Study On New Technique And Properties Of Electroplating Ni-Fe Alloys On Copper Plate For Continuous Casting Mold

The purpose of this dissertation, is to obtain excellent wear-resistance Ni-Fe alloy coating on the crystallizer bases: copper or copper alloys. With the extensive survey of the reported references of the coating technology on crystallizer surfaces, the preparation technology of Ni-Fe coating is intensively discussed.The conventional electrodepositing methods and jet electrodepositing methods are used to prepare the alloy coating on the copper substrate or copper alloys substrate. The coating with the substrate was then processed with de-hydrogenization at 400 centigrade to obtain the desirable binding strength between the coating and the substrate.For the coated Ni-Fe alloy, the effects of the electrolyte composition and the process parameters on the structure and properties of the coating are discussed, while for the jet eletrodeposited alloy coating, the effects of the jet rate and the current density are highlighted.The phases in the Ni-Fe coating are identified with X-ray diffraction, and SEM and EDS are used to determine the surface morphology and composition. The wear-resistance property is examined in a MPW wear test machine. The thermal expansion coefficient is determined by using a DIL 402C dilatometer, and the STA 449 C/6G analyzer is used to analyze the undercooling and crystallization processes as well as the oxidation behavior at high temperature.The results suggest that the desirable composition in this dissertation and certain processing technology together with the synthesized YD-JK additive facilitate the formation of a 2 mm thickness of Ni-Fe coating with grain sizes smaller than 20nm, whose wear-resistance is 2~3 times higher than that of the Ni coating of the same thickness. The adjustment of ratio of Fe2+/Ni2+ in the eletrolytes helps to obtain theγ-nanocrystalline containing Ni-Fe coating with 3~5% iron. The change of spray rate and current density helps to obtain theγ-nanocrystalline (grain size being smaller than 10nm) containing Ni-Fe coating with 3.54~5.02 wt % iron, and the deposition rate can reach 7.0μm·min-1 with the current efficiency being up to 80%, and the microhardness of the coating reaches HV 565. The thermal analyses suggest that while the Ni coating melt holds an undercooling degree of 411K, the Ni-Fe alloy coating melt has a value of 426K. With the superheating degree fixed, the undercooling degree of Ni and Ni-Fe coating melts rises with the cooling rates. The higher cooling rate leads to a shorter crystallization time. In parallel, with the cooling rate fixed, the deep undercooling can be reached in a certain temperature range by enhancing the superheating degree.