JPH09227243A - Molybdenum boride-containing composite thermal spraying material and thermally sprayed coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermal spraying material fit to form a thermally sprayed coating film excellent in resistance to a molten light metal. SOLUTION: This composite thermal spraying material consists of 30-70wt.% MoB, 20-40wt.% Ni or Co, 5-20wt.% Cr and 5-10wt.% boride of at least one kind of metal selected from among Cr, W, Zr, Ni and Nb.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molybdenum boride-based composite thermal spray material, and is particularly suitable as a material for forming a thermal spray coating for protecting mechanical equipment from erosion of light alloy molten metal such as aluminum, zinc and alloys thereof. It is something.

[0002]

2. Description of the Related Art Conventionally, a die casting method, a gravity casting method, a differential pressure casting method or the like has been used for casting a metal having a relatively low melting point such as aluminum, zinc or magnesium.

Particularly, the differential pressure casting method is said to be suitable for obtaining a large casting having few internal defects by using the apparatus shown in FIG. As shown in FIG. 2, the pressure in the mold 5 is kept lower than that in the holding furnace 1 by using the intake port 6, the molten metal 10 in the holding furnace 1 is raised through the Stokes 2, and is passed through the sleeve 4. The molten metal is made into a laminar flow, and the mold 5 is filled with the laminar flow. When the molten metal on the inner surface of the mold 5 is solidified, the next casting operation is started.
In the sleeve 4, the molten metal flows back into the holding furnace 1 below.

Since the molten metal 10 repeatedly passes through the sleeve 4 in each casting cycle in this manner, the inner surface of the sleeve 4 is washed by the molten metal 10 at a high temperature and is corroded. As a result, the sleeve 4 is eventually cut off and falls off. The higher the molten metal temperature, the shorter the life of the sleeve 4 will be.

The temperature for handling the molten light alloy is 700
It was a relatively low temperature of ˜750 ° C. Under such operating conditions, for example, as shown in JP-A-7-62516, tungsten carbide cobalt (WC /
A thermal spray coating of 12% Co) has been used.

[0006]

However, recently, many manufacturers have begun to adopt the differential pressure casting method for increasing the operating temperature of the molten metal to 750 to 850 ° C. to manufacture more precise products.

As the temperature of the molten metal rises, tungsten carbide has no durability against the molten metal (in particular, the oxidation resistance of WC), and oxidation of not only the sleeve but also the protective film on the surface of the mold has become severe. For this reason,
There was a problem that the die life became extremely short, leading to cost increase.

In view of the above, the present invention is to provide a thermal spray material that contributes to the formation of a thermal spray coating having excellent durability of a light alloy melt, and a thermal spray coating using the same.

[0009]

[Means for Solving the Problems]

(1) The present invention solves the above problems by using a thermal spray material having the following configuration.

That is, it is a molybdenum boride-based composite thermal spray material, molybdenum boride (MoB): 30 to 70 wt.
%, Nickel (Ni) or cobalt (Co): 20 to 4
0 wt%, chromium (Cr): 5 to 20 wt%, Cr, W, Z
It is characterized by comprising at least one metal boride selected from r, Ni and Nb: 5 to 10 wt%.

(2) The thermal spray coating of the present invention solves the above problems by the following constitution.

A thermal spray coating comprising three layers of first to third thermal spray layers sequentially laminated on a substrate to be protected, wherein the first thermal spray layer comprises:
The second sprayed layer is formed of a heat-resistant alloy having a thermal expansion coefficient similar to that of the protective substrate, and the second sprayed layer is molybdenum boride (MoB):
30-70 wt%, nickel (Ni) or cobalt (C
o): 20-40 wt%, chromium (Cr): 5-20 wt%
%, At least one metal boride selected from Cr, W, Zr, Ni and Nb: 5 to 10 wt%, and the third sprayed layer is a ceramic that is non-wettable to molten light metal. It is characterized by being formed.

The first sprayed layer serves as a buffer layer between the sprayed substrate and the molybdenum boride-based composite sprayed material,
Those having a thermal expansion coefficient intermediate between those of the substrate and the molybdenum boride-based sprayed layer are preferable. Alternatively, it may be formed by thermal spraying a metal having a thermal expansion coefficient similar to that of the molybdenum boride-based sprayed layer and having good compatibility with the substrate.

The second sprayed layer plays a major role of protecting the substrate from erosion due to the flow of the high temperature molten metal, and its details will be described below.

Since the third sprayed layer is a very hard coating, it plays a role of preventing the second sprayed layer from being physically damaged by a violent flow of the molten metal or an external force such as impact.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. Composition% is wt% unless otherwise specified
It is.

A. Composite Thermal Spray Material (1) The molybdenum boride-based composite thermal spray material of the present invention is molybdenum boride (MoB): 30 to 70 wt% (desirably, 40 to 60 wt%) nickel (Ni) or cobalt (Co): 20 to 40 wt
% (Desirably 20 to 30 wt%), chromium (Cr):
5 to 20 wt% (desirably 10 to 15 wt%), Cr,
At least one metal boride selected from W, Zr, Ni and Nb: 5 to 10 wt% (desirably 5
~ 8 wt%) is the basic constitution.

The action of each component is as follows.

MoB forms the hard phase of the sprayed layer, and W
It is more stable than C at high temperatures and improves the corrosion resistance to molten light metals. If it is less than 30%, the erosion resistance is poor, and if it exceeds 70%, it becomes brittle.

Ni or Co has malleability and ductility and serves as a binder phase. Below 20%,
The coating becomes brittle, and if it exceeds 40%, the coating becomes too soft.

Cr plays a role of imparting oxidation resistance to Co. If it is less than 5%, the oxidation resistance is not exhibited, and if it exceeds 20%, the effect is saturated.

The metal boride selected from any of Cr, W, Zr, Ni and Nb is a boride of a transition metal in the same group as Mo (group 6) or in the same period as Mo (5 periods). Molybdenum (base) and NiCr or CoCr
It has the function of increasing the bondability with (bonding phase). Here, among these, CrB ₂ is preferable because it has a large bonding action. If the content of such a boride is less than 5% by weight, the above-mentioned binding property-increasing effect is exhibited, and if it exceeds 10% by weight, the effect is saturated.

(2) The molybdenum boride-based composite thermal spray material having the above structure is prepared as follows.

The powder of each component (usually fine particles of 10 μm or less) is uniformly mixed, granulated, sintered, crushed and classified to produce.

Here, general-purpose mixers, granulators, and classifiers are used, and sintering (900 to 135) is used.
0) ° C. × (2 to 4) h, preferably (1000 to 12)
50) ° C. × (2-4) h. The particle size distribution after classification is 125 to 5 μm, preferably 106 to 10 μm.
Particles of 70% or more.

B. Thermal Sprayed Coating (1) The above molybdenum boride-based composite thermal spray material can be sprayed alone onto a protected substrate to form a protective sprayed layer, but the protected substrate is, for example, made of metal and is a molybdenum boride-based sprayed film. When there is a large difference in the coefficient of thermal expansion with, and more reliable non-wetting of molten metal is required, and
If the molten metal wears the sprayed layer due to vigorous movement,
The above-mentioned difficult problems can be solved by using a protective multilayer sprayed layer having the following constitution.

The structure of the thermal spray coating of the present invention is shown in FIG.

The thermal spray coating of the present invention is a multi-layer thermal spray layer in which the first to third thermal spray layers 13, 15, and 17 are sequentially laminated on the substrate 11 to be protected, and the first thermal spray layer 13 is to be protected. Base 1
1 is formed of a heat-resistant alloy having a thermal expansion coefficient close to 1, the second thermal spray layer 15 is formed of the molybdenum boride-based composite thermal spray material of the present invention, and the third thermal spray layer 17 is non-melting light metal. The basic structure is that it is made of a wettable hard ceramic.

The third sprayed layer 17 usually has micropores, is weak against thermal shock and easily cracks. Therefore, it is desirable to partially form the impregnated reinforced layer 19 with heat resistant organic silicon. .

(2) The substrate to be protected is not particularly limited, but is made of iron such as cast iron (coefficient of thermal expansion: 10 × 10 ⁻⁶ / ° C.), steel (coefficient of thermal expansion: 12 × 10 ⁻⁶ / ° C.). Material, aluminum alloy (coefficient of thermal expansion: 20 × 10 ^-6 / ° C), etc.
Can be preferably used.

The surface of the substrate to be protected may be roughened by shot blasting or the like prior to the formation of the first sprayed layer, because the adhesion of the first sprayed layer to the substrate to be protected increases. desirable.

(3) As a heat resistant alloy for forming the first sprayed layer, nickel chromium aluminum (Cr 18 to 48) is used.
%, Al 4-10%, Ni balance), Niklarie (Cr
16-25%, Al 6-13%, Y 0.5-1.0
%, Ni remaining), Coklary (Cr 20-25%, Al
11-15%, Y 0.5-1.0%, Co balance), Stellite (Cr 20-30%, C 0.1-2.5).
%, W 4-18%, Mo 1-6%, Ni 3-10
%, Si 1-2%, Fe 1-3%, Co balance) and the like. The coefficient of thermal expansion is roughly (15 to 1
6) It is in the range of × 10 ^-6 / ° C.

In particular, Niclary and Cochlary have an excellent thermal oxidation resistance because an oxide film of Cr ₂ O ₃ , Al ₂ O ₃ or the like is formed on the surface, and Y ₂ O ₃ is substantially ceramic. It exhibits a wedge effect with respect to the second sprayed layer made of a certain molybdenum diboride-based composite sprayed material, and exhibits good adhesion to the second sprayed layer.

The thickness of the first sprayed layer is 20 to 200 μm.
m, preferably 40 to 100 μm. When the thickness is smaller than the above range, it is difficult to exert a protective action on the protected substrate and a buffer layer action between the protected substrate and the second sprayed layer. Further, if the thickness exceeds the above range, further increase in effect cannot be expected, and the economy is rather lowered.

The thermal spraying method is not particularly limited, and it is carried out in the air or in a reduced pressure atmosphere by flame spraying such as gas spraying, explosion spraying or plasma spraying. Of these, plasma spraying is desirable because the quality of the sprayed material is small and the adhesion to the sprayed material is good.

(4) As the molybdenum diboride-based composite thermal spray material forming the second thermal spray layer, those described in A above are used.

The function of the second sprayed layer is mainly to impart heat resistance to the substrate to be protected and not to react with the molten metal.
It is to impart the molten metal erosion resistance to the protected substrate.

The thickness of the second sprayed layer is 20 to 200 μm.
m, preferably 50 to 150 μm. If the thickness is less than the above range, it is difficult to exert the protective action on the protected substrate. Further, if the thickness exceeds the above range, further increase in effect cannot be expected, and the economy is rather lowered.

The method of spraying the second sprayed layer is the same as the above first method.
It is performed in the same manner as in the case of the sprayed layer.

(5) Ceramics that are non-wetting with respect to the molten light metal forming the third sprayed layer include partially stabilized zirconia (ZrO ₂ .Y ₂ O ₃ , ZrO ₂ .CaO, etc.), alumina-zirconia ( Al ₂ O ₃ 60-70%, Zr
O ₂ 30-40%) can be preferably used. Especially,
Among zirconia, rare earth oxides (for example, Y ₂
O ₃ ), CaO, MgO, etc. are preferably added so that partially stabilized zirconia in which a phase transition does not occur is added.

The thickness of the third sprayed layer is 20 to 200 μm.
m, preferably 50 to 150 μm. When the thickness is less than the above range, it is difficult to achieve the effect of forming the third sprayed layer (ensuring the non-wetting property of the molten metal), and even if it exceeds 200 μm, further increase in the effect cannot be expected, and it is economical. Will be at a disadvantage.

The method of spraying the third sprayed layer is the same as the above first method.
It is performed in the same manner as in the case of the sprayed layer.

(6) Examples of the heat-resistant organic silicon material used for the impregnation strengthening treatment of the third thermal spray layer include polymetallocarbosilane and diphenyl silicone. Among these, polymetallocarbosilane is preferable because it is excellent in heat resistance and impregnability with respect to the third thermal spray layer (ceramic).

In the impregnation strengthening treatment, it is desirable to bake after impregnating the organic silicon material solution by spray coating, dip coating or the like. This baking condition is usually 2
The temperature is set to 00 to 500 ° C. for 10 to 60 minutes.

[0045]

The function and effect of the invention The molybdenum diboride-based composite thermal spray material of the present invention contributes to the formation of a thermal spray coating excellent in the durability of a light alloy molten metal, as shown in the examples described later. The thermal spray coating used has excellent molten metal durability.

[0046]

EXAMPLES Examples and comparative examples performed to confirm the effects of the present invention will be described below.

(1) Preparation of test piece <Example 1> Protective tube (material: 27Cr steel, thermal expansion coefficient:
6.0 × 10 ^-6 / ℃ Dimension: 21.3mmφ × 2.65mm
The following three-layer thermal spray coating was applied to t × 250 mm). The thermal spraying was performed by plasma spraying (plasma gas: Ar / H ₂ ).

First layer: Coclarie (Cr23%, Al1
3%, Y0.6%, Co residual) 100 μm Second layer: Molybdenum boride-based thermal spray material (Co30%, C
r15%, CrB ₂ 5%, MoB remaining) 100 μm Third layer: Alumina-zirconia (Al ₂ O ₃ 70%, Z)
rO ₂ 30%) 100 μm Impregnation strengthening treatment: Organosilicone resin impregnation drying (condition: 300
(° C x 120 minutes) <Example 2> Protective tube (material: 27Cr steel, thermal expansion coefficient:
6.0 × 10 ^-6 / ℃ Dimension: 21.3mmφ × 2.65mm
The following three-layer thermal spray coating was applied to t × 250 mm). The thermal spraying was performed by plasma spraying (plasma gas: Ar / H ₂ ).

First layer: Coclarie (23% Cr, Al1
3%, Y0.6%, Co residual) 100 μm Second layer: Molybdenum boride-based thermal spray material (Ni30%, C)
r8%, CrB ₂ 10%, MoB remaining) 100 μm Third layer: Alumina-zirconia (Al ₂ O ₃ 70%, Z)
rO ₂ 30%) 100 μm Impregnation strengthening treatment: Organosilicone resin impregnation drying (condition: 300
C. × 120 minutes) <Comparative Examples 1 and 2> Comparative Example 1 ... B / N glass having a thickness of 3 on the same substrate as in Example 1.
Prepared by mixing and coating to 00 μm and baking.

Comparative Example 2 ... Prepared by plasma spraying stabilized zirconia on the same substrate as in Example 1 to a thickness of 350 μm.

(2) Test Method (Aluminum Molten Metal Dipping Thermal Cycle Test) Two of each of the three test pieces were simultaneously attached to a dipping device filled with the AC2CAl-Si alloy molten metal having the composition shown in Table 1 for 7 minutes. A test was conducted in which the steel was immersed in the molten metal, pulled up, and left to cool in the atmosphere for 1 minute.

This heat cycle is repeated 5
The outer diameter was measured every 00 cycles to examine the damage of the coating. The outer diameter was measured at three points of 20 mm, 40 mm, and 60 mm from the tip.

The aluminum alloy adhering to the test piece was melted and removed by heating with a burner each time the dimension was measured, and great care was taken not to apply a shock such as mechanical impact, and only a thermal shock was applied.

(3) Test results: From the outer diameter measurement results shown in Tables 2 and 3, the thermal spray coating formed using the thermal spray material of the present invention has about twice the durability as compared with the conventional method. It can be seen that it has performance.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a thermal spray coating of the present invention.

FIG. 2 is a cross-sectional view showing an outline of an apparatus of a differential pressure casting method.

[Explanation of symbols]

 1 Holding Furnace 2 Stokes 4 Sleeve 5 Mold 6 Intake Port 10 Molten Metal 11 Protected Substrate 13 First Thermal Spray Layer 15 Second Thermal Spray Layer 17 Third Thermal Spray Layer 19 Impregnation Strengthening Layer

Front page continued (72) Inventor Tamuro Ito 230 Okita-machi, Nakamura-ku, Aichi Prefecture Chubu Sukegawa Kogyo Co., Ltd. Shiojiri Plant (72) Inventor Kuniki Ishibayashi Shiojiri City, Nagano Prefecture Soga Ichibanchi Showa Denko Co., Ltd.

Claims (8)

[Claims] 1. A molybdenum boride-based composite thermal spray material, wherein molybdenum boride (MoB): 30 to 70 wt%, nickel (Ni) or cobalt (Co): 20 to 40 wt.
%, Chromium (Cr): 5 to 20 wt%, at least one metal boride selected from Cr, W, Zr, Ni and Nb: 5 to 10 wt%, molybdenum boride characterized by the following: -Based composite thermal spray material. 2. The metal boride is chromium boride (CrB).
₂ ) The molybdenum boride-based composite thermal spray material according to claim 1, characterized in that 3. A thermal spray coating comprising first to third thermal spray layers sequentially laminated on a protected substrate, wherein the first thermal spray layer is formed of a heat-resistant alloy having a thermal expansion coefficient similar to that of the protective substrate. The second sprayed layer is molybdenum boride (MoB): 30 to 70 wt%, nickel (Ni) or cobalt (Co): 20 to 40 wt.
%, Chromium (Cr): 5 to 20 wt%, at least one metal boride selected from Cr, W, Zr, Ni and Nb: 5 to 10 wt%, and the third sprayed layer has , A thermal spray coating formed of a ceramic that is non-wetting with respect to molten light metal. 4. The heat-resistant alloy forming the first sprayed layer is nickel chrome aluminum (NiCrAl), niclaly (NiCrAlY), cokulary (CoCrAlY),
1 selected from among stellite (CoCrW series)
The thermal spray coating according to claim 3, wherein the thermal spray coating is a seed. 5. The metal boride forming the second sprayed layer is molybdenum boride (MoB) or chromium boride (C).
The thermal spray coating according to claim 3, which is rB ₂ ). 6. The ceramic forming the third sprayed layer is a part.
Minute stabilized zirconia (ZrO_Two ・ Y_Two O_Three Or ZrO_Two 
-CaO) or alumina-zirconia (Al _Two O_Three -Z
rO_Two ) Is any one of the following).
The thermal spray coating described. 7. The thermal spray coating according to claim 3 or 6, wherein the third thermal spray layer is impregnated and strengthened with a heat resistant organosilicon material. 8. The thermal spray coating according to claim 7, wherein the heat resistant organosilicon material is polymetallocarbosilane.