CN113526959B

CN113526959B - Method and device for rapidly sintering tungsten carbide powder without adhesive

Info

Publication number: CN113526959B
Application number: CN202111041619.3A
Authority: CN
Inventors: 索尔沃托瑞·格拉索; 胡春峰; 邓怀久; 林勇; 吴菁华; 戴智权
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2021-09-07
Filing date: 2021-09-07
Publication date: 2022-10-04
Anticipated expiration: 2041-09-07
Also published as: CN113526959A

Abstract

The invention provides a method and a device for rapidly sintering tungsten carbide powder without an adhesive, which comprises the following steps: the micron-sized particle size is 0.8 mu m; the die parts are assembled well, and WC powder is uniformly filled; sintering in three stages, preheating heating current for 1-2kA and 1-3s, sintering current for 5-6kA and 5-7 s and heat preservation current for 1.5-4 kA and 2-4 s; and applying a pressure of 15-30MPa; after the energization was completed, the pressure and argon atmosphere were maintained until the sample was cooled. The invention has the characteristics of energy saving, high sintering efficiency, high strength of prepared samples and the like.

Description

Method and device for rapidly sintering tungsten carbide powder without adhesive

Technical Field

The invention relates to rapid sintering of tungsten carbide, in particular to a method for rapidly sintering pure tungsten carbide powder without a binder under a specific process, wherein the sintering time is less than 10 seconds.

Background

In recent years, ultra-fast sintering methods have attracted much attention because they allow the consolidation time of sintering to be significantly reduced. Meanwhile, the ultra-fast sintering also limits the grain growth, and the microstructure of fine grains is more easily obtained.

Tungsten carbide (WC) is a technical ceramic with excellent mechanical properties, including high hardness, strength and wear resistance, high melting temperature and chemical resistance to corrosive media, which makes it suitable for use in the manufacture of cutting tools and abrasives. Because tungsten carbide has good conductivity of 5 multiplied by 10 ⁶ S/m, tungsten carbide and tungsten carbide matrix materials can be joule heated and sintered by electrical current.

Tungsten carbide (melting point 2870 ℃) has not previously been reported as a high melting compound for binderless ultra-fast sintering in a few seconds.

Chinese patent documents are disclosed as follows:

the first literature: "a cemented carbide and a method for its manufacture" (CN 201610882052.5); tungsten carbide powder, cobalt powder and diamond powder are mixed by molding glue, and then the mixture is heated, pressurized and sintered to prepare the hard alloy with good wear resistance and toughness.

Document two: "a hard alloy and its preparation method and application" (CN 2020116222110); the raw materials are coarse-grain and medium-coarse-grain tungsten carbide, adhesive, additive and forming agent, and the hard alloy is prepared by pressure sintering.

Sintering conditions are as follows: the temperature is 1360-1580 degrees, the time is 1-5 hours, the pressure sintering is carried out in nitrogen, and the nitrogen partial pressure is 50-200 MPa.

In both sintering methods, a binder needs to be added during sintering, and the sintering time is as long as several hours.

Disclosure of Invention

The invention aims to provide a method for rapidly sintering tungsten carbide powder without an adhesive, which can shorten the sintering time, improve the sintering efficiency and save the energy consumption aiming at the problems in the prior art.

The purpose of the invention is realized by the following steps: a method for rapidly sintering tungsten carbide powder without an adhesive is characterized by comprising the following steps:

step 1: taking a proper amount of WC powder, wherein the purity is required to be higher, and the average grain diameter is 0.8 mu m;

and 2, step: assembling the graphite molds and the carbon fiber mold components according to an assembly drawing, uniformly filling WC powder, and reducing gaps among the molds as much as possible;

and step 3: setting a current program for a machine, preheating current for 1-2kA and 1-3s, sintering current for 5-6kA and 5-7 s, and heat preservation current for 1.5-4 kA and 2-4 s in three stages;

and 4, step 4: introducing argon to enable the sintering process to be in an argon protection atmosphere, and applying pressure (15-30 MPa) by using an upper punch and a lower punch;

and 5: starting a current program to sinter and recording corresponding data such as voltage, temperature and the like;

step 6: and (5) after the electrification is finished, maintaining the pressure and the argon atmosphere until the sample is cooled, and taking out the sample after the electrification is finished.

The technical scheme adopted by the invention comprises the following main steps:

step 1: taking a proper amount of WC powder, wherein the purity is required to be high, and the granularity is required to be as small as possible (the micron order is good), the attached figure 1 shows the XRD of the WC powder used in the experiment, and the average grain size is 0.8 mu m;

step 2: assembling the graphite molds and the carbon fiber mold components according to an assembly drawing (see the attached drawing 2), uniformly filling WC powder, and reducing gaps among the molds as much as possible;

and step 3: the current program is set for the machine, and preheating current, sintering current and heat preservation current are divided into three stages. (the optimal current process is 1.5kA,2s +6kA,6s +2.5kA, 3s);

and 4, step 4: introducing argon to enable the sintering process to be in an argon protection atmosphere, applying pressure to the upper punch and the lower punch, wherein the experiment is 20MPa;

and 6: and (5) after the electrification is finished, maintaining the pressure and the argon atmosphere until the sample is cooled, and taking out the sample after the electrification is finished.

The beneficial effects of the invention are:

(1) The rapid sintering and cooling inhibit the growth of crystal grains, and the observation result shows that the tungsten carbide block crystal grains obtained by the method have no obvious growth, smaller size and better mechanical property;

(2) The experiment compares the rapid sintering used by the invention with the traditional sintering, and the result shows that the rapid sintering used by the invention is greatly reduced in time and energy consumption, improves the sintering efficiency and has no obvious disadvantage in the aspect of mechanical property. The invention can rapidly sinter the tungsten carbide powder without the adhesive within a plurality of seconds, the density can reach 94.6 percent, the hardness can reach 2123.9HV, and the invention can obviously save energy, save time and improve efficiency.

Drawings

FIG. 1 is an X-ray diffraction pattern of the original tungsten carbide powder used in the practice.

Fig. 2 is a diagram of an overall apparatus applied to sintering tungsten carbide powder.

FIG. 3 is a graph of the voltage profile measured using an oscilloscope during the experiments of examples 1, 2 and 3, and a is the voltage profile measured in example 1; b is the voltage curve measured in example 2; c is the voltage curve measured in example 3.

FIG. 4 is a graph of the temperature profile of the experimental runs of examples 1, 2, 3 and 4, a being the temperature profile measured using a pyrometer for example 1; b is the temperature profile measured using a pyrometer in example 2; c is the temperature profile measured using a pyrometer in example 3; d is a temperature profile measured using the pyrometer of the SPS apparatus of example 4.

FIG. 5 is an X-ray diffraction pattern of the sample obtained in the experiments of examples 1, 2, 3 and 4, and a is an X-ray diffraction pattern of the sample obtained in example 1; b is the X-ray diffraction pattern of the sample obtained in example 2; c is the X-ray diffraction pattern of the sample obtained in example 3; d is the X-ray diffraction pattern of the sample obtained in example 4 using SPS sintering.

FIG. 6 is a back-scattered image of the sample obtained in the experiments of examples 1, 2, 3 and 4, and a is a back-scattered image of the sample obtained in example 1; b is a back-scattered image of the sample obtained in example 2; c is a back-scattered image of the sample obtained in example 3; d is the back-scattered image of the sample obtained in example 4 using SPS sintering.

Detailed Description

The invention is further described with reference to the following figures and specific embodiments.

In fig. 2, a current input end 1, an upper copper alloy punch 2, an upper graphite pad 3, an infrared temperature measuring point 4, an upper graphite punch 5, tungsten carbide powder 6, a carbon fiber die 7, a lower graphite punch 8, a lower graphite pad 9, a lower copper alloy punch 10, a current output end 11 (the potential here is 0V), and a rotational symmetry axis 12.

A fast sintering device, an upper copper alloy punch 2 is pressed on the top of an upper graphite cushion block 3, the upper graphite cushion block 3 is pressed on the top of an upper graphite punch 5, a lower graphite punch 8 is pressed on the top of a lower graphite cushion block 9, the lower graphite cushion block 9 is pressed on the top of a lower copper alloy punch 10, fast sintering tungsten carbide powder 6 is pressed in a gap between the upper graphite punch 5 and the lower graphite punch 8, a carbon fiber die 7 is sleeved on the upper graphite punch 5 and the lower graphite punch 8 and completely covers the gap between the upper graphite punch and the lower graphite punch, a current input end 1 is connected with the upper copper alloy punch 2, a current output end 11 is connected with the lower copper alloy punch 10, and the potential of the current output end is 0V; the upper copper alloy punch 12 is a cylinder with a cylindrical inner concave surface in the middle of the bottom surface, the upper graphite cushion block 3 is formed by superposing a small cylinder on a large cylinder in the coaxial direction, the cylindrical inner concave surface is arranged in the middle of the bottom surface of the large cylinder, and the small cylinder of the upper graphite cushion block 3 can extend into the cylindrical inner concave surface of the upper copper alloy punch 2; the top of the upper graphite punch 5 extends into a cylindrical concave surface of the bottom surface of the large cylinder of the upper graphite cushion block 3; the upper copper alloy punch 2 and the lower copper alloy punch 10 are symmetrical in shape, and the upper graphite cushion block 3 and the lower graphite cushion block 9 are symmetrical in shape; the cylindrical upper and

lower graphite punches

5, 8 are symmetrical in shape.

Instrumentation apparatus

The equipment used in the sintering experiment is an intermediate-frequency direct-current pulse spot welder (1000 Hz) with the model of DNB-350KV; an oscilloscope is used for recording voltage data of the sintering process, the model of the oscilloscope is UNI-T (UPO 2104 CS), and a data point is recorded every 0.0076 seconds; recording temperature data of the sintering process by using a pyrometer, wherein the model of the device is Raynger 3i Plus, and recording a data point every 0.53 seconds; carrying out X-ray diffraction analysis (XRD) on the original powder and a sample, wherein the model of the instrument is DX-2700BH, a copper target material is selected, the scanning angle is 20-80 degrees, and the scanning speed is 2 degrees/min; carrying out scanning electron microscope observation on the sample, wherein the model of the instrument is Hitachi SU8220; performing Vickers hardness test on a sample, wherein the model of the instrument is HVS-1000Z, the loading load is 10 kg, the pressure maintaining time is 15 seconds, and randomly taking 5 points to calculate the average hardness value; a sample is subjected to density test by an Archimedes method, the model of an instrument is AE224J, and the standard deviation of the density is 0.2-0.4%.

Example 1

Step 1: taking 8g of WC original powder;

and 3, step 3: setting a current program for a machine, maintaining the current of 1.5kA for 2 seconds in a preheating stage, maintaining the current of 6kA for 6 seconds in a sintering stage, and maintaining the current of 2.5kA for 3 seconds in a heat preservation stage;

and 4, step 4: introducing argon to enable the sintering process to be in an argon protection atmosphere, and applying pressure by the upper punch and the lower punch, wherein the pressure value is 20MPa;

and 5: starting a current program to sinter, recording corresponding data such as voltage, temperature and the like, measuring the average voltage values of the three stages to be 8.2,9.5 and 5.6V respectively, measuring the maximum temperature to be 1843 +/-36 ℃, measuring the average heating rate to be 228.5 ℃/s, and showing the voltage curve and the temperature curve in attached figures 3 and 4;

step 6: and (5) after the electrification is finished, maintaining the pressure and the argon atmosphere until the sample is cooled, and taking out the sample after the electrification is finished. The tungsten carbide sample obtained by the scheme contains impurity phases beta' -W ₂ 5.2 percent of C, 12.2 percent of Graphite-2H, the average Vickers hardness of 1923 +/-59 HV, the theoretical density of 91.3 percent and the average grain size of 0.9 mu m.

Example 2

Step 1: taking 8g of WC original powder;

step 2: assembling the graphite molds and the carbon fiber mold components according to an assembly drawing (see the attached drawing 2), uniformly filling WC powder, and reducing the gaps among the molds as much as possible;

and 3, step 3: setting a current program for the machine, wherein the current of 1.5kA in the preheating stage is maintained for 2 seconds, the current of 6kA in the sintering stage is maintained for 6 seconds, and the current of 2.5kA in the heat preservation stage is maintained for 3 seconds;

and 5: starting a current program to sinter, recording corresponding data such as voltage, temperature and the like, measuring the average voltage values of the three stages to be 1.9, 10.9 and 2.9V respectively, measuring the maximum temperature to be 2086 +/-46 ℃, measuring the average temperature rise rate to be 277.3 ℃/s, and showing the voltage curve and the temperature curve in attached figures 3 and 4;

step 6: and (5) after the electrification is finished, maintaining the pressure and the argon atmosphere until the sample is cooled, and taking out the sample after the electrification is finished. The tungsten carbide sample obtained by the scheme contains impurity phases beta' -W ₂ 2.1 percent of C, 2.3 percent of Graphite-2H, the average Vickers hardness of 2124 +/-134 HV, the theoretical density of 94.6 percent and the average grain size of 0.91 mu m.

Example 3

Step 1: taking 8g of WC original powder;

and 2, step: assembling the graphite molds and the carbon fiber mold components according to an assembly drawing (see the attached drawing 2), uniformly filling WC powder, and reducing gaps among the molds as much as possible;

and 5: starting a current program to sinter, recording corresponding data such as voltage, temperature and the like, measuring the average voltage values of the three stages to be 1.2, 11.6 and 2.6V respectively, measuring the maximum temperature to be 2441 +/-48 ℃, measuring the average temperature rise rate to be 316.6 ℃/s, and showing the voltage curve and the temperature curve in attached figures 3 and 4;

step 6: and (5) after the electrification is finished, maintaining the pressure and the argon atmosphere until the sample is cooled, and taking out the sample after the electrification is finished. The tungsten carbide sample obtained by the scheme contains impurity phases beta' -W ₂ 10.5 percent of C, 1576 +/-65 HV of Vickers hardness average value, 98.1 percent of theoretical density and 4 mu m of average grain size.

Example 4 (this example is a conventional sintering process and is used for comparison)

Step 1: taking 8g of WC original powder;

and 2, step: taking a standard sintering graphite die, assembling, uniformly filling WC powder, reducing the gap between the dies as much as possible, and putting the dies into a sintering furnace after adjusting;

and step 3: setting a temperature program for an SPS machine (Ningbo Xinwei science and technology Limited liability company), vacuumizing to ensure that the sintering process is under vacuum protection, and applying pressure to the upper end and the lower end, wherein the pressure value is 20MPa;

and 4, step 4: starting a current program to carry out traditional sintering and recording related data, starting the sintering process to run according to a temperature program, wherein the heating rate is 100 ℃/min, slowly heating from room temperature to 2000 ℃, preserving heat for 5 minutes, and then slowly cooling to room temperature along with a furnace, wherein the temperature curve is shown in a figure 4;

and 5: and (5) after sintering is finished, taking out the sample. The tungsten carbide sample obtained by the scheme has high purity, the average Vickers hardness is 2057 +/-47 HV, the theoretical density is 96.7 percent, and the average grain size is 0.8 mu m.

Table 1

Table 2

Table 1 shows some important parameters of the experiments of examples 1, 2, 3 and 4, including phase composition and mass fraction, measured site maximum temperature and simulated sample center maximum temperature, temperature rise rate, theoretical density and average grain size, and the data are tabulated for comparison.

Table 2 shows a phase transition formula of tungsten carbide at high temperature, which can be used to explain the generation of ditungsten carbide, and is convenient for researchers in intensive research.

The starting tungsten carbide powder in examples 1, 2, 3, 4 was obtained from the Aladdin industries, inc. (MFCD 00011464) and had an average particle size of 800nm and a purity of greater than 99%.

The rapid sintering method used in the invention allows the tungsten carbide powder without adding the adhesive to be sintered within 10 seconds, the optimized process allows the density of the sample to reach 94.6%, the hardness to reach 2123.9HV, the purity to reach 95.6%, crystal grains do not grow obviously, and compared with the traditional sintering, the consumption of time and energy is greatly reduced. The process has great potential, can be widely applied to the rapid sintering of conductive materials, and has better effect on the rapid sintering of high-melting-point materials.

Claims

1. A method for rapidly sintering tungsten carbide powder without an adhesive is characterized in that a rapid sintering device has the structure as follows: the upper copper alloy punch (2) is pressed on the top of the upper graphite cushion block (3), the upper graphite cushion block (3) is pressed on the top of the upper graphite punch (5), the lower graphite punch (8) is pressed on the top of the lower graphite cushion block (9), the lower graphite cushion block (9) is pressed on the top of the lower copper alloy punch (10), rapidly sintered tungsten carbide powder (6) is pressed in a gap between the upper graphite punch and the lower graphite punch (5 and 8), a carbon fiber die (7) is sleeved on the upper graphite punch and the lower graphite punch (5 and 8) and completely covers the gap between the upper graphite punch and the lower graphite punch, a current input end (1) is connected with the upper copper alloy punch (2), a current output end (11) is connected with the lower copper alloy punch (10), and the potential of the current output end is 0V;

the upper copper alloy punch (2) is in a cylinder with a cylindrical inner concave surface in the middle of the bottom surface, the upper graphite cushion block (3) is formed by superposing a small cylinder on a large cylinder in a coaxial direction, the middle of the bottom surface of the large cylinder is provided with a cylindrical inner concave surface, and the small cylinder of the upper graphite cushion block (3) can extend into the cylindrical inner concave surface of the upper copper alloy punch (2); the top of the upper graphite punch (5) extends into the cylindrical concave surface of the bottom surface of the large cylinder of the upper graphite cushion block (3); the shapes of the upper copper alloy punch head (2) and the lower copper alloy punch head (10) are symmetrical, and the shapes of the upper graphite cushion block (3) and the lower graphite cushion block (9) are symmetrical; the cylindrical upper graphite punch head and the cylindrical lower graphite punch head (5, 8) are symmetrical in shape;

a method of rapid sintering comprising the steps of:

step 1: taking 8g of WC original powder; the average grain diameter is 800nm, and the purity is more than 99 percent;

step 2: assembling the graphite molds and the carbon fiber mold components according to an assembly drawing, uniformly filling WC powder, and reducing gaps among the molds as much as possible;

and step 3: setting a current program for the machine, wherein the current of 1.5kA in the preheating stage is maintained for 2 seconds, the current of 6kA in the sintering stage is maintained for 6 seconds, and the current of 2.5kA in the heat preservation stage is maintained for 3 seconds;

and 5: the current program was started to sinter and the corresponding voltage was recorded,temperature data, the average voltage values of the three stages are respectively 1.9, 10.9 and 2.9V, and the maximum temperature is measured

Average heating rate is 277.3 ℃/s;

step 6: after the electrification is finished, maintaining the pressure and the argon atmosphere until the sample is cooled, and taking out the sample after the electrification is finished; the tungsten carbide sample obtained by the scheme contains impurity phase

2.1 percent, graphite-2H 2.3 percent and the average value of Vickers hardness is

HV, theoretical density 94.6%, average grain size 0.91

。