Study On The Internal Stress, Morphology And Microstructure And Wear Resistance Of High Frequency Pulse Electroforming Ni-Co Alloy

In this paper, we study the internal stress, morphology and microstructure and wear resistance of nickel-cobalt alloy plating by high-frequency pulse plating technique (≥20kHz).About internal stress, we use some different parameters such as pulse plating current density, pulse frequency and duty cycle of the plating, in order to optimize the process parameters. we find the optimum parameters of the plating process is the pulse frequency80kHz, duty cycle0.30, the average current density2A/dm2. And on the ba-sis of the optimum parameters of the plating process, we also study the effects of inte-rnal stress of Ni-Co coating with the pulse frequency, the average current density and COSO4·7H2O concentration. When pulse frequency increases, it was found that the nickel-cobalt alloy coating internal stress the first decreases and then increases, and it has the minimum when the frequency is80kHz. When the average current is increased from the range of2A/dm2to10A/dm2, the alloy coating internal stress will continue to increase. When the pulse frequency is80kHz, with the COSO4·7H2O concentration in bath gradually increase, the Ni-Co alloy coating the first increases and then decreases. It has a maximum value26.4MPa when the Co concentration is35g/L.It studies the morphology and structure of the coating and finds that the number of cobalt content is particularly important for the morphology of the coating composition. At the same time, after nickel-cobalt alloy plating experiment analysis by optical micr-oscopy scanning electron microscopy and X-ray diffraction analyzer, it finds that the cobalt content will increase when the pulse frequency increases as well as bath cobalt concentration, but it fall when the current density increases. Pure nickel coating be sta-cked by face-centered cubic electrodeposited way. With increasing cobalt content of the coating, the Ni-Co coating change gradually from the face centered cubic deposit-ion to hexagonal close-packed, and finally the main deposition way is hexagonal close-packed. It is not uniform when the deposited coating own low cobalt content. When increases t-he cobalt content, the coating quality was significantly improved, decreased porosity,an-d better compactness.Nickel cobalt alloy coatings were prepared on stainless steel rings by pulse plating at high frequencies. The effects of pulse frequency, mass concentration of COSO4in bath, duty cycle, average current density, and pH on the surface morphology and wear resist- ance of Ni-Co alloy coating were studied. The Ni-Co alloy prepared by high-frequency pulse plating features lower porosity, better uniformity and compactness, and higher w-ear resistance as compared with that plated under direct current. The wear resistance of Ni-Co alloy coating is improved with increasing pulse frequency or CoSO4content in plating bath, but becomes worse with increasing duty cycle or current density, and is i-mproved initially but becomes worse later as increasing the bath pH. The optimal proc-ess conditions for preparation of Ni-Co alloy coatings by high-frequency pulse plating are as follows:CoSO4·7H2O35g/L, pulse frequency140kHz, duty cycle0.2,average current density2A/dm2,pH of plating bath3.5, temperature55℃, and time40min.