Improvement Of Properties Of Amorphous Carbon Films Deposition On Different Substrates By Ta Transition Layer

Amorphous carbon films are widely used in mechanical,optical,electricity,biology,decoration and other fields,due to their excellent properties such as high hardness,low friction coefficient,heat transmission speed,excellent corrosion resistance,good biocompatibility and insulation,and wide band gap.However,their properties are limited by the adhesion with substrates.The thermal expansion coefficient of substrate and their bonding effect with carbon determine the bonding strength between film and substrate,and then affect the modification of carbon film.The bonding strength between amorphous carbon film and substrate can be improved by adding transition layer or gradient layer.In this work,tantalum(Ta)transition layer was prepared by double glow plasma alloying technology between copper(Cu),Ti6Al4 V alloy and 304 stainless steel metal substrates,respectively.The aim of the work is to investigate the bonding strength,mechanical property and tribological property of the fabricated metal substrate.The main results are listed as follows:(1)As for Cu substrate,the surface morphology of the sample is mainly composed of cellular.With prolong alloying time of Ta,the thickness of transition layer increases,the size of the cellular on the surface increases,too.The existence of metallurgical bonding between transition layer and substrate enhances the bonding strength.The bonding strength between amorphous carbon film and substrate decreases gradually.The friction coefficient of sample is lower than that of the substrate,wear rate reduces greatly and thus the wear resistance of sample is improved.When the alloying time is 60 min and the corresponding thickness of transition layer is 8.2 ?m,the sample maintains the lowest friction coefficient of 0.201,the wear rate of it is 2.48% of that of the Cu substrate.(2)As for Ti6Al4 V alloy substrate,the surface morphology of the sample is mainly composed of cellular.With prolong alloying time of Ta,the cellular on the surface becomes obviously,and the number of cellular increases.The thickness of transition layer also increases.The existence of metallurgical bonding between transition layer and substrate enhances the bonding strength.The bonding strength changes little.The friction coefficient and wear rate decrease greatly,and the wear resistance of sample is improved.When the alloying time is 120 min and the corresponding thickness of transition layer is 7.7 ?m,the lowest friction coefficient of sample is 0.265 and the wear rate is 1.27% of the substrate.(3)As for 304 stainless steel substrate,the surface morphology of sample is relatively flat and composed of cellular.With the prolongation of Ta alloying time and the increase of the thickness of transition layer,the cellular on the surface of film appears obviously.The existence of metallurgical bonding between transition layer and substrate enhances the bonding strength.The bonding strength between substrate and amorphous carbon film is low,and the flakes of the film are exfoliated.The friction coefficient and wear rate decrease and wear resistance of sample is improved.When the alloying time is 30 min and the corresponding thickness of transition layer is 2.1 ?m,the lowest friction coefficient of sample is 0.133 and the wear rate is 1.72% of the 304 stainless steel substrate.(4)It is found that amorphous carbon films prepared on Ti6Al4 V substrates with Ta transition layer have better bonding strength and frictional properties.The internal stress in the transition layer on Cu substrate is relatively high due to a insolubility between Ta and Cu during the preparation process,the bonding strength and wear resistance of amorphous carbon film on Cu substrate are lower than that of Ti6Al4 V alloy,because its low hardness and loading property.The hardness of 304 stainless steel substrate is high,but the elements in 304 stainless steel have low solid solubility with Ta elements.Therefore,the internal stress of the sample is high,which causes a poor adhesion between the film and the 304 stainless steel.