Ti6Al4V合金作为应用最广泛的α+β型钛合金，兼具较高的强度、塑性、耐腐蚀性及优异的高温热稳定性，被广泛应用于航空发动机叶盘、低压压气机转子等部件的制造。电子束熔丝快速成形技术以其能量利用率高、成形质量好、生产周期短、成形成本低等优势，在航空发动机Ti6Al4V部件的绿色快速制造中展现出广泛的应用前景。由于其工作时存在强烈的定向散热效应与复杂的热循环，沉积态合金室温组织中连续分布的晶界α相在高温下严重弱化，为裂纹的扩展提供通道，故沉积态合金高温蠕变抗力较低，难以满足高温高应力复杂环境的服役需求。本文系统研究了基于微量元素强化与微观组织调控的电子束熔丝快速成形Ti6Al4V-xB合金高温蠕变行为，分析了微量B元素对蠕变强化的作用机理，揭示了基于热处理调控的B改性钛合金微观组织演变与蠕变性能内禀关联。本文具体研究内容与主要结论如下：

首先，系统研究了沉积态Ti6Al4V合金在500℃、250~350MPa下的蠕变行为。结果表明，合金的蠕变行为主要受位错攀移控制，并表现出各向异性：垂直样品的蠕变断裂与受最大剪切力相界面处的孔洞聚集、生长及颈缩现象有关，水平样品的蠕变断裂受与应力轴垂直的横向晶界处孔洞聚集、生长控制。由于合金内部存在较多难变形取向的α相，水平样品的蠕变抗力优于垂直样品。

其次，系统研究了微量B(0.07wt.%)添加对Ti6Al4V合金微观组织与蠕变行为的影响。B在凝固前沿的成分过冷效应显著抑制了β柱状晶的侧向生长，细化了柱状晶宽度。针状TiB主要在晶界处析出，改变了β→α的凝固过程，减小了α相的长径比。Ti6Al4V-0.07B合金蠕变变形行为主要受位错攀移控制，断裂行为受孔洞聚集、生长影响，其蠕变抗力在低温与低应力下提升明显，归因于微量B添加能够提升晶界稳定性，增加相界面数量，产生第二相高温强化。电子束熔丝快速成形Ti6Al4V-xB合金在500℃、250~350MPa下的蠕变性能相较传统成形技术和其他增材制造技术具有可比性。

进一步地，系统研究了热处理对Ti6Al4V-0.07B合金微观组织与蠕变行为的影响。位错攀移在热处理态合金蠕变变形行为中起主导作用，合金断裂行为受孔洞聚集、生长影响。热处理态合金蠕变过程中，未发生相转变的粗大初生α相高温下抵抗变形能力较弱；由高温退火形成的细针状二次α_s相对位错运动的阻碍作用较强；破碎的残余β相显著降低了高温下的界面稳定性；TiB的高温粗化现象不利于蠕变性能的提升。

As the most widely used α+β type titanium alloy with high strength, plasticity, corrosion resistance and excellent high temperature thermal stability, Ti6Al4V alloy is widely used in the fabrication of aero engine blades, low pressure pressurized rotors and other components. Electron beam directed energy deposition, with its advantages of high energy utilization, good fabricating quality, short production cycle and low fabricating costs, shows a wide range of application prospects in the green rapid fabricating of Ti6Al4V components in aero engine. Due to the strong directional heat dissipation and complex thermal cycling during fabricating, the continuous grain boundary α phase in the room temperature microstructure of the deposited alloy is severely weakened at high temperatures, providing a channel for the expansion of cracks. The deposited alloy has relatively low creep resistance, and it is difficult to meet the service requirements of high temperature, high stress and complex environments. This research carried out a systematic study based on trace element strengthening and microstructure controlling to explore the high temperature creep behavior of Ti6Al4V-xB alloy fabricated by electron beam directed energy deposition. The study analyzed the mechanism of the trace B elements on creep strengthening, and revealed the correlation between the microstructure evolution and creep performance of B modified titanium alloy based on heat treatment. The specific research content and main conclusions are as follows:

Firstly, the creep behavior of deposited Ti6Al4V alloy at 500°C and 250~350MPa was investigated. The results show that the creep behavior of the alloy is mainly controlled by dislocation climbing and exhibits anisotropy. The creep fracture of vertical samples is related to the aggregation and growth of holes at the interface subjected to maximum shear and necking phenomenon. The creep fracture of transverse samples is controlled by holes aggregation and growth at the transverse grain boundaries perpendicular to the stress axis. The creep resistance of the transverse samples is better than that of the vertical samples due to the presence of more hard-to-deform α phases inside the alloy.

Secondly, the effects of trace B (0.07 wt.%) addition on the microstructure and creep behavior of Ti6Al4V alloy were investigated. The constitutional supercooling of B at the solidification front significantly inhibits the lateral growth of β columnar crystals and refines the width. The needle-like TiB precipitates mainly at the grain boundaries, altering the solidification process of β → α. This reduces the length to diameter ratio of α phase. The creep deformation behavior of Ti6Al4V-0.07B alloy is mainly controlled by dislocation climbing. The fracture behavior is affected by holes aggregation and growth. The creep resistance of the alloy increases significantly at low temperatures and stresses, which is attributed to the fact that the addition of trace B can enhance the stability of the grain boundaries, increase the number of phase interfaces, and generate high-temperature strengthening of the second phase. The creep performance at 500℃ and 250~350MPa of Ti6Al4V-xB alloy fabricated by electron beam directed energy deposition is comparable to traditional fabricating technologies and other additive manufacturing technologies.

Thirdly, the effects of heat treatments on the microstructure and creep behavior of Ti6Al4V-0.07B alloy were investigated. Dislocation climbing plays a dominant role in the creep deformation behavior of heat-treated alloys. The fracture behavior is affected by holes aggregation and growth. During the creep process of heat-treated alloys, the thick primary α phase, which has not undergone phase transformation, has a weak resistance to deformation at high temperatures. The fine needle-like secondary α_s formed by high temperature annealing has a stronger hindering effect on dislocation movement. The broken residual β phase significantly reduces the high temperature stability of the interfaces. The high temperature coarsening phenomenon of TiB is not conducive to the improvement of creep performance.