Study On The Electrodeposition And Properties Of Ni-W Amorphous Alloys

In this dissertation, the Ni-W alloy coatings with different structures were fabricated by the electrodeposition method. The structure, morphology, micro-hardness, wear behavior and the electrochemical corrosion behavior of Ni-W alloy coatings were investigated by X-ray diffraction (XRD), X-ray fluorescence system (XRF), optical microscopy, micro-indentation, friction testing machine, electrochemical testing system and orthogonal experimental design. The effects of addition of La on the corrosion of Ni-W coatings have also been studied systematically.The Ni-W electro-deposition parameters were optimized by the orthogonal experimental design. And the data of orthogonal test was statistically analyzed based on range analysis. The effects of various factors on the coating properties such as hardness, morphology have been extensively studied. According to the orthogonal test, the influence on the structure, morphology and properties of the Ni-W coatings have been investigated and the mechanics of Ni-W electro-deposition is also tentatively discussed. It was found that the Ni-W alloy coatings can be deposited from multiple complex compounds and NH4Cl and Na3C6H5O7 play an important role as the complexing agent. The current density and deposition temperature are the main factors which respectively affect the crystallization kinetics and thermodynamics of the process. The structure and properties of the coatings are closely related to tungsten content. The structure of the deposits exhibits crystalline phase when the tungsten content in the electroplated alloy is less than 21 at%, but an amorphous structure when it is above the value. The coatings exhibit a columnar crystalline structure with the tungsten content around 20 at%.The friction wear testing machine was employed to characterize the frictional wear behavior of Ni-W coatings under the boundary lubrication conditions. The effects of rotational speed and loading on the friction behavior, and the friction relations between the coatings and wear pairs were systematically studied. It was found that rotational speed of the machine had less impact on the friction of coatings. The grade-abrasion takes place under the fractional load condition (100N) resulting in the formation of furrows and the pitting on the surface of the specimen; While the adhesion-abrasion occurs under the heavy load condition (300N) and cause a serious damage of the coatings with a large number of wide and deep furrows and pitting. Ni-W amorphous alloy also has good abradability compared with the GCr15 bearing steel.Electrochemical experimental results demonstrate that Ni-W alloy coating possesses a better corrosion resistance than 1Cr18Ni9Ti stainless steel, and that the corrosion of amorphous alloy is superior to its crystalline counterpart. The effect of addition of rare-earth element La on the synthesis and the corrosion behavior of coating was also investigated. It was found that the addition of La can enhance the wear resistance of Ni-W coating. When the addition of La reached 0.5 g/L, the alloy coating has the best performance.