| The quality and life of powder metallurgy dies directly affects the quality and life of powder metallurgy parts.As an important component of the powder metallurgy forming die,the die punch directly extrudes the metal powder during the billet forming process and the shape of its head determines the shape of the end face of the powder metallurgy billet.Due to the surface quality of the die punch,there is tissue segregation,uneven hardness and material flaking at the top of the local teeth,leading to increased wear and early failure of the die punch,which seriously affects the improvement of production efficiency.The composite treatment technology of intermittent vacuum gas nitriding and multi-arc ion plating is used to deposit CrAlTiN coating on the nitrided die punch surface to improve the uniformity of the die punch surface,increase the surface hardness gradient and wear resistance,and improve the service life and production efficiency.In this paper,based on experimental studies,the microstructure,interfacial characteristics and wear resistance of the CrAlTiN coating on the die-punch surface are analysed and studied,with the main work including.(1)An intermittent vacuum gas nitriding process was used to prepare a nitriding layer on the surface of the upper die punch.The thickness of the nitriding layer is 150 ?m and the hardness decreases gently in a gradient from 969 HV on the surface to 525 HV on the substrate,with a surface brittleness class of 1.The nitriding layer is mainly composed of ?'Fe4N and CrN.The nitriding pretreatment improves the resistance to plastic deformation of the die,which provides effective support for the coating on the die-struck surface and reduces the tendency of the coating to crack.This will improve the bonding strength of the film base.(2)Using multi-arcion plating technology,CrAlTiN coatings were deposited on the nitriding pretreated die-struck surface.The influence of the process parameters,such as substrate bias,cathode arc current and deposition air pressure,on the structure,mechanical properties and friction wear properties of CrAlTiN coatings was investigated and the process parameters were selected.The results show that the surface quality,hardness and film-base bond strength of the coating increase with the increase of the substrate bias voltage.The surface quality of the coating improves with increasing deposition pressure,and the average roughness of the coating decreases to 170 nm at a deposition pressure of 3.6 Pa;the hardness increases and then decreases with increasing deposition pressure.The hardness tends to rise and then fall with increasing deposition pressure,with a maximum value of 2971 HV0.025 at 2.8 Pa.The deposition pressure has a small effect on the bonding strength and frictional wear properties of the coating,with the bonding strength varying from 64 N to 72 N and the wear rate remaining at around 4.5×10'6 mm3/N·m.As the cathodic arc current increases,the average roughness of the coating increases and the deposition rate increases,with the coating thickness reaching 3.5 ?m at 120 A.The hardness of the coating surface tends to increase and then decrease,and shows the highest hardness of 3160 HV0.025 at 110 A.The wear rate of the coating increases with the increase of the cathodic arc current,with the wear rate of the coating at 120 A reaching Combined with the experimental results,the preferred process parameters for the CrAlTiN coating were-110 V to-130 V for the substrate bias,2.8 Pa for the deposition air pressure and 100 A for the arc current.(3)The frictional wear performance of the upper die punch after the composite treatment was investigated and the service life of the die was tested in conjunction with the pressing of a spiral bevel tooth of a powder metallurgical part.The coefficient of friction of the CrAlTiN coating(0.59,0.57 and 0.53 at 2 N,4 N and 6 N respectively)was lower than that of the die punch substrate(0.66,0.64 and 0.57 at 2 N,4 N and 6 N respectively).The test results show that the composite treated upper die punch has a service life of approximately 20,000 cycles,which is five times longer than the life of the untreated die punch,and the consumption cost of a single part for die production has decreased from RMB 0.098/pc to RMB 0.030/pc,a reduction of 70%. |
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