Microstructure And Grain Evolution Characteristics Of Industrial Electrodeposited Coatings Of Nickel

Nickel is widely used due to its excellent properties,whether in the traditional steelmaking and electroplating industries,or in aerospace materials,energy batteries and other fields that represent the development of new technologies.At present,the main industrial production method of high-purity nickel plates is electrolytic refining of nickel sulfide soluble anodes.For the study of nickel electrocrystallization process,there have been many achievements in a variety of electrolyte systems.However,for the nickel electrolysis process in the context of industrial production,due to the complexity of the electrolyte system and the fluctuation of the conditions in the process,the study of this process is difficult.The research group has studied the electrocrystallization behavior of nickel in industrial electrolyte system under laboratory conditions in the early stage,and also has a certain research on the structure and performance of industrial electrolytic nickel.This article takes industrial electrolytic nickel as the research object,and explores the growth and evolution process of electrodeposited coatings of nickel under industrial production conditions by analyzing the changes in the microscopic characteristics of nickel plates.Using XRD,SEM,EBSD to analyze the grain size,grain boundary character distribution,and preferred orientation of industrial electrolytic nickel with different production times(24h,72h,120h,168h,216h)on the surface and cross section.At the same time,a relatively short time electrodeposited coatings of nickel were prepared by using Hall cells,and the preferred orientation and surface micro-morphology changes were analyzed by XRD and SEM.The results show that the electrodeposited nickel plate exhibits different preferential growth planes on the surface and cross-section.The crystals mainly grow in the direction perpendicular to the (200) plane on the surface,while the cross-section exhibits (111) and (200) double preferential orientation,crystal growth mode is lateral growth.The surface morphology of the deposited nickel plate changed from "pyramid" to "cell" at 72 h,and the growth mechanism changed from spiral dislocation-driven growth to atomic accumulation and growth;the cross-sectional morphology of the nickel plate at each stage is always "lamellar" State.As the deposition progresses,unlike the cross-section,the surface grain morphology of the electrodeposited coatings of nickel appears as equiaxed crystals,and the grain size is gradually growing.In industrial production,nickel electrocrystallization nucleation growth is not carried out under a single mechanism.The continuous nucleation mechanism at the beginning of the deposition is the main one,and then the deposition changes the instant nucleation mechanism.When the nickel electrolysis process is 120 h～168 h,the continuous nucleation mechanism gradually dominates.After restarting for a period of time,the crystal growth speed of the deposited layer is accelerated,and instantaneous nucleation become the main form.The grain boundaries in the electrodeposited nickel plate are mainly high-angle grain boundaries,and the relative frequency of ∑3 twin boundaries in the characteristic grain boundary distribution reaches more than 60%.The electrolytic nickel plate exhibits a <001> orientation in the cross-sectional growth direction.In the production of electrolytic nickel plates,the stop tank has a limited effect on the growth of the deposited layer.The microscopic morphology of the cross-section of the nickel plate is still lamellar,and the crystal grains continue to grow,the orientation does not change.In the industrial electrolyte system,the nickel deposition layer crystals preferentially grow on the (220) plane,the crystal growth morphology changes from flaky to pyramid shape,and the deposition layer grows in a spiral dislocation-driven mode.Through the large-area EBSD splicing technology,the microstructure of the entire crosssection of the industrial electrolytic nickel plate with a production time of 24h was analyzed.The results showed that the grains on the growth section changed from equiaxed grains to columnar grains along with the deposition process.The grain size is gradually increasing;the grain size below 3.5 μm accounts for 91.36%.Under industrial production conditions,the orientation of the substrate has an epitaxial effect on the orientation of the nickel deposition layer at the initial stage of deposition,and then the orientation is affected by the deposition conditions.The growth orientation of the industrial electrodeposited coatings of nickel tends to the <001> direction.During the nickel electrodeposition process,lots of growth twins were produced,and the frequency of ∑3 grain boundaries of CSL boundaries reached more than 65%,followed by ∑9 and ∑27 grain boundaries.The twin boundary of ∑3 affects the orientation evolution of the deposited layer.In industrial production,different substrate surface conditions have an impact on the formation of crystal grains at the initial stage of deposition.On the surface of the fine grains of the starting sheet,the deposition has undergone a nucleation and growth process;the nickel atoms on the free deposition and growth surface are directly incorporated into the crystal lattice,and continuing the growth of the existing surface without the formation of new crystal nuclei.