当前，航空航天等领域对难焊镍基高温合金复杂结构件的需求不断提高。电子束选区熔化（EBSM）以其真空环境、高温预热等优势，在制备难焊镍基高温合金结构件方面独具优势。但在成形过程中依然存在热裂纹控制、组织性能调控、单晶制备等关键工艺问题。本文旨在通过工艺创新和装备创新对三个关键性问题进行研究。具体内容如下：针对IN738合金的成形液化裂纹问题，基于粉末床表面温度测量，开发了后预热工艺，降低了粉末床的温度波动，从而减小了成形件的内应力和低熔点相B2Cr和B3Cr5的析出，实现了致密无裂纹IN738合金试样的成形。后预热工艺抑制液化裂纹的同时还提高了粉末回收利用率。针对复杂零件结构成形截面突变处凝固裂纹的控制，为改进现有装备成形扫描需要停止预热的局限性，提出了同步预热工艺方案，研制了世界上首台双电子枪同步预热装备，实现了高温预热与成形加工的同步进行。相比于传统EBSM工艺，同步预热工艺降低了粉末床的温度波动，保证了1100 °C以上稳定的成形温度，解决了零件级难焊镍基高温合金成形的凝固裂纹问题，为零件级难焊镍基高温合金的应用提供了新装备、新工艺、新思路。表征了EBSM原位预热保温后的成形态组织，发现IN738合金成形态组织即含有达到临界尺寸、且均匀分布于γ基体中的细小γ'相，并有少量MC和M23C6碳化物均匀分布于晶界和晶内。表征了EBSM成形态IN738合金在不同温度（23 °C、850 °C、1000 °C和1100 °C）下的拉伸性能，确定了主要强化相γ'相和碳化物在四种不同温度拉伸下的位错变形行为。成形态柱状晶组织导致沿成形方向拉伸穿晶断裂、垂直成形方向沿晶断裂，是拉伸性能各向异性的原因。热等静压加标准热处理的热处理工艺方案闭合了成形缺陷，优化了成形组织，提高了EBSM制备IN738合金的力学性能。实现IN738合金的EBSM单晶选晶及制备，提出“回溯时间”是EBSM制备单晶及选晶的关键参数，通过对扫描间隔的“回溯时间”控制，制备出10 mm、15 mm、20 mm、25 mm不同尺寸的IN738单晶样品。所制备单晶的枝晶宽度细小，枝晶间偏析均匀，强化相析出比例高，拉伸、蠕变、疲劳性能均优于铸态IN738。

At present, the requirement continues increasing for complex structural parts of non-weldable nickel-based superalloys in aerospace and other fields. Electron beam selective melting (EBSM) has unique advantages in the preparation of non-weldable nickel-based superalloy structural parts because of the vacuum environment and high temperature preheating. However, there are still some key technological difficulties in the forming process, such as hot cracking control, microstructure and property control, and single crystal preparation. This paper aims to study the above-mentioned key issues through process innovation and equipment innovation. Details are as follows: Aiming at the control of liquefaction cracks for IN738 alloy, based on the surface temperature measurement of the powder bed, a post-preheating process was developed to reduce the temperature fluctuation of the powder bed, thereby reducing the internal stress of the prepared parts and the precipitation of the low melting point phases B2Cr and B3Cr5. The preparation of crack-free IN738 alloy specimens is achieved. The post-preheating process inhibits the liquefaction cracks and improves the powder recycling rate. Aiming at the control of the solidification cracks of the complex part structure, to improve the limitation that the existing machine needs to stop the preheating scanning when printing the parts, a synchronous preheating process was proposed, and the world's first dual electron gun machine for synchronous preheating was developed to carry out the high temperature preheating and printing simultaneously. Compared to the traditional EBSM process, the synchronous preheating process reduces the temperature fluctuation of the powder bed, ensures a stable printing temperature above 1100 °C, and solves the problem of solidification cracks for non-weldable nickel-based superalloys at the part level. The research provides a new machine, new processes, and new ideas for the application of non-weldable nickel-based superalloys parts. The morphological structure of EBSM after in-situ preheating was characterized, and it was found that the morphological structure of IN738 alloy contained small γ' phases reaching a critical size and uniformly distributed in the γ matrix, and a small amount of MC and M23C6 carbides were evenly distributed in the grain boundary and grain. The tensile properties of EBSM-ed IN738 alloy at different temperatures (23 °C, 850 °C, 1000 °C, and 1100 °C) were characterized, and dislocation deformation behavior of the main strengthening phase γ' phase and carbides were determined at four different temperatures. The morphological columnar crystal structure leads to tensile transgranular fracture along the forming direction and intergranular fracture perpendicular to the forming direction, which is the reason for the anisotropy of tensile properties. The post-treatment process scheme of HIP plus standard heat treatment closes the forming defects, optimizes the microstructure, and improves the mechanical properties of the IN738 alloy prepared by EBSM. The EBSM single crystal selection and preparation of IN738 alloy has been realized, and it is proposed that the "return time" is the key parameter of EBSM single crystal preparation and selection. The IN738 single crystal samples with different sizes of 10 mm, 15 mm, 20 mm, and 25 mm were prepared by controlling the "return time" of the scanning interval. The dendrite width of the prepared single crystal is small, the inter-dendritic segregation is uniform, the precipitation ratio of the strengthening phase is high, and the tensile, creep and fatigue properties are better than that of as-cast IN738.