激光熔覆镍基合金内部及表界面裂纹萌生耦合竞争与控制机理

由于激光熔覆修复过程快速熔化和非平衡凝固等特点，在镍基合金熔覆层内部或表界面很容易出现裂纹，不同工艺条件下，裂纹萌生的位置及演变的机理也不尽相同。目前国内外对该课题尚缺乏深度的理论分析和科学的控制方法。本项目以磨损和腐蚀损伤的轴类零件为研究对象，采用金属凝固学、金属材料学、损伤断裂力学等理论，以保证被修复零件的力学性能为目标，建立超高温移动熔池和熔覆层非平衡快速凝固过程数学物理模型，揭示激光熔覆过程材料熔化、固态相变、温度场、应力应变场以及残余应力场之间相互作用机理；结合相变应力、热应力变化等方面的研究，建立熔覆层内部和基体热影响区裂纹萌生模型，分析两者之间的耦合与竞争关系，揭示激光熔覆过程裂纹萌生的耦合竞争与扩展机理；最后采用工艺参数优化、添加强化相粉末和复合工艺等裂纹消除方法，提出一套有效的激光熔覆裂纹预防和控制方法体系。研究结果为镍基合金激光再制造工艺方案的制定提供理论支持。

Crack is occurred easily in interior, surface or interface of Ni-base alloy cladding layer on account of rapid melting and non-equilibrium solidification in laser cladding repair process. The crack initiation site and evolution mechanism vary with different processing conditions. The present investigation of domestic and international is short of deeply theoretical analysis and scientifically control method. This project, regarding the shafts parts with wear or corrosion damage as study objective, adopting the theory of Metal Solidification, Metal Material, Damage-Fracture Mechanics, etc., aims to ensure mechanical properties of repaired parts. The mathematic and physical model of ultrahigh temperature moving molten pool and non-equilibrium solidification process of cladding layer is established, to uncover the interaction mechanism of material melting and solidifying, solid phase transformation, temperature field, stress-strain field and residual stress field in laser cladding. The crack initiation models of cladding layer interior and substrate heat affected zone (HAZ) (including overlap region of cladding layer) are established respectively, combining the study of phase transformation stress, thermal stress change, etc. By the further analysis of coupling and competition relation between cladding layer interior and HAZ, the mechanism of crack initiation coupling competition and propagation in laser cladding is uncovered. Using multiple crack control methods, such as optimizing process parameters, adding strengthened phase powder and composite technology, an effective method system of crack prevention and control in laser cladding is proposed. This study provides theoretical support for making process program of laser remanufacturing of Ni-based alloy material.