Study On The Properties Of Electrodeposited W Alloys And The Blacking Of Tungsten Coatings

In resent years, electrodeposited tungsten alloy coatings were regarded as one of the potential chromium substitutes for many of their excellent properties, such as decorative appearance, good wear and corrosion resistance, high hardness, high thermal stability, high catalysed active property, good magnetism, environment friendly and its potential engineering applications. Because of the atrocious environment of the oil well where has abundant corrosion medium such as H2S,CO2 and Cl-, there is a serious destroy on the sucker rods and other equipments under oil well, and it brings great financial losses. At the same time, sucker rod and other equipments under oil well endure various loads, for example bend, torsion and so on. It is showed that the material must have high mechanical properties. In order to improve the properties of the sucker rods, we usually electroplated metal coatings on its surface. The traditional method is the chromium coatings by electroplating, but there is a serious contaminated to the environment during the producing process. The hydrogen embrittlement phenomenon which is the concomitant of the electroplating process generally affects the mechanical properties of the substrate and the coatings.In this paper, we choice the 35CrMo sucker rods as the object, and electrodeposited Ni-W-P & Fe-Ni-W alloys which applied abroadly in product line in order to study the corrosion resistance of the tungsten alloy in 3.5% NaCl solutions and the effect of tungsten alloy on their mechanical properties.Blackness not only has decorative appearance, but also possesses decalesence and extinction property. Its application was widely used take war industry, optics for instance. When power is cut off suddenly during the producing process, the product can not take out at once. Subsequently, some products turn to black. We paid attention to this interesting phenomenon, and studied the color-change reason and the possible mechanism. Throuhg resolving the trouble in producing process, we are looking forward to get black coating on tungsten alloy and apply it for practice. The meaning of this work is to guide the production practice and contribute to the black theory.In this thesis, following research were studied in detail.1. We obtained two tungsten alloys by electroplating methods and studied their corrosion resistance in 3.5% NaCl solutions. The corrosion mechanism of W alloy was researched through weight losses methods, anodic polarization curve measurement and EIS techniques. It is showed that the corrosion resistence of tungsten alloys was better than the substrate sucker rod, and heat treatment can increase the corrosion resistence of the tungsten coatings. The micro-appearance of W alloy and heat treatment was analysised by X ray diffraction, and explained the reason.2. Studied the mechanical property of tungsten alloys on the sucker rods and drill rods. The mechanical properties were tested by omnipotent examinational machine, metallograhg of the sucker rods and drill rods were observed by electron microscope. It is showed that there was no negative influence of the tensile intensity, and positive influence of tortuous intensity on the material.3. We have researched the formation of blacking film on the tungsten coatings during the plating process, analysis the blacking mechanism and the supposed a hypothesis about the blacking phenomenon. The blacking coating may be consists of oxalic acid complex, oxid of iron and nickel et.al. It is meaningful to the product line and blackness theory as well.