JPS6142786B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel diffusion bonding method for metals, and particularly to a diffusion bonding method for Ni-based heat-resistant alloys. Welding of heat-resistant alloys has problems such as the welded part being brittle and prone to cracking, and brazing having low joint strength and low melting point, which naturally limits its applicability. Against this background, diffusion bonding has been applied to obtain high-quality joints. Diffusion bonding methods are classified into two types: solid phase diffusion bonding and liquid phase diffusion bonding. The solid phase diffusion bonding method is
Relatively high pressure must be applied during bonding. For this reason, in the case of fragile parts or high-precision parts, the high pressure tends to cause deformation, limiting the range of use. Liquid phase diffusion bonding is a method of bonding members to be bonded by interposing a thin layer (foil, powder, etc.) with a low melting point. However, the foil or powder insert method has drawbacks such as poor workability and poor reliability when the bonding surface has a complicated shape or increases in size. In addition, in a joining method in which a low melting point alloy layer is provided on the joining surfaces of the members to be joined and then liquid phase diffusion bonding is performed, the state of formation of the low melting point alloy layer greatly influences the diffusion bondability.
It is the gas (O ₂ ,
N ₂ , H ₂ ) causes negative effects such as the formation of void defects, nonuniform melting points of the low melting point alloy layer and poor bonding due to insufficient depth of the alloy layer, and the formation of compounds in the diffusion bond. The purpose of the present invention is to suppress mixed gases as much as possible, make it possible to obtain a low melting point alloy layer with a uniform melting point, and also prevent voids and bonding defects that occur in the diffusion bonding part, and create a good layer with less compound formation. An object of the present invention is to provide a diffusion bonding method that allows a diffusion bond to be obtained. In the present invention, preferably 15
After forming a permeation layer in which boron (hereinafter referred to as B) is infiltrated to a depth of μm to 70 μm, heating and melting treatment is performed to heat and maintain the temperature from above the melting point of the B coating layer to below the solidus temperature of the parts to be joined. A low melting point alloy layer is formed. Furthermore, it is a diffusion bonding method in which diffusion bonding is performed using a low melting point alloy layer formed on the bonding surfaces of the members to be bonded. The diffusion bonding method of the present invention can compensate for the drawbacks of the conventional liquid phase diffusion bonding method, which is performed by inserting foil or powder. In other words, in the B permeation layer, B, which is an element that lowers the melting point, is diffused into the bonding surfaces of the parts to be bonded to form a coating layer. No shifting or peeling occurs, and workability with complex-shaped parts and large parts is also good. moreover,
The coating layer containing B, which is a melting point lowering element, promotes lowering of the melting point and requires less pressure, thereby preventing bonding deformation that occurs during solid phase diffusion bonding. In the method of the present invention, the depth of the coating layer containing B, which is a melting point depressing element, is set to a depth of 15 μm or more in order to prevent bonding defects (unwelded areas) due to insufficient molten metal in the low melting point alloy layer that occurs in the diffusion bonding area. is preferable. The thickness is preferably 70 μm or less in order to prevent excess intermetallic compounds from forming at the diffusion bonding portion.
25 μm or more, which is particularly effective in preventing bonding defects in diffusion bonding parts and minimizing the amount of intermetallic compounds generated.
A B coating layer depth of 55 μm is preferred. Heating and melting the B coating layer in the method of the present invention is effective in heating and melting the impurity gas contained in the B coating layer to degas it, and at the same time making the melting point of the B coating layer uniform. , and a good diffusion bond can be obtained. B
During the coating layer formation, impurity gases (O ₂ ,
N ₂ , H ₂ ) are also diffused and contained. For this reason, it is not preferable that many void defects occur in the bonded portion where the B coating layer is provided on the bonding surfaces of the members to be bonded and then diffusion bonded. However, the B coating layer is heated and
After performing melting treatment to form a low melting point alloy layer, a high-quality diffusion bonded portion is obtained without the occurrence of void defects in the bonded portion that is diffusion bonded. Furthermore, even when a coating layer of other elements (Si, P) is provided, the same effect as that obtained by heating and melting treatment, such as boriding treatment, can be obtained. Although the melting point of the B coating layer depends on the coating treatment temperature, the melting point of the low melting point alloy layer becomes uniform by performing the heating and melting treatment. Therefore, bonding defects that occur during diffusion bonding can be prevented. Furthermore, if the heating/melting treatment is performed at a temperature below the melting point of the B coating layer, the coating layer will not be melted and will not be very effective in degassing and making the melting point uniform. For example, in the case of Ni-based heat-resistant alloys, the heating temperature is 1140°C, which is effective in degassing the B coating layer and making the melting point uniform.
~1180℃. The materials to be joined to which the diffusion joining method of the present invention is applied are Fe
Suitable for Ni-base, Ni-base, and Co-base heat-resistant alloys, and is especially effective for Ni-base heat-resistant alloys. Examples of the present invention will be described below. Table 1 shows the chemical composition (W/O) of the sample materials.
The test material used was a Ni-based heat-resistant alloy. The B coating layer was formed on the joint surfaces of the test materials by boriding. First, a coating agent (1.0% B - 2.5% NH ₄ Cl - 96.5% Al ₂ O ₃
The test material was embedded in powder) and treated under the conditions shown in Table 2 to form a B coating layer on the joint surface of the test material. FIG. 1 shows the relationship between the depth and melting point of the B coating layer and the coating treatment temperature. The depth of the B coating layer increases as the processing temperature increases, and the melting point of the B coating layer tends to decrease as the processing temperature increases. Furthermore, it was found that a large amount of impurity gas (O ₂ , N ₂ ) was mixed into the B coating layer. Next, after providing a B coating layer on the joint surface of the present invention, heating and melting treatment is performed to form a low melting point alloy layer.

【table】

[Table] Describes the cases in which this has been achieved. Table 3 shows the heating/melting treatment conditions. As shown in FIG. 1, since the melting point of the B coating layer formed on the joint surface is at least 1130°C, the heating temperature was 1175°C and the holding time was constant for 5 minutes to form an alloy layer on the joint surface. FIG. 2 shows the relationship between the thickness and melting point of the alloy layer and the coating treatment temperature, and FIG. 3 shows the metal structure of the alloy layer. The thickness of the alloy layer increases by approximately 1.2 to 1.3 times the thickness of the B coating layer by subjecting the B coating layer to heating and melting treatment. Further, the melting points of all the alloy layers are constant at 1115°C to 1120°C, which is effective in making the melting points of the alloy layers uniform. Furthermore, the amount of impurity gas in the alloy layer is reduced and there is also a degassing effect. Next, a diffusion bonding experiment was conducted using the B coating layer described above and the alloy layer after heating and melting treatment, and a comparison was made. Table 4 shows the diffusion bonding conditions. Diffusion bonding has a bonding temperature of 1200℃, bonding time of 1hr, and a pressure of 0.15Kg/
This was done at a constant ^cm2 . Figure 4 shows the effects of heating and melting on the bonding rate of diffusion bonding.

【table】

[Table] Fig. 5 shows a comparison between the diffusion bonded portion made by the B coating layer and the diffusion bonded portion made by the method of the present invention. In the bonded portion where a B coating layer is formed on the bonding surface and diffusion bonding is performed, void defects occur due to impurity gas, and the bonding rate is 62 to 95%. On the other hand, in the joint where B coating was formed on the joint surface and the low melting point alloy layer was heated and melted, a high quality diffusion joint was obtained without any void defects. This has the effect of degassing the B coating layer through heating and melting treatment, which greatly helps to prevent void defects occurring in the diffusion bonding portion. However, when the depth of the B coating layer is less than 15 μm, bonding defects (unwelded portions) occur in the diffusion bonded portion. Further, when the depth of the B coating layer becomes 90 μm or more, the amount of intermetallic compounds generated at the diffusion bond increases. Therefore, in order to prevent bonding defects that occur at the diffusion bonding part and also to suppress the formation of intermetallic compounds, the depth of the B coating layer should be 15 to 70 mm.
It is preferable to set it to μm. According to the present invention, a mixed gas in the B coating layer can escape, a low melting point alloy layer with a uniform melting point can be formed, and voids and bonding defects occurring in the diffusion bonding part can be prevented, and the amount of intermetallic compounds generated can be reduced. It is effective even though it can be done in small quantities.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the depth and melting point of the B coating layer and the coating treatment temperature, FIG. 2 is a diagram showing the relationship between the depth and melting point of the low melting point alloy layer and the coating treatment temperature, and FIG. Figure 3 is a micrograph of a cross section of a low melting point alloy layer, Figure 4 is a diagram showing the influence of heating and melting treatment on the bonding rate of the diffusion bonded portion, and Figure 5 is a microscope photo of the cross section after diffusion bonding.

Claims (1)

[Scope of Claims] 1. A metal characterized by forming a boron permeation layer on the joint surfaces of members to be joined, heating and melting the boron permeation layer, and performing diffusion bonding using the molten alloy layer as the joint surface. diffusion bonding method. 2. The metal diffusion bonding method according to claim 1, wherein the thickness of the permeation layer is 15 to 17 μm.