Abstract: In order to explore novel pathways for preparing pure tungsten as a plasma?facing material in fusion reactor divertors and related components, this study investigates the correlation between microstructure and mechanical properties of pure tungsten fabricated via selective electron beam melting (SEBM). By employing SEBM, high?density tungsten specimens were produced, enabling an in?depth examination of the mechanism underlying microcrack initiation. Furthermore, both horizontal (X?Y) and vertical (X?Z) planes of the as?built parts were subjected to microstructural characterization and mechanical testing. The findings revealed that the density of pure tungsten fabricated by SEBM reached 99.3%. The corresponding Vickers hardness attained values as high as 430.44 HV0.3, while the compressive strength was measured to be up to 1790 MPa. Observations of the horizontal plane indicated that the dominant microstructural features were polygonal, cell?like grains; in contrast, the vertical plane exhibited elongated, columnar grains. Fracture surface analysis showed a river?like morphology, representing a characteristic brittle fracture mode.The anisotropic nature of the microstructure gave rise to observable differences in performance. Microcrack formation was predominantly attributed to the recurrent thermal cycles inherent in the SEBM process, which induced pronounced thermal gradient stresses. Consequently, dislocation movement and rearrangement occurred near subgrain boundaries, culminating in local stress concentrations that facilitated microcrack formation. In essence, this study underscored the effectiveness of SEBM for achieving near?full?density tungsten components and elucidated how microstructural evolution, driven by repeated thermal cycling, influenced both mechanical properties and failure mechanisms.

Key words: selective electron beam melting, tungsten, microstructure, crack

摘要： 为探索聚变堆装置偏滤器等部件面向等离子体材料纯钨制备的新途径，本工作研究了电子束选区熔化(Selective Electron Beam Melting, SEBM)技术制备纯钨的微观组织与力学性能之间的关系。利用SEBM技术制备高致密度的纯钨成形件，研究微裂纹产生的机制，并对成形件的水平面(X?Y面)和垂直面(X?Z面)进行微观组织观察及力学性能测试。结果表明，纯钨成形件的致密度达99.3%，纯钨样件维氏硬度可达430.44 HV0.3，抗压强度可达1790 MPa，在水平面上，组织主要为多边形状的胞状晶，在垂直面上主要为长条状的柱状晶，断口形貌表现为“河流状”，即典型的脆性断裂，组织的各向异性导致性能有所差异。微裂纹的产生主要是由于在成形过程中多次热循环导致产生热梯度应力，亚晶界处的位错进行运动和重排，导致晶界局部应力积累，微裂纹更易在亚晶界处产生。

关键词: 电子束选区熔化, 钨, 微观组织, 裂纹