KR20030050637A - Method for manufacturing surface composite, using high energy accelerated electron beam - Google Patents

Abstract

PURPOSE: A method for manufacturing surface composite material using high energy accelerated electron beam is provided to simplify surface composite material process by using high energy accelerated electron beam and greatly improve wear resistance by enabling formation of single layer and multilayer surface composite materials. CONSTITUTION: The method comprises first step of coating a mixed body(10) in which ceramic powder of vanadium carbide (VC) is mixed with calcium fluoride (CaF2) solvent on titanium alloy(12); second step of pressing the mixed body so that the mixed body is closely adhered to the titanium alloy; and third step of forming a surface composite layer on the titanium alloy by uniformly projecting high energy electron beam onto the mixed body coated surface, wherein the method further comprises a step of forming a multilayer of surface composite material by repeating the first to third steps for one or more times, wherein the titanium alloy(12) is Ti-6Al-4V, wherein a ratio of VC ceramic powder to solvent CaF2 is 6:4 in the mixed body(10), and wherein electron energy of the high energy electron beam is 1.4 MeV.

Description

Method for manufacturing surface composite, using high energy accelerated electron beam

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a multilayer VC (vanadium carbide) / Ti (titanium) surface composite material, and more particularly to a method for producing single layer and multilayer VC / Ti surface composite materials by an accelerated electron beam projection method.

Conventional surface treatment methods of titanium alloys known to date include plating, carbonization treatment, plasma spray, etc., but these methods have a disadvantage in that an interfacial bonding between the surface layer and the base metal is not good and the thickness of the surface layer is thin. In addition, chemical vapor deposition (CVD), which mainly introduces gas into the reaction chamber from outside and decomposes the compound of the introduced reaction gas using heat, laser or ultraviolet light energy, and then forms a thin film on the base material heated by chemical reaction. ), But in this case, since the thin film is formed at a high temperature, the base metal is warped or the physical properties are weak. Accordingly, there has been a demand for a surface treatment method of Ti alloy which has improved the disadvantage as a simpler process.

SUMMARY OF THE INVENTION The present invention has been made to meet the above-mentioned demands, and provides a method for forming a surface composite material having good interfacial bonding with a base metal, having no weakening of physical properties of the base metal, and having excellent wear resistance in a simple process. There is a technical problem.

Figure 1a is an optical microscope photograph of Ti-6Al-4V, a titanium alloy as a base material used in the embodiment of the present invention.

1B is a scanning electron microscope (SEM) photograph showing VC ceramic powder applied as a coating agent in an embodiment of the present invention.

2A to 2C are views illustrating a process of manufacturing a multilayer surface composite material by projecting a high energy accelerated electron beam.

FIG. 3A is a low magnification optical photograph of a cut plane parallel to the electron beam projection direction of the monolayer surface composite material shown in FIG. 2D.

FIG. 3B is a low magnification optical photograph of a cut plane parallel to the electron beam projection direction of the multilayer (two layer) surface composite material shown in FIG. 2E.

FIG. 4A is an optical microscope photograph of the microstructure of the surface composite layer in the single layer surface composite material illustrated in FIG. 2C.

4B is an optical microscope photograph of the microstructure of the surface composite layer in the multilayer (two layer) surface composite material shown in FIG. 2E.

5 is a graph showing the change in hardness according to the depth from the surface of the surface composite material prepared according to the production method of the present invention.

6 is a graph showing the amount of wear of the surface layer of the surface composite material prepared according to the production method of the present invention.

Method for producing a surface composite material using a high energy accelerated electron beam according to the present invention,

A first step of applying a mixture of a ceramic powder of vanadium carbide (VC) and a calcium fluoride (CaF ₂ ) solvent onto a titanium alloy; Pressurizing the mixture to be in close contact with the titanium alloy; And a third step of forming a surface composite layer on the titanium alloy by uniformly projecting a high energy electron beam onto the surface of the mixture of the VC ceramic powder and the solvent.

The method may further include repeating the first to third steps one or more times to form a multilayer surface composite layer.

In addition, the titanium alloy is characterized in that Ti-6Al-4V.

In addition, the VC ceramic powder and the solvent CaF ₂ in the mixture is characterized in that the ratio of 6: 4.

In addition, the electron energy of the high energy electron beam is characterized in that 1.4 MeV.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1A and 1B are optical micrographs and scanning electron microscopy (SEM) photographs of Ti-6Al-4V, a titanium alloy applied in an embodiment of the present invention, and ceramic powder, a VC (vanadium carbide) component, used as a solvent, respectively. In the titanium alloy of FIG. 1A, Equiaxed α represents an isotropic material, and intergraular β represents a boundary structure.

2A to 2D illustrate a process of manufacturing a multilayer surface composite material by projecting a high energy accelerated electron beam.

First, as shown in FIG. 2A, VC ceramic powder having a high hardness of 2000 to 3000 kg / mm ² and excellent heat resistance, abrasion resistance, and corrosion resistance (melting temperature; 2700). ) As a solvent CaF ₂ (melting temperature; 1423 A powder mixture mixed with powder in a ratio of 6: 4 is applied onto the titanium alloy 12. Here, the titanium alloy 12 used as the base material was applied to the Ti-6Al-4V alloy most widely used as aircraft structural materials and defense materials, the chemical composition thereof is shown in Table 1.

element Al V Fe O C N H Ti Content (% by weight) 6.27 3.28 0.17 0.17 0.01 O.O1 0.0006 BAL.

As shown in FIG. 2B, the VC / solvent mixture 10 of VC (vanadium carbide) + CaF ₂ (calcium fluoride) applied to the titanium alloy 12, which is the base material, is accelerated using a high energy electron accelerator. Project. The titanium alloy 12 is moved at a constant speed in the left direction in the fixed high energy full acceleration beam to uniformly project the VC / solvent mixture 10. When the high-output focusing energy obtained by accelerating the electron beam is directly transferred to the titanium alloy, the energy is instantly converted into thermal energy, which acts as a powerful heat source.

The projection conditions of the high energy electron accelerator are shown in Table 2.

Electron beam projection parameters Monolayer Multilayer (2 layers) Electronic energy 1.4 MeV 1.4 MeV Beam moving speed 2.45 cm / sec 2.45 cm / sec Beam scan width 5 cm 5 cm Beam current 26 mA 31 mA Beam size (diameter) 1.1 cm 1.1 cm atmosphere Waiting Waiting Heat input 2.73kJ / cm ² 3.26 kJ / cm ²

Here, the heat input received by the titanium alloy 12 and the VC / solvent mixture 10 is proportional to the beam power (electron beam energy X beam current), and is inversely proportional to the electron beam moving speed and scanning width. A certain amount of heat input is required in order for the surface melting of the metal base to occur with respect to a specific material. In the case of forming a single surface composite layer using a titanium alloy and a VC / solvent mixture as in the embodiment of the present invention, the heat input is 2.73 When forming the kJ / cm <^2> , two-layer (multilayer) surface composite layer, larger heat input amount of 3.26 kJ / cm <^2> is calculated | required.

Projecting a high-energy accelerated electron beam onto a titanium alloy coated with a VC / solvent mixture, preferentially results in surface compounding in a short period of time, with the melting of some of the low alloy temperature Ti alloy and the solvent melting and VC ceramic powder melting. do.

In the single-layer surface composite material 18 shown in FIG. 2C, when the accelerated electron beam is projected, the VC / solvent mixture 10 is melted to form a single-layer surface composite layer 16 of about 1.2 mm without pores or cracks. . In addition, although not shown slag is formed on the surface composite layer can be simply removed. The heat affected zone in the figure shows the portion affected by the thermal energy of the high energy electron beam in the surface of the titanium alloy 12 and in the region adjacent to the surface.

As shown in FIG. 2D, the mixture 10 of VC ceramic powder and CaF ₂ is applied to the titanium alloy 12, and the high energy electron beam is applied after pressurizing the VC / solvent mixture 10 and the titanium alloy 12 to be in close contact with each other. When projecting, a multilayer surface composite material 24 having two multilayer surface composite layers 20 formed as shown in FIG. 2E is produced. Here, the solvent CaF ₂ is applied to suppress the formation of the oxide layer and the generation of pores and cracks in the surface composite layer at the time of manufacturing the surface composite material.

The thickness of the surface composite layer is proportional to the magnitude of the electron beam current, and the density of the ceramic component important for improving hardness and wear resistance is increased as the current is increased due to the limitation of the thickness of the laminated VC ceramic powder 10 through which the electron beam can pass. Will be lowered. Therefore, in the case of forming the surface composite layer in multiple layers by projecting the electron beam several times, the heat input amount received by the surface composite layer is increased, so that the microstructure of the surface composite layer is uniform, and the density of the ceramic component element is increased. The volume fraction of the ceramic particles may be increased to form a surface composite layer having better hardness and wear resistance. In the case of manufacturing the multilayer surface composite layer, a 1.5 mm uniform surface composite layer 20 thicker than the single layer surface composite layer 16 shown in FIG. 2C is formed.

3A and 3B are low magnification optical photographs of cut planes parallel to the electron beam projection direction of the single layer and two layer surface composite materials shown in FIGS. 2C and 2E, respectively.

When cut and polished in parallel with the projection direction of the high energy electron beam and etched with a Kroll solution (100 ml H ₂ O + 10 ml HNO ₃ + 5 ml HF), the surface composite layer as shown in FIGS. 3a and 3b, It turns out that it is comprised from the heat-affected part and the titanium alloy which is a base material.

Figure 4a is an optical micrograph showing the microstructure of the single-layer surface composite layer, the lump of undissolved VC ceramic material and about 23 vol. It can be seen that the percentage of primary and process (Ti, V) C structures are unevenly distributed between β-Ti and martensite matrix. In addition, although it is not distinguished from the photograph of FIG. 4A, it can be seen that in the single-layer surface composite layer, some substrates are composed of martensite due to the nonuniformity of the matrix composition.

On the other hand, as shown in the optical microscope picture of FIG. It can be seen that a large amount of the structure of the primary and process (Ti, V) C of% is distributed. In addition, the carbide size of the multilayer (two-layer) surface composite layer is shown to be about two times larger (4.5 μm) than that of the single-layer surface composite layer, and as shown in FIGS. 4A and 4B using CaF ₂ solvent. It can be seen that no pores or cracks are observed in the surface composite layer of the two titanium alloys.

After cutting the surface of the titanium alloy projected by the accelerated electron beam in parallel with the projection direction, the change of the microhardness according to the depth from the surface of the specimen was examined, and the scratch wear test was measured using a dry sand / rubber wheel abrasive wear tester. It was. 5A and 5B are graphs illustrating the change in microhardness according to the depth before and after the acceleration electron beam projection after the surface composite material of the present invention is measured with a Vickers microhardness (load 500gf).

6 is a graph showing the amount of wear of the surface layer after manufacturing the surface composite material according to the present invention, the wear resistance test is based on the ASTM standard G65 under the wear test conditions of 0.5mm diameter, 20kg pressure, 600m wear distance After the abrasion test, the wear resistance was compared and evaluated by the weight loss of the wear specimen.

The hardness of the two-layer surface composite layer was increased 1.5 times from 330 VHN of the base titanium alloy to 503 VHN, and the abrasion resistance was improved by eight times compared to that of the base titanium alloy, and about twice the improvement of the single layer surface composite layer. . As can be seen from the microstructures shown in FIGS. 4A and 4B and the microhardness graphs of FIGS. 5A and 5B, the improvement in abrasion resistance of the two-layered surface composite layer is higher than 2000 VHN formed of high hardness (Ti, V It is made of) C carbide, it can be seen that the vanadium (V) due to the hardness improvement of the β-Ti matrix dissolved in a large amount of titanium substrate. In addition, the abrasion resistance is improved approximately eight times, thereby enabling the use of titanium alloys in areas where use has been restricted in areas where abrasion resistance is required.

In the above embodiment, a single layer and a two-layer surface composite layer are exemplified, but more than two layers may be formed by repeating the application of the VC ceramic powder and the solvent and the high energy electron beam projection.

As described above, preferred embodiments of the present invention have been described in detail, but those skilled in the art may implement the present invention in various forms without departing from the spirit or features of the present invention. to be.

According to the present invention, the high-energy accelerated electron beam projection method accelerates electrons and uses high-energy accelerated electron beams to allow electron beam transmission in the atmosphere, manufacturing process is simple, and thermal efficiency is about 80%. It is low in cost and can manufacture surface composite material continuously. In addition, since uniform heating and cooling is performed, almost no pores or cracks are formed, and the material is heated for a short time, thereby preventing oxidation of the surface of the material. In addition, by manufacturing the surface composite layer in multiple layers, it is possible to make the microstructure more uniform and to greatly improve wear resistance and surface properties.

Claims (5)

A first step of applying a mixture of a ceramic powder of vanadium carbide (VC) and a calcium fluoride (CaF ₂ ) solvent onto a titanium alloy; Pressurizing the mixture to be in close contact with the titanium alloy; And And a third step of forming a surface composite layer on the titanium alloy by uniformly projecting a high energy electron beam onto the surface on which the mixture is applied. 2. The method of claim 1, further comprising repeating the first to third steps one or more times to form a multi-layered surface composite layer. The method of claim 1, wherein the titanium alloy is Ti-6Al-4V. The method of manufacturing a surface composite material using a high energy electron beam according to claim 1, wherein the ratio of CaF ₂ to VC ceramic powder and solvent in the mixture is 6: 4. The method of claim 1, wherein the electron energy of the high energy electron beam is 1.4 MeV.