Ammonium Paratungstate Preparing Tungsten Carbide with Gradient Cobalt Content Change at Surface

Cobalt is the metal with shiny steel gray. The tool made by steel containing a certain amount of cobalt can significantly improve the wear resistance and cutting performance, so cobalt often used for making carbide. The content of cobalt at tungsten carbide surface affects its performance, specific performance as bellows:
1. The cobalt content of outermost layer is lower than the nominal cobalt content, and then the carbide will have high hardness and wear resistance;
2. The cobalt content of middle layer is higher than the nominal cobalt content, and then the carbide will have good hardness and abrasion resistance.



In this paper, a method that preparing tungsten carbide with gradient cobalt content change at surface from ammonium paratungstate, the carbide produced has normal core tissue, the mechanical properties and service life are improved. Steps are as follows:
1. Prepare a paste of ammonium paratungstate
APT is dissolved at a concentration of 2%~4% polyvinyl alcohol solution to obtain a paste of ammonium paratungstate, the amount of APT added is 6~8 times the amount of polyvinyl alcohol solution;
2. Carbide surface infiltration tungsten
Wrapping carbide in the paste ammonium paratungstate, and heated to 800~900°C in a hydrogen atmosphere, continually heated to 1400~1460°C after incubation for 20~40 minutes heating, then incubation for 1~2 hours, taken out and cooling down under a hydrogen atmosphere;
3. The solid carburizing
Add carbon black at a temperature of 1420~1450°C for 0.5~2 hours
4. Decarburization phase generated
Ammonium paratungstate is heated to about 900°C at a hydrogen atmosphere, activity W and tungsten oxide can be obtained, and then reacted at a constant temperature 1400~1460°C for some time, thus to get tungsten carbide with gradient cobalt content change at surface.

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