Study On Prepare Composite Coatings By Controlled Atmsphere Thermal Spraying

Thermal spraying under low vacuum condition (i.e. low pressure spray) is one of the new technologies developed in recent several years. Take advantage of this new kind of thermal spray technology, coatings with very low oxygen can be prepared. Which has been successful applied in the materials with easy oxidation and biomedical properties.A new type of low-pressure spraying device has been designed in this work. Two separate spraying guns can simultaneously be used to complete the preparation of coating. These approaches can flexibly design and preparation of various metal-metal composite coating and ceramic-metal composite coatings. It has provided a new technology not only for composite coating, but also offers a new way for the preparation of bulk composite materials by using thermal spraying.First, many kinds of sole metallic material coatings were prepared by using the low pressure thermal spraying method we developed. The connected morphologies between the spraying granule, the oxide compound content and the distribution in the coating have been analyzed and determined. Furthermore, through methods of such as compression and heating, the post-processing to the coating was discussed in order to investigate the ability of crystal grains traversing the oxide compound boundary to grow in the coating as well as the technique of formation of metallurgical combination between the parent metal and coating. Based on the study of the morphology in the low pressure spraying, Ti coating with extremely low oxygen content was prepared. The oxide compound, nitride quantity and the distribution were analyzed, which has provided some useful essential data for its application in the anti-corrosive coating and the biomedicine coating.Second, many metal-metal and ceramic-metal composite coatings were successfully produced using twin gun spraying technology under low-voltage. The microstructure, the composition and the characteristics and distribution of the constituent phases of the coating were investigated. The mechanical testing, such as hardness, strength, wear resistance of the coating were carried out in order to analyze the mechanism related to the composition formation processes during thermal spraying, which provides the academic background and rules for the flexible design of various composite coating in the future. Research also focuses on gradient coating and its related properties such as the microstructure, composition and continuous changes in the mechanical properties of the coating obtained by using low pressure spraying. Detailed analysis was given access to the forming rules and technological essential. Which provides a new way of thinking for preparation of gradient coating.