镍基高温合金厚板激光焊接熔凝瞬态行为与裂纹形成关联机制研究

Nickel-base high temperature alloy components for advanced ultra-supercritical (A-USC) coal-firing power plant are generally large in thickness and service at high-temperature for very long time. Welding is critical for manufacturing these components. However, hot cracks easily occur during welding of nickel-base high temperature alloy thick plates, which deteriorates toughness and fatigue properties of the joint. High quality welding of nickel-base high temperature alloy thick plates has considerable difficulties and challenges. In this project, we make a proposal to carry out fundamental research on laser welding of nickel-base alloy thick plates by using Inconel 617B as an example. Scientific problems, such as articles dissolution and constitute liquation，flow behavior of welding pool and liquation films, physical and chemical metallurgy of elements, transient solidification behavior of melted pool and liquation films, stress evolution and microstructure formation, et.al, will be investigated in detail. The formation mechanism and transient solidification behavior of liquation films in both weld seam and heat affected zone will be studied. Thermodynamics and dynamics of liquid film migration will be clarified to find out the correlation between it and transient solidification. The formation mechanism of hot cracks and its control factors and boundary condition will be elucidated, and then effective methods to avoid hot cracks during laser welding of nickel-base high temperature alloy thick plates will be put forward. Results of this project will be the theoretical foundation for laser welding of nickel-base high temperature alloy thick components for A-USC application.

高超超临界燃煤火电机组（A-USC）中镍基高温合金构件具有厚尺度和长期安全服役的特殊性，焊接对其制造至关重要。然而，镍基高温合金厚壁构件焊接时易出现热裂纹，导致接头韧性与疲劳性能明显下降。镍基高温合金厚壁构件的高质量焊接具有相当难度和挑战。本项目针对镍基高温合金这一应用背景，以Inconel 617B厚板为材料对象，研究镍基高温合金厚板在激光焊接过程中热影响区的颗粒溶解与成分液化、熔池与液膜流动行为、元素物理化学冶金、熔体与液膜的瞬态凝固行为、应力演化和组织结构演变等科学问题，阐明该焊接过程热影响区和焊缝液化膜的形成机理，澄清液化膜迁移的热力学与动力学条件及其对瞬态凝固行为的影响，重点揭示该焊接过程中热裂纹的形成机制及其控制因素和临界条件，从而形成镍基高温合金厚板激光焊接热裂纹抑制的有效举措，为推动激光焊接技术在A-USC机组中镍基高温合金厚壁构件制造中的应用提供理论支撑。

镍基高温合金在高超临界发电站机组中具有广泛和重要的应用，焊接是镍基高温合金构件制造过程中必不可缺的工艺方法。然而，镍基高温合金材料在焊接过程中容易产生热裂纹，对焊接接头的韧性和疲劳性能有很大影响，危及发电设备的长期安全的服役。基于此，项目系统研究了镍基合金在激光焊接过程中热裂纹的产生现象，阐明了镍基合金在激光作用下热、应力应变、冶金行为和裂纹形成关联机制，揭示了激光深熔焊过程中裂纹特征与产生机理，厘清了裂纹产生的关键因素，提出了裂纹抑制的相关措施；在此基础上进一步对实际工程应用中镍基合金厚板及镍基合金与钢异种金属厚板的激光焊接进行研究，详述了焊接工艺参数对焊缝成形及冶金缺陷的影响规律，阐明接头微观组织的形成机制，考察接头的力学性能及揭示不同测试条件下接头的失效机制，建立镍基高温合金厚板激光焊接方法，最终得到满足服役条件的焊接接头。研究成果将为高质量、高效率激光焊接技术在能源装备高温镍基合金构件制造中的应用提供理论指导和技术支撑。