JPH0633261A - Electro-discharge coated composite body - Google Patents

Abstract

PURPOSE:To obtain a coated composite body excellent in mechanical strength and thermal shock resistance without deteriorating the function of borides by executing electro-discharge coating using a boride sintered body having a specified componental compsn. contg. binary borides and having high strength as an electrode. CONSTITUTION:The electrode constituted of, by weight, 40 to 98% of one or more kinds among binary borides expressed by MxBy and 2 to 60% ternary complex borides of one or more kinds among Mo2FeB2, Mo2CoB2, Mo2NiB2, W2FeB2, W2CoB2, W2NiB2, MoCoB, WFeB and WCoB is used; where M denotes Ti, Zr, Ta, Nb, Cr and V as well as x=1 to 2 and y=1 to 4. Then, on a substrate such as steel having sufficient strength, a film having 5 to 300mum thickness is formed by an electro-discharge coating method. In this way, the coated composite body high in mechanical strength and excellent in wear resistance can be obtd. without deteriorating the characteristics of borides such as corrosion resistance, wear resistance and wetting resistance to molten metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention compensates for the brittle defect of boride-based ceramics, has high hardness and excellent wear resistance of boride-based ceramics, and has excellent corrosion resistance to molten metal and solution. The present invention relates to a member for a composite structure by a discharge coating method utilizing the above. In particular, regarding the materials used for casting machines and processing machines for low melting point non-ferrous metals, taking advantage of the fact that boride has excellent high-temperature characteristics, and is difficult to wet with low-melting point non-ferrous metals such as aluminum and has excellent corrosion resistance. .

[0002]

2. Description of the Related Art Generally, boride-based ceramics have high hardness, excellent wear resistance, corrosion resistance to molten metal and solution, and high temperature characteristics as compared with carbides. For this reason, many attempts have been made to put the boride-based ceramics into practical use as a structural corrosion-resistant wear-resistant member. Most of them are based on powder metallurgy, and hot isostatic pressing (HIP) and hot pressing have been used for forming methods, and sintering aids have been developed for sintering methods. Thus, for example, Japanese Patent Publication No. Sho 61-195
A large number of boride-based ceramics have been proposed, including high wear-resistant superhard materials containing TiB ₂ or ZrB ₂ as a main component, such as No. 93 and Japanese Patent Publication No. 61-50909.

Compared with steel materials, boride-based ceramics produced by powder metallurgy are not sufficient in terms of strength, toughness, thermal shock resistance, etc., and ordinary tool steels and high-speed steels can be used. It is said that it is difficult to apply it widely to structural members such as stainless steel.

On the other hand, since boride ceramics generally have low wettability with molten metal, they can be used as die-casting machine parts. For example, a material such as SKD61 obtained by subjecting a steel material such as SKD61 to a nitriding treatment such as gas nitriding or ion nitriding is mainly used for aluminum die casting parts. However, since steel materials easily react with molten metal and gradually corrode with these materials when used for a long period of time, seizure occurs, and further, the components of the steel materials are mixed in the die-cast product, resulting in deterioration of quality. Further, in the case of the plunger sleeve and the tip for extruding the molten metal, the molten metal is firmly attached to the sliding portion and is not peeled off, and an accident such as seizure or galling may occur. Therefore, workability and economic efficiency are very poor, such as applying a large amount of lubricant or mold release agent and replacing parts in a short period of time. Further, when a lubricant or a mold release agent is used, they are mixed in the product, which not only deteriorates the product quality but also significantly impairs the working environment.

Therefore, attempts have been made to produce a member for a low melting point metal die casting machine from a sintered body of ceramics having excellent corrosion resistance against molten metal, but ceramics are difficult to sinter and machine, and ceramics having complicated shapes and It is difficult to manufacture a large-sized member, and its application is largely restricted by the shape of parts. This also adds to the cost. Furthermore, since the toughness and thermal shock resistance are low, cracks and chips may occur during the work.

Utilizing the corrosion resistance of ceramics and the toughness and economy of steel, TiC, TiN,
The ceramics such as TiCN are coated by the PVD method or the CVD method. However, if the film thickness is thin, the effect is small, and if the film thickness is thick, peeling easily occurs, and the manufacturing cost increases.

[0007]

DISCLOSURE OF THE INVENTION The object of the present invention is to form a discharge coating layer on a steel material or the like by using a boride-based ceramics having the above-mentioned excellent characteristics as an electrode and to realize the original characteristics of boride. It is to provide a corrosion-resistant and wear-resistant member that makes full use of it. In particular, it is to utilize the feature of being excellent in wettability with molten metal and corrosion resistance so that it can be used as a structural mechanical member such as a die-cast mechanical member or a non-ferrous tool.

The sintering of boride-based ceramics, like other ceramics, requires a higher temperature than that of metals and cermets, and moreover, in order to obtain a high-strength sintered body, In addition, it is necessary to rigorously select the amount and kind of the sintering aid, control the sintering atmosphere precisely, and devise a molding method that applies pressure simultaneously with the sintering. Among them, boride-based ceramics are known to be particularly difficult to sinter, and it is extremely difficult to manufacture a material having a large wall thickness or a material having a complicated shape.

Furthermore, their machining is significantly more difficult than conventional materials such as steel. For this reason, the manufacturing cost is high, and it is not possible to compete with conventional materials in terms of cost / performance. These are the main reasons why ceramics have not been widely used industrially as structural materials while having many excellent and unique properties.

On the other hand, from the side of utilizing materials, in many cases, most of wear resistant members, corrosion resistant members, and heat resistant members need only their surface layers to fulfill their functions.
For this purpose, joining such as brazing, thermal spraying, padding, plating, etc. are performed, and they are used depending on their respective purposes.

However, since the melting point of ceramics is high, it is difficult to build them up, and it is generally very difficult to plate the ceramics themselves. Further, although a thermal spraying method in which a heat source and an atmosphere are improved has been developed, there are problems that pores remain and the characteristics of the bonded portion and the coating are significantly lowered from the original values of ceramics.

[0012] Therefore, generally, a ceramic sintered body is often used by being joined to a steel material by brazing, but when the temperature rises during use, the strength of the brazing material is unavoidably reduced due to softening of the brazing material. It is not possible to bring out the characteristics unique to ceramics. A high melting point brazing filler metal may be used to secure the strength at high temperature, but in order to heat the base material and ceramics to a temperature above the melting point of the brazing filler metal, there is a large residual difference in thermal expansion after joining. Distortion is unavoidable, and chips and cracks often occur during use.

In the discharge coating method, a workpiece is used as a cathode, an electrode is used as an anode, and while this electrode is vibrated or rotated, electric discharge and short circuit are repeated on the surface of the workpiece to transfer the electrode material to the workpiece for coating. Is the way to do it. Various pure metals, alloy steels, non-ferrous alloys, and carbides have been proposed for this electrode. However, these do not have sufficient corrosion resistance to molten metal.

Although coating of boride such as Ti, Zr, Ta with an electrode has been reported, it has not been widely adopted industrially. This is because the boride is difficult to sinter, its strength is not sufficient for discharge coating, and the electrode often breaks during its handling or coating operation, making it impossible to perform substantial work.

[0015]

In order to achieve the above-mentioned object, a high-strength boride sintered body containing 40% or more of a binary boride is used as an electrode, and by a discharge coating method, it is sufficiently used as a structural material. By coating on a base material such as steel having sufficient strength, a coating composite with excellent mechanical strength and thermal shock resistance can be obtained without impairing the functions of boride such as corrosion resistance and wear resistance. Obtainable.

That is, the electrode for forming the boride film is MxBy (where M is Ti, Zr, Ta, Nb,
Cr, V, x = 1 to 2, and y = 1 to 4) 40 to 98% of at least one selected from binary borides represented by Mo ₂ FeB ₂ and Mo. ₂ CoB ₂ , Mo
₂ NiB ₂ , W ₂ FeB ₂ , W ₂ CoB ₂ , W ₂ NiB ₂ , Mo
Discharge coating is performed by forming a sintered body containing 2 to 60% of one or more ternary compound boride selected from CoB, WFeB, and WCoB, and inevitable impurities contained in these alloys. It is possible to obtain an electrode that can sufficiently withstand the impact at the time of.

The electrodes for forming the film are Mx
At least one selected from binary borides represented by By is 30 to 78%, Mo ₂ FeB ₂ , Mo ₂ Co
B ₂ , Mo ₂ NiB ₂ , W ₂ FeB ₂ , W ₂ CoB ₂ , W ₂ Ni
₂ to 30% of one or more ternary compound boride selected from B ₂ , MoCoB, WFeB and WCoB, TiC, T
iN and at least one selected from TiCN having an atomic ratio of C / N of 0.25 to 4.0 is 10 or more.
Similar effects can be observed as a sintered body composed of .about.55% and unavoidable impurities contained in these alloys.

Binary borides include TiB ₂ and Zr.
B ₂ , TaB ₂ , CrB _{2 and the} like are preferable in terms of wear resistance and wettability with molten metal, and the added ternary boride plays a binding phase role and is 2% or more. If not included,
The strength of the sintered body is not sufficient, and if it exceeds 98%, the wear resistance is lowered and the molten metal is easily wetted.
In addition to ternary borides, TiC, TiN, and T
Addition of iCN has the effect of suppressing grain growth and improving the strength of the sintered body, and sufficient effects cannot be obtained unless the amount of these is 10% or more. On the other hand, if it exceeds 55%, the strength of the sintered body is lowered and the wear resistance is lowered.

Such a boride ceramics electrode is disclosed in Japanese Patent Publication No. 61-19593 or Japanese Patent Publication No. 61-50909.
It can be manufactured by the powder metallurgy method disclosed in, for example. For example, a binary boride TiB ₂ powder may be added to Mo ₂
NiB ₂ powder is blended so as to have a predetermined composition, wet milled and mixed by a ball mill or the like, and then dried. A graphite mold is filled with this mixed powder, and the mixture is vacuumed or in a neutral or reducing atmosphere such as argon gas, nitrogen gas, hydrogen gas, or the like,
1400 ° C to 190 under pressure of kg / cm ² or more
By hot pressing at a temperature of 0 ° C., or by pre-compacting the mixed powder with a hydraulic press or a hydrostatic press, the mixed powder is heated at 1500 ° C. to 2000 ° C. in the above-mentioned vacuum or in an inert or reducing atmosphere. It can be manufactured by performing ordinary sintering by heating at a temperature. The sintered body obtained by hot pressing or ordinary sintering may be subjected to hot isostatic pressing in order to enhance strength and its reliability. Alternatively, after the mixed powder is canned, it can be directly molded by a hot isostatic press or a sinter hip to obtain a sintered body.

The electrode may have various shapes depending on the symmetrical object to be coated, but it is usually a simple shape such as a round bar or a disc, and is easy to mold and sinter. Moreover, machining after sintering is not necessary except in special cases.

The discharge coating is carried out using these boride electrodes, and the coating may be carried out by using a discharge coating apparatus which is usually used. If the above-mentioned sintered body is used, the electrode may be broken or broken during the coating process. The workability is extremely excellent. Also,
The formed film is not only high in hardness and excellent in wear resistance as in the sintered body, but also excellent in wettability with molten metal and corrosion resistance as in the sintered body.

Further, the adhesion of the formed film to the base material is particularly excellent. For example, a film coated on a low carbon steel plate having a thickness of 3 mm does not show peeling even when bent about 180 °. In addition, resistance to thermal shock, T
Immediately after heating to ℃, it is put into water at t ℃ and judged by the presence or absence of cracks.
When evaluated by (° C.), Δθ is 200 to 400 in the sintered body.
° C, the coating composite of the present invention has a Δθ of 10
There is even more than 00 ° C.

The thickness of the coating is preferably 5 to 300 μm. That is, if it is thinner than 5 μm, the wear resistance and the corrosion resistance are not sufficient, and if it exceeds 300 μm, the effect on the wear resistance and the corrosion resistance is not improved so much and it is not economical.

The base material to be coated is generally a steel material or the like, but any material may be used as long as it is electrically conductive and can be selected according to the purpose of use.

Since the coated composite of the present invention is hardly wet with molten aluminum without using a special mold release agent or lubricant, it can be applied to a die casting die, a plunger tip or a sleeve without lubrication or weight loss. Can be used under lubrication. Lubricants and mold release agents are sprayed as mist, and if these are eliminated or reduced, it will lead to a significant improvement in the working environment, and further maintenance is not necessary, and the life can be extended. The cost can also be reduced.

In addition, the boride-coated composite of the present invention is a stalk, a runner plate, an extrusion pin, a core, a melting crucible, a ladle, a stirring rod, a temperature measuring protection tube, and a dipping heater used for casting a low melting point metal. It can also be applied to protective tubes and can be expected to have a long life. Further, this coating can be applied not only to aluminum but also to members for die casting machines and casting machines of low melting point metals such as zinc, magnesium, lead and tin, and alloys thereof.

[0027]

The present invention will be described in more detail with reference to the following examples.

Example 1 85% TiB ₂ powder and 15% Mo ₂ NiB ₂ powder were mixed and pulverized in acetone for 52 hours in a vibration mill, and then dry granulated in a nitrogen atmosphere. This mixed powder was filled in a graphite mold and hot pressed in an argon gas atmosphere (atmospheric pressure). Hot press condition is 200k
It was 20 minutes at 1550 ° C. and g / cm ² . The obtained sintered body had a relative density of 99.0%, a transverse rupture strength of 120 kg / cm ² ,
The Vickers hardness was 2400. Φ3 from this sintered body
A 25 mm x 50 mm x 5 mm nitriding treated SK by cutting out a round bar of mm x 100 mm and using this as an electrode
The surface of D61 was subjected to electric discharge coating to a thickness of 35 μm. The discharge coating was carried out using a commercially available coating device in the atmosphere at a frequency of 300 Hz and a capacitor capacity of 70 μf.

Example 2 50% TiB ₂ powder, 45% TiC powder, Mo ₂ CoB ₂
5% of the powder in an acetone for 8 hours,
After performing mixed pulverization, dry granulation was performed in a nitrogen atmosphere. This mixed powder was pressed at 1.5 ton / cm ² using a hydraulic press.
And molded into a green compact. This green compact was heated in an argon gas atmosphere at a temperature of 1700 ° C. for 30 minutes to obtain a sintered body. This was hot isostatically pressed at 1800 ° C. and 1500 atm to give a relative density of 99.5% and a transverse rupture strength of 96 kg / cm.
² , a sintered body with Vickers hardness of 2200 was obtained. A φ3 mm × 100 mm round bar was cut out from this sintered body, and using this as an electrode, the surface of the nitriding-treated SKD61 was subjected to discharge coating with a thickness of 20 μm. The discharge coating conditions are those of Example 1.
Same as above, but the thickness was changed by working time.

Example 3 70% ZrB ₂ powder and 30% Mo ₂ NiB ₂ powder were mixed and pulverized in acetone by a vibrating ball mill for 25 hours, and then dried and granulated in a nitrogen atmosphere. This mixed powder was filled in a graphite mold and hot pressed in vacuum. The hot press conditions are 160 kg / cm ² , 1530 ° C. and 3
It was set to 0 minutes. The obtained sintered body had a relative density of 99.2%, a transverse rupture strength of 93 kg / cm ² , and a Vickers hardness of 2150. A φ3 mm × 100 mm round bar was cut out from this sintered body, and this was used as an electrode for nitriding SKD61.
A 20 μm thick discharge coating was applied to the surface of the. The discharge coating conditions were the same as in Example 2.

This coated composite was treated with molten aluminum (ADC10: 92% Al-10% Cu-8% S) at 750.degree.
It was immersed in i) for 2.5 hours and the corrosion weight loss was measured. Also,
An Ogoshi-type wear test was performed. As the friction conditions, a SS41 ring was used as the mating material, the friction distance was 400 m, the friction speed was 4.39 m / s, and the final load was 18.9 kg.
The wear amount of the test piece is shown by the specific wear amount. The results are summarized in Table 1.

As can be seen from Table 1, the corrosion of the discharge coating composite due to molten aluminum is slightly inferior to the sintered body used as an electrode, but compared with the nitriding material of SKD61 which is often used for aluminum die casting parts. And is remarkably excellent. Further, since hardness is thin coating, but indicates a lower value under the influence of steel foundation, the specific wear rate are both located on the same order of 10 ^{@ 9} a sintered body, SKD61
It can be said that it is far superior to the nitride material.

[0033]

[Table 1] Comparative Example 1: Sintered body of Example 1 Comparative Example 2: Sintered body of Example 2 Comparative Example 3: Sintered body of Example 3

Example 4 A nitriding SKD61 having an outer diameter of 8 as shown in FIG.
The inner surface of the injection container 1 having a diameter of 0 mm, an inner diameter of 60 mm, a depth of 60 mm and a wall thickness of 10 mm was subjected to discharge coating using the sintered bodies of Examples 1 to 3 as electrodes. The coating conditions were the same as in Example 1.

3 molten aluminum (750 ° C., 92% Al-10% Cu-8% Si) was poured into the pouring container 1, and the aluminum was solidified while pressing with a pressing die 4 at P1 = 10 kg / cm ^2. And the temperature of aluminum is 30
After reaching 0 ° C., a force of P2 was applied by the take-out rod 5 to take out the ingot. Initially, the value of P2 is small while the molten aluminum does not react with the container and is easily separated, but when this operation is repeated and the molten aluminum begins to react with the container, P2 becomes a large value. Therefore, the measurement was stopped when P2 became a stress of ² kg / cm ² or more, and the number of times until that time was measured.

The results are shown in Table 2. As is clear from the table, the coating material of the present invention shows good characteristics even when the number of times exceeds about 35,000, whereas SKD61 causes the extraction force to exceed a predetermined value in a short number of times and to stop the test. Became.

[0037]

[Table 2]

[0038]

EFFECTS OF THE INVENTION The discharge coating composite of the present invention is a structural material which is coated with a boride ceramics on a steel material using a discharge coating method without impairing its original functions such as wear resistance and corrosion resistance. It can be put to practical use as a material. In particular, for low melting point metal die casting machine parts such as aluminum, if the whole parts are made of ceramics, the life will be improved, but not only the manufacturing cost will be expensive but also there is always the concern of cracking, which makes workability remarkable. descend. Furthermore, large-sized products and complicated-shaped products are very difficult to manufacture. However, since the coated composite of the present invention uses a conventionally used steel material or the like as a base material as it is, there is no problem in strength and it is easy to manufacture a large-sized product or a product having a complicated shape. Also, it has high adhesion to the substrate and excellent thermal shock resistance. Further, the base material is hardly affected by heat and the like, and residual stress is not applied. Moreover, the wear resistance of the film and the corrosion resistance to molten aluminum are as good as those of the sintered body.

[0039]

[Brief description of drawings]

FIG. 1 is a schematic view of a characteristic evaluation test method of a molten aluminum container coated with boride.

[Explanation of symbols]

1 Injection container (SKD61, ion nitride material) 2 Discharge coating layer 3 Molten aluminum at 750 ° C (92% Al-10%
Cu-8% Si) 4 Push type 5 Aluminum ingot take-out rod

Claims (5)

[Claims] 1. In a coating composite in which a film is formed on a substrate by an electric discharge coating method, the electrode for forming the film is Mx.
At least one selected from binary borides represented by By (wherein M represents Ti, Zr, Ta, Nb, Cr, V, and x = 1 to 2, y = 1 to 4). 40 to 9
8% by weight (hereinafter% is% by weight), Mo ₂ FeB ₂ , Mo ₂
CoB ₂ , Mo ₂ NiB ₂ , W ₂ FeB ₂ , W ₂ CoB ₂ , W _2
2 to 60% of one or more ternary compound boride selected from NiB ₂ , MoCoB, WFeB, and WCoB and inevitable impurities contained in these compounds, and the thickness of the film formed. Of 5 to 300 μm. 2. MxBy is TiB ₂ , ZrB ₂ , Ta
₂ of at least one selected from B ₂ and CrB 2
The discharge-coated composite according to claim 1, wherein the discharge-based composite is an original boride. 3. In a coated composite in which a film is formed on a substrate by a discharge coating method, the electrode for forming the film is Mx.
At least one selected from binary borides represented by By is 30 to 78%, Mo ₂ FeB ₂ , Mo ₂ Co
B ₂ , Mo ₂ NiB ₂ , W ₂ FeB ₂ , W ₂ CoB ₂ , W ₂ Ni
₂ to 30% of one or more ternary compound boride selected from B ₂ , MoCoB, WFeB and WCoB, TiC, T
iN and at least one selected from TiCN having an atomic ratio of C / N of 0.25 to 4.0 is 10 or more.
The discharge coating composite is characterized by comprising ˜55% and unavoidable impurities contained in these compounds, and forming a film having a thickness of 5 to 300 μm. 4. MxBy is TiB ₂ , ZrB ₂ , Ta
₂ of at least one selected from B ₂ and CrB 2
The discharge coating composite according to claim 3, wherein the discharge coating composite is an original boride. 5. The discharge coating composite according to claim 1 or 2, wherein a boride film is formed on a base material by a discharge coating method and is used for a die casting machine member.