JPH06340941A - Nano-phase composite hard material and its production - Google Patents

Abstract

PURPOSE:To enhance the strength and hardness of a hard material by dispersing a fixed amt. of a nano-phase of one or more among iron family metals and carbides, nitrides, borides and borocarbides of the metals as a 3rd phase in a hard phase of borides and a metallic bonding phase. CONSTITUTION:One or more among TiB, ZrB, Mo2NiB2, Mo2CrB2, Mo2FeB2 and WCoB are used as a hard phase and one or more among Fe, Co and Ni are used as a metallic bonding phase. One or more among Fe, Co, Al, Cu, Mg, Si, Ti, Zr, Hf, V, Nb, Cr, Mo and W as metals and carbides, nitrides, borides, oxides and borocarbides of the metals are selected as a nano-phase having <=300mum particle diameter and this nano-phase is added to the hard phase and the bonding phase so that the nano-phase accounts for 35-98vol.% of the amt. of the objective hard material. The resulting powdery mixture is compacted and sintered at such a relatively low temp. that the nano-phase does not grow or vanish by entering into solid soln. in the hard phase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a strength and hardness comparable to that of a typical hard material (also referred to as cermet), tungsten carbide-cobalt (WC-Co) type cemented carbide, at room temperature. The present invention relates to a hard material that retains excellent strength and hardness even at a high temperature of 600 ° C. or higher at which the material and cemented carbide cannot maintain strength and hardness.

[0002]

2. Description of the Related Art Given that WC-Co cemented carbide has excellent strength and hardness, it can be used for many purposes and has already formed a large market. Is superior in oxidation resistance to the hard phase of carbide of WC-Co cemented carbide, and is also excellent in corrosion resistance to molten metals such as aluminum and zinc. Expected to be pioneered.

However, simply combining a boride and a metallic binder phase often results in the formation of brittle compounds, which does not provide a practical hard material. For example, Ti
B ₂ and ZrB ₂ react with Fe and Ni to form fragile boride phase FeB and NiB.
It is difficult to manufacture a boride-based hard material having practical material properties.

There is a group of complex borides in borides, and complex borides such as Mo ₂ FeB ₂ , Mo ₂ NiB ₂ and W ₂ CoB ₂ have been reported in Steinitz et al.'S paper (Powder Met. Bull. .6,123
(1953)) and suggests that it can be used for the hard phase of hard materials. Mo ₂ FeB ₂ and Mo ₂ N
In the case of a complex boride such as iB ₂ , a hard material having a practical strength and hardness without generating the above-mentioned undesired boride phase even when combined with an Fe or Ni-based metal binding phase. Are obtained by sintering.

Therefore, in Japanese Patent Publication No. 60-57499, Japanese Patent Publication No. 62-196353, Japanese Patent Publication No. 63-143236, etc., Mo ₂ FeB ₂ , Mo ₂ NiB ₂ , W ₂ Co
A hard material composed of a compound boride such as B ₂ as a hard phase and a metal-bonded phase mainly composed of an iron group metal has already been proposed.

[0006] The hard material containing these double borides as the hard phase is preferable in that the boride has corrosion resistance to molten metals such as Al and Zn, and has strength and hardness even in a high temperature range of 600 ° C or higher. Since it has strength and hardness superior to that of cemented carbide in the high temperature range of 600 ° C or higher, it has been tried to be applied to members for die casting of aluminum, and its practical application is currently underway. Hard materials using boride as a hard phase are being reviewed.

On the other hand, the improvement of cemented carbide and TiC-based hard materials has also made remarkable progress since then, and a material having a very high level of strength and hardness at room temperature has been realized, and the bending strength of cemented carbide has been improved. A value of 500 kg / mm ² has also been reported.

On the other hand, on the other hand, JP-A-5-58751
In the crystal particles of ceramics is nm (nanometer)
It has been proposed to obtain a ceramic body that is superior in high temperature strength and toughness to conventional ceramics by dispersing the second phase of the order. If this idea can be applied to a boride cermet, which is a composite material of metal and boride ceramics, it is expected that the high temperature strength and hardness of the cermet often used under extreme conditions can be improved.

At present, in the case of a hard material containing a complex boride as a hard phase, even a material having a large bending strength is about 250 kg / mm ² . If it is possible to improve the strength of the hard material of compound boride at room temperature to a level comparable to that of cemented carbide,
It is expected that the strength at a high temperature of 600 ° C. or more will be remarkably increased, and if the strength at a high temperature is increased, it will be a driving force for the development of new technologies and should open up a wide range of applications.

[0010]

The present invention is based on the current state of the art in the above-mentioned hard materials, and is a hard material in which boride is combined with a metallic binder phase containing an iron group metal as a main component. The object is to provide a large hard material.

[0011]

The present invention has been made to achieve the above-mentioned objects, and the nanophase composite hard material of the present invention is selected from the hard phase of boride and Fe, Co, or Ni. And a nano phase having a particle size of less than 300 nm, which is contained in the hard phase in an amount of 0.01% by volume or more and 30% by volume or less. The nano phase is Fe, Ni, Co, Al, Cu, Mg, Si,
Metal groups consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W, carbide groups of these metals, nitride groups of these metals, boride groups of these metals, oxide groups of these metals, these It is characterized by being at least one selected from the group consisting of metal silicides and boron carbide.

In most cases, fracture of the hard material proceeds by cracks traversing the hard phase, which predominantly comprises the hard material, but in the nanophase composite hard material of the present invention, the hard phase of the boride is Since the fine third phase called nano phase with very small particle size is scattered inside, the hard phase of the compound boride is strengthened in both strength and hardness, and the strength and hardness of the hard material is improved. Has been.

The reason why the fracture strength of the hard phase is enhanced by the nano phases interspersed in the hard phase is not clear so far, but the stress concentration near the tip of the crack at the portion where the tip of the crack hits the nano phase is not clear. It is presumed that the rupture strength of the hard phase is improved by the relaxation.

In many cases, nano-phase composite hard materials in which nano phases are dispersed in the hard phase are difficult to obtain by normal pressure sintering which is usually adopted as a manufacturing method thereof, and the preparation conditions of raw materials and sintering It can be obtained only by a sintering method under strictly controlled conditions.

First, the nanophases dispersed in the hard material are made to exist in the raw material in advance as fine particles, preferably in the form of a metal or a compound finally dispersed. Sintering is carried out by strictly controlling the temperature at a relatively low temperature so that the nano phase does not grow into crystals having a particle size of 300 nm or more and the nano phase does not dissolve into the hard phase and disappear. It is necessary to conclude. Therefore, since the range of the sintering temperature can be widened, it is preferable to perform the sintering by hot pressing or hot isostatic pressing (HIP), which is easy to sinter even at a low temperature.

There is a technique for precipitating fine carbides in materials such as steel by quenching or tempering, but most boride phases have a higher melting temperature than iron group metals. Therefore, crystal growth is likely to occur, and it is not easy to precipitate the nano phase (third phase) in the double boride phase.

Fe, Ni, Co, Al, Cu, M may be used as the phase dispersed as a nano phase in the hard phase of boride.
g, Si, Ti, Zr, Hf, V, Nb, Ta, Cr,
Metal group consisting of Mo and W, Si, Ti, Zr, H
Carbides of f, V, Nb, Ta, Cr, Mo and W,
Al, Si, Ti, Zr, Hf, V, Nb, Ta, C
r, Mo and W nitride group, Fe, Ni, Co, A
l, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W boride group, Fe, Ni, Co, Al, Si, M
g, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W oxide group, Fe, Ni, Co, Ti, Zr, H
It is preferably at least one selected from the group consisting of silicides of f, V, Nb, Ta, Cr, Mo and W and boron carbide.

As the nano phase dispersed in the hard phase,
Phase stability and ease of manufacture during sintering of hard materials,
From the characteristics of the obtained sintered body, Ti, Z
More preferably, it is at least one selected from the group consisting of carbides, borides, oxides, boron carbide, alumina, silicon carbide and silicon nitride of r, Hf, V, Nb, Ta, Cr, Mo and W.

The size of the third phase is such that the particle size is 300 nm.
The effect of significantly improving the strength and hardness of the material is obtained when the nano phase is less than less than that, and the effect is small when the particle size is 300 nm or more.

Further, the amount of the nano phase dispersed in the hard phase has the effect of strengthening the hard material if the hard phase is contained in an amount of 0.01% by volume or more. It is less than 30% by volume because it is difficult to make it hard and the effect of further strengthening the hard phase of the hard material cannot be obtained. A preferable hard material having a well-balanced strength and hardness can be obtained by setting the amount of nano phase in the hard material to 0.03% by volume or more and 10% by volume or less.

The hard phase of the boride has practical utility such as showing corrosion resistance against molten metal, and a technique for producing a hard material having practically useful physical properties has already been developed. Sometimes, TiB ₂ , ZrB ₂ ,
WB, CrB, TaB ₂ , NbB ₂ , MoB, Mo ₂ N
iB ₂ , Mo ₂ CrB ₂ , Mo ₂ FeB ₂ , Mo ₂ Co
At least one selected from B ₂ MoCoB, W ₂ CoB ₂ and WCoB is preferable, and TiB ₂ , ZrB ₂ , Mo ₂
NiB ₂ , Mo ₂ CrB ₂ , Mo ₂ FeB ₂ and WC
More preferably, it is one or more selected from oB.

In consideration of the practical strength and hardness of the hard material, the hard phase of boride and the nano phase of the hard material are contained in the hard material in a total amount of 35% by volume to 98% by volume. Is preferred. If the total amount of the hard phase and the nano phase contained in the hard material is less than 35% by volume, the hardness is low and the wear resistance is poor, and if it exceeds 98% by volume, the material becomes brittle and the strength is also reduced. The more preferable amount of the hard phase contained in the hard material and the nano phase in the hard phase is 65% by volume or more and 90% by volume or less in consideration of the balance between the strength and the hardness of the obtained material.

Further, by interspersing the nano phases not only in the hard phase but also in the metal binding phase, the metal binding phase can be strengthened, and it is possible to contribute to the improvement of the strength and hardness of the hard material. That is, in the preferable nano phase composite hard material of the present invention, Ti, Zr, Hf,
A group of metals consisting of V, Nb, Ta, Cr, Mo and W,
Fe, Co, Ni, Al, Si, Cu, Mg, Ti, Z
At least one selected from the group consisting of carbides, nitrides, borides, oxides, silicides and boron carbides of r, Hf, V, Nb, Ta, Cr, Mo and W having a particle size of less than 300 nm. Scattered as nanophases.

It is considered that the nano phase in the metal-bonded phase can be introduced by a method such as quenching or annealing depending on the kind of the nano phase, unlike the case of the nano phase in the hard phase. As the nano phase dispersed in the metal-bonded phase, Ti, Z, as well as the nano phase dispersed in the hard phase,
It is more preferable to select one or more selected from the group consisting of carbides, borides, oxides, boron carbide, alumina, silicon carbide and silicon nitride of r, Hf, V, Nb, Ta, Cr, Mo and W.

The fact that the nano phase is contained in the hard phase and the metal-bonded phase of the hard material can be observed by a transmission electron microscope or the like, and the content thereof can be measured by analyzing a taken electron microscope photograph.

Metals that can be solid-solved in a metal bonding layer (alloy) containing Fe, Ni, and Co as main components to strengthen the metal bonding phase include Al, Si, Ti, V, Cr, Mn, and Zr.
There are Nb, Mo, Hf, Ta, W and Cu. The amount effective as a solid solution in the metal binding phase is 0.5% by weight or more and 50% by weight or less. Of these metals, Ta
When Nb and Nb form a solid solution in the range of 1.5% by weight to 30% by weight, a remarkable strengthening effect is recognized. The hard material usually has no problem even if it is contained in the raw material or inevitable impurities introduced in the pulverizing step or the like.

In fact, in the nanophase composite hard material obtained by sintering using hot pressing or HIP, nanophases composed of similar phases are scattered in both the hard phase and the metal bonding phase. It is often contained, in which case both phases are reinforced by nanophases, resulting in a hard material with better physical properties.

The nanophase composite material of the present invention comprises a raw material for forming a hard phase of boride, and a raw material for forming a metal bonded phase containing at least one metal selected from Fe, Ni and Co as a main component. Fe, Ni, having a particle size of less than 300 nm
Co, Al, Si, Cu, Mg, Ti, Zr, Hf,
V, Nb, Ta, Cr, Mo and W metals, carbides of these metals, nitrides of these metals, borides of these metals, oxides of these metals, silicides and carbides of these metals. It is obtained by sintering a mixed powder with one or more kinds of raw materials forming a nano phase selected from boron so that the nano phase remains. As a sintering method, pressureless sintering, hot pressing, HIP or the like can be adopted, and hot pressing or HIP is preferable. Particularly preferred is a two-stage sintering method in which HIP sintering is performed after pressureless sintering.

As an example of the nano phase composite hard material of the present invention, Mo ₂ NiB ₂ which is a double boride is used as a hard phase, and Ni
Description will be made by taking as an example those bonded with a metal binder phase containing as a main component. The main starting material for this hard material is MoB,
Combination of Mo, Ni and B, Mo ₂ NiB ₂ , M
A combination of o and Ni, a combination of Mo, Ni and B, etc. can be selected.

A mixed raw material obtained by further mixing Ta, TaO _x, etc., which form a nano phase, with these main starting raw materials is put into a vibration mill, a ball mill, an attrition mill, etc.
A medium such as ethyl alcohol, acetone, or hexane is added to perform wet mixing and pulverization, or dry mixing is performed in a state in which argon or nitrogen is enclosed in order to prevent oxidation.

The balls and pot of the pulverizer used for the mixed pulverization should be lined with stainless steel, cemented carbide, zirconia or these materials, and preferably the amount of the balls or pots worn and introduced into the raw material in advance. Considering this, wet-mix and pulverize. The slurry-like mixed raw material containing the mixed and pulverized medium is dried under reduced pressure by an evaporator and passed through a sieve, or is dried by a spray dryer to be a raw material for molding.

Next, the formed body is formed by an ordinary press or an isostatic press, the formed body is pre-sintered in vacuum, nitrogen, argon, etc., and if necessary, the pre-baked product is made into a Ni foil. Enclose in a bag such as, and sinter densely by HIP.

It should be noted that it is preferable to mix raw powder having a small particle size or powder pulverized in advance to a particle size of less than 300 nm into the mixed powder as a raw material for forming the nano phase. If the particle size of the raw material powder forming the is not sufficiently small, it is necessary to pulverize the raw material powder of the nanophase to a particle size that can form the nanophase during mixed pulverization, but fine pulverization with mixed pulverization is not so common. Not very efficient.

In order to obtain a powder having a fine particle size forming a nano phase, it is necessary to carry out grinding with a large grinding energy when grinding with a ball mill, an attrition mill or the like. For such pulverization, for example, it is preferable to prepare a ball and a pot made of a material of a similar system, which is a hard material with less consumption, further reduce the amount of powder to be pulverized with respect to the amount of the ball, and perform wet pulverization.

Further, since fine powder is very susceptible to oxidation, the mixed raw material or the molded body will not be oxidized by being exposed to oxygen in the air in the steps of storing, drying, molding and sintering the mixed raw material after pulverization. Consideration is needed.

The sintering of the nano-phase composite hard material of the present invention is carried out at 1300 ° C. as is done with conventional hard materials, and Ta and TaO _x phases are crystal-grown to 3 to 5 μm and the nano phase is formed. Will not remain. Therefore,
Sintering is preferably performed at a temperature as low as possible to enable densification, and in this sense, it is preferable to sinter by hot pressing or HIP.

[0037]

【Example】

[Example 1] MoB powder (average particle size 4.5 μm), Mo powder (average particle size 3.0 μm), Ni powder (average particle size 2 μm)
And Ta powder (average particle size 3.5 μm) each 5
7.9% by weight, 7.2% by weight, 32.0% by weight and 2.9% by weight were weighed out, put in a stainless steel pot, ethanol was added as a medium, and wet pulverization was carried out with a stainless steel ball for 72 hours. .

The slurry taken out of the pot was dried with a spray dryer in a non-oxidizing atmosphere to obtain 200 kg / c.
20 × 30 × 40 mm preform with pressure of m ² ,
Further, isostatic pressing was performed at a pressure of 1500 kg / cm ² to obtain a molded body.

This compact was pressureless sintered at 1250 ° C. for 2 hours in a vacuum of 10 ^-3 torr or less. The obtained pressureless sintered body was further put in a HIP device, and at 1150 ° C.
HIP treatment was performed at 1500 kg / cm ² for 1 hour. The physical properties of the obtained HIP sintered body (hard material of the present invention) were evaluated as follows.

A sample obtained by cutting this hard material with a diamond cutting machine is mirror-polished with diamond paste, and SEM is used.
Observation, transmission electron microscope (TEM) observation for examining the size and dispersion amount of the nanophase, and EPMA analysis were performed to identify the precipitation phase and examine its amount.

In order to evaluate the strength, the average particle size 34
A bending strength test piece of 3 × 4 × 30 mm was prepared by grinding with a μm (No. 400) diamond grindstone, and bending strength at room temperature and 800 ° C. (both in air) was measured by a three-point bending test.

The TEM observation confirmed the existence of both the fine nano-phase hard phase and the metal bonded phase. Further, in this hard material, a phase having a particle size of 3 to 5 μm coexisted in the form of TaN or TaO _x . From EPMA observation, it was also found that Ta was dissolved in the metal binding phase. Mo which is a hard phase
The average particle size of ₂ NiB ₂ was about 6.5 μm.

The photograph shown in FIG. 1 is a TEM photograph taken with a thin piece of the sample of Example 1, and the length of the broken line in the lower right of the photograph is 666 nm. A nanophase consisting of several spherical particles of TaO _{x with} a diameter of less than 300 nm is observed.

The bending strength of this hard material is 280 at room temperature.
It was 300 kg / mm ² in kg / mm ^2, 800 ℃.

Example 2 (Comparative Example) A hard material was obtained in the same manner as in Example 1 except that pressureless sintering was performed at 1300 ° C. for 2 hours instead of pressureless sintering at 1250 ° C. for 2 hours. Various physical properties were measured. No nanophase was observed in this hard material, either in the hard phase or in the metallic binder phase. Mo ₂ which is a hard phase
The average particle size of NiB ₂ was about 8 μm. The bending strength of this hard material was 200 kg / mm ² at room temperature and 210 kg / mm ² at 800 ° C.

The strength difference between Example 1 and Example 2 includes some contribution due to the small average grain size of the hard phase of Example 1, but even if the average grain size of the hard phase is 6.5 μm. Since such a high strength could not be obtained in the absence of nano phase, it was judged that the main contribution was due to the inclusion of nano phases in the hard phase in a scattered manner.

[Examples 3 to 12] With the prescription according to Example 1 except that only pressureless sintering was used, as raw materials, in addition to the above raw materials, TiB ₂ (average particle size 3 μm), Fe (average particle size) Diameter 2μ
m), Cr (average particle size 4 μm), TaC (average particle size 2 μm
m), TiN (average particle size 1.5 μm), WB (average particle size 4.5 μm), ZrB ₂ (average particle size 2.5 μm), Co
(Average particle size 2 μm), Al ₂ O ₃ (average particle size 0.5 μm
m) was used, a hard material was trial-produced by changing the blending composition and the pressureless sintering temperature, the existence of the nanophase and the evaluation of physical properties were evaluated, and the results are shown in Tables 1 and 2. In addition, Example 9, Example 10, and Example 1
The compounding compositions of Example 1 and Example 12 (all comparative examples) are the same as the compounding compositions of Example 3, Example 4, Example 5, and Example 6, respectively.

[0048]

[Table 1]

[0049]

[Table 2]

From the bending strength of the hard material shown in Table 2,
Bending strength, especially 800, for hard materials with composite nano-phase
It can be seen that the bending strength at ° C is significantly improved. In addition, when the Vickers hardness at room temperature was measured in Examples 1 and 2, it was 950 for a hard material containing no nanophase.
While there was a kg / mm ^2, in the hard material comprising nano phase was kg / mm ² at 1100, it was found to increase the Vickers hardness is effective conjugation of nanophase.

[0051]

From the above test results, in the hard material in which the nanophases having a particle size smaller than 300 nm are dispersedly contained in the hard phase of boride, a remarkable improvement in strength is recognized at room temperature, and Even at 800 ° C, this strength did not deteriorate at all, and at 800 ° C, 300 kg / mm ²
With such a boride-based hard material, we were able to reach an unprecedentedly high bending strength. Further, the Vickers hardness of the hard material is also improved at the same time, and the effect of improving the physical properties of the hard material by combining the hard material with the nano phase is very remarkable.

Considering that these hard materials are often used under extremely severe extreme conditions, and in many cases their durability depends on the strength of the material, they are made of the nanophase composite hard material of the present invention. It is certain that the durability of the components will be significantly extended, and if these components are incorporated into the manufacturing equipment and its mother machine, the yield and quality of industrial products will be significantly improved, and their industrial application will be improved. The value is enormous.

[Brief description of drawings]

FIG. 1 is a transmission electron micrograph showing a structure of an example of a nanophase composite material of the present invention.

Claims (6)

[Claims] 1. A hard phase of boride and a metal-bonded phase containing, as a main component, at least one metal selected from Fe, Co and Ni.
The hard phase is composed of 0.01 to 30% by volume of less than or equal to 30% by volume, and a nanophase having a particle size of less than 300 nm (nanometers) is contained, and the nanophase is Fe, Ni, Co, or A
l, Cu, Mg, Si, Ti, Zr, Hf, V, Nb,
Selected from the group of metals consisting of Ta, Cr, Mo and W, the group of carbides of these metals, the group of nitrides of these metals, the group of borides of these metals, the group of oxides of these metals, the group of silicides of these metals and boron carbide. A nanophase composite hard material, characterized in that it is one or more of the following: 2. The main hard phase of boride is TiB ₂ , ZrB.
₂ , Mo ₂ NiB ₂ , Mo ₂ CrB ₂ , Mo ₂ FeB ₂
The nano-phase composite hard material according to claim 1, which is one or more selected from and WCoB. 3. The nano phase is Ti, Zr, Hf, V, Nb, T.
The nanophase composite hard according to claim 1 or 2, which is at least one selected from a carbide group, a boride group, an oxide group, boron carbide, alumina, silicon carbide and silicon nitride of a, Cr, Mo and W. material. 4. In the metallic binder phase, Ti, Zr, Hf, V,
Metal group consisting of Nb, Ta, Cr, Mo and W, F
e, Co, Ni, Al, Cu, Mg, Si, Ti, Z
Carbides of r, Hf, V, Nb, Ta, Cr, Mo and W, nitrides of these metals, borides of these metals,
One or more selected from oxide groups of these metals, silicide groups of these metals, and boron carbide are contained in an amount of 0.01% by volume or more and 30% by volume or less as a nanophase having a particle size of less than 300 nm. Item 4. The nanophase composite hard material according to any one of items 1 to 3. 5. The nano phase according to any one of claims 1 to 4, wherein the hard material contains a combined phase of the hard phase and the nano phase in the hard phase in an amount of 35% by volume or more and 98% by volume or less. Composite hard material. 6. A raw material for forming a hard phase of boride, Fe,
Raw materials for forming a metal binder phase containing at least one metal selected from Ni and Co as a main component, and Fe, Ni, Co, Al, Cu, Mg, and S having a particle size of less than 300 nm.
i, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W metals, carbides of these metals, nitrides of these metals, borides of these metals, oxides of these metals, Manufacture of a nanophase composite hard material, characterized in that a mixed powder with a raw material forming one or more nanophases selected from the group of silicides of these metals and boron carbide is sintered so that the nanophase remains. Method.