颗粒增强型铝基金属陶瓷的激光选区熔化成形技术基础研究

The particle reinforced aluminum matrix ceramic composites have the advantages of light weight and high mechanical properties, however, their poor formability restricts their applications. Selective laser melting (SLM), a newly developed additive manufacturing process, which fabricates three dimentional part spot by spot, line by line and layer by layer, is expected to provide a new method to manufacture particle reinforced aluminum matrix ceramic composites parts with complex shape and structures, good quality and high accuracy. Due to the poor wettability at low temperature and high element loss rate at high temperature, the SLM of aluminum matrix cermet is very difficult. This project is focused on investageting the selective laser melting of Al2O3/Al and SiC/Al aluminum matrix ceramic composites which have been widely utilized in industry. The aboved problem may can be solved by using different wavelength laser and aluminium matrix. After investigating on the foundamental technologies, such as the interaction mechanism of laser and mixted powder, the interface chracteristics between the ceramic powder and metal matrix, the characteritics of the molten pool flowing, solidification microstructure, formation mechanism of metallurgical defects, post heat treatment technology, mechanical properties and the relationship between them and the materials, proportion, powder characteristics, process parameters and ambient conditions, the method to control the mcirostructure and mechanical properties, the design criteria of material and technical rules of SLM aluminum matrix cermets can be achieved. The results of this project are expected to provide scientific basis to fabricate aluminum matrix ceramic composites parts with high performance, accuracy and complex shape.

颗粒增强型铝基金属陶瓷重量轻、力学性能好，但成形性差限制了其应用。激光选区熔化成形技术（SLM）以其逐点逐线分层增材制造工艺特点，有望成为铝基金属陶瓷复杂零件高精度高质量制造新方法。然而陶瓷颗粒与铝合金低温润湿性差、铝合金元素高温易烧损，使得其SLM成形难度大。本项目以常用的铝基金属陶瓷Al2O3/Al和SiC/Al为研究对象，通过采用不同波长激光辐照和不同铝合金基体克服上述难题，在获得良好界面润湿性的同时减少铝合金元素烧损。项目通过系统研究不同工艺参数下激光与金属陶瓷粉末相互作用机理，和成形时陶瓷--基体界面特性、熔池流动特性、非平衡凝固组织、冶金缺陷与性能随材料体系构成、粉末特性和外部环境条件的变化规律，获得颗粒增强型铝基金属陶瓷的SLM成形组织结构和力学性能的影响规律及调控方法，并建立其材料体系设计准则和工艺规范。上述研究成果可为发展颗粒增强型铝基金属陶瓷的SLM成形提供理论基础。

铝基金属陶瓷兼具铝合金轻质高比强度和陶瓷耐磨高弹性模量的优点，在工业领域应用广泛。激光选区熔化（Selective Laser Melting，SLM）成形技术可制备复杂精密金属陶瓷零件，克服铸造和粉末冶金工艺精度低且需要模具的缺点，应用前景广阔，但相关研究技术基础薄弱。为了加速SLM成形技术在铝基金属陶瓷材料中的应用，本项目以工业界最常用的铝基金属陶瓷SiC/Al、Al2O3/Al为具体研究对象，开展了颗粒增强型铝基金属陶瓷的SLM成形技术基础研究。通过四年的研究，取得的主要科学研究成果如下：.（1）掌握了SLM成形工艺参数对两类（碳化物、氧化物）金属陶瓷界面润湿性、熔池流动特性、致密性以及冶金缺陷产生的影响规律，实现了其良好致密成形。在SLM成形条件下，由于高温熔融及固液界面反应等原因，陶瓷相与铝合金基体界面结合良好。Al2O3粉末在激光辐照下全部熔化并重新凝固形成蠕虫状形态的类短纤维显微组织，其分布与熔池驱动力有关。SiC陶瓷仍保持原颗粒状。陶瓷含量越高，熔池流动性越差，成形件孔洞越多，致密性越差。减小陶瓷颗粒粒度有利于致密度的提高，但更易产生裂纹。通过优化工艺，成功实现了15wt%SiC/AlSi10Mg金属陶瓷的SLM良好致密成形，其致密度达99.1%，抗拉强度为341.9MPa，屈服强度239.8MPa，延伸率2.2%，压缩强度达到763.9Mpa；.（2）系统研究了SLM成形铝基金属陶瓷过程中陶瓷相的烧损方式与机理。氧化物陶瓷颗粒在激光作用下与液态铝合金反应被还原，生成气态Al2O后逸出熔池，导致氧化物陶瓷的烧损；而碳化物陶瓷颗粒除了本身的升华外，还会与基体反应生成脆硬相；输入的激光能量越大，重熔次数越多，则烧损越多。因此，需要尽可能减少重熔次数，即增大扫描间距和铺粉层厚。.（3）掌握了退火、时效、固溶及时效+固溶等热处理工艺对SLM成形铝基金属陶瓷组织和性能的影响规律。虽然SLM成形金属陶瓷经过热处理后硬度明显降低，但仍明显高于同样热处理制度下的AlSi10Mg合金。.（4）制定了SLM条件下颗粒增强型铝基金属陶瓷的设计准则，包括陶瓷相种类、粒度和铝金属基体的选择原则等。