Microstructure And Wear Resistance Of Nibased Coatings Reinforced With In Situ Ceramic Particles By Laser Cladding

Most failures of mechanical components made of 45 steels occur on the working surface.Using laser cladding technology to prepare in situ TiC reinforced Ni-based coatings on the surface of 45 steel can significantly improve the surface performance of the substrate,allowing the purpose of repairing damaged work surfaces and strengthening surface quality to meet the requirements of the engineering field while ensuring a lower cost.This can significantly reduce the economic losses caused by component failures,which contribute to the implementation of national green and sustainable development strategies.For the preparation of Ni-based coatings with excellent mechanical properties,especially wear resistance,on 45 steel substrates,in this paper,thermodynamic calculations of in-situ ceramic particle-reinforced Ni-based coatings,analysis of the effects of different process parameters and graphite content on the temperature and stress fields of laser clad coatings,and research on the physicochemical and wear resistance properties of coatings prepared by laser cladding were carried out.The details include:Based on thermodynamic theory,the enthalpy changes of generation and Gibbs free energy of possible chemical reactions in the Ni60,Ti and C systems are calculated.The enthalpy changes of TiC,Ni Ti,Fe₂Ti and Ni₃Ti reactions are less than zero from 50 K to 2500K.The enthalpy changes of Cr₇C₃ and Cr₂₃C₆ reactions are-175.23 k J and-1130.29 k J respectively at 2500 K.All reactions are exothermic at high temperatures.The Gibbs free energies of the TiC,Cr₇C₃and Cr₂₃C₆ reactions are-145.42 k J,-476.40 k J and-236.46 k J at2500 K.The chemical reactions can occur spontaneously,and the resultants can be stable at high temperatures.Based on finite element theory,the simulation of the temperature and stress fields of single-pass Ni-based coatings with different process parameters and different graphite contents is completed,revealing the effect of different factors on the temperature and stress fields of the coatings.The increase in laser power is found to lead to a numerical increase in the temperature and stress fields of the coatings.The increase in scanning speed decreases the value of the temperature field,resulting in a dense isotherm in the longitudinal temperature field,decreases the value of the stress on the surface of the substrate and increase the stress at the coating intermediate interface and the coating surface to the substrate bottom surface.The addition of graphite slightly reduces the temperature values of the simulated coating and decreases the stress values in the clad area of the coating.The simulated peak coating temperature is as low as 2949 K,which allows for good metallurgical bonding of the coating to the substrate.In situ ceramic particle reinforced Ni-based coatings are prepared,the effects of different process parameters and graphite additions on the microstructure and properties of the coatings are analyzed.It is found that an increase in laser power,scanning speed and graphite addition results in a reduction in tissue grain size and a diffuse distribution of endogenous particles at grain boundaries,inhibiting grain growth.As the laser power increases,the hardness of the coating increases,the friction coefficient of the coating surface increases and the wear rate decreases.When the laser power is 1600 W,the hardness of the coating reaches 401.4 HV,which is 37.9%higher than that at 1200 W,and the wear rate is 8.518×10^-5 g/m,which is11.5%lower than that at 1200 W.With the increase of scanning speed,the hardness of the coating increases,the friction coefficient and wear rate of the coating surface decrease.When the scanning speed is 150 mm/min,the hardness of the coating reaches 416.5 HV,the friction coefficient and wear rate are 0.27 and 4.074×10^-5 g/m,which are 42.6%and 52.2%lower than those at 50 mm/min.With the increase of graphite addition,the microhardness gradually decreases and the friction coefficient and wear rate of the coating surface are significantly reduced.The friction coefficient and wear rate of the coating with 0.7 wt.%graphite addition are 0.25 and 3.333×10^-5 g/m,respectively,which are 46.8%and 60.9%lower than those of the coating without graphite addition.