CN110408830B

CN110408830B - Ti (C, N) -based metal ceramic material and carbon balance control method thereof

Info

Publication number: CN110408830B
Application number: CN201910803045.5A
Authority: CN
Inventors: 石增敏
Original assignee: China Three Gorges University CTGU
Current assignee: Hubei Maituo New Material Technology Co.,Ltd.
Priority date: 2019-08-28
Filing date: 2019-08-28
Publication date: 2020-09-15
Anticipated expiration: 2039-08-28
Also published as: CN110408830A

Abstract

The invention discloses a Ti (C, N) -based metal ceramic material with carbon balanceThe control method is characterized in that a staged sintering process is adopted in the sintering stage at the temperature of 1000-1500 ℃, the highest temperature and the heat preservation time of staged sintering are adjusted according to the component difference of the raw material, and methane CH is introduced₄The carbon potential in the sintering furnace is controlled by controlling the pressure of methane and the cracking of methane at high temperature, so that the carbon balance in the sintering body is controlled, and the cermet material with excellent performance is prepared. The method mainly controls the sintering high-temperature process effectively, realizes the effective control of the carbon potential in the furnace according to the reaction characteristics of carbon elements in the preparation process of the metal ceramic, and achieves the stability of product quality and optimized toughness of the material.

Description

Ti (C, N) -based metal ceramic material and carbon balance control method thereof

Technical Field

The invention relates to the field of machining and powder metallurgy, in particular to a Ti (C, N) -based metal ceramic material and a carbon balance control method thereof.

Background

The Ti (C, N) -based cermet cutter has high hardness, high wear resistance, high red hardness, high chemical stability and very low friction coefficient, and is mainly used for high-speed fine machining, semi-fine machining and semi-coarse machining of steel and cast iron. The high-temperature hardness of the material is superior to that of high-speed steel and WC-based hard alloy, the toughness of the material is superior to that of ceramic and superhard material cutters, and the blank between the WC-based hard alloy cutter and the ceramic cutter is just filled in the processing range.

Relevant departments in China have developed and developed Ti (C, N) -based metal ceramic cutters of certain brands, and the Ti (C, N) -based metal ceramic cutters can partially replace hard alloy cutters such as YG8, YT15 and the like in the cutting field, and China shows an increasing trend in research, development and production of the metal ceramic cutters in three years. However, the overall production condition of the domestic metal ceramic cutter is still not optimistic, and the expressed characteristic is that the production quality is unstable and cannot be compared favorably with that of an imported blade. The comprehensive performance of the metal ceramic cutter which is being tried on the Chinese market is obviously lower than that of the metal ceramic cutter which is commonly used on the Japan market, and the product performance is unstable, especially the obdurability is poor. Most high-grade cutters in the current Chinese cutter market are imported, but the cost of the imported cutters is quite expensive, and sometimes the imported cutters are matched with imported machine tools, so that the cost of workpiece processing is greatly increased.

With the increasing requirements of machining precision in the machining industry, the requirements on dimensional precision and uniformity of machining service performance of cutter products required by precision machining and high-end machining are more strict, so that the mechanical property index of the cutter needs to be accurately controlled. The control of carbon balance during the preparation of the cermet material significantly affects the final properties of the sintered body. The influence of the carbon content is mainly shown in the solid solution of the alloy elements of the binding phase in the sintering process, the composition and the grain size of the hard phase, the second stepThree-phase η -phase TiNi₃Or the formation of graphitic phases has a more pronounced effect. The heating body, the heat insulation box, the heat insulation layer, the support boat and the like of the current industrial furnace for sintering the metal ceramic or hard alloy products are all prepared from graphite or carbon materials. In the high-temperature sintering region, the components are released by heat to form a carbon atmosphere environment in the furnace, which causes carbon loss and carbon potential change in the sintered body, thereby affecting the grain size of the sintered body, solid solution strengthening of the binder phase and the hard phase, and formation of a third phase. According to the invention, the carbon atmosphere environment in the furnace is controlled by using the binder phase components and matching with the sintering process route, the carbon generated by cracking of methane gas at high temperature is fully used for controlling the carbon potential in the furnace, further the carbon loss and the recarburization in the sintered body are controlled, and the tissue evolution process and the final mechanical property are regulated and controlled, so that the homogeneous matrix material with high hardness and toughness matching combination performance is obtained. The sintered body is compact and has no air holes, the hard phase is connected by a reticular framework, the hard phase particles have a core-shell structure, and the production quality is stable.

Disclosure of Invention

In order to solve the above technical problems, the present invention provides a Ti (C, N) -based cermet material and a carbon balance control method thereof.

The scheme of the invention is as follows:

a Ti (C, N) -based cermet material comprising a hard phase having the formula (Ti, M) (C, N) wherein M is selected from the group consisting of W, Cr, Re, Ta in combination with a binder phase;

the binding phase is Ni-based solid solution, and the solute elements are Ti, W, Co, Cr, Re, Ta or the combination thereof.

Further, the cermet material comprises the following components in parts by mass: 34.0-51.8, W: 5.7-12.1, Co: 3.0-6.0, Cr: 0 to 1.0, Ni: 12.0 to 28.0, Ta: 0 to 10.0, Re: 0-10.0, C: 7.0-11.8, N:3.0 to 4.6; the material is prepared from the following raw material powder: ti (C, N) powder, (Ti, Re) (C, N) powder, TaC powder, WC powder, Cr powder₃C₂Powder, (Ta, Re) C powder, Ni powder, Co powder, Re powder and graphite powder.

The method for preparing the Ti (C, N) -based cermet material comprises the step of introducing methane into a sintering stage at 1000-1500 ℃ in the preparation process to control the carbon balance in a sintering body to prepare the Ti (C, N) -based cermet material.

A method for preparing the Ti (C, N) -based cermet material, comprising the steps of:

1) fully mixing the raw material powder in a ball milling tank by adopting a wet mixing process to obtain slurry, and drying the slurry to obtain a mixture;

2) pressing and forming the mixture in a die to obtain a pressed blank;

3) firing and forming the pressed compact in a vacuum sintering furnace;

4) cooling after sintering;

and finishing the preparation of the Ti (C, N) -based cermet material.

Further, the pressing pressure in the step 2) is 100-300 MPa.

Further, the material of the pressed compact carrying boat in the step 3) is graphite, so that a pure carbon environment in the furnace is ensured.

Further, a sintering low-temperature stage below 1000 ℃ in the step 3) and a cooling stage in the step 4) adopt a vacuum sintering mode, and the vacuum degree in the furnace is 10^-1～10^-2Pa。

Further, a step sintering process is adopted in the step 3) at a temperature of more than 1000 ℃, and methane gas is introduced. Mainly ensures the full separation of gas, the phase reaction among substances and the regulation of the carbon potential in the furnace during solid-phase sintering and liquid-phase sintering.

Further, the step 3) adopts a step sintering process at a temperature of more than 1000 ℃ specifically as follows: sectional heat preservation is respectively carried out at 1180-1280 ℃ and 1335-1365 ℃, the heat preservation time is 90-180 min and 20-30 min, so that gas is volatilized and removed as much as possible before a liquid phase appears in a sample, and the density of the material during subsequent sintering is improved; the sintering temperature is 1400-1500 ℃, and the heat preservation time is 50-90 min.

Still further, methane CH is introduced in the step 3) segmented sintering process₄The methane pressure in the furnace is 50-200 Pa (as a solid phase sintering stage) at 1000-1350 ℃ to remove the adsorbed oxygen in the sintered body, reduce the carbon loss of the sintered body and ensure the carbonBalancing; the temperature is higher than 1350 ℃ to the sintering temperature, the methane pressure in the furnace is 1-10 Pa (the liquid phase sintering stage), and the diffusion and solid solution of solute in the binding phase and the growth of hard phase grains are mainly controlled.

Further, in the step 4), the cooling method after sintering is as follows: firstly, rapidly cooling to prevent crystal grains from coarsening, wherein the cooling speed is 5-12 ℃/min; then slowly cooling to reduce the internal stress of the sample, wherein the cooling speed is 0.5-2 ℃/min; and then furnace cooling.

According to the control method for the carbon balance of the Ti (C, N) -based metal ceramic material, the carbon potential in the furnace is controlled by controlling the pressure of methane in the furnace in the high-temperature sintering stage, so that the carbon balance in a sintered body is controlled, and the structure evolution process and the final mechanical property of the sintered body are regulated and controlled. The obtained sintered body was dense without significant pores, and its structure was a typical cermet structure, as shown in fig. 1, with hard phase particles having a core-shell structure. The quality of the preparation process is stable.

The invention has the beneficial effects that:

1. the invention controls the carbon potential in the furnace by controlling the pressure of methane in the furnace in the high-temperature sintering stage, thereby controlling the carbon balance in the sintering body, and the sintering process is simple and easy to accurately control.

2. The invention makes full use of carbon formed by methane gas cracking to effectively remove oxygen in the sintered body, improves the density of the sintered body, has no obvious air holes in the sintered body, and can obviously improve the toughness of the metal ceramic material. The quality of the preparation process is stable.

3. The carbon loss and the carbon-nitrogen ratio of a hard phase and the solid solution amount and diffusion of alloy elements in a binding phase are regulated and controlled through the change of the carbon potential in the furnace, so that the effects of controlling the grain size of a sintered body and the solid solution strengthening effect of the binding phase are achieved, and higher mechanical properties are obtained through regulating and controlling the structure evolution process of the sintered body.

Drawings

FIG. 1 is a scanning electron microscope histological image of a sintered body of the material of the present invention;

FIG. 2 is a schematic diagram of the sintering process and methane pressure distribution of example 1;

FIG. 3 is a metallographic structure of a sintered body according to example 1 of the present invention;

FIG. 4 is an XRD pattern of a surface layer of a sintered body of example 1 of the present invention;

FIG. 5 is a metallographic structure of a sintered body according to example 2 of the present invention;

FIG. 6 is a scanning electron microscope structure of a sintered body of example 2 of the present invention;

FIG. 7 is an XRD pattern of sintered bodies of examples 2 and 4 of the present invention.

Detailed Description

The invention is further illustrated by the following examples, but the scope of the invention as claimed is not limited to the scope of the examples.

Example 1

Firstly, preparing a mixture: adopts Ti (C, N) powder, (Ti, Re) (C, N) powder, WC powder and Cr powder₃C₂Preparing raw materials such as powder, Ni powder, Co powder, Re powder, graphite powder and the like, preparing a mixture of Ti 51.8, W5.8, Co 3.0, Cr 0.6, Ni 22.0, Re 0.7, C11.5 and N4.6 in parts by weight, adopting absolute ethyl alcohol as a ball milling medium, adopting the proportion of absolute ethyl alcohol to alcohol material ratio of 0.7: 1, adopting YG8 hard alloy balls as grinding balls and the ball material ratio of 7: 1, mixing on a planetary ball mill, rotating at a speed of 200r/min for 36 hours, obtaining the mixture, drying in an oven at a temperature of 80 ℃, pressing the mixture into a shape under a certain pressure (160MPa), putting the pressed compact into a vacuum carbon tube furnace for vacuum sintering, wherein the schematic diagram of the sintering process is shown in figure 2, the vacuum degree in the furnace below 1000 ℃ is 4.0 × 10^-2Pa, introducing methane gas at a temperature of above 1000 ℃, introducing methane gas at a pressure of 250Pa in a furnace at a temperature of 1000-1350 ℃, performing secondary heat preservation at a temperature of 1280 ℃ and 1350 ℃ respectively for 90min and 20min, preserving heat at a temperature of 1420 ℃ for 90min, and preserving heat at a temperature of 1350 ℃ to the sintering temperature range, wherein the pressure of the methane atmosphere after sintering is 2 Pa., the cooling method adopts a combined mode of sectional control cooling-quick cooling and slow cooling, wherein the cooling speed is 10 ℃/min, the slow cooling speed is 0.7 ℃/min, the furnace cooling is performed later, and the vacuum degree in the cooling stage is 1.0 × 10^-2Pa。

The carbon potential in the furnace is controlled by introducing methane atmosphere at the high temperature stage because the methane can be cracked at the high temperature:

CH₄→C+2H₂ΔH＝90.5kJ/mol,ΔG＝—10.492kJ/mol

the metal ceramic binding phase mainly comprises Ni, wherein Ni atoms have unfilled d electron orbitals and can accept C-H sigma electrons in methane molecules, so that C-H bonds in the methane molecules are weakened to break, and the metal ceramic binding phase can serve as a catalyst for methane cracking at high temperature. Co and Re in the binder phase component enhance the catalytic action of Ni. The following reforming reaction can thus be produced at the cermet sintered body surface site S:

CH₄+S→C_adsorption+2H₂

O_Adsorption+C_Adsorption→CO+S

C adsorbed on the cermet diffuses into the sample, part of the C can balance the carbon potential in the sintered body, and part of the C can remove the oxygen adsorbed in the sintered body.

FIG. 3 is a metallographic structure of the obtained sintered body, in which a black flocculent graphite phase distributed in the structure can be clearly seen; fig. 4 shows a surface XRD pattern of the sintered body, indicating that a large amount of graphite phase and binder phase Ni are present on the surface of the sintered body. Therefore, the mixture of the component can be concluded to precipitate a great deal of metal Ni, CH on the surface in the sintering process of higher carbon atmosphere₄The reforming reaction proceeds by the catalytic action of the binder phase Ni to deposit carbon (graphitic carbon) on the surface of the sintered body, thereby causing the formation of a large amount of Ni phase and graphitic phase on the surface layer of the sintered body. The carbon on the surface layer diffuses into the sintered body to cause the C content in the sintered body to be too high to form a flocculent graphite phase. The mechanical property indexes of the obtained sintered body are as follows: hardness 1516HV, bending strength 1284MPa, fracture toughness K_IC7.6MPa·m^1/2。

Example 2

The ingredient combinations, compounding methods, preparation processes and sintering routes of example 1 were used. In the sintering process of the embodiment 2, the methane pressure in the furnace is adjusted at the solid phase sintering stage of 1000-1350 ℃, and the methane atmosphere pressure is reduced to 200 Pa; the methane atmosphere pressure in the liquid phase sintering stage is the same as that in example 1; the cooling rate in the slow cooling stage was increased from 0.7 ℃/min to 1.3 ℃/min, and the vacuum degree was the same as in example 1.

FIG. 5 shows the metallographic structure of the sintered body, which is dense and free of defects. Fig. 6 shows the SEM structure of the sintered body, and further confirms that the sintered body structure is dense, and no graphite phase and other phases are found. Fig. 7 shows an XRD pattern of the sintered body, which indicates that the sintered body has a two-phase structure, a hard phase of Ti (C, N), and a binder phase of Ni solid solution, and that no graphite phase and other phases are present. The mechanical property indexes of the obtained sintered body are as follows: hardness 1461HV, bending strength 2130MPa, fracture toughness K_IC9.0MPa·m^1/2. The properties of the sintered body, particularly the flexural strength and toughness, are greatly improved. The method can definitely adjust and control the carbon potential in the furnace and influence the carbon loss in the sintered body through the methane atmosphere pressure in the high-temperature section segmented sintering process, thereby adjusting the tissue composition and the final performance of the sintered body.

Example 3

Changing the component proportion of the raw materials, and preparing the cermet with the following components in parts by weight: 48.7, Ni: 20.5, Co: 4.3, W:8.9, C:10.8, N:4.3, Cr: 0.6 percent of Re:1.9, the material mixing process, the preparation process and the sintering route are the same as those of the embodiment 1, and the methane pressure in the furnace is reduced to 70Pa in the solid phase sintering stage at the temperature of 1000-1350 ℃; the methane atmosphere pressure and cooling stage of the liquid phase sintering stage were the same as in example 1. Through analysis, the metallographic structure and the scanning structure of the sintered body have no other phase, and are typical of the two-phase structure of the cermet. The mechanical property indexes of the sintered body are as follows: hardness 1489HV, bending strength 1930MPa, fracture toughness K_IC8.8MPa·m^1/2. Compared with example 1, the content of Ti, which is a main carbide-forming element, was reduced by adjusting the ratio of binder phase components in the starting material, and the adsorption of carbon on the surface of the sintered body was suppressed by using an appropriate methane atmosphere pressure, thereby obtaining a sintered body having high toughness.

Example 4:

the components and the composition in the embodiment 3 are adopted, the material mixing method, the preparation process and the sintering route are the same as those in the embodiment 1, the high-temperature sectional sintering is adjusted as follows, and the methane pressure in a furnace is adjusted to 160Pa in the sintering stage at 1000-1350 ℃; the methane atmosphere pressure is 5Pa from 1350 ℃ to the sintering temperature; sintering system and vacuum degree in cooling stageThe same as in example 2. The mechanical property indexes of the sintered body are as follows: hardness 1530HV, bending strength 1880MPa, fracture toughness K_IC8.7MPa·m^1/2. Compared with example 3, the bending strength of the sintered body was slightly reduced by adjusting the sintering process route, but the hardness was significantly improved and the fracture toughness was comparable.

Comparative examples 1 to 7:

two groups of raw materials are prepared, and the raw materials respectively comprise: comparative example component 1 was a titanium alloy containing, in parts by mass, 34.0 parts of Ti, Ni: 26.5, Co: 6.0, W:11.4, C:7.5, N:3.0, Ta:8.6, Re: 3.0; comparative example composition 2, Ti: 41.0, Ni: 13.6, Co: 3.9, W: 12.1, C: 9.1, N: 3.7, Cr: 0.7, Ta: 8.3, Re: 7.6, respectively carrying out three groups of sintering processes on the two groups of samples of the comparative example, wherein the route of the first group of sintering processes is as in example 3; the second set of sintering routes was as in example 2; the third set of sintering process routes were adjusted as follows: in the segmented sintering process at the temperature of more than 1000 ℃, the methane atmosphere pressure is 100 Pa; the temperature of 1350 ℃ to the sintering temperature range, and the methane atmosphere pressure is 8 Pa; the sintering temperature is 1450 ℃, and the temperature is kept for 60 min. The cooling after sintering was performed in the same manner as in example 1. As described above, a cermet sintered body having a typical composition of a two-phase structure was obtained, and the properties of the obtained sintered body are shown in Table 1:

table 1 performance test results of the sintered bodies of comparative examples

Comparative example	Combination of ingredients	Sintering process route	Hardness HV	Bending strength MPa	Fracture toughness MPa m^1/2
						Comparative example 1	Component 1	Example 1 route	1451	2102	12.2
Comparative example 2	Component 1	Example 2 route	1447	2412	12.7
						Comparative example 3	Component 1	Third set of routes	1485	2702	13.1
Comparative example 4	Component 2	Example 1 route	1671	1651	7.2
						Comparative example 5	Component 2	Example 2 route	1702	1800	7.8
Comparative example 6	Component 2	Third set of routes	1723	1890	8.0

Comparative example 7:

the ingredient combinations, compounding methods, preparation processes and sintering routes of example 1 were used. In the sintering process of comparative example 7, a vacuum sintering process was employed from 1000 ℃ or higher to the sintering temperature, and the degree of vacuum was maintained at 10^-1～10^-2XRD test shows that the obtained hard phase of the sintered body has a lattice constant of 4.2773 × 10^-10m, it can be seen that N-rich hard phase particles are formed. And the sintered body surface showed a golden yellow-like color due to a large carbon loss (the reason why Ti (C, N) is decarburized to form TiN). The mechanical property indexes of the sintered body are as follows: hardness 1456HV, flexural strength 1356MPa, fracture toughness K_IC7.2MPa·m^1/2。

The above-described embodiments are merely preferred embodiments of the present invention, and should not be construed as limiting the present invention, and the scope of the present invention is defined by the claims, and equivalents including technical features described in the claims. I.e., equivalent alterations and modifications within the scope hereof, are also intended to be within the scope of the invention.

Claims

1. A preparation method of a Ti (C, N) -based cermet material is characterized by comprising the following steps: the material comprises a hard phase and a binding phase, wherein the chemical formula of the hard phase is (Ti, M) (C, N), and M is selected from one or more of W, Cr, Re and Ta;

the bonding phase is Ni-based solid solution, and solute elements of the bonding phase are Ti, W, Co, Cr, Re or Ta or the combination of Ti, W, Co, Cr, Re or Ta; the cermet material comprises the following components in parts by mass: 34.0-51.8, W: 5.7-12.1, Co: 3.0 to 6.0, Cr: 0 to 1.0, Ni: 12.0 to 28.0, Ta: 0 to 10.0, Re: 0-10.0, C: 7.0-11.8, N:3.0 to 4.6; the material is prepared from the following raw material powder: ti (C, N) powder, (Ti, Re) (C, N) powder, TaC powder, WC powder, Cr powder₃C₂Powder, (Ta, Re) C powder, Ni powder, Co powder, Re powder or graphite powder; the method is characterized in that methane is introduced during sintering at 1000-1500 ℃ in the preparation process to control the carbon balance in a sintering body to prepare the Ti (C, N) -based cermet material.

2. The method of claim 1, comprising the steps of:

2) pressing and forming the mixture in a die to obtain a pressed blank;

3) firing and forming the pressed compact in a vacuum sintering furnace;

4) cooling after sintering;

and finishing the preparation of the Ti (C, N) -based cermet material.

3. The method of claim 2, wherein: and 3) the pressed compact carrier in the step 3) is made of graphite.

4. The method of claim 2, wherein: the sintering low-temperature stage below 1000 ℃ in the step 3) and the cooling stage in the step 4) adopt a vacuum sintering mode, and the vacuum degree in the furnace is 10^-1~10^-2Pa。

5. The method of claim 2, wherein: and 3) adopting a segmented sintering process at the temperature of more than 1000 ℃ in the step 3) and introducing methane gas.

6. The method of claim 5, wherein: the step 3) is implemented by adopting a step sintering process at 1000 ℃ or above, and comprises the following steps: setting sectional heat preservation at 1180-1280 ℃ and 1335-1365 ℃, wherein the heat preservation time is 90-180 min and 20-30 min respectively; the sintering temperature is 1400-1500 ℃, and the heat preservation time is 50-90 min.

7. The method of claim 6, wherein: introducing methane CH in the step 3) segmented sintering process₄The methane pressure in the furnace is 50-200 Pa at 1000-1350 ℃; the temperature is higher than 1350 ℃ to the sintering temperature, and the methane pressure in the furnace is 1-10 Pa.

8. The method according to claim 2, wherein in the step 4), the cooling manner after sintering is as follows: firstly, rapidly cooling at a cooling speed of 5-12 ℃/min; then slowly cooling at the cooling speed of 0.5-2 ℃ per min; and then furnace cooling.