Research On Fabrication And Wettability Of Lyophilic Nickel Coating On Cooling Roll Surface

As new functional materials,amorphous ultra-thin strip has been widely used in high-tech fields such as aerospace equipment,power system,medical devices and intelligent wear.At present,the amorphous ultra-thin strip was prepared by single roll quenching technology.The metal melt was sprayed to the surface of the high-speed rotating cooling roll,spread rapidly,and solidified at the speed of 10~6 K/s to form an amorphous structure.The preformed metal was quickly thrown out by centrifugal force and formed into an amorphous ultra-thin strip with a thickness of only tens of microns.It is found that the hydrophilicity of the metal melt on the surface of the cooling roll accelerates the cooling rate,and improves the magnetic conductivity,strength and corrosion resistance of the formed amorphous ultra-thin strip products.The polished copper roller was used as the solidification base of metal melt.However,due to the low high temperature strength of copper,wear and fatigue failure were easy to occur under the combined action of molten metal spraying force,alternating thermal stress and friction wear.The hydrophilicity the cooling roll tended to weakened,resulting in the decline of the characteristic performance of the amorphous strip.Therefore,the main research objective of this thesis is to prepare the cooling roll surface with long-term hydrophilicity,so that it can maintain the metal hydrophilicity,high surface energy state and wear resistance in the environment of high temperature aging,friction wear and natural aging.This thesis provides guidance for improving the amorphous properties of materials,extending the work cycle of cooling rolls,and is of great significance for promoting the research,development and innovation of amorphous ultra-thin strip preparation technology.In this thesis,the Butler Volmer dynamic formula,turbulent flow field model,secondary current distribution model and Tafel electrochemical equation were used to simulate the electrochemical deposition process coupled with multiple physical fields,such as ion transfer,fluid turbulence,deposition evolution and hydrogen evolution reaction.The variation rules were found,including the coating thickness and its distribution uniformity under the coupling effect of electrochemical deposition process parameters.The influence rules were analyzed,such as the influence of the composition of the electrochemical deposition solution on the surface microscopic characteristics and wettability of the nickel deposition layer.Response surface methodology was used to construct the relationship agent model of influencing factor space.The uncertainty analysis method based on stochastic convergence analysis was used to study the change rule of the distribution uniformity and surface wettability of the deposition layer under the interaction and coupling of the deposition process,solution composition and other factors.The significance of the selected parameters was evaluated,and the key parameters were selected for further research.An optimization scheme was proposed to reduce the edge effect of the electrode plate,weaken the concentration polarization phenomenon,and obtain uniform surface wettability.The surface of the prepared nickel deposit was modified by chemical etching and ultraviolet irradiation,and the influence rule was obtained,which was surface wettability such as surface micromorphology,roughness,chemical element content and surface free energy.The variation of surface free energy and its components are calculated by van Oss Chaudhury Good method.The corresponding relationship has been obtained,which includes the polar Lewis acid base component of surface energy and surface wettability.Cassie Baxter model was used to analyze the mechanism of adsorption of hydrocarbon particles in gas phase and the change of surface wettability caused by the difference of surface roughness.The irregular ridge like structure and multi convex block structure prepared by chemical etching method can still maintain good wettability in the long physical aging process.The liquid metal contact angle on the surface of the deposition layer can also be effectively reduced by preparing laminated sheet structures and large pyramid structures through ultraviolet irradiation.Considering the working environment of the cooling roll,the law of surface free energy transition and wettability change mechanism has been studied,which refers to the process of long-term physical aging,short-term high-temperature aging and wearing.The experimental results show that the contact angles of tin melt with low surface tension and aluminum melt with high surface tension are less than 20°and 62°on the surfaces with ridge uplift structure,polygonal layered cavity structure and lamellar structure,while the contact angles of other modified surfaces were between 24°～34°and 70°～75°.The contact angles of polished copper samples were much lower than 40.3°and 82.2°.After high-temperature wearing,the samples with the above three kinds of microstructure still maintained Lewis acid-base interactions,which were 7.32 m J/m~2,7.46 m J/m~2 and 7.15m J/m~2,respectively.However,the surface energy of the sample with multi-raised block structure decreased significantly,and was only 6.7 m J/m~2,while the surface energy of copper was only 6.2 m J/m~2.The modified surfaces prepared in this thesis has relatively stable liquid philicity of metal melt,high surface energy state and good high-temperature wear resistance,which has important academic value and guiding significance for improving the quality stability and production efficiency of amorphous ultra-thin strip and promoting the development and innovation of amorphous strip technology.