Preparation Of Ultrafine Gradient Cemented Carbide Cutting Tools And Its Cutting Performance

Titanium alloy and stainless steel have low thermal conductivity and chemical activity,when the cutting tools maching these alloys,the tool wear will increase seriously due to its poor heat dissipation condition.It is ususlly using cemented carbides coating tools to high-speed machining due to their good wear resistant and heating resitant.However,the adiabatic coating will increase the temperature and accelerate the tool wear.Gradient cemented carbide with surface zone enriched in binder phase,can effectively reduce the thermal stress and improve thermal shock resistance.The gradient cemented carbide is mainly used for coating substrates,and is rarely used for cutting tools without coating.Because the grain size of gradient cenmened carbide is so large that its wear resistant is not very well.Ultrafine grain cemented carbide tools with high hardness and high wear resistance,can prolong the service life of the tool.Cryogenic treatment can increase tool wear resistance,prong service life and reduce surface roughness of workpiece and energy consumption.In order to further improve the performance of cutting tools,ultrafine grain gradient cemented carbide cutting tools was prepared and subjected to cryogenic treatment,and then used for high-speed cutting experiments of titanium alloy and stainless steel.This paper studied ball milling time on the performance of powders and the microstructure and properties of ultrafine grain gradient cemented carbide.The alloy compositions were also studied,including the content of Co,Ti(C,N)and(Ta,Nb)C.And then the effect of different cryogenic treatments on the microstructure and properties of cemented carbide were also studied.Finally,high-speed cutting experiments of titanium alloy and stainless steel were performed,and tool wear mechanism of ultrafine grain gradient cemented carbide was discussed.The results are as follows:(1)With the ball milling time increasing,gradient layer thickness and fracture toughness increase.When ball mill time is lower than 15h,the microstructure is not uniform.However,when the ball mill time is longer than 35h,there are more abnormal grains growths.The best ball milling time is 25h.(2)With the content of Co increasing,the gradient layer thickness become thicker,but grain size of WC become larger and hardness is lower.The content of Co should be controlled in 8-10%.The addition of(Ta,Nb)C and Ti(C,N)will improve the hardness,but decrease the thickness of the gradient layer and fracture toughness.(3)Continuous cryogenic treatment and cryogenic tempering treatment can promote phase transformation of α-Co→ε-Co and improve the fracture toughness.Continuous cryogenic treatment has no significant effect on the microstructure and hardness.With the increase of the number of tempering treatment,hardness increases significantly.(4)Compared ultrafine grain gradient cemented carbide cutting tools with ultrafine grain carbide coating cutting tools YBG202 and GC1105 when cutting titanium alloy in the same distance,the flank wear of Co10Ti2Ta4 is 36.4%of YBG202 and 89%of GC1105 respectively.(5)Compared ultrafine gradient cemented carbide coating tools with GC4225 and YBG202,when cutting stainless steel in the same distance,the flank wear of Co10Ti2Ta2 is 36%of YBG202 and 144%of GC4225 respectively.