Surface Structure Control And Performance Of Cemented Carbide CVD Coated Tool

TiCN and TiCN-Al₂O₃ coatings of different thicknesses were prepared by chemical vapor deposition and the TiCN-Al₂O₃ coating was modified by high current pulsed electron beam(HCPEB)in this paper.X-ray diffractometer(XRD),optical microscope(OM),3D laser scanning microscop(3D-LSM)and scanning electron microscope(SEM)were used to characterize the phase composition and microstructure morphology of the CVD coatings of different system and before and after irradiation.At the same time,establishing the internal relationship between the microstructure morphology and performance combined with nanoindentation,scratch testing,friction and wear,high temperature oxidation and cutting testing.The microstructure characterization result showed:the TiCN and TiCN-Al₂O₃coated by chemical vapor deposition was uniform and compact.With the increase of thickness,the grain size and the crack gradually increased.The friction and wear testing result showed:The 4?m-TiCN coating sample showed the best wear resistance,and the6?m-TiCN+2?m-Al₂O₃ coating sample showed the worst.The wear mechanisms of TiCN coatings included abrasive,adhesive and oxidative wear.There were just abrasive and adhesive wear for TiCN-Al₂O₃ coatings.The result of the oxidation testing showed:TiCN and TiCN-Al₂O₃ coating exhibited better oxidation resistance than uncoated cemented carbide substrate under the condition of 600?,TiCN-Al₂O₃ coating samples exhibited better oxidation resistance than TiCN coating samples under the condition of800?,and the oxidation resistance of the both system coating sample decreased with the increase of coating thickness.Electrochemical corrosion result showed:corrosion resistance of the TiCN-Al₂O₃ coating samples were better than the TiCN coating samples since the outermost layer of the TiCN-Al₂O₃ coating sample was Al₂O₃.At the same time the corrosion resistance decreased as the thickness increased.The scratch testing result showed:the bonding strength of the 8?m-TiCN coating sample was the worst,which did not meet the actual machining requirement of cemented carbide coating tool,however other samples showed excellent bonding strength,especially the critical load of the 4?m-TiCN coating even exceeding 150 N.The TiCN-Al₂O₃ coating tool was irradiated by HCPEB,the thermal mismatch stress was formed due to the difference in thermal expansion coefficient between the coatings.The diffraction peak of the sample firstly shifted to higher angle then offsetting at lower angle with the increase of the number of irradiation by XRD analysis.Meanwhile,the volcano-like craters occurred on the surface and the surface roughness was significantly reduced.in addition,microstructure around the cracks on the surface were remelted which sewed cracks.Correspondingly,The nano-hardness(H)and elastic modulus(E)of the sample were improved effectively after irradiation.The H/E and H³/E² values were firstly increased and then decreased with the increase of the number of irradiation.The H/E and H³/E² values reached to the maximum,respectively0.069 and 0.137 GPa,after 5-pulsed indicating the strongest resistance to plastic deformation.The friction coefficient and wear rate of the sample were reduced as the surface roughness was significantly reduced after irradiation,and the wear resistance was improved.The wear mechanism included abrasive wear and adhesive wear.Otherwise,the bonding strength of the coating after the appropriate number of irradiation was also improved.the critical load reached 73.92 N after 5-pulses,which was significantly higher than the initial,then dropped sharply with the increase of the number of irradiation.The critical load was only 56.88 N after 15-pulses.Since the samples after 5-pulses possessed the best mechanical properties,wear resistance and bonding strength,it exhibited excellent cutting performance,and the cutting lifetime was increased by 14.3%compared with the initial.The failure mode only included flank wear.