal.

In general, non-oxide ceramics, such as silicon nitride and silicon carbide, have poor wettability, and one of the keys is to find a brazing filler metal that has a full length. is being developed.

This activated metal brazing material is made by adding activated metals such as manganese, titanium, and zirconium to noble metals such as gold, silver, copper, and nickel.The activated metals have the effect of lowering the melting point of the brazing material, and also act as a ceramic substrate. It has the effect of improving wettability. Another key to fully bonding ceramics and metals is reducing thermal stress.

Because ceramics have a smaller coefficient of thermal expansion than metals, internal stress is generated while the filler metal solidifies and is cooled to room temperature, and this internal stress rarely causes the joint to break during cooling. It's not that. As a means for reducing such thermal stress, a method using a metal having a small coefficient of thermal expansion is generally used.

Problems to be Solved by the Invention As mentioned above, many methods have been proposed for joining ceramics and metals, but these are still technologies under development and have many problems.

When improving the wettability between the brazing material and ceramics by adding an active metal to the brazing material, there is a problem in that the active metal reacts with the ceramic matrix to form a brittle layer. For example, when soldering is performed using a silicon nitride all-Cu, -Mn-Ti solder, an embrittled layer enriched with un, Ti, and Si is formed.

Active metals still have a strong affinity for oxygen, and unless a high degree of vacuum is used as a brazing atmosphere, active metals will oxidize.
■ There is a problem when the wettability decreases significantly. For example, Ti
For a Cu-Mn-Ti solder containing 5 wt% of , a degree of vacuum of at least 1 OTorr is required. Therefore, if the wettability is to be improved by other means, it is desirable to reduce the amount of the active metal added or to substitute an element with a lower activity.

On the other hand, a method that attempts to reduce the total thermal stress by using a metal with a small coefficient of thermal expansion also has many problems. Examples of metals with a low coefficient of thermal expansion include tungsten, molybdenum, zirconium, tantalum, and titanium. The coefficient of linear expansion of these materials is 1/2 to 1/3 that of steel, but it is still larger than that of silicon nitride or silicon carbide, and it is difficult to completely reduce thermal stress to zero. Tungsten and molybdenum, which have a particularly small coefficient of thermal expansion, have an elastic modulus 1.5 to 2 times that of copper, and this has the effect of increasing thermal stress. Furthermore, since these are high melting point metals, stress relaxation by recrystallization cannot be expected, which is a disadvantage. Further, there are problems in that it is easily oxidized and forms a fragile intermetallic compound at the interface with the brazing material.

The present invention has been made in view of the above circumstances, and its purpose is to obtain high bonding strength between ceramics and metal, and to provide sufficient wettability as a brazing material using component elements with low activity. It is an object of the present invention to provide a method for joining ceramics and alloys that can be secured and that requires less vacuum in the joining work.

Means and Action for Solving the Problems In the present invention, ceramics and metal are heated in a vacuum or in an inert atmosphere while their joint surfaces are pressed together by an external force with a brazing filler metal interposed, and the liquid phase of the brazing filler metal is heated in a vacuum or in an inert atmosphere. When the formation temperature is reached, a portion of the melted filler metal is forcibly discharged from the joint surface, cleaning the interface between the ceramic surface and the filler metal.
The wettability between the brazing filler metal and ceramics is improved.

As a result, it is possible to use a brazing filler metal with a small amount of active metal, which could not be used in the non-pressure method due to insufficient wettability, and it is possible to suppress oxidation of the brazing filler metal and the formation of a brittle layer. Furthermore, the formation of bubbles in the brazing filler metal, which is often observed in non-pressure methods, can be completely prevented, and stress concentration can be eliminated.

In the present invention, we select a metal whose melting point Tm satisfies the relationship 0.8Tm≦TL<Tm in terms of absolute temperature with the liquid phase formation temperature TL of the brazing filler metal as the metal to be bonded to the ceramic. It is necessary to apply sufficient pressure to plastically deform the metal.

By using a metal that has a melting point relatively close to that of the brazing filler metal in this way, recrystallization can occur sufficiently during the cooling process after the brazing filler metal has solidified, and thermal stress can be completely relaxed. If the melting point of the metal is still low, deformation will proceed only in the thin brazing material layer, and the brazing material layer itself may be destroyed during the cooling process1.
Furthermore, even if no breakage occurs within the brazing filler metal layer, large thermal stress is present and a small external force causes breakage. The method of the present invention can solve these problems.

Although the necessity of increasing the pressing force to the extent that it causes plastic deformation of the metal is not fully understood, it is presumed that one reason is to provide a driving force for recrystallization by plastically deforming the metal by an external force. As is clear from the examples described later, the bonding strength is highly dependent on the bonding force, and when a bonding force greater than that which causes plastic deformation of the metal is applied, a large bonding strength is obtained.

Example Embodiments of the present invention will be described below with reference to the drawings.

A silicon nitride heating element and metal were laminated with a brazing filler metal interposed therebetween as shown in FIG. (a) is silicon nitride, (b) is metal,
(c) is a brazing material. The dimensions of the nitride silica and metal are 12m+nX1oax 3trrm, and the joints are 1OwxXlomm. The dimensions of the filler metal are lo
It is a rolled plate with a thickness of 0.1-0.3 rra in mmXlOm. The test piece (assembly) as shown in FIG. 1 was mounted on a jig so that its mutual positions would not deviate, placed in a graphite die, and pressurized and crimped through a graphite punch. Next, the inside of the graphite die was evacuated to 4 to 6 x l O Torr and heated 17 at a rate of 20 C/mil using a heater provided outside the die. Total displacement of graphite punch for crimping is 0.
It was designed to be detected by a differential transformer with an accuracy of O1w or higher, and when it was observed that the brazing filler metal (c) was melting and a part of it was expelled from the joint, heating was immediately stopped and pressing force was applied. After cooling to near room temperature and cooling with a shaker, the load was unloaded and the test piece was taken out. The liquid phase formation temperature of the brazing filler metal (c) is approximately 870 to 900°C. Further, in the case of no pressure application in the comparative example, heating was stopped and cooling was performed when the temperature reached a temperature 50° C. higher than the liquid phase formation temperature of the brazing material (c). The crimp force in the case of no pressure is only the weight of the test piece. The cooling rate is about 5°C/min at around 600°C. The condition of the test piece taken out is as shown in Figure 2 (a).
is silicon nitride, (b) is a metal, H is a brazing filler metal, and (b) is a discharged brazing filler metal and a metal portion protruded by plastic deformation. After removing the protruding metal portion by machining, a shear test was conducted as shown in Figure 3. The crosshead speed is 7771L fL at 0.5am.

An example of the test results is shown in the table.

The effect of the method of the present invention is clear when compared with the comparative example. When steel (SS, 41)k was used as the metal, some neutral deformation was observed at a crimp surface pressure of 100 yen. However, its melting point is approximately 1.5 degrees higher than the liquid phase formation temperature of the brazing filler metal.
Because it was 5 times thicker, the thermal stress was not sufficiently relaxed, and the silicon nitride broke inside the test piece when it was taken out of the furnace. When molybdenum is used as the metal, it is expected to reduce thermal stress because its coefficient of thermal expansion is approximately 1/3 that of steel, and in fact, joining was possible even without pressure. However, its melting point is -f, which is the liquid phase formation temperature of the brazing filler metal.
: Because it is extremely thick (3 times as large), thermal stress relaxation due to recrystallization does not occur and the bonding strength is low. In addition, even if the pressure is forcibly crimped, no apparent deformation is observed at this level of surface pressure.
Since recrystallization does not occur, the effect of improving bonding strength by applying pressure is small. In addition, in the case of molybdenum, it was found that silicon, which is thought to have melted into the brazing filler metal from silicon nitride, diffused to the molybdenum, resulting in the formation of brittle silicides on the molybdenum surface.

When copper is used as the metal, its melting point is as low as about 1.15, which is the liquid phase permeability of the brazing material, and it is expected to alleviate thermal stress even during cooling after the brazing material has solidified. Fact comparison example A
As shown in 4.5, although it has a larger coefficient of thermal expansion than steel, it was possible to obtain a bonding strength with low strength.

Therefore, the importance of using a metal having a melting point close to the liquid phase formation temperature of the brazing filler metal, which is a component of the method of the present invention, is clear from this comparative example.

However, simply meeting this requirement alone will result in inferior results compared to conventional bonding using molybdenum or the like.

On the other hand, the effects of the method of the present invention shown in j6.1 to 3 are remarkable; copper is used as a metal and has a melting point close to the liquid phase formation temperature of the brazing material, and the copper deforms plastically at the joining temperature. The bonding strength was significantly improved by applying the full crimping surface pressure, and the Cu-Mn solder, which had insufficient wettability when no pressure was applied, showed good wettability without the addition of the more active TiF. More active and less oxidizing Ti f
By not including Cu-1'i, the requirement for the degree of vacuum was relaxed, and no precipitates were formed in the brazing filler metal, which is presumed to be composed of Cu-1'i, resulting in greater bonding strength.

Effects of the Invention The first effect of the invention is that a large bonding strength can be obtained between ceramic and metal.

The second effect is that sufficient wettability can be secured with component elements with low activity as a brazing material, and the vacuum level required in bonding work can be made more relaxed.1 These are extremely important factors in industry. Effect 1. Note that the implementation of the method of the present invention is not necessarily limited to the examples. The example is just an example, and the gist is to select a metal with a melting point close to the liquid phase formation temperature of the brazing filler metal, and to select a metal with a melting point close to the liquid phase formation temperature of the brazing filler metal, that is, close to the brazing temperature. The purpose of this invention is to combine two novel methods of forcibly applying sufficient pressure to plastically deform the metal.

Therefore, ceramics are not limited to silicon nitride,
It doesn't matter if it's silicon carbide or other ceramics. The metal is not limited to copper, and may be a copper alloy or other metal. However, the melting point Tm is close to the liquid phase formation temperature TL of the brazing filler metal <0. BT匍≦TL＜Tm
It is desirable that it be within the range of . However, just because 0.8rrL exceeds Tf f does not mean that there is no effect at all.

It is generally said that recrystallization occurs above 0.4 to 0.5 Tm, and an effect is expected at 0.5 T m<TL. The brazing filler metal is determined depending on the type of ceramic, and any known brazing filler metal may be used. The pressure bonding force is determined by the type of metal used and its flow stress at the brazing temperature, and is difficult to specify, but it is necessary to apply pressure to at least a level that gives plastic deformation to the metal.

Moreover, it is also possible to apply not only the pressure force but also the mutual sliding of the joint surfaces. Furthermore, the pressure bonding force does not need to be constant throughout the entire bonding process; for example, the pressure may be low at the initial stage of heating, and the pressure may be increased as the temperature approaches the liquid phase formation temperature of the brazing material. Further, the pressure may be further increased in the cooling step after the brazing filler metal has solidified to further give plastic deformation to the metal. However, in this case, it is necessary to carry out the process in a temperature range where the internal stress caused by plastic deformation is sufficiently relaxed by diffusion.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the entire laminated state of ceramics and metal in an embodiment of the method of the present invention, FIG. 2 is a perspective view showing the state of ceramics and metal bonded by the method of the present invention, and FIG. FIG. 3 is an explanatory diagram of a shear test.

Claims (3)

[Claims] (1) Interposing a brazing material between ceramics and metal,
In a method of joining ceramics and metal by heating above the liquid phase formation temperature of the brazing metal, the melting point T_m of the metal and the liquid phase formation temperature T_L of the brazing metal are expressed in absolute temperature 0.
．． A method for joining ceramics and metal, characterized in that a pressure is applied that is within the range of 8T_m≦T_L<T_m and is sufficient to plastically deform the metal in a temperature range immediately above T_L in a brazing process. (2) The method for joining ceramics and metal according to claim 1, wherein the ceramic and the metal are silicon nitride and a copper alloy, respectively, and the brazing material is a copper-manganese alloy or a copper-manganese-titanium alloy. . (3) The method for joining ceramics and metal according to claim (2), wherein the pressure bonding force is 60% or more.