Study On Self-lubricating Graphite Coating Prepared By Electrospark Deposition On 45 Steel Substrate And Its Properties

In this paper,graphite self-lubricating coating was prepared on 45 steel substrates by electrospark deposition on ESD-03 B EDM repair machine according to the preparation parameters designed by orthogonal test.The surface and cross-section morphologies of graphite self-lubricating coatings were analyzed by scanning electron microscopy.The surface and cross-section of self-lubricating coatings were analyzed by energy spectrum analysis.The roughness,thickness and friction and wear of graphite self-lubricating coatings were measured by LEXT OLS 4100 3D measuring laser microscope,TT260 coating thickness gauge and HSR-2M high-speed reciprocating friction and wear tester respectively,and the optimum preparation parameters were determined.The friction and wear characteristics and wear mechanism of graphite self-lubricating coatings were studied.Graphite self-lubricating coatings were prepared on 45 steel substrates by electrospark deposition.The surface and cross-section morphologies of graphite self-lubricating coatings were observed by SEM photographs.The micro-morphology shows that the graphite self-lubricating coating has irregular surface,high bonding strength and uneven surface.There are pores and holes on the surface of the coating,and there are local cracks.From the cross-section micro-morphology,it can be seen that graphite rod electrode and 45 steel matrix formed a good combination of gold treatment.Through surface scanning EDS and line scanning EDS,it can be seen that the coating surface mainly contains C elements,and C,Fe,Si,Cr elements are reflected in the coating and matrix.According to the preparation parameters designed by orthogonal experiment,16 groups of specimens were prepared by EDD.The optimum preparation parameters of roughness were obtained by orthogonal experiments: electrode speed 260 r/min,power20 uF,discharge frequency 70 Hz and deposition time 15 min.The optimum preparation parameters of thickness are: electrode speed 180r/min,power 80 uF,discharge frequency 90 Hz,deposition time 15 min.The optimum preparation parameters of friction coefficient and wear rate are:electrode speed 220 r/min,power60 uF,discharge frequency 90 Hz and deposition time 5 min.In this paper,the friction and wear characteristics of self-lubricating coatings were systematically studied,and the effects of different load on the friction pairs,reciprocating friction frequency and friction time on the friction and wear properties of coatings were discussed.When the pair is bearing steel(GCr15),the friction coefficient of graphite self-lubricating coating decreases with the increase of load and reciprocating friction frequency.The wear loss increases with the increase of load and frequency of reciprocating friction.When the pair of friction pairs is Si3N4,the friction coefficient of graphite self-lubricating coatings increases with the increase of load,and the friction coefficient does not change obviously with the increase of reciprocating friction frequency.With the increase of load and frequency of reciprocating friction,the wear loss decreases first and then increases.The friction coefficient of bearing steel(GCr15)to friction pair is lower than that of silicon nitride ceramic(Si3N4),but the wear rate is higher.Friction and wear tests of bearing steel(GCr15)and silicon nitride ceramics(Si3N4)were carried out on coated 45 steel and uncoated 45 steel respectively.The results show that the friction coefficient and wear amount of graphite self-lubricating coating are lower than those of 45 steel matrix under any pair of friction pairs.It shows that graphite self-lubricating coating can reduce friction coefficient and improve wear resistance.The wear mechanism of coated 45 steel and uncoated 45 steel was analyzed by wear morphology.