JP2005281084A - Sintered compact and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sintered compact excellent in hardness, strengths, and toughness, and capable of non-pressurized sintering at a low temperature, in regard to a Ti/Si/C base sintered compact which is used as a cutting tool, an abrasion resistant tool, a sliding part, or the like. <P>SOLUTION: The sintered compact which is a sintered compact containing a first hard phase of a titanium containing compound and a second hard phase of a titanium/silicon compound, satisfies both 0.20≤Si/(Ti+Si)≤0.30 wherein Si/(Ti+Si) is the atomic ratio of the titanium element to the total of the titanium element and the silicon element in the sintered compact, and 0.30≤C/(Ti+Si)≤0.55 wherein C/(Ti+Si) is the atomic ratio of the carbon element to the total of the titanium element and the silicon element in the sintered compact, is excellent in hardness, strengths, and toughness, and capable of non-pressurized sintering. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a hard sintered material used for cutting tools, wear-resistant tools, sliding parts, and the like, and more particularly to a sintered body optimal for applications requiring wear resistance in a high temperature or corrosive environment. It is.

Since titanium carbide has high hardness and low affinity with steel, it is frequently used for cutting tools and wear-resistant tools as additive components or hard coatings of TiC-based cermets, cemented carbides and alumina-based ceramics. However, a sintered body made only of titanium carbide is difficult to sinter and inferior in strength, toughness, oxidation resistance, etc., and has not been put into practical use. As one of the solutions, various methods for adding silicon have been proposed.

Concerning a sintered body containing titanium carbide, the main component is at least one of boride, carbide, nitride, and carbonitride of titanium, and at least one of group 4, 5, 6 B and iron group silicide is 0. There is a titanium-based ceramic sintered body containing 1 to 50% by weight (for example, see Patent Document 1). This titanium-based ceramic sintered body has a silicide that generates a liquid phase at a low temperature to improve sinterability. However, when titanium silicide is added to titanium carbide, a large amount of silicon carbide is added. There arises a problem that the strength and toughness are insufficient because the titanium silicide is coarsened by high temperature sintering at 1650-1800 ° C.

Further, there is a titanium carbide sintered body obtained by sintering a mixture of titanium carbide powder and an organosilicon polymer, and comprising 2 to 10% by weight of silicon carbide and 2% by weight or less of free carbon (for example, patent document). 2.). Although the titanium carbide sintered body described in this publication has improved sinterability by fine silicon carbide generated from an organosilicon polymer, there is a problem that high strength sintering is required due to low strength and toughness.

Furthermore, there is a titanium silicon carbide sintered body characterized by having a crystal grain size of 10 μm or less and a titanium carbide (TiC) content of 8 wt% or less (see, for example, Patent Document 3). There is a titanium silicon carbide (Ti ₃ SiC ₂ ) metallic ceramic sintered body having a titanium carbide (TiC) content of 7 wt% or less (see, for example, Patent Document 4). These titanium silicon carbide sintered bodies are obtained by inserting a mixed powder of titanium, silicon or silicon carbide, and titanium carbide into a carbon mold and performing pulsed current pressure sintering, and high purity Ti ₃ SiC ₂ by reaction synthesis. Although it is going to obtain a sintered compact, since manufacture is difficult and it cannot respond to a complicated shape, there exists a problem that it becomes expensive.

Japanese Laid-Open Patent Publication No. 05-139834 Japanese Patent Laid-Open No. 08-40772 JP 2003-2745 A JP 2003-20279 A

The present invention solves the above-described problems. Specifically, the ratio of titanium, carbon, and silicon is limited to a predetermined range, and a raw material powder is selected so that no additive is applied at a low temperature. An object is to provide a sintered body that enables pressure sintering and has excellent hardness, strength, and toughness.

The present inventor has been studying further improvement of sinterability and improvement of strength and toughness of a sintered body containing titanium carbide and a titanium silicon compound. As a raw material powder, titanium carbide having a low bonded carbon content ( If a mixed powder of TiC _1-X ) and silicon is used, a liquid phase is generated at a low temperature, so that densification is easy, and low-temperature sintering makes the structure of the sintered body uniform and fine, In addition, when the component composition is in the vicinity of Ti: Si: C = 3: 1: 1 to 2 in atomic ratio, the knowledge that hardness, strength and toughness are further improved has been obtained, and the present invention has been completed. Is.

That is, the sintered body of the present invention is a sintered body including a first hard phase of a titanium-containing compound and a second hard phase of a titanium silicon compound, and is a total of titanium element and silicon element contained in the sintered body. The atomic ratio of silicon element to (Si / (Ti + Si)) satisfies 0.20 ≦ Si / (Ti + Si) ≦ 0.30, and the carbon element to the total of titanium element and silicon element contained in the sintered body The atomic ratio (C / (Ti + Si)) satisfies 0.30 ≦ C / (Ti + Si) ≦ 0.55.

The sintered body containing the first hard phase of the titanium-containing compound of the present invention and the second hard phase of the titanium silicon compound contains 80% by volume or more of the first hard phase and the second hard phase, and the rest is In addition, it refers to a sintered body composed of at least one of the group 4a, 5a and 6a elements of the periodic table excluding titanium, carbides, nitrides and oxides of Al and Si, and their mutual solid solutions.

In the sintered body of the present invention, the atomic ratio of silicon atoms to the total of titanium atoms and silicon atoms: Si / (Ti + Si) is less than 0.20, since the amount of silicon compound serving as a sintering aid is small, the sinterability Deteriorates to form burrows, and even after high temperature sintering, coarse grains become hard and strong. On the other hand, when it exceeds 0.30, the amount of titanium carbide is relatively reduced, so that the hardness is lowered, and the silicon compound is coarsened and the strength is also lowered. On the other hand, if the atomic ratio of carbon atoms to the total of titanium atoms and silicon atoms: C / (Ti + Si) is less than 0.30, the amount of bonded carbon in titanium carbide decreases, so that the hardness decreases. If it exceeds 55, a large amount of silicon carbide is produced, so that strength and toughness deteriorate.

The first hard phase of the titanium-containing compound in the sintered body of the present invention is composed of titanium carbide, carbonitride, composite carbide of periodic table 4a, 5a, 6a elements excluding titanium and titanium, and composite carbonitride. It consists of at least one of them. Titanium carbide contained in the first hard phase has a B1 type cubic crystal structure and a non-stoichiometric composition. Specifically, when titanium carbide is expressed as TiC _1-X , 0.6 ≦ Titanium carbide is in the range of x ≦ 0.8 and has a low amount of bonded carbon. When nitrides of Group 4a and 5a elements in the periodic table are added to and contained in the sintered body, nitrides of Group 4a and 5a elements of the Periodic Table 4a and 5a elements are dissolved in the entire surface or partially in composite carbide nitriding. Form things.

Further, the second hard phase of the titanium silicon compound in the present invention is composed of at least one of an intermetallic compound containing a titanium element and a silicon element, carbide, nitride, and carbonitride. Specific examples include titanium silicon carbide such as Ti ₃ SiC ₂ and titanium silicon intermetallic compounds such as TiSi ₂ , Ti ₅ Si ₃ , TiSi, Ti ₃ Si ₄ , and Ti ₃ Si. Of these, if it is _{TiSi 2, Ti 5 Si 3,} Ti 3 at least one among SiC _2, the mechanical properties of the sintered body is improved preferably. For example, TiSi ₂ improves hardness and strength, Ti ₅ Si ₃ improves toughness, and Ti ₃ SiC ₂ improves strength and toughness.

The sintered body of the present invention preferably contains 0.1 to 5% by weight of aluminum element with respect to the entire sintered body because the mechanical properties of the sintered body are improved. When metallic aluminum is added, an eutectic liquid phase of Al—Si is formed, so that the sinterability is improved and a sintered body with a fine structure is obtained, and the amount of Ti ₃ SiC ₂ is increased, so that strength is increased. And toughness is improved. However, if the aluminum element is contained in a large amount exceeding 5% by weight, the Ti ₃ SiC ₂ is coarsened, and at the same time, the brittle Al ₂ Ti ₄ C ₂ phase is generated, so that the strength and toughness are remarkably lowered. Conversely, if it is less than 0.1% by weight, the effect of containing an aluminum element cannot be obtained. The added aluminum element is presumed to be a solid solution in the titanium silicon compound, but a part of the aluminum element becomes fine particles of aluminum oxide and is dispersed in the sintered body.

The sintered body of the present invention comprises a first hard phase: 35 to 85% by volume and a second hard phase: the remainder, or a first hard phase: 35 to 85% by volume, aluminum oxide and / or Alternatively, a sintered body composed of a third hard phase composed of silicon carbide: 0.1 to 5% by volume and a second hard phase: the balance is preferable because it is easy to manufacture and has a good balance of mechanical properties. Within the composition range of the present invention, for example, the amount of titanium silicon compound (Ti ₃ SiC ₂ ) can be 80% by volume. However, since the amount of titanium carbide is relatively reduced, the hardness is significantly reduced. . In particular, silicon carbide contained as the third hard phase causes a rapid decrease in toughness, so that it is preferably 2% by volume or less based on the entire sintered body.

The average particle diameter of each hard phase is preferably 3 μm or less for the first hard phase and 5 μm or less for the second hard phase because the sintered body has high hardness and strength. However, since it is technically difficult to make both the first hard phase and the second hard phase less than 0.1 μm, the average particle diameter of the first hard phase is 0.1 to 3 μm, and the average particle diameter of the second hard phase is 0.1-5 micrometers is preferable. In order to obtain a fine structure, the raw material powder needs to be made into fine particles and sintered at a low temperature.

The production method of the present invention comprises a mixture containing titanium carbide and silicon represented by TiC _1-x (0.5 <x <0.9, _1-x represents an atomic ratio of carbon to titanium element). A mixing step to obtain, a forming step for pressure-molding the obtained mixture, and a sintering step for sintering the formed mixture in a vacuum of 1300 to 1500 ° C. In the mixing step, the mixture may include at least one of nitrides of Group 4a and 5a elements of the periodic table and / or metal aluminum in addition to titanium carbide and silicon having a low bonded carbon content.

The method for producing a sintered body according to the present invention involves pressureless sintering in the sintering step, and a sintered body having a fine and fine structure excellent in mechanical properties can be easily obtained.

In the production method of the present invention, silicon reacts with TiC _1-X to produce a Ti—Si low-temperature liquid phase (1330 ° C. in the Si—TiSi ₂ system and 1330 ° C. in the Ti—Ti ₅ Si ₃ system) while being fine. Since titanium carbide and titanium silicon compounds such as TiSi ₂ , Ti ₅ Si ₃ , and Ti ₃ SiC ₂ are generated, the sinterability is improved and a fine and high-strength sintered body is obtained. Here, the same result can be obtained by using TiC and TiH ₂ (or Ti) instead of TiC _{1 -X} , and SiC instead of silicon, but it is better to reduce the amount of TiH ₂ (or Ti). . This is because if the amount of TiH ₂ added is large, cracks are generated in the sintered body due to the dissociation reaction of hydrogen and the reaction heat with SiC.

The sintering atmosphere in the production method of the present invention must be heated and held in a vacuum of 100 Pa or less to sufficiently remove oxygen contained in the raw material powder. This is because oxygen dissolved in titanium carbide or oxide (SiO ₂ ) dispersed in a titanium silicon compound significantly reduces the toughness of the sintered body. The sintering temperature is preferably in the range of 1300 to 1500 ° C. If the sintering temperature is less than 1300 ° C., the under-sintered pores are produced. Conversely, if the temperature exceeds 1500 ° C., the titanium silicon compound becomes extremely coarse. Hardness and strength are reduced. Here, when it is desired to further improve the composition, hardness and strength with insufficient sinterability, it is preferable to perform HIP (hot isostatic pressure) treatment.

The sintered body of the present invention is a fine titanium carbide produced by a sintering reaction in which a low-temperature liquid phase generated from titanium carbide (TiC _1-X ) and silicon having a low bonded carbon content improves the sinterability. Has a function of improving hardness, a titanium silicon compound has an effect of improving strength and toughness, and a limited composition range of titanium, silicon and carbon has an effect of further improving these characteristics.

The sintered body of the present invention has high hardness, strength, and toughness, and can be sintered without pressure. Excellent performance when used for cutting tools, wear-resistant tools, sliding parts, etc.

TiC _0.7 having an average particle diameter of 1.2 μm (carbon content is 15.0 wt%), TiC having an average particle diameter of 1.5 μm, TiH _{2 having} an average particle diameter of 5 μm, Ti having an average particle diameter of 1.2 μm ( C _0.5 N _0.5 ), Si with an average particle size of 10 μm, SiC with an average particle size of 0.5 μm, TiSi ₂ with an average particle size of 3.5 μm, Al (flat stamp powder) with an average particle size of 1.5 μm, average particle size Each powder of 1.2 μm TiN, VN having an average particle diameter of 2.1 μm, TaN having an average particle diameter of 1.2 μm and ZrO _{2 having an} average particle diameter of 0.2 μm (containing 3 mol% Y ₂ O ₃ ) is shown. 1. After blending for 48 hours using ethyl alcohol solvent, urethane lining pot, alumina grinding ball, and blending into the composition shown in No. 1, 4.0% by weight while drying. Paraffin wax was added to obtain a mixed powder. These mixed powders are filled into a mold, and a 5.5 to 17 43 mm compact is produced with a pressure of 198 MPa, placed on a boron nitride setter and heated in a vacuum of 50 Pa. After dewaxing at 400 ° C. for 1 hour, sintering was carried out at the temperature shown in Table 2 for 1 hour. Furthermore, except for some sintered bodies, the HIP treatment (in 100 MPa of Ar) for 1 hour at the temperature shown in Table 2 was performed to sinter the inventive products 1-12 and comparative products 1-9. Got the body.

Each sintered body thus obtained was ground with a # 400 diamond grindstone to obtain a JIS test piece of 3.0 × 4.0 × 35.0 mm, and then the bending strength was measured. Moreover, after lapping one surface of each JIS test piece with a 1 μm diamond paste, test load using a Vickers indenter: hardness (HV) at 196 N and fracture toughness value (K1C ) Was measured. These results are shown in Table 2.

Next, the JIS-processed JIS test piece was subjected to X-ray diffraction to identify the constituent components. Then, after confirming each phase of the constituent component by elemental mapping with a field emission analytical electron microscope, a structure photograph (1,500 times) is taken using an optical microscope, and the content of the constituent component and the average particle are measured by an image processing apparatus. The diameter was determined. The results are shown in Table 3. When observed with an optical microscope, TiC is gray, titanium silicon compounds such as TiSi ₂ , Ti ₅ Si ₃ and Ti ₃ SiC ₂ are white, and the third hard phase such as SiC, Al ₂ O ₃ and ZrO ₂ is black. appear.

Furthermore, after calculating | requiring content of Ti and Si with said analytical electron microscope, a test piece is grind | pulverized in a cemented carbide mortar to make a passing powder of # 100 sieve, and the content of C is also measured using a carbon analyzer. Asked. From these analysis results, the atomic ratio of Si / (Ti + Si) and the atomic ratio of C / (Ti + Si) were calculated. The results are shown in Table 4.

Claims (7)

In a sintered body including the first hard phase of the titanium-containing compound and the second hard phase of the titanium-silicon compound, the atomic ratio of silicon element to the total of titanium element and silicon element contained in the sintered body (Si / ( Ti + Si)) satisfies 0.20 ≦ Si / (Ti + Si) ≦ 0.30, and the atomic ratio of carbon element to the total of titanium element and silicon element contained in the sintered body (C / (Ti + Si)) is , 0.30 ≦ C / (Ti + Si) ≦ 0.55. The second hard _{phase, TiSi 2, Ti 5 Si 3} , Ti 3 sintered body of claim 1 is at least one in the SiC _2. The said sintered compact is a sintered compact of Claim 1 or 2 containing 0.1 to 5 weight% of aluminum elements with respect to the whole sintered compact. The said sintered compact is a sintered compact of any one of Claims 1-3 comprised by 1st hard phase: 35-85 volume% and 2nd hard phase: remainder. The sintered body is composed of a first hard phase: 35 to 85% by volume, a third hard phase composed of aluminum oxide and / or silicon carbide: 0.1 to 5% by volume, and a second hard phase: the balance. The sintered body according to any one of claims 1 to 3. 6. The sintered body according to claim 1, wherein the sintered body has an average particle diameter of the first hard phase of 0.1 to 3 μm and an average particle diameter of the second hard phase of 0.1 to 5 μm. Sintered body. A mixing step of obtaining a mixture containing titanium carbide and silicon represented by TiC _1-x (0.5 <x <0.9, _1-x represents an atomic ratio of carbon to titanium element), and A method for producing a sintered body, comprising: a molding step of pressure-molding the obtained mixture, and a sintering step of sintering the molded mixture in a vacuum of 1300 to 1500 ° C.