Study On Microstructure And Process Optimization Of Electro-spark Deposition Coating On Titanium Alloy

Titanium alloy has good comprehensive properties and is widely used in various industries.However,the low hardness of titanium alloys limits its application in some aspects.It is especially important to improve the hardness of titanium alloy.Surface treatment technology is a direct way to improve material properties.Electro-spark deposition technology is a surface treatment technology developed in recent years.The deposition coating not only does not cause thermal deformation,but also improves the overall performance of the coating,which makes metallurgical bonding between the coating and the substrate,and has been widely concerned by researchers.This research focuses on the research of titanium alloy ESD NiCr-3 coating experiment.The effects of electro-spark deposition process parameters on coating surface quality,interface behavior,thickness and hardness were analyzed and multi-objective process parameters were optimized by BP neural network and NSGA-?.The main research contents are as follows:(1)TC4 titanium alloy and nickel-based alloy electrode were selected as experimental materials.Designed an electro-spark deposition experiment of titanium alloy under different nickel-based alloy electrodes.NiCr-3 was determined as the electrode material of the experiment by analyzing the hardness of the coating under different experimental conditions.The single factor experimental design of titanium alloy ESD is carried out by three factors:deposition voltage,deposition frequency and deposition time.And the process rule experiment of electric-spark deposition processing for titanium alloy workpieces.The influence of deposition parameters,deposition voltage,deposition frequency and deposition time on the surface morphology and surface roughness of the coating was studied.(2)Experiment on the process of electro-spark deposition of NiCr-3 coating on titanium alloy.Coatings are detected by X-ray diffractometer,scanning electron microscope,electron spectrometer and microhardness tester.For the microstructure of the coating,The effects of process parameters on the white area of the coating and the movement of the main elements of the substrate and the electrode were studied by the interface morphology of the coating under different process parameters and the distribution of the main elements in the electrode and the substrate.The X-ray diffraction pattern was analyzed according to the coating.Phase composition of the coating.For the coating properties,the influence of different process parameters on the thickness and hardness of the coating was analyzed.(3)Orthogonal experiment was designed based on the results of single factor experiment of titanium alloy electro-spark deposition.The results of single factor experiment and orthogonal experiment were used as training samples.A process prediction model for ESD process parameters,coating thickness and surface roughness was established by BP neural network algorithm and used experiments to verify the accuracy of the model.The NSGA-?theory,predictive process model established for the fitness function.The multi-objective process parameters were optimized for the surface roughness and thickness of the coating and the optimal solution set of the titanium alloy ESD was obtained and tested by experiments.In summary,this research mainly starts from the principle of ESD process.Analysis of the influence of process parameters on coating surface quality,interface behavior and properties by single factor experiments.Based on single factor and orthogonal experimental data,BP neural network was used to establish process prediction model,and the model was used as the fitness function of NSGA-? to optimize multi-objective process parameters.It will play a guiding role in the future electro-spark deposition technology.