Study On Properties And Mechanism Of Electro-brush Plating Metastable State Ni-B Alloy Coating

Metastable state alloy coatings are widely used in surface engineering field due to their excellent mechanical and physicochemical properties, such as high hardness and good corrosion resistance. However, in the practical production and application, when they are under thermal and mechanical stress, phase transition and microstructure evolution are prone to occur. It leads to the obvious reduce of their desirable properties. In addition, excessive residual stress can cause bulges and flaking, resulting in the failure of the coatings.Electro-brush plating technology not only plays an important role in rePairing Parts without disassembling the machine, but also can be applied to produce metastable nanocrystal coating. In this research, metastable Ni-B and Ni-B/La2O3 coatings were prePared on 1045 steel substrate through electro-brush plating technology. Optical microscopy and Scanning Electron Microscopy (SEM) were used to study the morphology on surface and cross-section of the coatings. Elements and contents in the coatings can be measured by Energy Dispersive X-Ray Spectroscopy (EDS). The results of phase structure,the degree of crystallinity and grain size were obtained by using X-Ray Diffraction (XRD). And the coating microstructure was analyzed by Transmission Electron Microscopy (TEM). Corrosion resistance, wear resistance and nano-mechanical property were characterized by electrochemical workstation,friction-abrasion testing machine and nano-indenter, respectively. Finally, according to load-displacement curves, the residual stress can be calculated by Suresh model and Lee model.From the results, properties of metastable Ni-B/La2O3 alloy coatings depend on the degree of crystallinity. When the degree of crystallinity is 42.66%, the coatings have the excellent resistance of corrosion and wear. Based on the principle of nanoindentation, with the assistance of conclusions from Lee model, residual compressive stress exists in Ni-B coatings at as-plated state. And its value of residual stress is directly related to the total area of grain boundaries. It increases with the decreasing total area. The analysis of thermal stability shows that the coatings have excellent thermal stability. Especially when the annealing temperature reaches to 600?, the grain size still remains less than 50nm. Therefore, the addition of La2O3 can improve the formation of dense coatings as well as their thermal stability.