Unbonded Tungsten Carbide Cemented Carbide Preparation

Unbonded tungsten carbide cemented carbide has better high temperature resistance, wear resistance, corrosion resistance, oxidation resistance and higher hardness than traditional cemented carbide. It is becoming an important development direction of high wear resistant cemented carbide.

However, the high melting point of pure tungsten carbide, the high sintering temperature, the difficulty of Sintering Densification and the inability to effectively inhibit the abnormal grain growth are the urgent problems to be solved in the preparation of unbonded tungsten carbide-based cemented carbides. Many companies and scholars at home and abroad are burning their heads for this problem.

Recently, some scholars have proposed a preparation method of tungsten carbide-based cemented carbide with unbonded phase. The process is as follows:

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 240g tungsten carbide powder with average grain size of 400 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 515mL and drip it slowly into the oxalic acid ammonia solution containing tungsten carbide powder obtained in step 2. In this process, continue 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, wash the powder three times with deionized water, and then put it into a vacuum drying chamber at 60 ℃ for drying. The precursor of tungsten carbide composite powder doped with trace active element yttrium was obtained.

Step 5: Vacuum is pumped in tubular furnace, then protected by argon gas. The calcination temperature is 850 ℃, the heating rate is 5 ℃/min, and the sintering temperature is kept for 1 h. Then tungsten carbide composite powder doped with 1% active element yttrium is prepared with furnace cooling.

Step 6: The unbonded tungsten carbide-based cemented carbide with 1% yttrium doped active element was prepared by spark plasma sintering with sintering temperature of 1650 ℃, heating rate of 150 ℃/min and sintering pressure of 40 MPa.

In this scheme, tungsten carbide composite powder doped with trace active elements is used as raw material. Because of the uniform doping of trace active elements, the sintering temperature of unbonded tungsten carbide-based cemented carbide is greatly reduced, with high compactness and excellent mechanical properties. The test results show that the grain size is consistent with the original powder size, and the relative compactness is over 97%, and the hardness is over 2400HV30.

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