Li Changjiu's Academic Achievements

Professor Li Changjiu has been engaged in the basic research of surface modification and forming based on thermal spraying. Through the continuous in-depth study of the frontier of the discipline, the following distinctive research results have been achieved in the microstructure of the coating, the characterization method of properties and the collision behavior between thermal spraying particles and the substrate related to the formation mechanism of the coating. A tracer method is proposed and established to visually and quantitatively characterize the layered structure of plasma sprayed coatings, and quantitative characterization parameters are introduced to reveal the structural change law of plasma sprayed coatings. The characteristic that the interlayer bonding of traditional plasma spraying coating is about 32% at most is expounded. It is revealed that the interface temperature is the controlling factor of bonding in the process of particle flattening, and the methods to greatly improve the interface bonding rate and adjust the coating structure are found. The theoretical relationship between elastic modulus, erosion rate, fracture toughness and coating structural parameters is established, and the framework of the relationship between coating structure and properties is constructed, which provides a theoretical basis for revealing the structural parameters that determine coating properties. The change law of flat particle morphology in plasma spraying is expounded, and the splash mechanism models are put forward: "evaporation-induced splash model of surface evaporable adsorbent" and "surface melting-induced splash model" Combined with the liquid fluctuation effect caused by high-speed particle collision, the essential factors to control particle splash are revealed. This paper reveals the essential influence of the liquid-solid two-phase state of sprayed particles on the coating deposition characteristics in supersonic flame spraying cemented carbide, puts forward the deposition mechanism model of liquid-solid two-phase particles, and expounds the influence law of solid particle characteristics on the particle deposition characteristics, coating structure and properties. It is found that semi-molten metal particles can significantly improve the bonding strength of HVOF coating. The influence of particle state on the bonding strength of coating is expounded, and it is revealed that the liquid-solid two-phase particle state is a necessary condition for HVOF to obtain high bonding strength. A particle deposition model considering particle distribution and collision angle and a method for measuring the critical velocity of cold spraying are proposed. It is found that the critical deposition rate of alloy particles is significantly affected by their surface oxidation state. It is revealed that the interface of alloy particles in cold spray coating presents a metastable structure of micro-nanocrystals, and the idea of in-situ preparation and strengthening based on the activity of metastable structure to control the structure and properties of coating is put forward. In recent five years, SCI has published 63 papers (73 in total) and EI has published 84 papers (1 16). Based on the originality of the research results, 627 published papers were cited by others, and 5 papers were cited by others for more than 30 times, with a maximum of 47 times. Based on the above achievements, it won the first prize of Shaanxi Science and Technology Award in 2004, the second prize of National Natural Science Award nominated by the Ministry of Education in 2004, and was granted the invention patent of 1 1.