Preparation Technology And Wear Resistance Of Ni-P-Al₂O₃ Nanocomposite Deposit By Pulse-assisted Chemical Deposition

With the rapid development of the industry,the problem of part wear and tear in various equipment has become more prominent,leading to an increased demand for surface protection technology.The nanocomposite deposition layer has unique surface protection advantages over typical surface protection technologies such as single metal coating and alloy coating.Incorporating nanoparticles into the coating can effectively improve some aspects of the coating,such as wear resistance,corrosion resistance,high hardness,etc.,to meet some special occasions with high performance requirements.It has been widely used in aerospace,medical equipment,textile coating,ion batteries,energy storage applications,and other industrial fields.There are many preparation processes for nanocomposite deposition layers,such as chemical deposition processes,electrochemical deposition processes,physical vapor deposition processes,etc.However,the traditional chemical deposition method and electrodeposition method to prepare the nanocomposite deposition layer,due to the defects in the process method,such as slow deposition speed,high porosity of the deposited layer,poor performance of the deposited layer,etc.This limits the further development and application of nanocomposite deposition layers.Regarding this problem,combining the advantages and disadvantages of both chemical deposition and electrochemical deposition processes,this project proposes the use of a pulse-assisted chemical deposition process to prepare Ni-P-Al₂O₃nanocomposite deposits and investigates its properties and co-deposition principles.The main research work and results are as follows.(1)The preparation of Ni-P deposited deposits by pulse-assisted chemical deposition process was investigated.A three-factor,three-level orthogonal test was designed by varying the average current density,pulse frequency and duty cycle.The deposition rate and hardness value of the deposits were used as indicators to evaluate each group of experimental data using the integrated equilibrium method,so as to obtain the optimal process parameters.The optimal process parameters were:average current density was 0.6 A/dm~2,pulse frequency was 1000 Hz,and duty cycle was 10%.The influence of each factor on the index is ranked from highest to lowest priority:average current density,duty cycle,and pulse frequency.(2)The Ni-P-Al₂O₃nanocomposite deposits were prepared by adding a nanoscale sol-gel Al₂O₃ dispersion to the Ni-P plating solution and using a pulse-assisted chemical deposition process.Meanwhile,the same deposition conditions were ensured by the controlled variable method,and then the conventional chemical deposition process was used for the preparation of Ni-P and Ni-P-Al₂O₃deposits.The properties of the deposits were evaluated using scanning electron microscopy,energy spectrum analyzer,hardness tester and nanoindentation tester,and the advantages of the pulse-assisted chemical deposition process over the conventional process were investigated by comparative analysis of the deposit properties.The experimental results showed that the nanocomposite deposits with high hardness and good toughness could be prepared rapidly by the pulse-assisted chemical deposition method.(3)An in-depth study on the preparation of Ni-P-Al₂O₃nanocomposite deposits by pulse-assisted chemical deposition process was carried out,and it aimed to prepare nanocomposite deposits with better performance by optimizing the process.The effect of each pulse parameter on the performance of Ni-P-Al₂O₃nanocomposite deposits was investigated by varying the average current density of 0.25 A/dm~2,0.375 A/dm~2,0.5 A/dm~2,0.625 A/dm~2,0.75 A/dm~2,respectively.Scanning electron microscopy and energy spectrometry were used to analyze the surface morphology and composition of the nanocomposite deposits.The hardness,wear resistance and toughness of the nanocomposite deposits were rated by hardness experiments,friction wear experiments and nanoindentation experiments.The Young's modulus(E)and hardness(H)of the deposited layer were detected by nanoindentation experiments,and the toughness of the deposited layer was characterized by the H~3/E~2ratio.The results indicated that the nanocomposite deposits prepared with a average current density of0.375 A/dm~2were optimized in terms of surface morphology,deposition rate and the above-mentioned properties.The deposition rate was 31.81?m/h,the hardness value was 630.6 HV,the wear bandwidth was 96.8?m,and the elastic recovery ratio(h_e/h_max)and H~3/E~2were 0.3218 and 0.043 GPa,respectively.The best wear resistance was achieved when the deposited layer had both high hardness and good toughness.(4)The effect law of pulse parameters on the nanocomposite deposits was further investigated.The effect on the Ni-P-Al₂O₃nanocomposite deposits was investigated by changing by varying the duty cycle,which was 0,10%,20%,30%,40%,and 50%,respectively.The experimental results indicated that,when the duty cycle of the pulsed current was 20%,the Ni-P-Al₂O₃nanocomposite deposits was prepared with an optimal performance,which reached a deposition rate of 45.99?m/h,a hardness value of 629 HV,a friction coefficient of 0.395,a wear bandwidth of 126.33?m,an elastic recovery ratio(h_e/h_max)of 0.3976,and a maximum value of H~3/E~2reached a maximum value of 0.0505 GPa.The optimization of the pulse parameters for this process revealed that the optimal parameters were:the pulse frequency was 1000 Hz,the average current density was0.375 A/dm~2,and the duty cycle was 20%.(5)Based on the experimental study,the deposition principle was analyzed for the preparation of Ni-P-Al₂O₃nanocomposite deposits by the pulse-assisted chemical deposition process.The effects of dispersion enhancement of nanoparticles,the working principle of pulsed current,the principle of co-deposition of metal cations and nanoparticles,and the principle of chemical reaction during the deposition process were studied,so as to reveal the deposition principle and advantages of the process.And the research concluded and gave an outlook on the preparation and performance of the process in nanocomposite deposits.