KR101576505B1 - Brazing method of attaching titanium-based alloy to base steel using wet plating - Google Patents

Abstract

The present invention relates to a brazing bonding method of a steel and titanium-based alloy. More specifically, disclosed is the brazing bonding method of steel and titanium-based alloy using wet plating which suppresses or prevents a generation of carbide on a surface of the steel by forming strong solid diffusion combination which a nickel element has a gradual concentration gradient since going to the steel from an interface of a nickel layer, comprising: a first step of forming the nickel layer by wet plating of a nickel or a nickel-based alloy on a steel base metal; a second step of forming a nickel-based insertion layer by wet plating the nickel-based alloy for a filler on the nickel layer; and a third step of arranging the titanium-based alloy base metal on the nickel-based insertion layer, and then bonding by heating the same at a melting temperature of the nickel-based insertion layer for the filler or more, and then cooling the same. According to the present invention, in bonding the steel and the titanium-based metal, the brazing bonding method of the present invention has an effect of securing excellent wetness since suppressing the generation of carbide on the surface of the steel, solving a problem of generating heat stress at the same time by reducing a gap of thermal expansion coefficients of the titanium-based metal and the insertion layer and the steel, and performing a continuous process in accordance to a shape of the bonding base metal as simplifying the brazing process.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brazing method of joining a steel and a titanium-based alloy using a wet plating method,

The present invention relates to a method of joining a steel and a titanium-based alloy, and more particularly, to a method of joining a steel and a titanium-based metal, And a brazing method of a steel and a titanium-based alloy using a wet plating method so as to reduce a difference in the thermal expansion coefficient of the steel to solve the problem of occurrence of thermal stress at the same time.

Brazing is a technique of joining two base materials using a filler with a melting point lower than that of the base metal to be bonded. It is a technique to bond two base materials by applying heat below the melting point of the base material. it means. Therefore, among the joining methods using a filler, the brazing is distinguished from welding by melting at a melting point of the base material, and by soldering at a melting point of 450 ° C or less.

These brazes are used extensively throughout the industry, including automotive, aircraft, nuclear equipment, air conditioning and refrigeration, refrigeration and air conditioning equipment, accessories, hard metal tools, defense components, power tools, electrical and electronic equipment, This method has a wide range of applications and applications in bonding technology, enables various bonding between different types of metals, facilitates joining of products having different sizes and thicknesses, and has a merit that a beautiful and elaborate joint can be obtained.

In particular, nickel-based brazing fillers are widely used as fillers for the structural steel brazing, and nickel-based brazing fillers are excellent in high temperature strength, corrosion resistance and high temperature oxidation resistance, and are used in aircraft parts, various engines, turbines, And so on.

The main principle of this brazing is that the filler metal is melted when the filler metal is applied between the base materials in various forms such as paste or sheet and heated, and the melted filler is wetted and capillary action ) To penetrate between the base materials to be bonded. Wettability is determined by the affinity of the filler metal with the base material when it is melted, or by the flux or atmosphere. Capillary phenomena are closely related to the bonding spacing, and are also closely related to the types of filler metals and fluxes, viscosity, density, location of gravity on the bonding surfaces, and heating methods. If the wettability between the filler metal and the base material is poor, the bonding is not performed. If the bonding interval is large, the filler metal is not sufficiently charged between the base materials, resulting in incomplete bonding.

On the other hand, TiAl alloy has excellent high-temperature stiffness, noble strength and oxidation resistance and is attracting attention as a next-generation high-temperature and light-weight material to be applied to turbine wheels.

As a solution to this problem, a method of joining TiAl alloy to structural steel having strength and toughness has been proposed. At this time, there is a problem that Ti, which is an activating metal, reacts with a trace amount of C existing in steel when joining with structural steel to form TiC, thereby lowering the bonding strength. In particular, when Nb, Mo, V or the like, which is a strong carbide former as an alloying element, is added, various carbides are formed in addition to TiC to induce stress concentration phenomenon, thereby causing a problem of greatly lowering the strength of the bonding interface. That is, when the brazing method is applied, the filler metal is melted so that the titanium alloy element dissolves in the filler metal, the dissolved elements diffuse to the steel and react with the carbon present in the steel to form carbide along the surface of the steel Resulting in a problem of drastically reducing the strength of the interface.

Further, since the titanium alloy and the nickel-based bonding layer and the steel have a very different thermal expansion coefficient, when the continuous thermal cycle is given in the bonded state, there is a problem that stress concentrates on the interface and the interface rapidly becomes unstable.

Furthermore, the nickel-based alloy, which is a filler metal to be applied in brazing, has poor wettability on the surface of the steel during melting, and it is required to solve the technical problem that it is difficult to form a sound interface depending on the shape and size of the interface.

Accordingly, in the present invention, in bonding the steel to the titanium-based metal, it is possible to secure superior wettability while suppressing the generation of carbide on the surface of the steel, and to reduce the difference in thermal expansion coefficient between the titanium- To provide a brazing method of a steel and a titanium-based alloy using a wet plating method so as to simultaneously solve the above problems.

According to an aspect of the present invention,

A first step of wet-plating a steel base material with nickel or a nickel-based alloy to form a nickel layer;

A second step of wet-plating the nickel layer with a nickel-based alloy for filler to form a nickel-based intercalation layer; And

A third step of disposing a titanium-based alloy base material on the nickel-based intercalation layer, heating the same at a temperature not lower than a melting temperature of the nickel-based intercalation layer for the filler,

Characterized in that the nickel element has a gradual concentration gradient as it goes from the interface of the nickel layer to the steel and a strong solid diffusion bond forming a steel solution is formed to suppress or prevent carbide formation on the surface of the steel. The present invention provides a brazing method of a steel and a titanium-based alloy using a plating method.

Preferably, in the present invention, the nickel layer in the first step is composed of 0.1 to 35 atomic% of at least one alloying element selected from Fe, Cu, Zn, Mn, Sn and Co, the balance Ni and inevitable impurities .

Preferably, the nickel-based intercalation layer in the second step is composed of 3 to 20 atomic% of at least one element selected from P and B, the balance Ni and inevitable impurities.

Preferably, the heating in the third step is performed in a temperature range of 850 to 1100 ° C, more preferably in a temperature range of 920 to 1100 ° C for 4 to 30 minutes .

Preferably, the brazing method is a continuous process.

Also preferably, the brazed joint of the steel and the titanium-based alloy bonded by the above method has a shear strength of at least 55 Mpa or more.

According to the present invention, by forming a nickel layer having a strong interface with steel by wet plating on the steel surface, the reaction between the carbon and the titanium alloy element present in the steel during brazing can be inhibited to prevent generation of carbide, Can be remarkably improved.

In addition, according to the method of the present invention, a nickel-based intercalation layer is formed on the nickel layer by a wet plating method to secure an excellent wettability of the nickel layer and the intercalation layer, thereby providing a titanium alloy having a hard interface with minimized interfacial defects, It is possible to realize a high strength bonding structure.

Further, according to the method of the present invention, diffusion of nickel into the steel from the interface between the nickel layer and the steel formed by the wet plating method during the fusion bonding results in strong diffusion bonding between the steel and the nickel layer and reduces the thermal expansion coefficient of the steel, It is possible to simultaneously solve the problem of concentration of thermal stress occurring in the interface during the solidification process of the system insert layer and the cyclic heating and cooling that may occur during use.

In addition, when the wet plating method is used in accordance with the method of the present invention, it is possible to drastically reduce the restrictions on the shape, surface state, and size of the bonding material compared to the conventional dry coating method. Particularly, In a similar case, a batch or continuous plating process is also effective. In addition, the brazing process can be simplified by omitting the step of positioning the filler as compared with a process using an independent ribbon or powder type filler.

Fig. 1 schematically shows a structure in which a steel and a titanium-based metal according to the present invention are brazed.
FIG. 2 is a flowchart showing a brazing method of a steel and a titanium-based metal according to the present invention.
3 is a SEM photograph of a microstructure of a joint according to an embodiment of the present invention.
4 is a SEM photograph of the microstructure of the joint according to the comparative example of the present invention.
5 is a SEM photograph of a shear test failure portion of a joint according to an embodiment of the present invention.
FIG. 6 is a SEM photograph of the shear test failure portion of the joint according to the comparative example of the present invention.
7 is a graph showing bonding strengths of joints according to Examples and Comparative Examples of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the drawings.

FIG. 1 is a schematic view of a structure in which a steel and a titanium-based metal according to the present invention are brazed together, and FIG. 2 is a flowchart showing a brazing method of a steel and a titanium-based metal according to the present invention.

The present invention relates to a method for manufacturing a nickel base plate, comprising: a first step of wet-plating a steel base material 110 with nickel or a nickel-based alloy to form a nickel layer 120; A second step of wet-plating the nickel layer 120 with a nickel-based alloy for filler to form a nickel-based intercalation layer 130; And a third step of disposing a titanium-based alloy base material (200) on the nickel-based insert layer (130), heating the same at a temperature not lower than a melting temperature of the nickel-based insert layer for the filler, Characterized in that a strong solid diffusion bond is formed in the nickel layer (120) from the interface to the steel (110), the nickel element having a gradual concentration gradient, thereby suppressing or preventing carbide formation on the surface of the steel (110) The present invention relates to a brazing method of a steel and a titanium-based alloy.

According to the present invention, a wet bonding interface is formed by the wetting between the titanium alloy base material 200, the nickel-based insert layer 130, the nickel-based insert layer 130 and the nickel layer 120 by wet plating . In addition, a strong solid diffusion bonding between the nickel layer 120 and the steel matrix is performed, and nickel is diffused into the steel to reduce the difference in thermal expansion coefficient between the nickel alloy layer and the steel matrix, The molten nickel-based intercalation layer 130 has excellent wettability, so that a bond between the sound nickel layer and the nickel-based intercalation layer is achieved.

That is, compared to the conventional process of mechanically inserting filler metal by pretreating steel using a wet plating method when brazing a steel and a titanium-based alloy according to the present invention, it is possible to minimize the constraint according to the bonding interface shape and size, . In addition, wet plating is performed in a second step to ensure a good wetting property at the time of brazing, thereby ensuring a sound bonding interface in which interface defects are minimized and suppressing the generation of carbides on the surface of the steel to increase the bonding strength, It is possible to reduce the thermal expansion coefficient deviation between the bonded materials and to minimize the occurrence of thermal stress due to the thermal cycles occurring during or after the bonding process.

In addition, since the present invention uses the wet plating method, the constraint on the shape, the surface condition, and the size of the bonded material is remarkably reduced. In particular, when the bonded material is similar in shape to the plate or wire, Or a continuous plating process. In addition, brazing is achieved by simplifying the brazing process by omitting the process of positioning the filler, as compared to conventional processes using an independent ribbon or powdered filler.

Hereinafter, the steps will be specifically described.

The first step is a step of electrolytically plating a steel base material with nickel or a nickel-based alloy to form a nickel layer. In the case of the above electrolytic plating, the nickel or nickel-based alloy forms a nickel layer with excellent adhesion force (shear strength: 208 MPa) to the interface of the steel base material, thereby improving the corrosion resistance and wear resistance of the steel base material.

At this time, by applying the wet plating method, it is possible to drastically reduce the surface state (roughness, irregular shape, etc.), shape (screw shape, cast iron shape, etc.) and size of the steel compared to the conventional dry coating process.

Also, the nickel layer thus formed is diffused so that the nickel element has a gradual concentration gradient toward the steel at the interface between the nickel layer and the steel at the brazing temperature to form a strong solid diffusion bonding while forming a steel (nickel) solid solution. In this case, as the content of nickel in the steel increases, the coefficient of thermal expansion decreases and has a minimum value at about 36 wt% Ni. Therefore, the gradual decrease of the thermal expansion coefficient at the interface can minimize the occurrence of thermal stress. In addition, during the brazing process in which the nickel-based intercalation layer for filler is melted and bonded to the titanium-based alloy base material, the titanium-based alloy elements diffused from the titanium-based alloy base material inhibit and prevent the carbides from forming at the interface with the carbon of the steel base alloy So that the bonding strength of the brazed joint can be improved.

On the other hand, since the nickel layer has very good wettability with the Ni-based intercalation layer compared to the steel and Ni-based intercalation layer, a sound interface with minimized interface defects can be secured.

At this time, the steel includes most structural alloy steels based on iron (Fe).

Further, the nickel layer is characterized by comprising 0.1 to 35 atomic% of at least one element selected from the group consisting of Fe, Cu, Zn, Mn, Sn and Co and the balance Ni and inevitable impurities.

Next, the second step is a step of wet-plating the nickel layer with a nickel-based alloy for filler to form a nickel-based intercalation layer. When the electroless plating is performed, a nickel-based intercalation layer having a uniform thickness and excellent chemical, mechanical and physical properties is formed. At this time, in the case of the present invention, the nickel-based intercalation layer is formed of the metal for the filler. In the third step, the melting point of the joint portion is lowered during the bonding with the titanium-based metal matrix to promote diffusion among the components, So that a sound bonding can be achieved.

At this time, the nickel-based intercalation layer may be composed of 3 to 20 atomic% of at least one element selected from P and B, the remaining Ni and inevitable impurities.

In the case of the nickel-based alloy for filler, when the P and B are added in an amount of 3 to 20 atomic%, the melting temperature of the insert layer is effectively lowered and the amorphous layer is formed to form an insert layer having a homogeneous component distribution . In one embodiment of the present invention, a nickel-based intercalation layer containing 10 atomic% of P was formed.

In addition, in the nickel-based alloy, the impurities must be inevitably included in the manufacturing process or raw material of the Ni-based filler metal. Therefore, these impurities are contained in an amount of 1 wt% or less, preferably 0.1 wt% Is not more than 0.01% by weight.

Next, the third step is to place the titanium-based alloy base material on the nickel-based insert layer, heat it to a temperature not lower than the melting temperature of the nickel-based alloy for the filler, , The steel base material and the titanium base metal base material in which the nickel layer and the nickel base intercalation layer are sequentially formed are fixed at a predetermined pressure and then heated so as to be heated to a temperature not lower than the melting temperature of the nickel base intercalation layer for the filler, The diffusion of the alloying element due to the difference in the compositional components between the nickel-based intercalation layer for the melted filler and the titanium-based alloy and the nickel layer takes place, resulting in strong bonding. Also, diffusion of the same principle occurs between the steel base material and the nickel layer, so that strong bonding is achieved. At this time, the titanium-based alloy may include Al and Nb.

The heating temperature for the bonding may be varied depending on the composition of the nickel-based alloy for filler, but it may be heated to a temperature above the melting point of 150 ° C as the temperature above the melting point of the nickel-based intercalation layer for filler. Preferably from 850 to 1100 < 0 > C.

In an embodiment of the present invention, a nickel-phosphorus alloy is used as a nickel-based alloy for a filler to form a nickel-based intercalation layer. The nickel-phosphorus alloy has a melting point of 920 캜, a nickel layer melting point of 1455 캜, Since the starting point of the alpha transformation of the titanium aluminum alloy base material of the structure is 1120 캜, it was heated to a temperature range of 920 캜 to 1100 캜 and maintained for 4 to 30 minutes.

As described above, according to the brazing method of the present invention, a nickel layer is formed on the steel base material to control the interfacial reaction to prevent carbide from reacting with the elements of the titanium-based metal base material at the steel interface during brazing, The strength of the joint portion can be improved. The brazed joint portion can have an excellent shear strength of at least 55 Mpa or more and an excellent shear strength of 100 Mpa or more according to the heating time.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

<Examples> Brazing bonding of titanium aluminide alloy and structural steel

A nickel layer of 150 占 퐉 in nickel metal was formed on the structural steel base material (SCM 440, C: 0.38-0.43 Si: 0.15-0.35Mn: 60-0.85Cr: 0.90-1.20Mo: 0.15-0.30, wt% . That is, a seed layer was formed at a current density of 2 ASD for 2 minutes by a wood strike plating bath, and then a nickel electroplating layer was formed using a nickel plating bath.

Next, a nickel-phosphorus filler was used as a nickel-phosphorus filler to form a nickel-phosphorus layer 10 (thickness: 10 μm) using an electroless plating method (ENP solution, Youngin Plastics, stirring speed: 2000 RPM, plating temperature: 90 ° C., wt%) intercalation layer.

Then, brazing was performed with a titanium aluminide alloy (Ti: 57 Al: 27 Nb: 16, wt%) in a vacuum state at 950 ° C. for 10 minutes. After 10 minutes of bonding at a heating rate of 8K / s, the wafer was air-cooled.

<Comparison example> Brazing bonding of titanium aluminide alloy and structural steel

A nickel-phosphorus filler was used as a nickel-phosphorus filler to form a nickel-phosphorus (Ni-phosphor) layer by using an electroless plating method (ENP solution, Youngin Plastics, stirring speed: 2000 RPM, plating temperature: 10 wt%).

Thereafter, brazing was performed with a titanium aluminum alloy at 950 ° C for 10 minutes in a vacuum state. After 10 minutes of bonding at a heating rate of 8K / s, the wafer was air-cooled.

&Lt; Test Example 1 >

In the above Examples and Comparative Examples, the following bonding surface analysis was carried out in order to confirm the bonding state of the bonded portions of the titanium aluminum alloy-structural steel bonded.

First, the microstructure of the bonded portion of the titanium aluminum alloy and the structural steel according to the above-described Examples and Comparative Examples was observed with a scanning electron microscope, and the results are shown in FIG. 3 to FIG.

FIG. 3 shows the microstructure of the joints when a nickel layer and a nickel-phosphorus intercalation layer are formed using a wet plating method according to the embodiment, wherein a nickel layer is formed on the structural steel, and a nickel-phosphorus insertion layer and a titanium aluminum alloy Layer is sequentially formed. This means that the nickel layer inhibits the reaction of the element such as titanium dissolved from the titanium aluminum alloy with the carbon at the interface of the structural steel to inhibit the generation of carbide.

On the other hand, FIG. 4 shows the microstructure of the joint when only the nickel-phosphorus intercalation layer is formed by the wet plating method according to the comparative example. Titanium and niobium elements dissolved from the titanium aluminum alloy at the interface of the structural steel react with carbon, - NaBr-based carbide was produced.

&Lt; Test Example 2 > Shear test

In order to examine the bonding strength of the brazed joints of the titanium aluminum alloy-structural steel bonded in the examples and the comparative examples, the bonding strength of the brazed joints over time was measured through a shear test. The results are shown in Figs. 5 to 7 and Table 1 below.

FIG. 5 is a SEM photograph of a shear test failure portion of a joint portion when a nickel layer and a nickel-phosphorous intercalation layer are formed using the wet plating method according to the embodiment. FIG. 6 is a cross- SEM photographs of the shear test breaks of the joints when only the nickel-phosphorus intercalation layer is formed.

The Figure 5 and as compared to Figure 6, titanium aluminum created at the interface AlNi ₂ Ti The rupture occurs along the intermetallic compound layer same as the comparative example, if there are broken along the carbide layer forming the interface structural lecture more easily occurs .

7 and Table 1 below show the shear strength of the brazed joints bonded according to the above Examples and Comparative Examples.

Time (min) Shear Strength (MPa) Comparative Example Example 4 14 55 5 13 124 10 17 159 30 39 146

As can be seen in Table 1 and FIG. 7, in the case of the embodiment in which the nickel layer was formed using electrolytic plating and then the nickel-phosphorus insertion layer was formed by electroless plating, the generation of carbide was suppressed by the nickel layer As a result, it was confirmed that the bonding strength was remarkably improved as compared with the case where the bonding was performed by heating for about 30 minutes in the comparative example.

From the results of these embodiments, it is possible to improve the strength of the interface by forming a nickel layer and a nickel-based intercalation layer by using the wet plating method to form a solid interface by completing the bonding with excellent characteristics in the state where formation of carbide is suppressed at high temperature It is possible to provide a brazing bonding method capable of simultaneously overcoming the unstability of bonding occurring in a thermal cycle owing to the large difference in thermal expansion coefficient of a steel, a titanium alloy or an intermetallic compound.

100: Structural steel in which a nickel layer and a nickel-based intercalation layer are formed
110: Structural steel base material
120: Nickel layer
130: Nickel-based insertion layer
200: Titanium-based metal base material

Claims (7)

A first step of wet-plating a steel base material with nickel or a nickel-based alloy to form a nickel layer;
A second step of wet-plating the nickel layer with a nickel-based alloy for filler to form a nickel-based intercalation layer; And
A third step of disposing a titanium-based alloy base material on the nickel-based intercalation layer, heating the same at a temperature not lower than a melting temperature of the nickel-based intercalation layer for the filler,
Wherein strong solid diffusion bonding is progressively formed in the nickel layer at the interface between the nickel layer and the steel to progressively increase the concentration gradient of the nickel element so as to suppress or prevent carbide formation on the surface of the steel. Bonding method. The method according to claim 1,
Wherein the nickel layer in the first step is composed of 0.1 to 35 atomic% of at least one element selected from the group consisting of Fe, Cu, Zn, Mn, Sn and Co, the balance Ni and inevitable impurities. METHODS FOR BRAZING JOINTS OF RUBBER AND TITANIUM ALLOYS. The method according to claim 1,
Wherein the nickel-based intercalation layer in the second step is a nickel-
And 3 to 20 atomic% of at least one element selected from P and B and the balance of Ni and unavoidable impurities. The method according to claim 1,
In the third step,
Wherein the heat treatment is carried out in a temperature range of 850 to 1100 占 폚. The method of claim 3,
In the third step,
Wherein the heating is performed at a temperature of 920 to 1100 占 폚 for 4 to 30 minutes. The method according to claim 1,
The method of brazing a steel and a titanium-based alloy using the wet plating method, wherein the brazing method is a continuous process. The method according to claim 1,
Wherein the brazed joint of the steel and the titanium-based alloy bonded by the above method has a shear strength of at least 55 Mpa or more.

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