JP2011184276A - Method for producing high density metal boride - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method producible of a high density titanium boride sintered compact at relatively lower temperature than conventional methods. <P>SOLUTION: The method for producing the high density titanium boride sintered compact comprises: a process A of preparing titanium boride powder which is uniformly mixed with 3 to 10 vol.% of titanium oxide powder and of molding the mixed powder to produce a molding; and a process B of subjecting the molding obtained by the process A to pulse energizing pressure sintering to produce the titanium boride sintered compact of ≥90% relative density. In order to obtain a sintered compact having higher density and excellent mechanical characteristic, titanium boride powder which is uniformly mixed with 3 to 7 vol.% of titanium oxide powder and 1 to 4 vol.% of magnesium oxide powder is prepared and a molding produced by using the mixed powder is subjected to pulse energizing pressure sintering. As conditions of the process B, it is preferable that sintering is carried out under vacuum of 10 Pa or less, at sintering temperature of 1,650°C, with holding time of 10 minutes and pressurizing force of 30 MPa and at temperature rising speed of 100°C/min. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a high-density metal boride, particularly a titanium boride sintered body.

Many metal borides have excellent properties such as high hardness, high melting point, high electrical conductivity and high thermal conductivity. Among them, titanium boride TiB ₂ is used as a protective plate for underground buried cables and the like because it can be processed by electrical discharge with particularly high hardness. It is reported that the point bending strength (σ _b ) is 400 MPa, the Vickers hardness (H _v ) is 22 GPa, and the fracture toughness value (K _IC ) is 5.2 MPa · m ^1/2 .

Ronald G. Munro, J. Res. Inst. Stand. Technol. 105, 709-720 (2000).

  However, since this titanium boride is a covalently bonded substance, it is very brittle and has a weak point that it is difficult to sinter, and it is difficult to produce a dense material. There are still issues to be improved.

This invention solves said subject which should be improved, and makes it a subject to provide the method which can manufacture a precise | minute and high-density metal boride, especially a high density titanium boride.
As a result of various studies, the present inventors have added a predetermined amount of titanium oxide TiO ₂ powder (rutile) as a sintering aid to the hardly sinterable titanium boride TiB ₂ powder, and applied energy-saving pulse energization. It has been found that pressure sintering (Pulsed Electric-Current Pressure Sintering: PECPS) enables densification at a relatively low temperature than conventional methods, and can produce a high-density TiB ₂ sintered body having excellent mechanical strength. The present invention has been completed. It has also been found that when a predetermined amount of magnesium oxide MgO powder is added in addition to the titanium oxide powder and the pulsed current pressure sintering is performed, the mechanical properties are further improved.

The method for producing a high-density metal boride of the present invention capable of solving the above problems
Step A: A step of preparing a titanium boride powder in which 3 to 10% by volume of titanium oxide powder is uniformly mixed, and molding the mixed powder to produce a molded body, and Step B: obtained in Step A above It comprises a step of producing a titanium boride sintered body having a relative density of 90% or more by subjecting the formed body to pulse-current pressure sintering.
Moreover, in the manufacturing method having the above-described features, the present invention is characterized in that the pulsed current pressure sintering in the step B is performed under a vacuum of 10 Pa or less, a sintering temperature of 1600 to 1900 ° C., a holding time of 3 to 30 minutes, It is also characterized by being carried out under conditions of a pressing force of 10 to 70 MPa and a heating rate of 50 to 150 ° C./min.
In addition, the method for producing a high-density metal boride of the present invention includes
Step A: preparing titanium boride powder in which 3 to 7% by volume of titanium oxide powder and 1 to 4% by volume of magnesium oxide powder are uniformly mixed, and molding the mixed powder to produce a molded body, And Step B: including a step of producing a titanium boride sintered body having a relative density of 94% or more by subjecting the formed body obtained in Step A to pulse current compression sintering. is there.
Furthermore, the present invention relates to the production method having the above characteristics, in which the pulse current pressure sintering in the step B is performed under a vacuum of 10 Pa or less, a sintering temperature of 1600 to 1700 ° C., a holding time of 5 to 20 minutes, It is also characterized by being carried out under conditions of a pressing force of 30 to 50 MPa and a heating rate of 50 to 100 ° C./min.

  By using the production method of the present invention, a titanium boride sintered body having a high density can be produced at a relatively low temperature (a temperature lower by about 200 to 300 ° C.) than the conventional method. Is superior in mechanical properties (three-point bending strength, Vickers hardness, fracture toughness value) to the sintered body obtained by the conventional method, and has a high melting point, high hardness, chemical stability, thermal conductivity, electrical conductivity As a material with good properties, it can be used for new applications other than protective films for underground cables.

It is a flowchart which shows an example of the manufacturing method of this invention. It is the schematic which shows the internal structure of the apparatus suitable for implementing the pulse current pressurization sintering in the manufacturing method of this invention. Is an X-ray diffraction (XRD) patterns and SEM photograph of TiB ₂ powder after (b) and before (a) performing a jet milling. (A) is 1650 ° C., a (b) is 1800 ℃, (c) is 10 minutes at 1900 ° C., SEM photographs of the sintered TiB ₂ ceramic crushing surface at 30 MPa. Is a graph showing the relationship between the sintering temperature and the TiB ₂ ceramic bulk density. FIG. 3 is a shrinkage profile of a powder compact using various compositions as a function of soaking time, where (a) is the heating temperature, (b) is the shrinkage curve of TiB ₂ monolith, and (c) is 7 vol% TiO _2. Is a shrinkage curve of TiB ₂ ceramic to which is added. x vol% TiO ₂ is TiB ₂ ceramic XRD patterns added. TiB the x vol% TiO ₂ was added ₂ ceramic (1650 ° C. / 10 min / 30 MPa) is a SEM photograph of a fracture surface of the. The figure on the left is a graph showing the relationship between TiO ₂ content, relative density (a), and bulk density (b) in a TiB ₂ ceramic (1650 ° C./10 minutes / 30 MPa) to which x volume% TiO ₂ is added. The right figure is a graph showing the relationship between the TiO ₂ content and the particle diameter in a TiB ₂ ceramic (1650 ° C./10 min / 30 MPa) to which x volume% TiO ₂ has been added. TiO ₂ content, and (a) bending strength (σ _b ), (b) Vickers hardness (H _V ), in a TiB ₂ ceramic (1650 ° C./10 minutes / 30 MPa) to which x volume% TiO ₂ was added ( c) A graph showing the relationship of crushing strength (K _IC ). Shrinkage profiles of powder compacts using various compositions as a function of soaking time, where (a) is the heating temperature, (b) is the shrinkage curve of TiB ₂ with 5 volume% TiO ₂ added, ( c) Shrinkage curve of 10 volume MgO / 4.75 volume% TiO ₂ doped TiB ₂ ceramic. It is an XRD pattern of 10MgO-4.5TiO ₂ -85.5TiB ₂ (volume%) ceramic (30 MPa). It is a SEM photograph of the crushing surface of 10MgO-4.5TiO ₂ -85.5TiB ₂ (volume%) ceramic (30 MPa). It is a XRD pattern of x.MgO- (100-x). (5TiO ₂ -95TiB ₂ ) (volume%) ceramic (1650 ° C./10 minutes / 30 MPa). The figure on the left shows the MgO content and relative density (a) in MgO-added (5TiO ₂ -95TiB ₂ ) ceramic (1650 ° C./10 min / 30 MPa) as a function of MgO content (% by volume), It is a graph which shows the relationship of bulk density (b), and the figure on the right side shows the relationship between the MgO content and the particle diameter in the MgO-added (5TiO ₂ -95TiB ₂ ) ceramic (1650 ° C./10 min / 30 MPa). It is a graph to show. It is a SEM photograph of the crushing surface of (5TiO ₂ -95TiB ₂ ) ceramic (1650 ° C./10 minutes / 30 MPa) added with MgO. MgO content, (a) flexural strength (σ _b ), (b) Vickers hardness (H _V ), (c) in (5TiO ₂ -95TiB ₂ ) ceramic (1650 ° C./10 min / 30 MPa) added with MgO ) Is a graph showing the relationship of crushing strength (K _IC ).

Each process in the manufacturing method of the high-density metal boride of this invention is demonstrated below. FIG. 1 is a flowchart showing a procedure of a preferred example in the production method of the present invention. FIG. 1 shows a case where magnesium oxide is added as a sintering aid in addition to titanium boride powder and titanium oxide powder in order to further improve mechanical properties.
First, in Step A in the production method of the present invention, titanium oxide powder is added to titanium boride powder as a starting material, and 3 to 10% by volume, preferably 3 to 7% by volume of titanium oxide powder is uniformly mixed. A mixed powder is prepared and the mixed powder is molded to produce a molded body. At this time, if the content of titanium oxide powder is less than 3% by volume, the relative density of the sintered body is 90% or less, and sufficient mechanical properties (bending strength, Vickers hardness, fracture toughness value) cannot be obtained, Conversely, if the content of titanium oxide powder exceeds 10% by volume, the particles grow abnormally by sintering and the particle diameter increases, and the three-point bending strength does not decrease, but the Vickers hardness and fracture toughness value decrease. .

  In the present invention, when further adding magnesium oxide as a sintering aid to improve mechanical properties, 3 to 7% by volume (preferably 4 to 6% by volume) of titanium oxide powder and 1 to 4% by volume ( Titanium boride powder that is preferably mixed with magnesium oxide powder of preferably 2 to 3.5% by volume) may be prepared. When the content of magnesium oxide powder is less than 1% by volume, titanium oxide is added. Even if the content is 5% by volume, a relative density exceeding 94% cannot be obtained. Conversely, if the content of the magnesium oxide powder exceeds 4% by volume, the bending strength decreases, which is not preferable.

In the present invention, in order to improve the sinterability, it is preferable to pulverize the starting titanium boride powder in advance so that the particle diameter is 1 μm or less. In order to reduce contamination by contamination as much as possible, a dry jet mill in which titanium boride powders collide with each other in an inert gas (for example, argon gas) and is pulverized is preferable. Commercially available products can be used as they are for titanium oxide and magnesium oxide.
In the present invention, the mixing method in the case of mixing titanium boride powder and titanium oxide powder (when further improving the mechanical properties, the magnesium oxide powder is also mixed) is a method that can achieve homogeneous mixing. Although there is no particular limitation as long as it is present, wet mixing is preferably performed in an alcohol (for example, in methanol) for a certain period of time using a zirconium oxide pot and balls by a planetary ball mill. The mixture obtained by the above mixing is dried and then sized, and formed into a desired shape by molding or the like. This molded body is then preferably subjected to cold isostatic pressing (CIP) treatment.

In step B, which is the next step, the compact obtained in step A is subjected to pulsed current pressure sintering using a pulsed current pressure sintering apparatus having an internal structure as shown in FIG.
In this pulse energization and pressure sintering (PECPS), a pulsed DC large current is applied at a low voltage to cause a spark discharge phenomenon between the particles, thereby generating high energy instantaneously. When high-speed diffusion occurs by heating, a dense sintered body (relative density of 90% or more) in which grain growth is suppressed at a relatively low temperature in a short time can be obtained, and high strength and high toughness ceramics can be produced. It becomes possible.
In the present invention, depending on the particle diameter, blending ratio, etc. of the raw material powder to be used, the conditions for pulse current pressure sintering in step B can be selected as appropriate, but the mixing of titanium boride powder and titanium oxide powder When using powder, it is performed under a vacuum of 10 Pa or less under conditions of a sintering temperature of 1600 to 1900 ° C., a holding time of 3 to 30 minutes, a pressing force of 10 to 70 MPa, and a heating rate of 50 to 150 ° C./min. It is preferable that the pulsed pressure sintering is particularly preferably performed under a vacuum of 10 Pa or less, a sintering temperature of 1650 ° C., a holding time of 10 minutes, a pressing force of 30 MPa, and a heating rate of 100 ° C./min. At this time, when the sintering temperature is less than 1600 ° C., the relative density becomes low (about 85% or less). Conversely, when the sintering temperature exceeds 1900 ° C., TiB ₂ particles in the sintered body grow abnormally and the mechanical properties are lowered. This is not preferable. In addition, the holding time is sufficiently densified in 3 to 30 minutes, but if the applied pressure is less than 10 MPa, the sintering density is lowered, and conversely if it exceeds 70 MPa, the strength of the mold used for the current pressure sintering is increased. There is an upper limit and it cannot be used. On the other hand, when the rate of temperature increase is less than 50 ° C./min, the heat treatment takes a long time and the manufacturing cost increases.
When a mixed powder of titanium boride powder, titanium oxide powder and magnesium oxide powder is used, the sintering temperature is 1600 to 1700 ° C., the holding time is 5 to 20 minutes, and the applied pressure is 30 under a vacuum of 10 Pa or less. It is preferable to carry out under the conditions of -50 MPa and a temperature increase rate of 50-100 ° C./min. At this time, when the sintering temperature exceeds 1700 ° C., the TiB ₂ particles in the sintered body grow abnormally, and the mechanical properties Is unfavorable because it decreases. In addition, the holding time is sufficiently densified in 5 to 20 minutes, but if the applied pressure is less than 30 MPa, the sintering density is lowered, and conversely if it exceeds 50 MPa, the strength of the mold used for the current pressure sintering is increased. There is an upper limit and it cannot be used. On the other hand, if the rate of temperature rise is less than 50 ° C./min, the heat treatment takes a long time and the manufacturing cost increases. Conversely, if it exceeds 100 ° C./min, the microstructure inside the sintered body becomes uneven, resulting in a homogeneous and large Since preparation of a sample becomes difficult, it is not preferable.

Example 1: Example of production of high-density titanium boride by this production method (in the case of addition of titanium oxide)
In this sintering experiment, as a raw material powder, titanium boride powder (average particle size P) prepared by the metallothermic reduction method described in Katsumi Nishiyama, Powder and Powder Metallurgy, 37 [4] 500-507 (1990) the _{s ~1.92μm ^φ),} it was used as atomized by a dry jet mill (P _s ~0.57μm ^_φ) in order to improve the sinterability. The average crystal grain size was determined by the intercept method (MI Mendelson; “Average Grain Size in Polycrystalline Ceramics”, J. Am. Ceram. Soc., 52 (1969) 443-446). FIG. 3 shows XRD patterns and SEM photographs of titanium boride powder before and after pulverization by a jet mill. At this time, RINT-2500 manufactured by Rigaku Corporation was used for the XRD measurement, and the fine structure of the fractured surface of the sintered body was observed with a field emission scanning electron microscope (FE-SEM, manufactured by JEOL Ltd .: JEOL7000).
From the XRD pattern of FIG. 3, it can be seen that a small amount of titanium oxide is present as an impurity in the titanium boride powder.

And before conducting the sintering experiment in the case of adding titanium oxide, as a preliminary experiment, the crushed surface state of the sintered body and the sintering in the case of using titanium boride before the titanium oxide is added The relationship between temperature and bulk density was investigated. The bulk density was measured by the Archimedes method.
FIG. 4 shows an SEM photograph of the crushed surface of the sintered body obtained when sintering is performed at (a) 1650 ° C., (b) 1800 ° C., and (c) 1900 ° C. for 10 minutes under 30 MPa. FIG. 5 shows the relationship between the sintering temperature and the bulk density when no titanium oxide is added. From the graph of FIG. 5, it was found that when titanium oxide was not added, the bulk density was only about 91 Mg · m ⁻³ even when sintered at a high temperature of 1900 ° C.
Then, 0 to 15% by volume of titanium oxide (rutile) powder (P _s ˜15 nm ^φ ) is added to the above-mentioned atomized titanium boride powder as a sintering aid, and the product made of zirconium oxide by a planetary ball mill. Wet mixing and crushing were performed for 60 minutes in methanol using a pot and a ball (1 mmφ). After the mixed powder obtained by drying in the air is sized, it is die-molded (30 MPa), then pressed with cold isostatic pressure (245 MPa), and then using a commercially available pulsed electric current pressure sintering apparatus. Under pressure of 10 Pa or less, sintering temperature 1650 ° C., holding time 10 minutes, pressurizing pressure 30 MPa, heating rate 100 ° C./minute (PSS Shintex Co., Ltd./SPS-510A) The sintered body was obtained.

FIG. 6 shows a curve (a) showing the relationship between the soaking time and the heating temperature, a shrinkage curve (b) of a titanium boride monolith without addition of titanium oxide, and a ceramic using a titanium boride powder containing 7% by volume of titanium oxide. The shrinkage curve (c) is shown, and it was found that the curve (c) is located below the curve (b) from the vicinity of over 1000 seconds, and the shrinkage is improved.
In FIG. 7, each sintered body obtained by the above-described sintering experiment ((a) has no titanium oxide added, (b) contains 3% by volume of titanium oxide, (c) contains 5% by volume of titanium oxide, ( (d) contains 7% by volume of titanium oxide, (e) contains 10% by volume of titanium oxide, and (f) contains 15% by volume of titanium oxide). This XRD analysis shows that the titanium boride phase Only the diffraction peak was confirmed, and the added titanium oxide disappeared in each case after sintering. This is probably because the titanium oxide was reduced and the titanium melted and flowed out. From these experimental results, it was found that a titanium boride sintered body can be produced without adding it as an impurity even when titanium oxide is added.

FIGS. 8A to 8F show a fracture surface of TiB ₂ ceramic (1650 ° C./10 minutes / 30 MPa) containing x volume% (x = 0, 3, 5, 7, 10, 15) TiO _2. From this SEM photograph, it is considered that (a) to (d) have almost the same particle diameter, but (e) and (f) have larger particle diameters due to abnormal growth. You can see that
The diagram on the left side of FIG. 9 shows the relationship between titanium oxide content, relative density (a), and bulk density (b) in a titanium boride ceramic (1650 ° C./10 minutes / 30 MPa) containing x volume% titanium oxide. From this graph, when the addition amount of titanium oxide is up to 10% by volume, an increase in bulk density and relative density is observed, and the inclusion of 3% by volume or more of titanium oxide results in a relative density of 90% or more. all right. On the other hand, the diagram on the right side of FIG. 9 is a graph showing the relationship between the titanium oxide content and the particle diameter in a titanium boride ceramic (1650 ° C./10 minutes / 30 MPa) containing x volume% titanium oxide. From the results, it was found that the particle diameter suddenly increased when the content of titanium oxide exceeded 7% by volume.

FIG. 10 shows the titanium oxide content, (a) bending strength (σ _b ), and (b) Vickers hardness (titanium boride ceramic (1650 ° C./10 min / 30 MPa) containing x volume% titanium oxide. H _V ), (c) A graph showing the relationship between crushing strength (K _IC ) is shown, and a test piece for measuring mechanical properties (˜3 × 4 × 15 mm ³ ) from each sintered body with a diamond cutter. The four sides were cut and mirror-polished (diamond abrasive grains: 1 to 3 μmφ). The mechanical properties were measured at a three-point bending strength (σ _b ) at a span of 8 mm, a crosshead speed of 0.5 mm / min, a load of 19.6 N, a holding time of 15 s, and a Vickers hardness (H _v ) and IF method (K. Niihara, R. Morena, DPH Hasselman, “Evaluation of K _IC of Brittle Solids by the Indentation Method with Low Crack-to-Indent Ratios”, J. Mater. Sci. Lett., 1 (1982) 13-16) (K _IC ) was evaluated.
From the results of FIG. 10, the bending strength and fracture toughness values are maximum when the titanium oxide content is 5% by volume, and the Vickers hardness is maximum when the titanium oxide content is 7% by volume. Overall, it was found that high mechanical properties were exhibited when the content of titanium oxide was 3 to 10% by volume, particularly 3 to 7% by volume.

Example 2: Example of production of high-density titanium boride by this production method (in the case of addition of titanium oxide + magnesium oxide)
As the raw material powder, the above-mentioned atomized titanium boride powder (P _s ˜0.57 μm ^φ ) is used, and as the sintering aid, a commercially available magnesium oxide powder (P _s ˜50 nm ^φ ) and the above titanium oxide are used. (Rutile) powder (P _s ˜15 nm ^φ ) was added so that the respective contents were 10% by volume and 4.75% by volume, and in the same manner as in Example 1, wet mixing in methanol for 60 minutes.・ We disintegrated. After the mixed powder obtained by drying was sized, a mold was formed, followed by cold isostatic pressing (245 MPa), followed by pulsed current pressure sintering to obtain a sintered body.
About the 10% by volume magnesium oxide / 4.75% by volume titanium oxide-containing titanium boride sintered body thus obtained and the 5% by volume titanium oxide-containing titanium boride sintered body obtained in Example 1 above. Curve (a) showing the relationship between soaking time and heating temperature, shrinkage curve (b) of 5% by volume titanium oxide-containing titanium boride sintered body, 10% by volume magnesium oxide / 4.75% by volume titanium oxide-containing boron The shrinkage curve (c) of the titanium boride sintered body is shown in FIG. 11, and from this drawing, the magnesium oxide and the oxide are oxidized more than the shrinkage curve (b) of the titanium boride sintered body to which only titanium oxide is added. The shrinkage curve (c) of the titanium boride sintered body to which titanium was added was located on the lower side, and it was found that the shrinkage was improved by the inclusion of magnesium oxide.

FIG. 12 shows a sintering temperature at a composition of 10 volume% MgO / 90 volume% (5 TiO ₂ -95 TiB ₂ ), that is, 10 MgO-4.5 TiO ₂ -85.5 TiB ₂ (volume%) in terms of 100%. The XRD pattern is shown when the temperature is changed between 800 and 1650 ° C. and when the holding time is changed at 1650 ° C., and only the diffraction peak of the titanium boride phase is confirmed at a temperature of 1400 ° C. or higher. Neither the diffraction peak of magnesium oxide nor the diffraction peak of titanium oxide was observed. Moreover, although it was not confirmed in the sample to which only titanium oxide was added, in the sample to which titanium oxide and magnesium oxide were added, the diffraction peak shifted to the high angle side as the amount of magnesium oxide added increased. Was observed. This is considered to be because magnesium oxide was dissolved in titanium boride.
FIG. 13 shows a green compact (a) from a mixed powder having a composition of 10 MgO-4.5 TiO ₂ -85.5 TiB ₂ (volume%), and a sintered body obtained under various sintering temperature conditions. SEM photographs of the fractured surfaces of (b) to (h) are shown, and in particular, as the sintering time at a temperature of 1650 ° C. becomes longer from the SEM photographs of (f) to (h), the particle diameter gradually increases. It turns out that becomes large.

Next, the content of titanium oxide is fixed to 5% by volume to be constant (95% by volume of titanium boride), and further added to a content of 0 to 20% by volume of magnesium oxide powder (P _s up to 50 nm ^phi) was added, after performing wet mixing for 60 minutes, the mixture powder obtained by drying and uniaxially molding (50 MPa), after cold isostatic pressing treatment (245 MPa), in a vacuum, Pulse current pressure sintering (1650 ° C./10 minutes / 30 MPa) was performed.
FIG. 14 shows each sintered body obtained by the above experiment ((a) without addition of magnesium oxide, (b) containing 1% by volume of magnesium oxide, (c) containing 3% by volume of magnesium oxide, (d) XRD pattern of 5% by volume of magnesium oxide, (e) containing 10% by volume of magnesium oxide, (f) containing 15% by volume of magnesium oxide, and (g) containing 20% by volume of magnesium oxide) is shown. In this XRD analysis, only the diffraction peak of the titanium boride phase was confirmed, and it was confirmed that the added titanium oxide and magnesium oxide disappeared after sintering in any case. From these experimental results, it was found that even when both titanium oxide and magnesium oxide were added, they did not remain as impurities, and a titanium boride sintered body could be produced.

  The left and right graphs in FIG. 15 are graphs related to changes in the microstructure when the content of magnesium oxide is changed, and the left graphs are x volume% (x = 0, 1, 3, 5, 10, 15). 20) A graph showing the relationship between magnesium oxide content, relative density (a), and bulk density (b) in a titanium oxide-titanium boride ceramic (1650 ° C./10 min / 30 MPa) containing magnesium oxide. From the graph, the relative density and bulk density are increased by adding magnesium oxide, the relative density is 94% or more by containing 1% by volume or more of magnesium oxide, and the relative density is about 98% by containing 5% by volume or more of magnesium oxide. I found out that On the other hand, the graph on the right side is a graph showing the relationship between the amount of magnesium oxide added and the particle diameter in a titanium oxide-titanium boride ceramic containing x volume% magnesium oxide. From this graph, a small amount (1 volume%) of It can be seen that the particle size increases with the content of magnesium oxide, and this indicates that the titanium boride ceramic (1650 ° C./10 min / x) to which x volume% magnesium oxide is added, as shown in FIGS. It is also shown in the SEM photograph of the fractured surface of 30 MPa). In addition, when comparing the SEM photograph of the sintered body obtained by adding only titanium oxide, it can be obtained by adding more magnesium oxide than the sintered body obtained by adding only titanium oxide. It was found that the sintered body was more densified.

FIG. 17 shows the content of magnesium oxide in a titanium oxide-titanium boride ceramic (1650 ° C./10 min / 30 MPa) containing x volume% magnesium oxide, and (a) bending strength (σ _b ), (b). A graph showing the relationship between Vickers hardness (H _V ) and (c) crushing strength (K _IC ) is shown, and each physical property was measured in the same manner as the method described in Example 1.
From the results shown in FIG. 17, the Vickers hardness and fracture toughness values do not change greatly even when magnesium oxide is added. However, regarding the bending strength, if the magnesium oxide content is excessively increased (the content is increased to 5% by volume or more). The optimum content of magnesium oxide is considered to be 1-4% by volume, preferably 2-3.5% by volume.
In order to confirm the effect of the combined use of titanium oxide and magnesium oxide, a titanium boride ceramic (1650 ° C./10 minutes / 30 MPa) was manufactured using titanium boride powder containing only 3% by volume of magnesium oxide. However, the bulk density was 4.15 g / cm ³ , the relative density was 92.3%, the Vickers hardness was 25.4 GPa, the fracture toughness value was 6.33 MPa · m ^1/2 , and the three-point bending strength σ _b 620 MPa. A particularly excellent sintered body was not obtained.

Summary From the experimental results of Example 1, when the manufacturing method of the present invention is carried out, a titanium boride sintered body densified at 1650 ° C., which is a relatively lower temperature than the conventional method, can be manufactured (none It was confirmed that the relative density in the case of addition was increased to 86% by adding titanium oxide, and the mechanical properties (bending strength, Vickers hardness, fracture toughness value) were improved.
Further, from the experimental results of Example 2 above, a compact obtained by using titanium boride powder containing 3 to 7% by volume of titanium oxide and 1 to 4% by volume of magnesium oxide was subjected to pulse current compression sintering. As a result, it was confirmed that a sintered body having a higher density and excellent mechanical properties could be produced.
Table 1 below shows titanium boride monoliths sintered in vacuum at 1650 ° C./10 minutes / 30 MPa, 5 vol% titanium oxide titanium boride ceramics, 3 vol% magnesium oxide—4.85 vol% oxidation. Typical characteristics of titanium-92.2 vol% titanium boride ceramics are shown.

  From the physical property values shown in Table 1 above, the relative density, Vickers hardness and fracture toughness of the titanium boride ceramics obtained by adding titanium oxide and the titanium boride ceramics obtained by adding titanium oxide and magnesium oxide. It can be seen that both values have improved.

  Titanium boride can be added at a relatively low temperature by the manufacturing method of the present invention in which a predetermined amount of titanium oxide is added to titanium boride or a predetermined amount of titanium oxide and magnesium oxide is added and sintering is performed by pulsed current pressure sintering. It can be sintered, and the mechanical strength of the obtained titanium boride sintered body can be improved, and the application development of metal boride materials with excellent characteristics is possible by producing a dense material. Become.

Claims (4)

A method for producing a high density metal boride having a relative density of 90% or more,
Step A: A step of preparing a titanium boride powder in which 3 to 10% by volume of titanium oxide powder is uniformly mixed, and molding the mixed powder to produce a molded body, and Step B: obtained in Step A above A method for producing a high-density metal boride comprising a step of producing a titanium boride sintered body having a relative density of 90% or more by subjecting the formed body to pulse-current pressure sintering. In the above-mentioned step B, pulsed current pressure sintering is performed under a vacuum of 10 Pa or less, sintering temperature 1600 to 1900 ° C., holding time 3 to 30 minutes, pressurizing force 10 to 70 MPa, heating rate 50 to 150 ° C./min. The method for producing a high-density metal boride according to claim 1, wherein the method is performed under conditions. A method for producing a high density metal boride having a relative density of 94% or more,
Step A: preparing titanium boride powder in which 3 to 7% by volume of titanium oxide powder and 1 to 4% by volume of magnesium oxide powder are uniformly mixed, and molding the mixed powder to produce a molded body, And a step B: a step of producing a titanium boride sintered body having a relative density of 94% or more by subjecting the formed body obtained in the step A to pulse-current pressurization and sintering. A method for producing a metal boride. The pulsed current pressure sintering in the above-mentioned step B is under a vacuum of 10 Pa or less, sintering temperature 1600 to 1700 ° C., holding time 5 to 20 minutes, pressurizing force 30 to 50 MPa, heating rate 50 to 100 ° C./min. The method for producing a high-density metal boride according to claim 3, wherein the method is performed under conditions.