CN106756168B - The method that one kind prepares Ti (C, N) based ceramic metal based on carbon thermal reduction molybdenum trioxide - Google Patents

Abstract

The invention discloses a method for preparing Ti(C,N)-based cermet based on carbothermal reduction of molybdenum trioxide. The mass parts of the cermet are as follows: Ti is 31.5-39.7, C is 10.6-11, and N is 3.6 ~4.6, O is 5.4~6.6, Ni is 22~31, Mo is 10~12.4, W is 4.2~7.7. The characteristics of the preparation method are: when preparing the mixture, molybdenum trioxide is used as the molybdenum source, and it is directly added to the mixture, and then the mixture is mixed, the molding agent is added, the molding is pressed, the molding agent is removed, and a special combination is adopted Vacuum sintering method to obtain dense cermet sintered body. The invention can greatly reduce the production cost, effectively improve the microstructure of the cermet, improve its mechanical properties, and has broad application prospects.

Description

A method for preparing Ti(C,N)-based cermets based on carbothermal reduction of molybdenum trioxide

technical field

The invention relates to a method for preparing Ti(C,N)-based cermets based on carbothermal reduction of molybdenum trioxide, which belongs to the technical field of powder metallurgy.

Background technique

Ti(C,N)-based cermets have the advantages of low density, high red hardness, high wear resistance, high temperature creep resistance and oxidation resistance, low friction coefficient with metal, and good corrosion resistance. , molds, wear-resistant parts, corrosion-resistant devices and many other fields have broad application prospects. If used as a tool material, compared with commonly used carbide tools, it can allow higher cutting speed and larger feed rate, higher resistance to crater wear, and better surface quality of the processed workpiece; As a mold material, it not only has high red hardness, excellent thermal stability and oxidation resistance, but also has good toughness; if it is used as a wear-resistant and corrosion-resistant material, its service life is longer than other similar materials. In recent years, the development of Ti(C,N)-based cermets in various countries in the world is very rapid.

The main problem of the currently developed Ti(C,N)-based cermets is that under the condition of maintaining a certain hardness, the flexural strength and fracture toughness are still low, so that the theoretical advantages have not been fully utilized, resulting in Its scope of application is limited. In recent years, some researchers have tried to introduce various whiskers, carbon nanotubes, etc. into Ti(C,N)-based cermets to achieve strengthening and toughening of cermets. Although the above methods have obtained relatively good experimental results, the strength and toughness of Ti(C,N)-based cermets have been improved to a certain extent. However, additives such as whiskers and carbon nanotubes are expensive, and the purity needs to be further improved, and they are extremely easy to absorb oxygen and agglomerate. Before being added to the mixture, pretreatments such as impurity removal, deoxidation and dispersion must be carried out. The above-mentioned additives are not only very expensive, but also difficult to distribute evenly in the mixture, which greatly increases the preparation cost of cermets and significantly increases the complexity of the preparation process, and in mass production, it is easy to form metallurgical defects and produce defective products, so So far, it is difficult to obtain practical application in the industrial field. On the other hand, some researchers have prepared fine-grained Ti(C,N)-based cermets by using special sintering methods such as hot pressing sintering, low pressure-hot isostatic pressing sintering, and spark plasma sintering, so that the properties of the material can be improved to a certain extent. However, these special sintering methods have high requirements for equipment, large initial investment, and significantly increased production costs.

In view of the above, in order to make Ti(C,N)-based cermets can be applied in more fields, it is necessary to conduct further research on this material and develop a high-performance and low-cost Ti(C,N)-based Cermet.

Contents of the invention

In view of the above technical problems, the object of the present invention is to provide a method for preparing Ti(C,N)-based cermets based on carbothermal reduction of molybdenum trioxide. The method can prepare a Ti(C,N)-based cermet with high comprehensive mechanical properties and stable performance, and the manufacturing cost is low.

The technical solution that realizes the object of the present invention is:

A method for preparing Ti(C,N)-based cermets based on carbothermal reduction of molybdenum trioxide, the specific steps are as follows:

1) Prepare the mixture, including the following components in parts by mass: Ti is 31.5-39.7, C is 10.6-11, N is 3.6-4.6, O is 5.4-6.6, Ni is 22-31, Mo is 10-12.4 , W is 4.2～7.7;

When preparing the mixture of the above components, the raw materials used are Ti(C,N) solid solution powder, _MoO3 powder, WC powder, Ni powder, and the particle size of the powder is micron;

2) Mixing in a planetary ball mill, the speed of the ball mill is 300-400rpm, and the time is 24-36h;

3) Adding a molding agent, the concentration of the molding agent is 7wt.% polyvinyl alcohol aqueous solution, and the addition ratio is 3-5wt% of the mixture;

4) Pressing and molding under a pressing pressure of 150-200 MPa;

5) The molding agent is removed in a vacuum furnace with a vacuum degree higher than 10Pa, and the heating rate between 200 and 400 °C is 0.3 to 0.4 °C/min;

6) Vacuum sintering, carried out in a vacuum sintering furnace, the vacuum degree is higher than 1.0×10 ^-2 Pa; the vacuum sintering is divided into four stages, first, continue to heat up the green compact from which the molding agent has been removed to 600-800°C , keep warm for 2-4h; then raise the temperature to 1200-1240°C, keep warm for 1-2h; then raise the temperature to 1400-1440°C, keep warm for 0.5-1h; finally, the furnace temperature is rapidly dropped to 1000°C at a cooling rate of 20°C/min Hereinafter, a Ti(C,N)-based cermet is obtained.

To achieve this purpose, when preparing the mixture in step 1) of the present invention, the Mo in the mixture is introduced in the form of _MoO3 powder. In general, in Ti(C,N)-based cermets, oxygen is regarded as a harmful element because they can increase the wetting angle between the hard phase and the binder phase during liquid phase sintering, reducing the Its wettability will deteriorate the structure and performance of the material, so the oxygen content in the powder is reduced as much as possible in the process of preparing cermets. The present invention introduces Mo and O elements into the Ti(C,N)-based cermet mixture in the form of MoO ₃ powder, and simultaneously introduces the corresponding content of C in the form of graphite powder. By reasonably controlling the sintering process, the MoO ₃ powder The following solid phase reaction occurs with graphite powder before 800°C: MoO ₃ +C→MoO ₂ +CO; MoO ₂ +2C→Mo+2CO; 2Mo+C→Mo ₂ C, remove O and combine with C in situ Mo ₂ C is generated. At this time, the sintered body is still in the early stage of solid-phase sintering, its relative density is low, and the pores are open. The gas generated by the reaction can escape smoothly under vacuum conditions, and will not adversely affect the subsequent liquid-phase sintering. . At the same time, the reducing gas CO released during the carbothermal reduction process of the introduced large amount of graphite powder and MoO ₃ powder can make the adsorbed oxygen on the surface of other original powders be removed more thoroughly, and the gap between the ceramic phase and the metal binder phase can be purified. The interface can effectively improve the microstructure of the cermet and enhance the bonding strength of the phase interface, so as to achieve the purpose of improving the toughness of the Ti(C,N)-based cermet.

In order to achieve this purpose, the preparation method has the following characteristics: vacuum sintering is divided into four stages. First, the temperature of the green compact removed from the molding agent is raised to 600-800°C, and the temperature is kept for 2-4 hours; ~2h; then raise the temperature to 1400~1440°C, keep it warm for 0.5~1h; finally, quickly drop the furnace temperature below 1000°C at a cooling rate of 20°C/min. Keeping at 600-800°C for 2-4 hours is to allow MoO ₃ powder and _graphite powder to generate Mo ₂ C through in-situ carbothermal reduction reaction; 1. The solid solution of WC and Ti(C,N) in the mixture forms an inner annular phase on the surface of the ceramic hard phase particles through solid phase reaction, so as to improve the wettability of the metal bond relative to the ceramic phase in the subsequent liquid phase sintering stage, and prevent The crystal grains aggregate and grow; the temperature is raised to 1400-1440°C, and the temperature is kept for 0.5-1h to make the cermet enter the liquid phase sintering stage, and complete the densification and uniform structure of the sintered body; finally, the furnace is cooled at a cooling rate of 20°C/min. The rapid temperature drop below 1000 °C is to make the sintered body solidify quickly and prevent the ceramic hard phase from staying in the liquid phase for too long and growing excessively through the dissolution-precipitation mechanism.

The beneficial effects of the present invention are:

1. The Ti(C,N)-based cermet prepared based on carbothermal reduction of molybdenum trioxide provided by the present invention has high comprehensive mechanical properties, and its hardness, flexural strength and fracture toughness can be adjusted according to the performance of different application fields Adjust as required. The prepared cermet material not only has the advantages of good red hardness, high wear resistance, strong oxidation resistance, and low friction coefficient with metals, but also has significantly improved strength, toughness and performance stability. It can not only be used in the field of tool cutting, but also It can be applied to fields such as mining, petroleum, and coal mining, and can also be widely used as wear-resistant parts, high-temperature-resistant parts, and corrosion-resistant parts.

2. The Ti(C,N)-based cermet prepared based on carbothermal reduction of molybdenum trioxide provided by the present invention does not contain precious elements, and the price of _MoO3 powder used as Mo source is cheaper than Mo powder or _Mo2C powder, and the raw material The cost is lower.

3. The Ti(C,N)-based cermet prepared based on carbothermal reduction of molybdenum trioxide provided by the present invention is prepared by a conventional vacuum sintering method, which has no special requirements for production equipment and is conducive to industrial promotion and application; the process is simple and can be used in Completed in a complete thermal cycle, it can significantly save energy consumption, reduce production costs and increase productivity.

Detailed ways

Below in conjunction with example further illustrate technical effect of the present invention. The raw materials used in the following examples are Ti(C,N) powder, Ni powder, MoO ₃ powder, WC powder, graphite powder.

Table 1 is a mix of 4 ingredient formulations. Three different process parameters of Examples 1-3 were used to prepare it into Ti(C,N)-based cermets, and their hardness, flexural strength and palmqvist fracture toughness were measured respectively, wherein 1 ^# and 2 ^# in the composition formula The metal bonding phase is low and the hardness is high. It is suitable for cutting tools and wear-resistant parts. The 3 ^# and 4 ^# composition formulas have a high metal bonding phase and good strength and toughness. They are suitable for making mines, petroleum, and coal mining. Parts needed in other fields.

The composition formula of four kinds of mixtures of table 1

Element Ti C N o Ni Mo W 1 ^# 39.7 10.6 4.6 5.4 twenty two 10 7.7 2 ^# 37.2 11 4.3 5.8 25 10.8 5.9 3 ^# 33.2 10.8 3.9 6.4 28 11.6 6.1 4 ^# 31.5 10.7 3.6 6.6 31 12.4 4.2

Example 1:

1. Prepare 4 kinds of mixtures according to Table 1;

2. Put the mixture in a planetary ball mill for mixing, the speed of the ball mill is 300rpm, and the time is 36h;

3. Add molding agent: the molding agent adopts polyvinyl alcohol aqueous solution with a concentration of 7wt.%, and the addition amount is 3wt% of the mixture;

4. Compression molding: the pressure used for compression molding is 150MPa;

5. Removal of molding agent: The removal of molding agent is carried out in a vacuum sintering furnace, the vacuum degree is higher than 10Pa, and the heating rate between 200 and 400°C is 0.3°C/min;

6. Vacuum sintering: carried out in a vacuum sintering furnace, the vacuum degree is higher than 1.0×10 ^-2 Pa. Vacuum sintering is divided into four stages. Firstly, the green compact from which the molding agent has been removed is heated up to 600°C and held for 4 hours; then the temperature is raised to 1240°C and held for 1 hour; then the temperature is raised to 1440°C and held for 30 minutes; The cooling rate of min quickly lowers the furnace temperature below 1000°C to obtain Ti(C,N)-based cermets.

Under the above-mentioned preparation process conditions, the mechanical properties of cermets with different composition formulations are shown in Table 2.

Table 2 Mechanical properties of different cermets prepared by process 1

Element 1 ^# 2 ^# 3 ^# 4 ^# Bending strength σ _b (MPa) 1715 1938 2217 2461 Hardness (HRA) 92.3 91.1 89.7 88.0 Fracture toughness (MN m ^-3/2 ) 12.4 14.6 17.9 22.3

Example 2:

1. Prepare 4 kinds of mixtures according to Table 1;

2. Put the mixture in a planetary ball mill for mixing, the speed of the ball mill is 350rpm, and the time is 30h;

3. Add molding agent: the molding agent adopts polyvinyl alcohol aqueous solution with a concentration of 7wt.%, and the addition amount is 4wt% of the mixture;

4. Compression molding: the pressure used for compression molding is 180MPa;

5. Removal of molding agent: The removal of molding agent is carried out in a vacuum sintering furnace, the vacuum degree is higher than 10Pa, and the heating rate between 200 and 400°C is 0.4°C/min;

6. Vacuum sintering: carried out in a vacuum sintering furnace, the vacuum degree is higher than 1.0×10 ^-2 Pa. Vacuum sintering is divided into four stages. Firstly, the green compact from which the molding agent has been removed continues to be heated to 700°C and kept for 3 hours; then the temperature is raised to 1220°C and kept for 1.5h; then the temperature is raised to 1420°C and kept for 40 minutes; The cooling rate of /min quickly lowers the furnace temperature below 1000°C to obtain Ti(C,N)-based cermets.

Under the above-mentioned preparation process conditions, the properties of cermets with different composition ratios are shown in Table 3.

Table 3 Mechanical properties of different cermets prepared by process 2

Element 1 ^# 2 ^# 3 ^# 4 ^# Bending strength σ _b (MPa) 1724 2017 2256 2473 Hardness (HRA) 92.1 91.0 89.5 88.2 Fracture toughness (MN m ^-3/2 ) 11.8 14.3 18.1 22.5

Example 3:

1. Prepare 4 kinds of mixtures according to Table 1;

2. Put the mixture in a planetary ball mill for mixing, the speed of the ball mill is 400rpm, and the time is 24h;

3. Add molding agent: the molding agent adopts polyvinyl alcohol aqueous solution with a concentration of 7wt.%, and the addition amount is 5wt% of the mixture;

4. Compression molding: the pressure used for compression molding is 200MPa;

5. Removal of molding agent: The removal of molding agent is carried out in a vacuum sintering furnace, the vacuum degree is higher than 10Pa, and the heating rate between 200 and 400°C is 0.4°C/min;

6. Vacuum sintering: carried out in a vacuum sintering furnace, the vacuum degree is higher than 1.0×10 ^-2 Pa. Vacuum sintering is divided into four stages. Firstly, the green compact from which the molding agent has been removed is heated up to 800°C and kept for 2h; then the temperature is raised to 1200°C and kept for 2h; The cooling rate of min quickly lowers the furnace temperature below 1000°C to obtain Ti(C,N)-based cermets.

Under the above-mentioned preparation process conditions, the properties of cermets with different composition ratios are shown in Table 4.

Table 4 Mechanical properties of different cermets prepared by process 3

Element 1 ^# 2 ^# 3 ^# 4 ^# Bending strength σ _b (MPa) 1709 1997 2233 2469 Hardness (HRA) 92.0 91.2 89.4 88.1 Fracture toughness (MN m ^-3/2 ) 12.1 14.1 18.3 21.9

Within the value range of this right, the technical parameters of the first stage of the sintering process have a relatively large impact on performance, only when the sintering temperature and holding time at this stage are matched reasonably (when the holding temperature is high, the time is shortened accordingly; the holding temperature When the time is lower, the time should be extended appropriately), and the cermets with the above-mentioned composition formulas can obtain relatively good comprehensive mechanical properties. In short, within the scope of the claims, the above-mentioned process factors have limited influence on the mechanical properties of the material.

The above-mentioned embodiments are only used to illustrate the content of the present invention, not to limit, so any changes within the meaning and scope equivalent to the claims of the present invention should be considered to be included in the scope of the claims.

There are many specific application approaches of the present invention, and the above description is only a preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, some improvements can also be made without departing from the principles of the present invention. If other components are replaced by corresponding oxides, and the oxides are reduced by in-situ carbothermal reduction during the sintering process, these improvements should also be regarded as the protection scope of the present invention.

Claims (5)

1. a method for preparing Ti(C,N)-based cermets based on carbothermal reduction of molybdenum trioxide, is characterized in that comprising the following steps: 1) Prepare the mixture, including the following components in parts by mass: Ti is 31.5-39.7, C is 10.6-11, N is 3.6-4.6, O is 5.4-6.6, Ni is 22-31, Mo is 10-12.4 , W is 4.2 to 7.7; when preparing the mixture of the above components, the raw materials used are Ti(C,N) solid solution powder, MoO ₃ powder, WC powder, Ni powder, and graphite powder; 2) mixing; 3) Add molding agent; 4) Compression molding; 5) Remove molding agent; 6) Vacuum sintering, carried out in a vacuum sintering furnace, the vacuum degree is higher than 1.0×10 ^-2 Pa; the vacuum sintering is divided into four stages, firstly, continue to heat up the green compact from which the molding agent has been removed to 600-800°C , keep warm for 2-4h; then raise the temperature to 1200-1240°C, keep warm for 1-2h; then raise the temperature to 1400-1440°C, keep warm for 0.5-1h; finally, the furnace temperature is rapidly dropped to 1000°C at a cooling rate of 20°C/min Hereinafter, a Ti(C,N)-based cermet is obtained. 2. The method for preparing Ti(C,N)-based cermets based on carbothermal reduction of molybdenum trioxide according to claim 1, characterized in that: the mixing process in step 2) is carried out in a planetary ball mill, The speed of the ball mill is 300-400rpm, and the time is 24-36h. 3. The method for preparing Ti(C,N)-based cermets based on carbothermal reduction of molybdenum trioxide according to claim 1, characterized in that: the forming agent used in step 3) is polyethylene with a concentration of 7wt.% Alcohol aqueous solution, the addition ratio is 3-5wt% of the mixture. 4. The method for preparing Ti(C,N)-based cermets based on carbothermal reduction of molybdenum trioxide according to claim 1, characterized in that: the pressing pressure used in the pressing forming process in the step 4) is 150-200 MPa. 5. The method for preparing Ti(C,N)-based cermets based on carbothermal reduction of molybdenum trioxide according to claim 1, characterized in that: in the step 5), the forming agent removal process is performed at a vacuum degree higher than 10Pa It is carried out in a vacuum furnace with a heating rate of 0.3-0.4°C/min between 200°C and 400°C.