JP3626378B2 - TiB2-Ti (CN) -based composite and production method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a TiB ₂ —Ti (CN) composite having high density and high hardness and excellent fracture toughness, and a method for producing the same.
[0002]
[Prior art]
Titanium carbides, borides, nitrides, and their composites are promising as structural materials because of their relatively light weight and excellent mechanical properties, and many synthetic studies have been conducted. These can be used for cutting tools, target materials, drawing dies, nozzles, electrodes, automotive parts, molds, and the like.
In such circumstances, TiB ₂ —Ti (CN) -based composites are attracting particular attention because of their high hardness and excellent fracture toughness values. (Note that the ratio of C to N in Ti (CN) varies over a wide range and does not necessarily correspond to 1: 1. Therefore, unless otherwise stated in the present specification, these ratios vary. The ratio of TiB ₂ and Ti (CN) can be variously changed and does not necessarily correspond to 1: 1, and unless otherwise specified in this specification, the entire ratio range is included. (All of these blending ratios are appropriately changed.)
However, it is generally difficult to normally sinter the above materials without adding a sintering aid, and sintering is performed by hot pressing or HIP. In addition to the sintering method in which pressurization and heating are performed, a method in which synthesis and sintering are performed simultaneously, for example, pressure self-combustion sintering that is solidified by sintering synthesis while applying pressure or solid phase substitution while hot pressing is performed. Reactive hot presses that cause reactions have also been applied to solidify these compounds.
[0003]
Since these methods are solidified while causing mass transfer due to a chemical reaction, there is a feature that a structure that cannot be generated simply by mixing is obtained, which is of interest. In recent years, discharge plasma sintering, which is a kind of energizing pressure sintering method, has begun to be applied to densification of difficult-to-sinter materials.
This is an attractive method of energy saving because rapid heating can be performed because the sample and the mold are directly heated by applying a pulsed current while pressing the powder. If a method of reactive hot pressing can be applied to this discharge plasma sintering, this method may be widely applicable to densification of difficult-to-sinter materials.
[0004]
On the other hand, the TiB ₂ -Ti (CN) -based composite is conventionally mixed with TiB ₂ powder, TiC powder, TiN powder or Ti (CN) powder and sintered at high temperature (atmospheric pressure sintering, hot pressing, It has been performed to use a HIP method or the like to obtain a sintered body.
However, when such powders are used, the target hardness, density and fracture toughness values cannot be achieved unless fine raw material powders controlled to the order of several μm or less are used and mixed uniformly. There is a problem that the cost is high.
[0005]
Further, TiC and TiN mixed with TiB ₂ have strong non-stoichiometry, which greatly affects the strength of the sintered body. For this reason, when mixing TiC powder, TiN powder, or Ti (CN) powder with TiB ₂ powder as described above and directly sintering, the non-stoichiometry cannot be controlled by the sintering process. There was a problem that the ratio greatly affected the properties of the product.
In order to produce a TiB ₂ —Ti (CN) -based composite having a stable quality, the raw material itself needs to be excellent in sinterability, and at the same time, the non-stoichiometry is low, that is, x = 1. The raw powder must be or very close to this.
However, in general, there is a contradictory relationship that the sinterability deteriorates as x = 1, which is a condition with less non-stoichiometry, and there is a problem that manufacturing becomes difficult.
From the above, the TiB ₂ -Ti (CN) -based sintered composite itself was considered to be a material having high density and high hardness and excellent properties such as fracture toughness value, but its production is not always easy. It could not be said that a satisfactory sintered body was obtained.
[0006]
[Problems to be solved by the invention]
From the above, it is not necessary to use a fine raw material powder controlled to the order of several μm or less as a sintering powder, and even if the raw material powder has non-stoichiometry, it is undefined by changing the mixing ratio of the powder. Manufacturing method and sintered composite capable of easily obtaining a TiB ₂ -Ti (CN) composite having high density, high hardness and excellent fracture toughness in which the specificity can be easily controlled Is an issue.
[0007]
[Means for Solving the Problems]
As described above, the present invention 1) sinters mixed powder mainly composed of titanium powder (Ti), boron carbide (B ₄ C) powder and boron nitride (BN) by sintering accompanied by solid phase substitution reaction. A method for producing a TiB ₂ -Ti (CN) -based composite 2) A method for producing a TiB ₂ -Ti (CN) -based composite as described in 1), which has a relative density of 99% or more 3) One or more elements selected from V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ta, and W are contained in an amount of 0.001 to 20% by weight 1) Or 2) The TiB ₂ -Ti (CN) -based composite production method described in 2) 4) The TiB ₂ -Ti according to any one of 1) to 3), wherein the sintering is performed by pulsed current pressure sintering. production method ₅ (CN) _{composites) TiB 2 -Ti (C x N} x _{1) y} (where, 0 <x <1,0.7 ≦ y ≦ 1.0) based _TiB 2 -Ti according to any one of 1) to 4), which is a complex (CN) 6) A composite structure of TiB ₂ particles having an average particle diameter of 20 μm or less and Ti (C _x N _x-1 ) particles (however, 0 <x <1) having an average particle diameter of 20 μm or less is provided. to provide a manufacturing method, the _TiB 2 -Ti (CN) based composite according to any one of 1) to 5), wherein.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Titanium powder (Ti), boron carbide (B ₄ C) powder, and boron nitride (BN) powder are used as the mixed powder for sintering. B ₄ C has nonstoichiometry, but BN does not. Therefore, if the analytical value is known, the non-stoichiometry can be easily controlled by changing these mixing ratios, and the non-stoichiometry of the raw material does not affect the product.
The hot press method can be used as the sintering method, but if the pulsed current pressure sintering method (discharge plasma sintering method) is used, a high temperature can be obtained in a short time, and the time to obtain the product can be greatly reduced. Has characteristics.
[0010]
Pulsed current pressure sintering is a method in which a sintered material is put into a graphite mold and heated by directly applying a large pulsed current while pressing it. When a pulse current is applied, the current flows between the material particle gaps. Flows and gets hot locally. It is considered that the diffusion of atoms is promoted by this local high temperature and a solid phase reaction is efficiently generated.
Titanium carbides, borides, and nitrides are difficult to sinter materials and were originally difficult to be densified without the addition of sintering aids. In this method, solid phase substitution of Ti, B ₄ C, and BN It is possible to obtain a dense TiB ₂ —Ti (CN) -based sintered composite by solidifying in a short time while causing a reaction.
[0011]
The sintering temperature is required to be 1600 ° C. or higher and the applied pressure is 20 MPa or higher. In particular, 1800 ° C. or higher and the applied pressure is preferably 30 MPa or higher. (The sintering temperature at this time means the temperature of the surface of the graphite mold (next to the portion filled with the sintered material) used in hot pressing and pulse current compression sintering.) These temperatures The pressing force can be appropriately determined according to the kind of the sintered material.
[0012]
The movement distance of the substance by the solid phase substitution reaction is estimated to reach several tens of μm to 100 μm. Ti, B ₄ C, and BN powder sintered materials are those having a purity of 99% or more, Ti powder particle size of 30 μm or less (preferably 10 to 30 μm), B ₄ C particle size of 10 μm or less, BN powder particle size It is desirable to use a powder of 10 μm or less, but it is also possible to use a powder having a purity of 95% or more, a Ti powder particle size of 100 μm or less, a B ₄ C particle size of 20 μm or less, and a BN powder particle size of 10 μm or less. Thus, even when a relatively large raw material powder is used, the structure is rearranged and a fine TiB ₂ —Ti (CN) -based sintered composite can be obtained. Incidentally, B 4 _C powder and the larger the particle size of the Ti powder than the particle size of the BN powder is desired.
In this way, it is necessary to use a fine raw material powder controlled to the order of several μm or less, and strictly control the raw material powder so that the target hardness, density and fracture toughness values cannot be achieved unless they are mixed uniformly. In addition, the method of the present invention has a great advantage that the manufacturing cost can be greatly reduced as compared with the conventional method in which the manufacturing cost is high.
[0013]
The structure of the obtained TiB ₂ -Ti (CN) -based sintered composite is TiB ₂ particles having an average particle size of 20 μm or less and Ti (C _x N _x-1 ) particles having an average particle size of 20 μm or less (provided that 0 <x <1) The mixed structure is provided. FIG. 1 shows a micrograph of the structure.
Note that this Ti, B 4 _C, the powder sintering temperature 2000 ° C of BN, retention time 20 minutes, at a pressure _{50MPa, 2B 4 C + 2BN +} 9Ti → 5TiB reaction _{2 + 4Ti (C 0.5 N 0.5} ) showing a sintered body tissue _TiB 2 -Ti (CN) based complexes sintered by.
In FIG. 1, the white portion is Ti (C _x N _x-1 ) particles, and the black portion is TiB ₂ particles. This structure can also be expressed as Ti (C _x N _x-1 ) particles are uniformly mixed in a network-like TiB ₂ structure. Such a dense structure has high hardness and high toughness, and the reason that the high toughness is expressed is the network structure generated by the reaction.
Thus, the sintered composite of the present invention provides a TiB ₂ -Ti (CN) -based composite having a relative density of 99% or more, a fracture toughness value of more than 4.0 MPam ^1/2 , and a Vickers hardness of 2120. be able to.
[0014]
The TiB ₂ —Ti (CN) -based composite of the present invention further contains at least one element selected from V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ta, and W in an amount of 0.00. 001 to 20% by weight can be contained. Thereby, the fracture toughness value can be further improved and a sintered composite reaching 10 to 15 MPam ^1/2 can be obtained.
The reason why the lower limit of the amount added is 0.001% by weight is that if the amount is less than 0.001% by weight, there is no effect of addition, and the upper limit is 20% by weight. This is because it decreases and is not preferable.
[0015]
In addition, the present invention changes the compounding ratio of titanium powder (Ti), boron carbide (B ₄ C) powder, and boron nitride (BN) powder to obtain TiB ₂ —Ti (C _x N _x−1 ) _y (where, TiB ₂ —Ti (CN) composites having various compositions having a 0 <x <1, 0.7 ≦ y ≦ 1.0) sintered structure can be obtained.
As shown in the examples described later, as x increases, the bulk density decreases but the relative density increases, the Young's modulus increases (Poisson's ratio decreases conversely), and the fracture toughness value and Vickers hardness also increase. .
[0016]
Moreover, when y increases in the range of 0.7 ≦ y ≦ 1.0, the bulk density increases but the relative density decreases, and the Poisson's ratio decreases slightly, but the Young's modulus increases, and the fracture toughness value and Vickers Hardness tends to increase.
That is, as the value of _y in Ti (C _x N _x-1 ) _y decreases, it becomes denser and sintering becomes easier.
As described above, in the present invention, control of the non-stoichiometry in Ti (C _x N _x-1 ) _y can be easily achieved by simply changing the blending ratio of the raw material powder. Compared to a conventional sintering method in which a raw material having an appropriate non-stoichiometric ratio must be synthesized in advance, it has a great feature that it can be controlled much more easily.
[0017]
【Example】
Hereinafter, a description will be given based on examples. In addition, a present Example shows a suitable example, This invention is not limited to these Examples. Accordingly, modifications and other examples and aspects within the scope of the technical idea of the present invention are included in the present invention.
[0018]
(Example 1)
B ₄ C powder (average particle size 1.5 μm, purity 99%), BN powder (average particle size 24.5 μm, purity 99.5%), and Ti powder (average particle size 6.0 μm) were used as sintering powders. , Purity 99.5%) was used.
These powders Scheme _{2xB 4 C + 2 (1-} x) BN + 3 (x + 1) Ti → (3x + 1) TiB 2 + 2Ti (C x N 1-x) were mixed variously varied weighed x assumes.
This mixed powder is filled into a graphite mold having an inner diameter of 20 mm and an outer diameter of 50 mm, and using a discharge plasma sintering apparatus under the conditions of a pressure of 50 MPa, a heating rate of 50 ° Cmin ⁻¹ , a sintering temperature of 2000 ° C., and a holding time of 20 min. Sintered in vacuum.
The obtained sintered body was measured for density, Young's modulus, Poisson's ratio, Vickers hardness, fracture toughness value, and analyzed by X-ray diffraction and EPMA.
[0019]
x = 0 to 1 (samples for x = 0 and x = 1 were also used as test samples.) x, relative density, and bulk density of samples subjected to reactive discharge plasma sintering using powder The relationship is shown in FIG. The bulk density gradually decreased, but the relative density increased rapidly when x increased from 0 to 0.1, and then gradually increased.
When x = 0, TiN _1.0 having a poor sinterability has a bad influence on densification, and the sinterability is improved by increasing the non-stoichiometry of TiN as x increases. Inferred.
The relationship between the Young's modulus and Poisson's ratio and x is shown in FIG. Similar to the relative density, the sintered body with x = 0 had a low Young's modulus because of the low relative density, and increased rapidly when x was 0.1, and then increased gradually. The Poisson's ratio was almost constant from 0.16 to 0.19.
[0020]
The relationship between Vickers hardness and x is shown in FIG. The hardness of the sintered body at x = 0 was low, but increased as x increased, and reached a maximum at x = 0.5. The Vickers hardness at that time was 2120.
The relationship between the fracture toughness value and x is shown in FIG. While fracture toughness of the sintered body of x = 0 is low, and increases as x increases, becomes maximum in x = 0.5, fracture toughness value at that time was 4.0MPam ^1/2. Also showed a tendency to decrease once at x = 0.7, but equivalent fracture toughness value at x = 1 showed 4.0MPam ^1/2.
From the above Young's modulus, hardness, and fracture toughness values, it can be seen that the value of x in the above reaction formula is 0.3 to 1, particularly around 0.5.
In particular, although not shown in the figure, destruction is further caused by adding 0.001 to 20% by weight of one or more elements selected from V, Cr, Mn, Fe, Co, Ni, Cu, ZrNb, Mo, Ta, and W. The toughness value could be further improved, and a sintered composite reaching its fracture toughness value of 10 to 15 MPam ^1/2 could be obtained.
[0021]
(Example 2)
Using the same powder as in Example 1, fixing x = 0.5, which has good values of the Young's modulus, hardness, and fracture toughness value, the reaction formula B ₄ C + BN + (5/2 + 2 / y) Ti → ( _{5/2) TiB 2 + 2 / yTi} (C 0.5 N 0.5) assumes the _y were mixed variously varied weighed y.
Further, this mixed powder was filled in a graphite mold having an inner diameter of 20 mm and an outer diameter of 50 mm in the same manner as in the Examples, and discharged under the conditions of a pressure of 50 MPa, a heating rate of 50 ° Cmin ⁻¹ , a sintering temperature of 2000 ° C., and a holding time of 20 min. Sintering was performed in a vacuum using a plasma sintering apparatus.
The obtained sintered body was measured for density, Young's modulus, Poisson's ratio, Vickers hardness, fracture toughness value, and analyzed by X-ray diffraction and EPMA.
[0022]
FIG. 6 shows the relationship between y, relative density, and bulk density when y is changed in the range of 0.7 ≦ y ≦ 1.0. As y increases, the bulk density gradually increases, but the relative density, on the other hand, reaches a maximum at y = 0.7, reaching 99.8%. However, after that, as y increases, the relative density decreases and decreases to 99.1 when y = 1. It can be seen that a decrease in the amount of y is effective in improving the density.
Similarly, FIG. 7 shows the relationship between y, Young's modulus, and Poisson's ratio. Similar to the relative density, when the ratio of y decreases from y = 0.7 to 1.0, the Young's modulus tends to decrease. The Poisson's ratio was almost constant.
[0023]
FIG. 8 shows the relationship between Vickers hardness and y. The hardness of the sintered body with y = 0.7 was low, but increased as y increased, and reached the maximum when y = 1. The Vickers hardness at that time was 2120. However, it can be seen that the Vickers hardness exceeds 2000 even when y = 0.7.
FIG. 9 shows the relationship between the fracture toughness value and y. While fracture toughness of the sintered body of y = 0.7 is low, and increases as y increases, becomes maximum at y = 1.0, fracture toughness value at that time was more than 4.0MPam ^1/2 .
From the above relative density, Young's modulus, hardness, and fracture toughness values, it can be seen that the value of y in the above reaction formula is effective in the range of 0.7 to 1.0.
[0024]
【The invention's effect】
Sintering with solid phase substitution reaction using pulsed current pressure sintering etc., using mixed powder mainly composed of titanium powder (Ti), boron carbide (B ₄ C) powder and boron nitride (BN) powder Is advantageous in that it is not necessary to use a fine raw material powder controlled to the order of several μm or less, and a TiB ₂ -Ti (CN) -based composite is obtained with high workability and low cost. It has a great feature that it can.
In addition, even if the raw powder has non-stoichiometry, it is possible to easily control the non-stoichiometry by changing the mixing ratio of the powder. Moreover, TiB has high density, high hardness, and excellent fracture toughness in a short time. It has an excellent effect that a _2- Ti (CN) -based composite can be obtained.
In addition, from the controllability of the production or the ease of work, 0.001 or more elements selected from V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ta, and W are added. Addition of ˜20% by weight makes it possible to improve the properties of the TiB ₂ —Ti (CN) -based composite and to further improve the fracture toughness value and the like.
[Brief description of the drawings]
FIG. 1 is a photomicrograph of a sintered body structure of a TiB ₂ —Ti (CN) -based composite.
FIG. 2 shows the reaction formula 2xB ₄ C + 2 (1-x) BN + 3 (x + 1) Ti → (3x + 1) TiB ₂ + 2Ti (C _x N _1-x ), and variously changes x to perform reactive discharge plasma sintering. It is a figure which shows the relationship of x of the performed sample, relative density, and bulk density.
FIG. 3 is a graph showing the relationship between Young's modulus and Poisson's ratio and x.
FIG. 4 is a graph showing the relationship between Vickers hardness and x.
FIG. 5 is a diagram showing the relationship between the fracture toughness value and x.
[6] Scheme _{B 4 C + BN + (5} /2 + 2 / y) Ti → (5/2) TiB 2 + 2 / yTi (C 0.5 N 0.5) variously changed the y assuming _y, reactive It is a figure which shows the relationship between y of the sample which performed discharge plasma sintering, a relative density, and a bulk density.
FIG. 7 is a graph showing the relationship between Young's modulus and Poisson's ratio and y.
FIG. 8 is a diagram showing the relationship between Vickers hardness and y.
FIG. 9 is a diagram showing the relationship between the fracture toughness value and x.

Claims (6)

TiB ₂ − characterized in that a mixed powder mainly composed of titanium powder (Ti), boron carbide (B ₄ C) powder and boron nitride (BN) powder is sintered by sintering accompanied by a solid phase substitution reaction. A method for producing a Ti (CN) -based composite. The process according to claim 1 _TiB 2 -Ti (CN) based composite according to characterized in that it has 99% or more of relative density. 2. One or more elements selected from V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ta, and W are contained in an amount of 0.001 to 20% by weight. 2. A method for producing a TiB ₂ -Ti (CN) -based composite according to ₂ . Method for producing a TiB 2 _-Ti (CN) based composite according to claim 1, characterized in that the sintering by the pulse current pressure sintering. The TiB ₂ -Ti (C _x N _x-1 ) _y (where 0 <x <1, 0.7 ≦ y ≦ 1.0) -based complex is provided. method for producing a _TiB 2 -Ti (CN) based composite according to. _2. A mixed structure of TiB ₂ particles having an average particle diameter of 20 μm or less and Ti (C _x N _x-1 ) particles having an average particle diameter of 20 μm or less (where 0 <x <1) is provided. method for producing a _TiB 2 -Ti (CN) based composite according to 5 any one of.

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