非平衡凝固与深冷处理协同作用下Al-Sc合金沉淀析出机理研究

随着激光熔覆和增材制造技术的发展，材料制备过程中非平衡效应显著增强，所形成的高固溶组织在后续加工服役中易发生沉淀相转变，其中晶界处所析出的粗大条状或层片状组织严重危害材料的安全使用。本项目拟将快冷液固相变与深冷固态转变有效结合，协同影响时效析出过程以期改善沉淀相组织。首先采用典型非平衡制备技术（喷铸、甩带和选区激光成形），制备出宽冷速范围内快速凝固Al-Sc合金。综合考虑局域非平衡及溶质拖拽、弛豫效应，建立快速凝固枝晶生长模型，揭示高固溶组织形成规律。利用深冷技术进一步提高基体中位错和空位等缺陷密度，降低形核能垒，为析出提供有利形核位置。通过建立耦合溶质过饱和度和缺陷密度的析出动力学模型，推导不同析出模式下临界形核功、转变激活能及生长指数变化行为，获得晶界不连续析出向晶内连续析出发生转变的判据。项目的完成有利于丰富完善非平衡凝固及其固态转变科学认知，为高性能结构材料的研制开发提供理论支撑。

With the development of laser cladding and additive manufacturing technique, the non-equilibrium effect during the material processing is significantly strengthened. Precipitation transformation is prone to occur from the as-formed high saturation structure during the subsequent fabrication and service stage, and the coarse strip or lamellar phase at grain boundary is greatly harmful to safe application. According to the adoption of rapid solidification for liquid-solid phase transformation and cryogenic treatment of solid state transition, cooperative influence on the aging process is investigated to modify the precipitations. Rapid solidification of Al-Sc alloys with wide cooling range are firstly prepared by copper injection casting, melt spinning and selective laser forming. By considering local non-equilibrium, solute dragging and relaxation effects, dendrite growth model is established to reveal the formation mechanism of high saturation structure. After cryogenic treatment, the defect densities including dislocation and vacancy are further enhanced to reduce the nucleation barrier and provide favorable site for the nucleation of precipitation. On these basis, the kinetics transformation model for precipitation is established by coupling solute super-saturation and defect density, which can be used to deduce the critical nucleation work, activation energy and growth index for different precipitation modes and the transition criterion from discontinuous precipitation at grain boundary to continuous precipitation within the matrix. The accomplishment of this project is beneficial to the scientific understanding of non-equilibrium solidification and its influence on solid state transformation, which can provide theoretical support for the fabrication of high performance structure material.