Study On Microstructure And Mechanical Properties Of Electroless Ni-P-PTFE Composite Coating

With the continuous development of science and technology,electroless Ni-P coating technology is becoming more and more important in surface treatment technology.Introducing the PTFE particles with the excellent self-lubricating properties into Ni-P alloy,the Ni-P-PTFE composite coating can present both very low friction coefficient and the comparatively high hardness at the same time,greatly improving the performance of Ni-P-PTFE coating.As a kind of composite coating with excellent lubricating properties,the pre-treatment,process parameters and post-treatment have an important effect on the microstructure and mechanical properties of Ni-P-PTFE composite coating,which has a very important significance.To this end,the main research contents of this thesis are as follows:the pretreatment process of electroless Ni-P-PTFE composite coating on stainless steel substrate,the pretreatment process of electroless Ni-P-PTFE composite coating on brass substrate,structural and process parameters of electroless Ni-P-PTFE composite coating,post-heat treatment of electroless Ni-P-PTFE composite coatings.The main conclusions can be made as follows.(1)The pretreatment process parameters of stainless steel and brass substrates have a great influence on the microstructure and mechanical properties of Ni-P-PTFE composite coating.For the stainless steel substrate,when the current density of pre-plating process is 3.3A/dm~2 and the pretreatment time is 6min,the comprehensive properties of Ni-P-PTFE coating can be attained with the hardness of 3.874GPa,the bonding strength of 27.45N,the friction coefficient of 0.145.For brass substrate,when the removing oil temperature is 70?and pickling time is 4min,the electroless Ni-P-PTFE composite coating can achieve the best comprehensive performance with the hardness of 5.16GPa and the friction coefficient of 0.135.(2)The structural and process parameters of electroless process have a great influence on the microstructure,hardness and friction coefficient of Ni-P-PTFE composite coating.With the fixed PTFE concentration and pH value,the hardness and tribological properties of Ni-P-PTFE composite coating change with the deposition time of Ni-P transition layer.With the fixed deposition time of Ni-P transition layer and the pH of plating solution,the composite coating hardness firstly increases and then decreases with the increase of PTFE concentration,while the friction coefficient of composite coating firstly decreased and then increased.With the fixed the deposition time of Ni-P transition layer of 15min and the concentration of PTFE of 50ml/L,the hardness of the coating firstly decreases and then increases and finially decreases with the increase of the pH value of the plating solution,while the friction coefficient of composite coating firstly decreases and then increases.(3)Through optimizing of the structural and process parameters of electroless Ni-P,Ni-P-PTFE composite coating,when the deposition time of electroless Ni-P transition layer is 15min,the concentration of PTFE is 50ml/L and pH is 5.5,the electroless Ni-P,Ni-P-PTFE double layer composite coating can achieve the excellent comprehensive properties with the minimal friction coefficient of 0.145 and the hardness of 4.548GPa.(4)The time and temperature of post-heat treatment have a great influence on the microstructure and hardness of the Ni-P-PTFE composite coating.With the fixed heat treatment temperature,the hardness of Ni-P-PTFE composite coating firstly increases and then decreases with the increase of annealing time.With the fixed the annealing time of 80min,the hardness of the coatings firstly increases and then decreases with the increase of annealing temperature.(5)By optimizing pro-heat treatment process,when the annealing time is 80min and annealing temperature is 400?,the electroless Ni-P-PTFE composite coating on 70brass substrate can achieve the maximal 9.081GPa,greatly improving the strength of Ni-P-PTFE composite coating.The friction and wear resistances of the coatings accordingly increase.(6)Through the comprehensive study of the Ni-P-PTFE composite coatings,including substrate pretreatment process,optimization of structural and process parameters,and subsequent heat treatment process,it can be concluded that the optimized parameters of pre-plating treatment process are current density of 3.3A/dm~2,the depostion time of 6min;the removal oil temperature of 70?and pickling time of4min.The optimized structural and process parameters of Ni-P-PTFE composite coating are the deposition time of electroless Ni-P transition layer of 15min,the concentration of PTFE in the bath of 50ml/L,and the pH value of 5.5.The optimized subsequent heat treatment parameters are the annealing time of 80min and the annealing temperature of400?.With the optimized parameters,the Ni-P-PTFE composite coating with uniform microstructure and high hardness,excellent friction and wear resistances can be obtained.