高能束流表面加工与处理的超常热物理问题

High energy-density materials surface processing is characterized by high energy flux density, large spatial and temporal gradients, and complex physical and chemical changes. The unusual thermophysical problems involved are often crucial to the technology. Accumulated experiences from the past have helped greatly in the applications, but deep understanding of the mechanisms and relationships among the influencing factors are still insufficient for further development and full exploitation of the technologies. The purpose of this project is to.study the special thermophysical problems involved to gain more rational.understanding of them, with the purpose of improving control over the.processes and quality of the products, and developing new technologies..The project was carried out in three general areas: In materials surface treatment by lasers and electron-beams, studies are made with the main objective of discretized strengthening of metal surfaces. Heat transfer in the molten pool of the melting/solidification.process using pulsed or CW lasers and the formation and separation of.various phases in multi-component material systems during solidification.were studied. Through heat transfer modeling using experimentally.measured molten pool boundary, computing method for obtaining more.realistic results in typical discretized molten pools has been developed. By studying the microstructure of rapidly melted/solidified typical.multicomponent materials, the dynamic model of microstructure formation.in such processes has been developed. A highly efficientmelting/solidification/compounding technology for strengthening metal.surfaces has been developed and has found important military application..In laser deep welding, thermal efficiency, melting efficiency, and.temperature and density of the laser-induced plasma plume were.experimentally determined, and an improved model for the laser deep.welding process, taking into account the influence of transmission.efficiency and the laser-induced plasma has been established. It not only.can indicate the correct mechanism of the process, but also is useful as.a guide in practical production. Three-dimensional mathematical modeling.is carried out for heat transfer, flow, and behavior of the laser-induced.plasma plume in the welding process, the predicted width of the weld bead.is checked reasonably by experiments. In plasma arc welding, the dynamic.behavior of light emission from the arc during the welding process is.characterized and applied to real-time control of the key-hole behavior.and weld pool stability. Using the study of elemental distribution and.real time measurements with ultrasound, optical emission spectroscopy and.transmission electric current, a better understanding of the motion in.the molten pool and mechanisms of weld defect formation in E-beam deep.welding has been obtained. The results can be used for establishing a.dynamic model and control of the welding process..In plasma jet materials surface processing, heat transfer and flow.in thermal plasma systems have been extensively and systematically studied..Three-dimensional modeling is made on plasma generators and 2-phase plasma.flows, obtaining results agreeing with reality. For the 2-temperature.plasmas, new derivations have been made on the controversial basic.problems of the Saha equation, diffusion of components and reactive.thermal conductivity and new results were obtained. These works have.brought good attention from international scientists of the field. The newly developed atmospheric pressure laminar plasma jet generator can produce steady plasma jets of L/D>70, providing a new tool for theoretical and applied research in thermal plasmas. Laminar plasma jets at both normal and reduced pressure are used in materials surface modification and thermal spraying experiments, with the purpose of understanding the effect.of influencing factors on materials behavior and searching for new.processing techniques.Through the

研究高能束流材料加工中的特殊热物理问题及其与形成的材料组织结构间的关系，以提高加工质量和设计水平。主要研究内容：激光和电子束表面快凝加工的熔池特性及相关规律；激光和电子束深熔焊过程，光致等离子体对传热效率的影响以及匙孔动力学行为；等离子体表面喷涂与强韧化处理的热物理过程。研究结果在国民经济和国防建设中将起很大作用。