| As the development of science and technology, people are increasingly demanding the properties of materials. The service life of parts and components under bad working condition is a worring problem all the time. For example, the components of plane, the wearable parts of oil exploration, the blades of steam turbine in order to reclaim excessive energy of current in petrochemical, the tubes of boils'heat-exchanger and so on. Along with researching deeply in surface engineering technology, preparing nano structured coatings in common substrate by thermal spraying instead of making parts used of high performance materials. It has advantages that operating easily and saving materials. And it could solve the problem which it is hard to cut the high performance materials. This text is based on the trailblazers'productions, study on spraying technics and properties about nanostructured WC-Co ceramic coatings which are prepared by High Velocity Oxy-Fuel(HVOF) .The main contents of this text as follows:Basic characteristic of nano ceramic materialThe nano-material applies in many realms in the life because it has some special functions. The nano ceramic material means having the nano levle microstructure (1nm～100nm) or kinds of ceramic that its sizes at least in one dimensional are nanostructured. As the wafer is so thin that the number of crystal boundary increase greatly. Therefore, the material's intensity, toughness and wear-resisting property increase greatly. Compared with the traditional ceramic material, nano ceramic has more excellent performance.Basic theories on HVOFHigh Velocity Oxy-Fule(HVOF) is a spraying technology which heat the powder and spray it into melting or half melting droplets, then they are accelerated and collide on substrate or coatings which have formed before, and form a piece of coating at last after flatting subsequently. Compared with other thermal technices, High Velocity Oxy-Fule(HVOF) has much higher velocity of the flame and lower firebox's temperature. So it suit for spraying ceramic powder which could be oxidated easily in the air. The process of HVOF spraying includes preparation of substrate, pretreatment of substrate, spraying, treatment after spraying and finish machining etc. The propane and oxygen flows , spray distance and feed rate etc are the most important parameters which influence the temperature and velocity of droplets in HVOF spraying, and they are interacted each other.Theoretical analysis on the process of coatings'formingThe main style of integration between coatings and substrate or coatings and coatings which has formed is mechanical bonding. The residual stress of coating is composed of several stresses, chilling and cooling stress are in dominant position. It suit to make much thicker coatings that due to compress stress in it for HVOF spraying.The structure of coating is determined by droplet's condition before colliding the substrate and the process of flating subsequently which influence the coating's mechanical property.1. When the droplets were heated in firebox, the bigger or higher density it is, the lower it could reach the highest temperature. The same as it would takes much long time to reach an aim temperature.2. The factors that influence the droplets'acceleration in current are curent's velocity, the size and density of droplets etc.And the acceleration is directly proportional to the velocity's subtractor beween current and droplets, is inversely proportional to the diameter and density of droplet.3. The higher density, size or velocity of droplet is, the higher flat ratio is.Experimental research on nano-WC-Co ceramic coatingsThis paper has obtained the best technical parameters of preparing nano-WC-Co ceramic coatings by application of orthogonal tests. It has observed and analysed the coatings by SEM and XRD test. Furthermore, it has tested bonding strength, micro-hardness and wear-resisting property etc by experiment. The results were as follows:1. The best technical parameters is as follows: the powder feed rate is 36g/min, the propane flows is 35L/min, the oxygen flows is 425L/min and the spraying distance is 210mm.2. It can be seen from coatings'Scanning Electric Microscopy(SEM) photos that the grains of coating is thin, the micro-crack hasn't been found and the pore has been found on coating, and the coating is basically composed of nanometer and sub-micrometer particles.3. From the curve of the coating's X-Ray Diffraction(XRD) analysis it can be concluded the coating is composed of WC phase and Co phase, and there isn't W2C phase and C phase been found in it. It can be proved that the powder hasn't been oxidezed or some little.4. The maximum of coating's micro-hardness reached to HV0.21628. Compare with common coating, it conform to the law of Hall Patch:which is the micro-hardness increases with the fall of the dimension of grains.5. The maximum of coating's bonding strength is 58.64MPa, it's break all takes place at cementation plane. So there is no way to give an exact data, and it is worthy of further studying.6. The difference of the loss between coating and substrate was diminshied along with the abrasion. But in all, the wear-resisting property of coating is much better than substrate.
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