异质材料激光熔覆多尺度界面组织演化模型研究

with the advantages of low dilution rate, little thermal deformation and high metallurgical bonding strength, it has outstanding superiority in the field of parts surface engineering for laser cladding. The bonding strength of strengthened layer and matrix is determined by interface bonding property, which is an important parameter for surface strengthening of heavy-duty transmission parts. Aiming at the laser cladding process of heterogeneous materials, the project focuses on the mechanism of the microstructure evolution of the interface between the strengthened layer and the matrix during the cladding process. The research work of interface microstructure evolution is consisted of solidification process of molten pool and microstrucuture transformation of matrix. Firstly, multi-phase flow model of cladding process is established based on the consideration of the driving effects on melt flow and temperature change, which are caused by Marangoni force, buoyancy force and addition of heterogeneous materials. Based on the multi-phase flow, the composition distribution of molten pool alloys is analyzed and the grain growth model based on material dilution is established. the microstructure transformation of matrix during cladding process is simulated according to the phase change dynamic parameters of matrix material that measured under rapid temperature change. The accuracies of the above models are verified by observing the microstructure distribution of the cladding samples through laser cladding process experiments of heterogeneous materials. The transformation law of micro-structure at the interface during the cladding process can be revealed by the research results, which can provide theoretical basis for regulation of surface/interface microstructure during laser cladding surface strengthening process.

激光熔覆具有稀释率低、热变小、冶金结合强度高等特点，在零件表面工程领域有显著的应用优势。界面结合性能决定了强化层和基体结合强度，是重载传动零件表面强化重要性能参数。本课题针对异质材料激光熔覆工艺，重点研究熔覆过程中强化层与基体界面的组织演化机理。界面组织演化研究主要包括熔池凝固过程和基体组织转变过程。首先考虑马兰戈尼力、浮升力、异质材料添加等因素对熔体流动、温度变化的驱动效应，建立熔覆过程多相流模型。在此基础上，分析熔池合金成分分布，建立基于材料稀释条件下的晶粒长大模型。并测试基体材料在快速温变条件下的相变动力学参数，进行熔覆过程基体微观组织转变模拟。通过异质材料激光熔覆工艺实验，分析熔覆试样微观组织分布，验证上述模型的准确性。研究成果将揭示熔覆过程界面处微观组织转变规律，为激光熔覆表面强化进行表/界面组织调控提供理论依据。

激光熔覆具有稀释率低、热变小、冶金结合强度高等特点，在零件表面工程领域有显著的应用优势。界面结合性能决定了强化层和基体结合强度，是重载传动零件表面强化重要性能参数。本课题针对异质材料激光熔覆工艺，重点研究熔覆过程中强化层与基体界面的组织演化机理。界面组织演化研究主要包括熔池凝固过程和基体组织转变过程。.基于同轴送粉激光熔覆熔池流动模型，通过热力学计算软件及实验测试获得相关材料参数，对试样后处理后，光学显微镜观察其熔覆层形貌，并通过图像处理软件测量其特征参数，通过数值计算结果，分析熔池熔覆过程的变化。采用高斯热源模型，分析熔池材料熔化-凝固过程，建立多层多道次多场耦合模型，研究温度场、微观组织转变和应力场。研究基体的不同曲率表面和不同倾斜位置角度对激光熔覆结果的影响，对不同直径和角度试样进行熔覆实验；采用润湿角表征熔覆层形貌，分析稀释率和试样直径及位置之间的关系。.以42CrMo为基体，T15高速钢粉末为熔覆材料，采用同轴送粉激光熔覆系统制备T15高速钢熔覆层，研究工艺参数对熔覆层显微组织和摩擦学性能的影响。针对单层多道熔覆层表面组织不均匀性和较大的硬度梯度，采用后续改善工艺进行组织与性能调控。