How to Activate Unbonded Tungsten Carbide

Tungsten carbide cemented carbide is widely used in cutting, drilling, mining, tool forming and wear-resistant parts because of its high hardness, high strength, high toughness, wear resistance, high temperature resistance and low expansion coefficient. Generally speaking, tungsten carbide alloys need cobalt and nickel as bonding phases. Although metal bonding phases promote sintering densification, they also reduce hardness, wear resistance, corrosion resistance, oxidation resistance and so on. At the same time, there are large differences in thermal expansion coefficients between metal phases and tungsten carbide and other hard phases, which lead to the material. Because of the large thermal stress, the application area is limited.

Some scholars have proposed a method for preparing tungsten carbide based cemented carbide without bond, including the following steps:

Step 1: 20 g oxalate ammonia was dissolved in 1 L deionized water to prepare 20 g/L oxalate ammonia solution. 0.02 g sodium hexametaphosphate was added to oxalate ammonia solution to obtain solution a.

Step 2: Take 500 mL solution a, add 120 g tungsten carbide powder with average grain size of 200 nm, and stir for 60 minutes by ultrasound.

Step 3: Dissolve 20g yttrium nitrate in 1L deionized water to prepare yttrium nitrate solution with a concentration of 20g/L.

Step 4: Take the solution obtained in step 3 of 515 ml and drip slowly into the oxalate ammonia solution containing tungsten carbide powder obtained in step 2. In this process, continue to stir by ultrasonic stirring until the yttrium nitrate solution is dripped and stirred for 30 minutes. Then, put it in a static position, pour out the upper liquid and wash the powder three times with deionized water. Then, the precursor of tungsten carbide composite powder doped with trace active element yttrium was obtained by drying in a vacuum drying chamber at 60 ℃.

Step 5: Tungsten carbide composite powder precursor doped with 2% yttrium is roasted in a tubular furnace. The tubular furnace evacuates the vacuum, and then is protected by argon. The roasting temperature is 800 ℃, the heating rate is 5 ℃/min, until the sintering temperature, holding for 1 h, and then cooling with the furnace, the doping mass fraction is obtained. The 2% active element yttrium tungsten carbide composite powder;

Step 6: The tungsten carbide composite powder with uniform doping mass fraction of 2% active element strontium is sintered by spark plasma sintering technique, the sintering temperature is 1600 ℃, the heating rate is 150 ℃ / min, and the sintering pressure is 40 MPa. An unbonded phase tungsten carbide-based cemented carbide having an active element cerium doped with a mass fraction of 2% was obtained.

Due to the uniform doping of trace active elements, the sintering temperature of the unbonded phase tungsten carbide-based cemented carbide is greatly reduced, the compactness is high, and the mechanical properties are excellent. The sample test results show that the grain size is consistent with the original powder particle size, the compactness is high, the relative density is 99%, and the hardness exceeds 2600HV30.

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