Study On The Microstructure And Properties Of Electroless Ni-p Based Composite Platings

The synchronous ring as one of the most important components in the automotive gearbox requires good wear resistance and high friction coefficient.In order to improve the wear resistance and friction coefficient of the synchronous ring material TL084 copper alloy,the Ni-P,Ni-P-TiN and Ni-P-TiN-Re platings were successfully prepared on the surface of TL084 copper alloy by electroless composite plating.The influence of TiN particles,Re elements and heat treatment temperature on electroless plating was studied.The phase structure,surface morphology,cross section morphology,elemental composition and crystallization temperature of the plating were analyzed by XRD,SEM,TEM,EDS,DSC.The surface microhardness and tribological properties of the platings were also tested and researched.The results show that the structure of all electroless platings is amorphous.The content of P in both Ni-P and Ni-P-TiN platings is about 12 wt.%,which belongs to high P content.However,the content of P in Ni-P-TiN-Re plating decreases with the increase of Re.The crystallization of platings occured after heat treatment,and the stable phase compositions were Ni and Ni3 P phases at high temperature(600?).The crystallization temperatures of Ni-P and Ni-P-TiN platings are the same,but the thermal stability and the crystallization temperature of Ni-P-TiN-Re platings are increased due to the addition of Re.Ni-P and Ni-P-TiN platings are composed of Ni,Ni3 P nanocrystals,and the Ni-P-TiN-Re platings also have a few amorphous components in addition to the nanocrystals at 400 °C for 1 h.The microhardness tests show that the hardness of Ni-P-TiN and Ni-P-TiN-Re platings is higher than that of Ni-P platings and improves with the increase of TiN particles and Re content in the platings.The hardness of each electroless plating increases first and then decreases as the heat treatment temperature increases.The hardness of Ni-P and Ni-P-TiN platings reaches the highest at 400°C,and is around HV0.11100.The Ni-P-TiN-Re plating reaches its maximum hardness at higher temperatures and the maximum hardness also increases.Wear resistance tests show the wear resistance of the Ni-P-TiN plating is improved when the content of TiN particles in the is small,and the friction coefficient is between 0.4-0.5,much higher than the friction coefficient(0.08)of TL084 copper alloy copper.The Ni-P-TiN-Re plating also has better wear resistance and the friction coefficient is between 0.15-0.28.The wear mechanism is mainly oxidation wear.The wear resistance of each plating is enhanced after heat treatment at different temperatures,and the plating friction coefficient is related to the hardness.Generally,the friction coefficient increases with hardness.The wear rates of Ni-P-TiN-Re plating with 8g/L TiN and 2g/L NH4 Re O4 addition contents at all temperatures are low,and the wear scars are narrow.Among them the lowest wear rate is 1.14×10-8 g/(N·r)at 400°C for 1 h,which is 84.8% lower than that of the original copper alloy and the wear mechanism is mainly oxidation wear and slight adhesive wear.