Ti3SiC2/SiC复相陶瓷反应熔渗/送粉激光复合成形机理研究

In this project, a reactive melt infiltration/laser engineered net shaping compound technology is proposed to meet the demands of adjusting the shape and performance of complex SiC parts for aero engines application. It is promising to solve the performance adjustment and the shape controlling problem of the direct laser additive manufacturing complex SiC parts. However, due to the synergic effects of laser irradiation and chemical reactions, the principle of manufacturing, the evolution of microstructure and internal stress distribution of ceramics have not been well understood. In this project, the Ti-Si-C powder system which can react to form Ti3SiC2 / SiC multiphase ceramics is selected to systematically study the interaction mechanism between laser and raw ceramic powder during compound forming process of the reactive infiltration/laser engineering net shaping. Then detailed study on the evolution principles and manipulation mechanism of microstructure and internal stress distribution during the compound forming process would be performed. And the mechanical properties and fracture behavior of the multiphase ceramics fabricated by the compound forming technology would also be investigated. Based on the optimization of processing parameters, we hope to inhabit the residual stress and minor crack formed during the fabrication process. And after foregoing investigations，The Ti3SiC2/SiC multiphase ceramic parts with high performance would be produced according to the optimized design of macro-micro structure. It is envisaged that the success of the present research project can break through the bottle-neck of manufacturing of multiphase carbide ceramic parts, and consequently has a more important scientific and practical significance.

本项目面向航空发动机对碳化硅构件形性控制的需求，提出反应熔渗/送粉激光复合成形技术，有望解决碳化硅构件直接激光增材制造中控形控性的难题。然而由于复合成形过程受到激光辐照与化学反应的协同影响，该技术的陶瓷成形机理以及材料微观结构、应力分布的演变规律尚不清楚。本项目拟选择可反应生成Ti3SiC2/SiC的Ti-Si-C粉末体系为对象，系统研究反应熔渗/送粉激光复合成形过程中激光与原料粉体在反应熔渗条件下的交互作用机理；研究在复合成形过程中的微观结构和应力分布的演变规律、控制机制；研究复合成形复相陶瓷的力学性能和断裂行为。通过工艺优化，抑制残余应力及微裂纹，最后通过宏微观结构设计制造出高性能Ti3SiC2/SiC复相陶瓷构件。本项目的研究对突破碳化物复相陶瓷构件的直接成形加工瓶颈，促进其工程应用具有较为重要的科学和工程意义。

本项目以反应熔渗技术与激光成型技术研究相结合，阐明了反应熔渗/激光成形复合成形技术对Ti/SiC成形与组织演变的影响规律，获得了激光与复合粉体材料相互作用的规律与调控方法。通过对激光工艺参数、粉体粒径、压力等进行综合研究发现，球化过程对粉床本身的致密度最为敏感，其次与能量密度的敏感性，而粉体粒径的变化敏感性则最低。反应熔渗激光成形Ti/SiC复合材料裂纹产生主要原因是热应力以及成分分布不均。本项目揭示了激光成形与反应熔渗技术结合时Ti/SiC复合粉体的组织结构与物相变化规律，研究发现在激光辐照条件下，随激光能量密度的增加，硅含量随之增加，并导致材料内部液相量增加，致密度增大。项目通过试验表征了光辐照条件下合金/陶瓷润湿行为规律，熔池稳定性影响因素的敏感性依次为扫描速度>扫描间距>激光功率。研究了硼改性对反应熔渗/激光成形中微观结构和内部应力的影响，明晰了粉体改性对复合材料组织结构、性能等的影响规律。对碳化硼等对Ti/SiC进行改性后研究发现，碳化硼在激光辐照作用下生成了二硼化钛，添加B元素使得样品的成形缺陷得到了控制，降低了样品的开裂倾向，使样品的成形完整度得到了提高。.本项目研究了重熔工艺对反应熔渗/激光成形样品的微观结构和应力分布影响规律，激光重熔工艺对样品的表面形貌、成形性以及性能都有着明显的影响，与未重熔样品相比，使用75 W激光功率,1000 mm/s扫描速率，螺旋扫描策略进行重熔的样品尺寸误差降低了27.49 %，开孔率降低了1.85 %，而使用175 W激光功率，1000 mm/s扫描速率，棋盘扫描策略重熔样品抗压强度相较于未重熔可提高284.67 %。最后通过模拟仿真计算，设计了具有嵌套结构的极小曲面样件，所制备样品致密度和强度均优于未进行结构优化的对比组。