Preparation Of Nanocrystalline Gradient Cemented Carbide Tools And Research On Its Cutting Performance

Due to the poor thermal conductivity,high chemical activity,strong affinity and other characteristics of titanium alloy and stainless steel,it is easy to accelerate the tool wear during high-speed cutting.At present,the most widely used cutting tools are the coated carbide tools.The coating is to increase the wear resistance of the cemented carbide tools,but the coating also worse heat dissipation conditions of the tip of the tool and further accelerate the tool wear.Gradient cemented carbide with surface zone enriched in binder phase,can effectively reduce the thermal stress,improve the thermal conductivity.Nnocrystalline cemented carbide can improve the wear resistance of cemented carbide with strong degrees due to grain refinement.Therefore,nanocrystalline gradient cemented carbides have the advantages of gradient cemented carbides and nanocrystalline cemented carbides,it can meet the requirements of high speed cutting directly applied to titanium alloy and stainless steel.Firstly,appropriate powder was choosen to prepare nanocrystalline gradient cemented carbide;Secondly,the effect of the composition of the of nanocrystalline cemented carbide was studied;Finally,the alloy with excellent microstructure and properties were selected to prepare the nanocrystalline gradient carbide tools for highspeed cutting of titanium alloy and stainless steel.(1)The reduction of powder size can effectively reduce the grain size of nanocrystalline gradient cemented carbides,improve the thickness of gradient layer and properties of the alloy.However,when the powder size was too fine,the structure of the sintered alloy is not uniform,the grain size is large,and the properties of the alloy are poor.Therefore,the particle size of WC(200nm)and Co(100nm)is selected as the original powder size.(2)With the content of Co increasing,the fracture toughness and gradient layer thickness of nanocrystalline gradient cemented carbides also increase,but the grain size becomes large,and the hardness of the alloy reduces.(3)As gradient forming elements,Ti(C,N)can be used to prepare the gradient cemented carbides with surface zone enriched in binder phase,and the gradient layer thickness of the alloy decreases with the increase of Ti(C,N)contents.As gradient forming elements,V(C,N)can used to prepare the gradient cemented carbides with surface zone enriched in binder phase and the gradient cemented carbides with surface zone poor in binder,but when the content of V(C,N)exceeds 2%,the properties of the alloy reduces.(4)Comparing the results of nanocrystalline gradient cemented carbide tool with ultra-fine cemented carbide coated tool YBG202 and GC1105 cutting titanium alloy at high speed,it was found when cutting titanium alloy in the same distance,the flank wear of Co10Ti2 was 22.7%of YBG202 and 55.6%of GC1105 respectively.(5)Comparing the results of high-speed cutting of stainless steel with the ultrafine grain cemented carbide coated tool YBG202 and the medium-size gradient cemented carbide coated tool GC4225,it is found that when cutting stainless steel in the same distance,the flank wear of Co10Ti2 is 22.6%of YBG202 and 83%of GC4225 respectively.