Al₂O₃/Al₆Ti₂O₁₃ composite ceramics with low thermal expansion properties are promising for the rapid preparation of large-scale and complex components by directed energy deposition-laser based (DED-LB) technology. However, the wider application of DED-LB technology is limited due to the inadequate understanding of process conditions. The shaping quality, microstructure, and mechanical properties of Al₂O₃/Al₆Ti₂O₁₃ (6 mol% TiO₂) composite ceramics were systematically investigated as a function of energy input in an extensive process window. On this basis, the formation mechanism of solidification defects and the evolution process of microstructure were revealed, and the optimized process parameters were determined. Results show that high energy input improves the fluidity of the molten pool and promotes the uniform distribution and full growth of constituent phases, thus, facilitating the elimination of solidification defects, such as pores and strip gaps. In addition, the microstructure size is strongly dependent on the energy input, increasing when the energy input increases. Moreover, the morphology of the α-Al₂O₃ phase gradually transforms from cellular into cellular dendrite with increasing energy input due to changing solidification conditions. Under the comprehensive influence of solidification defects and microstructure size, the fracture toughness and flexural strength of Al₂O₃/Al₆Ti₂O₁₃ composite ceramics present a parabolic law behavior as the energy input increases. Optimal shaping quality and excellent mechanical properties are achieved at an energy input range of 0.36-0.54 W*min² g^-1 mm^-1. Within this process window, the average microhardness, fracture toughness, and flexural strength of Al₂O₃/Al₆Ti₂O₁₃ composite ceramics are up to 1640 Hv, 3.87 MPa m^1/2, and 227 MPa, respectively. This study provides practical guidance for determining the process parameters of DED-LB of melt growth Al₂O₃/Al₆Ti₂O₁₃ composite ceramics.

研究了激光填丝焊接工艺参数对哈氏合金薄板纵向挠曲变形的影响,结合样件弯曲刚度和等效载荷分析了焊接工艺参数对纵向挠曲变形的影响。结果表明:激光填丝焊接过程的线能量和相对送丝量通过影响弯曲刚度和等效载荷,进而影响纵向挠曲变形;随着线能量的逐渐增大,等效载荷也逐渐增大,样件的弯曲刚度呈减小—增大—减小的变化趋势。在一定范围内增大线能量会使等效载荷和弯曲刚度同时增大,从而导致挠曲变形的变化幅度相对较小。相对送丝量增大使弯曲刚度在等效载荷不变的情况下明显增大,从而导致焊接变形减小。在合理的参数范围内尽量选择小线能量和大相对送丝量有利于抑制变形。

介绍了铝合金增材制造的相关技术研究进展。着重阐述了选区激光熔化、电弧填丝增材制造、激光-电弧复合增材制造在铝合金增材制造领域的优势与发展前景。研究结果表明,选区激光熔化的研究主要集中在成形件致密度的改善、微观组织控制和力学性能提升等方面,现阶段的成形件的致密度已接近100%,微观组织和力学性能优于铸件的但差于锻件的;电弧填丝增材制造的研究主要集中在大型结构的尺寸控制,但较大的热输入量限制了成形结构的性能提升;激光-电弧复合铝合金增材制造的相关研究较少,完善相应的工艺技术及激光与电弧的耦合行为是其发展方向。

Al₂O₃-YAG共晶陶瓷材料以其出色的高温强度、抗氧化性、高温结构稳定性成为航空航天领域高温合金的理想替代材料。本文采用激光近净成形技术，分别在普通基底、水冷恒温基底上进行了Al₂O₃-YAG共晶陶瓷薄壁件成形实验，得到了不同基底上成形的薄壁样件，比较了两者的微观组织及显微硬度差异。结果表明，采用普通基底成形的薄壁件微观组织呈三维网状结构，平均共晶间距为0.96 μm；采用水冷恒温基底后，薄壁顶部微观组织形貌呈晶团结构，薄壁底部呈枝状晶结构，微观组织逆热流方向生长特性明显，平均共晶间距减小至0.21 μm；和普通基底上成形的Al₂O₃-YAG共晶陶瓷薄壁件显微硬度相比，使用水冷恒温基底成形的Al₂O₃-YAG共晶陶瓷薄壁件硬度提高约10%.

Laser engineered net shaping is a promising additive manufacturing technique that can be used for building three-dimensional components directly from CAD models by layer-wise deposition. Components with high performance and complex geometry can be achieved rapidly by this technology, and components of metal, ceramic or composite material have been successfully fabricated and used in many industrial field. High properties of fabricated specimens and high deposition efficiency are both important for laser engineered net shaping, but few researches have been done on the relationship between them. In this paper, single-bead multilayer structures of 316L stainless steel are fabricated by laser engineered net shaping system. Using the same laser power and scanning speed, different deposition efficiencies are achieved by adjusting powder flow rate and layer increment. Microstructure of each specimen is analyzed by SEM. Tensile strength and micro-hardness of the deposited structures under different deposition efficiencies are tested, respectively.

利用激光近净成形技术进行了316L不锈钢单道多层结构的制备。在相同的激光功率及扫描速度条件下，通过调整送粉率及层间提升量实现了不同沉积效率的成形，并讨论了不同沉积效率下成形结构的微观组织及力学性能特征。结果表明，在一定的激光功率及扫描速度条件下，随着送粉率及层间提升量的提升，沉积效率由初始工艺参数条件下的12.14 mm3/s提高至22.62 mm3/s，提高了86.3%。同时成形单位有效体积消耗的激光能量由初始工艺参数条件下的98.84 J/ mm3降低至53.06 J/mm3，能量利用效率提高了46.32%。成形结构的微观组织呈柱状枝晶形态，随着沉积效率的提高，枝晶长度呈明显的增大趋势。性能检测结果显示，不同沉积效率下的样件力学性能保持了较高的一致性，并未随沉积效率的提高而降低，成形样件抗拉强度及屈服强度分别稳定在510 MPa与290 MPa，延伸率稳定在40%左右，显微硬度也未出现明显波动，处于180 HV，均达到了锻造的同等水平。该研究表明，在一定的工艺参数范围内，可以实现沉积效率及力学性能的协同优化，达到低能耗高效制备高性能零件的效果。

为了解决激光自熔焊接时薄板焊缝易产生负余高的问题及满足高装配精度的要求，提出了激光填丝焊接(LWFW)工艺，开展了Hastelloy C-276屏蔽套材料的LWFW实验，研究了工艺参数对焊缝形貌的影响，分析了接头不同区域的显微组织、元素分布及显微硬度特征。结果表明，运用LWFW可以获得上下表面正余高可控的焊接接头，在优化工艺参数条件下可获得上下余高、接触角基本一致的焊缝形貌。焊缝晶粒细化明显，母材与熔化线交界处无明显热影响区，焊缝不同熔化区域元素分布均匀，没有明显的元素宏观偏析，但柱状枝晶区Mo元素存在显微偏析。接头不同熔化区域显微硬度分布均匀，硬度值与母材的基本相当。