采用光镜(OM)、扫描电镜(SEM)对激光立体成形TC11DT钛合金显微组织和疲劳裂纹扩展断口进行了观察，研究分析了不同取样方向的裂纹扩展机制与失效方式，包括缺口方向平行于沉积试样(平行试样)及缺口方向垂直于沉积方向(垂直试样)。结果显示，未经热处理的沉积态试样的宏观组织主要由贯穿多个熔覆层呈外延生长的粗大β柱状晶组成，柱状晶内为编织细密的α板条和板条间β相。无论是平行试样还是垂直试样，经受载荷时失效方式均由韧性断裂逐渐转变为韧-脆混合断裂，但在瞬断区两者的失效方式区别较大，并且沉积态组织抗裂纹扩展能力的强弱与缺口的加工方向有密切联系。和盘模锻件相比，沉积态试样的抗裂纹扩展能力较低。

The microstructures and fatigue crack fractures of TC11DT titanium alloy samples fabricated by laser solid forming(LSF) were observed using OM and SEM. Crack propagation mechanism and failure mode of crack propagation rate of different sampling directions were analyzed. The sampling directions included samples with notch parallel to deposited direction and samples with notch verticall to deposited direction. The results show that the macrostructure of the as-deposited TC11DT alloy without heat treatment mainly consists of coarse columnar βgrains, which grows epitaxially across several deposition layers. The microstructure of the βgrain is characterized of fine woven αlaths and β-phase between α laths. No matter which kind of sample, when subjected to loading, the failure mode of LSFed specimen both were from ductile fracture changed into ductile and brittle mixed-fracture gradually, but there is a big difference in the short interrupt region between the two kinds of LSFed samples, which has different notch directions. The direction of the notch has great influence on the cracking propagation resistance of LSFed samples. The cracking propagation resistance of the LSFed samples was lower than that of the disk die forging samples.