JPS585982B2 - Wear-resistant high-pressure phase boron nitride aggregate and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a wear-resistant high-pressure phase boron nitride agglomerate and a method for producing the same, in particular, when obtaining high-pressure phase boron nitride in the form of a fine particle powder as a agglomerate, promoting the agglomeration of the agglomerate, The present invention also relates to a block using nickel and titanium as a binder, which imparts toughness to the block, and a method for producing the same.

When boron nitride is chemically synthesized, it is generally a soft powder with a crystal structure similar to graphite, and is usually called hexagonal boron nitride.

In this section 5, to avoid confusion with high-pressure phase boron nitride described below, it will be expressed as graphite-type boron nitride (hereinafter referred to as g-BN).

This g-BN is used as a semiconductor dope material, a nuclear reactor material, a crucible material, an anti-friction material, and the like.

Another effective use of such g-BN is to use it as a raw material for the synthesis of boron in a high-pressure phase chamber.

That is, by applying ultra-high pressure using an explosion to g-BN, hexagonal wurtzite boron nitride (hereinafter referred to as W
-BN) is obtained, and when Si and a catalyst such as AI or an alkali metal or alkaline earth metal are added to g-BN and a pressure of approximately 60 Kb and a temperature of approximately 1600°C are simultaneously applied, cubic boron nitride is obtained. (Hereafter, this will be referred to as C-B
) is obtained.

The high-pressure phases of W-BN and C-BN obtained in this way boron nitride are extremely hard substances, and in particular, C-BN has a hardness that is second only to diamond.5 Heat resistance and reaction resistance with iron group element materials It has superior properties than diamond in terms of hardness, and exhibits excellent performance as an abrasive grain in whetstones used to grind these materials.

However, such high-pressure phase boron nitride is obtained as a powder, and in order to utilize its properties more effectively, it is desired to obtain it in the form of a lump obtained by sintering the powder.

The crystals of both W-BN and C-BN are composed of strong covalent bonds.

Therefore, in order to sinter these microcrystals into a lump, a high temperature is required to facilitate the diffusion of atoms.

However, for example, when C-BN is heated under normal pressure, it reversely transforms into soft g-BN from about 1500°C, and cannot be stably brought to a sufficiently high temperature required for sintering.

For this reason, sintering of W-BN and C-BN is usually performed under extremely high pressure and high temperature conditions.

Applying ultra-high pressure also has the effect of increasing the packing density of the powder, promoting adhesion between particles, and aiding sintering.

However, for example, even if C-BN is held for 30 minutes at a pressure of 65 Kb and a temperature of 1700°C, pores remain between the particles, and the adhesion between C-BN is not strong enough to be used as a strong material. not high.

For this reason, the voids remaining between particles are filled,
And it is common to deepen the binder to hold these particles in sufficient "wet" with the high pressure phase boron nitride.

Requirements for the binder include (1) good "wetting" with the high-pressure phase boron nitride, (2) excellent high-temperature strength, and (3) sufficient toughness even at room temperature.

Regarding (1) above, there are technical problems and it cannot be said that it has been fully elucidated at present.

Although many ceramic and wood-based binders satisfy the requirement (2), they do not satisfy the requirement (3).

On the other hand, metal-based binders have insufficient performance (2).

In particular, in order to fully exhibit the performance (1), metal-based binders are usually melted under sintering conditions to take the form of so-called liquid phase sintering.

Metallic binders conventionally used for this purpose include cobalt and nickel.

However, when a block of high-pressure phase boron nitride is used as a cutting tool such as a cutting tool and subjected to high-speed cutting to fully utilize its properties, the temperature of the cutting edge will be approximately 100°C.
reach even.

The strength of cobalt and nickel at such high temperatures is insufficient.1. Therefore, the strength of the lumps using cobalt or nickel as a binder was reduced, resulting in accelerated wear.

The present invention was conceived in view of the above, and includes a block of high-pressure phase boron nitride, particularly C-BN, with great toughness and wear resistance using an intermetallic compound of nickel and titanium as a binder, and a method for producing the same. This is what we are trying to provide.

The intermetallic compound NiTi is an intermetallic compound with a slight composition spread around the stoichiometric composition, a so-called bertholed compound, and while many general intermetallic compounds are extremely fragile, it has exceptionally high toughness. It is a unique material.

It has a CsC1 type regular lattice structure and is known as Nitinol due to the shape memory effect caused by thermoelastic martensitic transformation.

Another feature of NiTi is its wear resistance.

In the process of researching wear-resistant metal materials, the inventors found that the wear resistance increases as the hardness increases and as the work hardening index increases.

Although the hardness of NiTi is quite low at Hv230, its work hardening index is extremely high at 0.43.

Since the work hardening index of nickel-chromium-molybdenum steel (SNCM8) is 0.038, its remarkable magnitude can be understood.

As a result, when comparing the wear volume when pressed against a SiC grindstone with a predetermined surface pressure and rubbed over a predetermined distance with hardened steel with a hardness of Hv700, the wear volume of NiTi is less than 1 of steel, that is, 3
It was revealed that it has more than twice the wear resistance.

The excellent wear resistance of NiTi is due to the large work hardening characteristic of its regular lattice structure.

Having a regular lattice structure is also advantageous in terms of high temperature strength (hardness).

In particular, NiTi maintains a regular lattice up to its melting point, and the generation of antiphase boundaries accompanying plastic deformation suppresses strength loss at high temperatures.

In other words, the hardness at room temperature is as low as Hv230,
Also, the melting point is as low as 1310℃, but it is still 1000℃.
Its hardness at high temperatures is greater than that of cobalt and nickel.

Furthermore, the necessary conditions for the binder are the high-pressure phase boron nitride and
Good wettability.

For this purpose, a wetting test between C-BN and NiTi was conducted.

N melted in a button-type arc melting furnace on top of C-BN powder
i-50at%Ti was placed and heated to 1400°C in an ultra-high purity argon atmosphere.

As a result, NiTi melts and penetrates into the C-BN powder,
It was found that there was sufficient "wettability".

As a result of the preliminary tests mentioned above, NiTi has "wettability" with high-pressure phase boron nitride, which has toughness, wear resistance, and high-temperature strength.
It has been found that it has excellent properties and is effective as a binder for high-pressure phase boron nitride.

Therefore, a manufacturing test of a high-pressure phase boron nitride block was conducted as shown in the following example.

The ultra-high pressure device used is a belt-type cylindrical graphite heater with a g-BN sleeve with good self-lubricating properties as a pressure medium and upper and lower plugs as a pressure medium. A tantalum capsule was placed in the sample chamber.

The dimensions of this sample chamber are the internal diameter of the tantalum capsule, which is 6I.
IB, height 5'm.

The pressure is 24°C for Bi and Ba, respectively, at room temperature.
．． 5Kb.

It was measured as a fixed point of 59Kb.

However, it is empirically known that the generated pressure generally decreases by about 30% at high temperatures, and from this perspective the pressure at high temperatures was corrected.

The temperature was measured up to 1550° C. with a platinum/platinum 10 rhodium thermocouple to determine the relationship between heating power and temperature, and higher temperatures than this were estimated by extrapolation.

Note that pressure correction for thermoelectromotive force was not performed.

Example 1 A disk-like plate of Ni-50 at% Ti alloy and C-BN powder of 1 to 5 μm were filled in a tantalum capsule in a layered manner, and 65
Kb, a pressure and temperature of 1700° C. were simultaneously applied for 30 minutes.

As a result, a lump having a diameter of approximately 6 m + 1° and a height of approximately 2.5 II was obtained.

These lumps can damage cemented carbide, and
I could hardly polish it with the C whetstone.

Example 2 Commercially available NiTi alloy (FEDIG-NT) manufactured by Furukawa Electric
55Kb using a disk and C-BN powder, 2 at 1600℃
It was held for 0 minutes.

As a result, C-BN aggregates similar to those in Example 1 were obtained.

Example 3 N1 powder and Ti powder of 325 mesh or less were mixed to have a 1:1 stoichiometric structure, packed in a layer with C-BN powder, and held at 50 Kb and 1500° C. for 20 minutes.

The obtained lump was polished with a diamond and the Knoop hardness was measured, and it showed a high value of 3800 f/llI2.

Further, the fracture surface was observed with a scanning electron microscope after being broken with a hammer. As a result, it was found that the NiTi phase maintains a skeleton in which C-BN molecules are well bonded to each other.

Example 4 W-BN was added to the same Ni and Ti mixed powder as in Example 3.
and C-BN were added in a ratio of 1:5 by weight and thoroughly mixed.

This powder was filled and held at 50 Kb and 1500° C. for 10 minutes.

As a result, a lump similar to that in Example 1 was obtained.

Example 5 325 with Ti deposited by chemical vapor deposition (CVD)
/ C-BN of 400 meshes and N of 325 meshes or less
When the i powder was added and held at 45 Kb and 1350 °C for 10 minutes, a lump similar to that in Example 1 was obtained.≦ The high-pressure phase boron nitride lump obtained in this way can be used for high-temperature applications such as blades for cutting tools. It is suitable for materials that require strength and wear resistance, and is effective in demonstrating the excellent performance of high-pressure phase boron nitride.

In practicing the present invention, the binder is not necessarily Ni-50.
It is not limited to at%Ti.

For example, higher Ni than the stoichiometric composition, or higher T than the stoichiometric composition.
When shifted to the i side, the hardness at room temperature increases, and a liquid phase is produced at a temperature lower than that of Ni-50at%Ti due to eutectic reaction and peritectic reaction.

Forming a liquid phase at a low temperature has the effect of facilitating infiltration, and is advantageous when manufacturing at a low temperature is desired due to the intended use of the lump or the convenience of manufacturing equipment.

However, although NiTi with a stoichiometric composition has a low vacancy concentration and low low temperature hardness, it has higher strength at high temperatures, for example around 1000° C., than the high Ni side or the high Ti side.

Therefore, in order to fully exhibit the characteristics of high-pressure phase boron nitride, it is desirable to select a composition very close to ItLNi-50at$i.

However, during sintering, a portion of titanium may react with boron nitride to produce borides and nitrides, and this tendency becomes more pronounced as the sintering temperature increases.

Therefore, since the composition of the binder added and the composition of the binder in the lump do not necessarily match, it is necessary to consider the selection of sintering conditions and the composition of the binder added.

Further, a small amount of iron, cobalt, etc. may be added for the purpose of preventing the shape memory effect.

Ni and Ti can be used in the form of an alloy, or in the form of an elemental Ni or elemental Ti.
It may be filled in the sample chamber of an ultra-high-pressure device in the form of , or it may be mixed with the high-pressure phase boron nitride in advance, or it may be arranged in a layer and infiltrated.

C-BN is desirable as the high-pressure phase boron nitride.

However, part or all of C-BN may be replaced with W-BN.

Some or all of the added W-BN becomes C-BN during sintering.
You can transform into

N contained in the high-pressure phase boron nitride layer of the high-pressure phase boron nitride block
If the amount of i-Ti alloy exceeds 40 modulus in terms of volume, the hardness of the lump will be too low, and if it is less than 1 modulus, the effect of improving toughness as a binder will be small.

Generally, a ratio of about 5 to 15 is preferable. Various oxides, carbides, nitrides, borides, and silicides may be added to the lumps.

Sintering should be carried out under pressure and temperature conditions in which the W-BN or C-BN is thermodynamically stable.

W-BN and C-B are sintered under conditions where g-BN is stable.
When part or all of the N transforms into soft g-BN, the strength of the aggregate is significantly reduced.

Even when sintering is performed under conditions where W-BN or C-BN is considered stable, it is often observed that g-BN is produced in small amounts.

This is thought to be due to the low pressure in the voids where the powder particles are not in contact with each other, and the above-mentioned macroscopic pressure has a somewhat different meaning.

It is desirable to sinter at as high a pressure, high temperature, and for a long time as possible in order to promote close contact between high-pressure phase boron nitride particles and to activate atomic diffusion, but these requirements increase the price of the product. Make it.

Therefore, as a commercially and substantially effective condition, a temperature of at least about 45 Kb or more and a temperature of at least about 1200° C. or more should be simultaneously applied for at least 1 minute.

The device for applying the pressure and temperature is not necessarily limited to a belt-type device, but may be a cubic-type device or the like.

It should be noted that it is difficult to accurately measure pressure at high temperatures using current technology, and ultra-high pressure manufacturers are well aware that some errors should be accepted.

Claims (1)

[Claims] For high-pressure phase boron nitride in which the size of one crystal is 200μ or less, the ratio of nickel element and titanium element is 45 to 55.
A wear-resistant high-pressure phase boron nitride characterized by containing an intermetallic compound of nickel element and titanium element within the range of atomic percent of 1% or more and 40% or less of the total volume including the high-pressure phase boron nitride. Massive body. 2 High-pressure phase boron nitride with a crystal size of 209μ or less, the ratio of nickel element and titanium element to each other is 45 to 55 atomic percent, and the total volume of nickel element and titanium element includes high-pressure phase boron nitride. 45Kb or more, and a pressure and temperature of 1200℃ or more are simultaneously added to the mixture so that the amount is 1% or more and 40% or less of the total volume.
1. A method for producing a wear-resistant high-pressure phase boron nitride mass, which comprises bonding high-pressure phase boron nitride with an intermetallic compound of nickel and titanium elements by adding the boron nitride for a minute or more.