CN113201676B - Preparation method of high-temperature oxidation-resistant low-bonding-phase metal ceramic - Google Patents

Abstract

The invention discloses a preparation method of a low-binding phase Ti(C,N)-based composite cermet with high temperature oxidation resistance, belonging to the technical field of cermet materials and powder metallurgy. The Ti(C,N)-based composite cermet preparation method of the present invention goes through the steps of raw material proportioning, wet grinding, baking, pressing and partial pressure sintering, etc., by adjusting the content of Mo ₂ C and Co, and using partial pressure sintering. In this way, a Ti(C,N)-based cermet with relatively high oxidation resistance is formed. The low-binding phase Ti(C,N)-based composite cermet with high temperature oxidation resistance of the present invention has the following components by weight: Ti(C _0.5 N _0.5 ): 35-65%, WC: 15-35%, Mo ₂ C: 10-15%, Co: 10-15%, Ni: 10-20%, graphite 0.8-1.0%. The Ti(C,N)-based composite cermet prepared by the invention not only has good compactness. At the same time, it also excels in high temperature oxidation resistance, which has positive significance in semi-finishing cutting tool materials for special steels.

Description

A kind of preparation method of high temperature oxidation resistance low binding phase cermet

technical field

The invention belongs to the preparation of Ti(C,N)-based cermet materials, in particular to a low-binding phase Ti(C,N)-based cermet with high temperature oxidation resistance and a preparation method thereof.

Background technique

In recent years, with the improvement of machine tool performance, the cutting speed is getting faster and faster, and the cutting temperature is also rising, and the temperature near the cutting edge can be as high as 1000 ℃. In this case, the tool material is easily oxidized, which will cause tissue changes, resulting in a decrease in tool performance, and even failure of the tool edge. High-speed cutting requires that the cutting tool material must have good high-temperature oxidation resistance and high-temperature mechanical properties. Existing cemented carbide tools are difficult to meet the demands of working at higher cutting speeds and larger feed rates. Ti(C,N)-based cermets have excellent high temperature stability and are gradually replacing cemented carbides for high-speed cutting. Therefore, the high-temperature oxidation resistance of Ti(C,N)-based cermets has become an important factor in determining their commercial applications.

Ti(C,N)-based cermets are a class of functional structural materials with intermetallic compounds as hard phases and Ni and Co as binder phases. Its excellent mechanical properties make it particularly prominent in the comparison of cemented carbide, with high hardness, high flexural strength and good wear resistance in terms of mechanical properties. The characteristics at high temperature have high oxidation resistance and heat resistance; and it is not easy to generate chips when cutting as a tool; in terms of comprehensive performance, cermet materials are better than cemented carbide.

In recent years, cermets, especially Ti(C,N)-based cermets, have made great breakthroughs in cutting tool materials and become the most potential tool materials to replace WC-Co. The superior wear resistance and high temperature stability not only improve the service life of the tool, but also achieve the effect of improving the quality of the cutting surface of the tool. Cermets with low binder phase (≤20%) have high hardness while taking into account the strength and fracture toughness, and are widely used in turning tools and milling tools. However, the sintering process of cermet also plays a crucial role in its comprehensive mechanical properties.

Therefore, it is more important to study the sintering atmosphere. The partial pressure sintering of Ti(C,N)-based cermets is mainly sintered in an argon atmosphere in the solid phase sintering stage, and rapid cooling is used during cooling. It is beneficial to the formation of the core-ring phase, which has a certain positive significance for the stability control of mechanical properties. In this patent, the atmosphere sintering experiment is carried out in the solid phase sintering stage where the alloy has not yet been densified. In the solid phase sintering stage, vacuum and argon gas atmospheres are used for the experiment. In the liquid phase stage, nitrogen partial pressure sintering is used to create a nitrogen atmosphere to suppress nitrogen gas. The volatilization of Ti(C,N)-based cermet improves its compactness, which has a certain positive significance for the quality and stability control of Ti(C,N)-based cermets. At the same time, the effect of the ratio of Mo and Co on its oxidation resistance was also studied.

SUMMARY OF THE INVENTION

The present invention provides a partial pressure sintered Ti(C,N)-based cermet, as well as a raw material ratio and a preparation method thereof, so as to make the Ti(C,N)-based cermet not only have good mechanical properties, but also have Excellent antioxidant properties.

The purpose of the present invention is to overcome the deficiencies of the existing cermets with low fracture toughness through partial pressure sintering, and to provide a preparation method of a low-binding phase Ti(C,N)-based composite cermet with high temperature oxidation resistance, using the method of the present invention. According to the technical solution, the produced tool material not only has good compactness, but also has high strength, toughness and high temperature oxidation resistance, and can be applied to the semi-finishing cutting tool material of steel.

In order to achieve the above purpose, a method for preparing a low-binding phase Ti(C,N)-based composite cermet with high temperature oxidation resistance of the present invention comprises the following steps:

(1) Mixing powder: Weigh Ti (C _0.5 N _0.5 ) powder, WC powder, Mo ₂ C powder, Co powder, Ni powder, graphite and cemented carbide balls and ball-mill in absolute ethanol to obtain slurry, which is dried , pass at least 80 mesh sieve to obtain powder; the weight percentage of the raw material is: Ti(C _0.5 N _0.5 ): 35-65%, WC: 15-35%, Mo ₂ C: 10-15%, Co: 10- 15%, Ni: 10-20%, Graphite 0.8-1.0%. In step (1), cemented carbide balls are added in a ratio of 1:5 to 1:7, the big and small cemented carbide balls are mixed at 1:1, and the mixed materials are wet-milled on a planetary ball mill, and the rotational speed is set to 220r/ min, set forward and reverse rotation, the interval between forward and reverse rotation is 25 minutes, and wet grinding on a ball mill for 24 to 36 hours.

(2) Pressing: put the powder into the embryo after drying, and press and shape; in the process of pressing, first press under the pre-pressure of 2000-2800N, and then press and mold under the pressure of 200MPa-220Mpa for 45-60s.

(3) Partial pressure sintering: place the pressed embryo in a pressure sintering furnace for partial pressure sintering, the vacuum degree should be less than 5Pa, the furnace temperature is heated from room temperature to 1200 ° C, and then heated to 1200 ~ 1260 ° C for low argon separation. Press sintering, then heat up to 1260~1350℃ for vacuum or low argon partial pressure sintering, further heat up to 1350~1490℃ for nitrogen partial pressure sintering, 1490℃ for nitrogen partial pressure sintering, keep for 1~2h and then cool to room temperature to obtain high temperature Oxidation resistant low binder phase cermet.

The heating rate of each stage described in step (3) is: normal temperature～1200 ℃ is 3～8 ℃/min, 1200～1260 ℃ is 1～3 ℃/min, 1260～1350 ℃ is 1～3 ℃/min, 1350 ~1490°C is 2 to 3°C/min. Among them, when sintering at 1200-1260°C and 1260-1350°C with low argon partial pressure, the pressure is 300-400 mbar. And when nitrogen partial pressure sintering is performed at 1350-1490°C, the pressure is 15-20 mbar; while nitrogen partial pressure sintering is performed at 1490°C, the pressure is 15-20 mbar.

In step (3), in the process of rapidly cooling to room temperature, the temperature is lowered to 1350°C at 8～10°C/min, and the temperature is lowered to 1350°C to 1000°C at 5～7°C/min; and the temperature is lowered to 1～2°C/min. room temperature.

In the partial pressure sintering process in step (5), the cermet material is gradually densified in a relatively long period of time through the addition of inert gas and the energy given, and at the same time, a high vacuum can be maintained all the time through the continuous gas exchange through the partial pressure process It can discharge the gas in the tiny pores inside the material and achieve the effect of controlling the crystal growth, so as to further obtain the Ti(C,N)-based composite cermet material with good compactness.

Adopting the technical scheme provided by the present invention, compared with the existing known technology, has the following remarkable effects:

(1) The preparation method of a low-binding phase Ti(C,N)-based composite cermet with high temperature oxidation resistance of the present invention can prepare a Ti(C,N)-based composite cermet with uniform structure and good compactness Material: Scanning electron microscope (SEM) analysis and porosity evaluation of the material show that the material obtained by the present invention has a Ti(C,N)-based ring core structure, which is complete and uniform in structure distribution.

(2) According to a method for preparing a low-binding phase Ti(C,N)-based composite cermet with high temperature oxidation resistance of the present invention, the HV hardness of the prepared material reaches 1337-1564, and the fracture toughness reaches 9.7-11.7MPa·m ^{1 /2} , the flexural strength reaches 1672-1864MPa, and it can be seen that it has high toughness. ;

(3) At the same time, the slow partial pressure sintering method can be used to prepare cermets with stronger high temperature oxidation resistance.

Description of drawings

FIG. 1 is a scanning electron microscope (SEM) backscattered electron imaging picture of the Ti(C,N)-based cermet microstructure of No. 10. FIG.

2 is the metallographic diagram of the sample of Example 2, wherein (a) is No. 1, (b) is No. 3, (c) is No. 5, (d) is No. 9, and (e) is No. 11.

3 is a scanning electron microscope (SEM) photograph of the Ti(C,N)-based composite cermet material prepared in Example 1 of the present invention, wherein (a) is No. 1, (b) is No. 3, and (c) No. 5, (d) No. 9, (e) No. 11.

Detailed ways

In order to further understand the content of the present invention, the present invention will be further described below in conjunction with the embodiments, it should be noted that these embodiments are only used to illustrate the present invention rather than limit the scope of the present invention.

Example 1

Weigh each raw material powder according to the composition ratio in Table 1 to prepare Ti(C,N)-based cermets with different compositions, mix them in a ball mill, add 500g of cemented carbide balls and 72ml of absolute ethanol; After ball milling at 220r/min for 36h, the mixed slurry was poured out after passing through a 325-mesh sieve, dried in a 75°C oven, and the dried powder was passed through a 60-mesh sieve before use. According to the shape of the tool, take an appropriate amount of the above powder and put it in an alloy grinding tool for dry pressing at 100MPa, and then place it in a vacuum sintering furnace for sintering. The sintering conditions are shown in Table 2, and then cool down. The temperature is lowered to 1350°C at a cooling rate of 7°C/min from 1350 to 1000°C, and the cooling rate is 1°C/min from 1000 to room temperature to obtain a low-bonded phase cermet with high temperature oxidation resistance. The solid-phase sintering and liquid-phase sintering processes are shown in Table 2:

Table 1 Composition of Ti(C,N)-based cermet

Table 2 Partial pressure sintering process of Ti(C,N)-based cermet

The measurement of transverse rupture strength (TRS) of sintered samples refers to GB/T 3851-1983 "Determination of transverse rupture strength of cemented carbide", and the measurement of Vickers hardness (HV) refers to GB7997-1987 "Test method of Vickers hardness of cemented carbide", The fracture toughness (K _1C ) was determined with reference to BS ISO 28079-2009 "Hardmetals-Palmqvist toughness test". The samples prepared by partial pressure sintering were tested for mechanical properties: as shown in Table 3 below

Table 3 Mechanical properties of Ti(C,N)-based cermet and volume fraction of binder phase in microstructure

From the mechanical properties of Nos. 1, 5, and 14 in Table 3, it can be seen that the addition of Mo ₂ C and Co can improve fracture toughness; from No. 3, 8, 9, 10, and 11 in Table 3, the partial pressure Sintering can greatly improve the fracture toughness, and the performances of Nos. 10 and 11 are more excellent. It can be seen that sintering in a nitrogen atmosphere in the liquid phase is beneficial to the improvement of mechanical properties. Overall, it can be seen that solid phase sintering Ar gas partial pressure sintering has an effect on the improvement of fracture toughness for processes III and V. In addition, the improvement of mechanical properties with nitrogen partial pressure in liquid phase will be more obvious. The improvement of the mechanical properties of cermets is of great guiding significance. From Figures (d) and (e) in Figure 3, it can be seen that the partial pressure sintering makes the microstructure more uniform and the annular phase more complete, which also provides strong evidence for the improvement of mechanical properties. Figure 1 is a scanning electron microscope (SEM) backscattered electron imaging picture of the microstructure of the Ti(C,N)-based cermet with the above number 10. It can be seen from the figure that the microstructure has black core phase, inner ring phase, Outer ring term, white core phase, annular phase and bonding phase several structures. In the data in Table 3, the volume fraction of the binder phase is basically between 12 and 15%. Compared with the common high binder phase of more than 25%, the volume ratio of the binder phase is lower.

Example 2

The samples numbered 1, 3, 5, 9, and 11 in Table 4 were selected for high-temperature oxidation experiments, and their density was measured by using Archimedes' principle, and the polished surface was photographed under a microscope at 40 times magnification. for the evaluation of porosity. The specific experimental steps are: grinding and polishing the surface of the sample, placing the polished sample on a platinum wire mesh, and placing it in a resistance furnace for high-temperature oxidation at 1000 °C for 10 hours. Weigh on an analytical balance with an accuracy of 0.0001g, and measure and record at the same time. After the experiment is completed, the measurement of its oxidation weight gain is shown in Table 4 below:

Table 4 Density and oxidative weight gain of the samples

After sintering, the samples were coarsely ground on a grinding wheel and finely ground with a diamond disc, and then polished. The porosity of the samples was observed under an optical microscope according to the ISO4505 standard. Samples with larger porosity will lead to the formation of crack sources during the fracture process of the cermet material, resulting in a decrease in the flexural strength and fracture toughness of the cermet material. From Table 4 and the metallographic pictures (b) in Figure 2 above, it can be seen that the addition of Mo and Co improves the porosity to a certain extent, and also plays a role in the oxidation resistance; from Table 4 and the metallographic pictures (d) (e) It can be seen that the sample prepared by partial pressure sintering has a smooth surface and few pores, which shows that its compactness has been greatly improved, and its oxidation resistance is also quite excellent.

The present invention and its embodiments have been described above schematically, and the description is not limiting, and the actual method is not limited thereto. Although the present invention has been described in detail and cited some specific embodiments, if those of ordinary skill in the art are inspired by it, without departing from the purpose of the present invention, creatively design similar technical solutions The structure and embodiments of the invention should belong to the protection scope of the present invention.

Claims (3)

1. The preparation method of the high-temperature oxidation-resistant low-bonding-phase cermet is characterized by comprising the following steps of:

(1) powder preparation: weighing Ti (C)_0.5N_0.5) Powder, WC powder, Mo₂Ball-milling C powder, Co powder, Ni powder, graphite and hard alloy balls in absolute ethyl alcohol to obtain slurry, drying, and sieving by at least 80 meshes to obtain powder; the weight percentage of each raw material is as follows: ti (C)_0.5N_0.5):46%，WC:19%，Mo₂12 percent of C, 12 percent of Co, 10 percent of Ni and 1.0 percent of graphite;

(2) pressing: putting the dried powder into a pressing blank, and pressing and forming;

(3) and (3) vacuum sintering: placing the pressed compact in a pressure sintering furnace for partial pressure sintering, wherein the vacuum degree is less than 5Pa, heating the furnace temperature from room temperature to 1200 ℃ at the speed of 3-8 ℃/min, then heating to 1200-1260 ℃ at the speed of 1 ℃/min for low argon partial pressure sintering, heating to 1260-1350 ℃ at the speed of 1 ℃/min for low argon partial pressure sintering, heating to 1350-;

when low argon partial pressure sintering is carried out at the stage of 1200-1260 ℃ and 1260-1350 ℃, the pressure is 350mbar, the temperature is further increased to 1350-1490 ℃ for nitrogen partial pressure sintering, the nitrogen partial pressure sintering is carried out at 1490 ℃, and when the nitrogen partial pressure sintering is carried out at 1350-1490 ℃, the pressure is 15 mbar; and (3) performing nitrogen partial pressure sintering at 1490 ℃, keeping the temperature for 1h, and cooling to room temperature to obtain the high-temperature oxidation-resistant low-bonding-phase cermet.

2. The method for preparing the high-temperature oxidation-resistant low-bonding-phase cermet according to claim 1, wherein the cermet is prepared by pressing at a pre-pressure of 2000-2800N and then at a pressure of 200-220 MPa for 45-60 s.

3. The method for preparing the high-temperature oxidation-resistant low-bonding-phase cermet according to claim 1, wherein in the step (3), the temperature is reduced to 1350 ℃ at a rate of 8-10 ℃/min and is reduced to 1000 ℃ at a rate of 5-7 ℃/min during the cooling to the room temperature; cooling to room temperature at 1-2 deg.C/min.

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