为了指导Ti2AlNb大型薄壁件电子束焊接的工程化应用，本工作主要针对不同焊接速率下的Ti2AlNb合金电子束焊接接头，建立组织-应力-裂纹之间的关系，阐明了Ti2AlNb合金电子束焊接接头的微观组织演变规律、力学性能以及焊缝裂纹产生机制。在粉末冶金态Ti2AlNb合金电子束焊接接头中，焊缝区主要是由β/B2相和少量的α2相组成；热影响区组织可分为两个部分：靠近焊缝一侧的热影响区主要由β/B2相和少量的α2相组成，而靠近母材一侧的热影响区主要由β/B2相、α2相以及O相组成。随着焊接速率的增加，热影响区和母材中晶界处的α2相逐渐变得粗大，且针状的O相逐渐转变为粗大的板条状O相。α2相抵抗拉伸过程塑性变形能力差，粗大的O相对裂纹的钉扎能力差，导致接头的抗拉强度降低。焊接速率为8 mm/s时，接头最高抗拉强度可达499 MPa。接头断裂发生在热影响区，接头断裂形式表现为解理断裂。裂纹产生的主要原因在于接头中存在的脆性相及焊接过程中产生的高残余应力。

This paper primarily studies the microstructure, mechanical properties, and crack formation mechanism of electron beam welded joints of powder metallurgy Ti2AlNb alloy. In the electron beam welded joints of powder metallurgy Ti2AlNb alloy, the weld zone is mainly composed of β/B2 phase and a small amount of α2 phase. The heat-affected zone (HAZ) can be divided into two parts: the heat-affected zone near the weld is mainly composed of β/B2 phase and a small amount of α2 phase, while the heat-affected zone near the base material is mainly composed of β/B2 phase, α2 phase, and O phase. As the welding speed increases, the α2 phase at the grain boundaries in the heat-affected zone and base material gradually becomes coarser, and the needle-like O phase gradually transforms into coarse plate-like O phase. The α2 phase has poor resistance to plastic deformation during tensile processes, and the coarse O phase has poor pinning ability for cracks, resulting in a decrease in the tensile strength of the joint. Mechanical performance test results indicate that when the welding speed is 8 mm/min, the maximum tensile strength of the joint can reach 499 MPa. The fracture of the joint occurs in the heat-affected zone and exhibits cleavage fracture. The main reason for the formation of weld cracks in the joint is the presence of brittle phases and the high residual stresses generated during the welding process.