The crack initiation mechanism and fatigue behaviour of thermomechanically processed PM Ti–6Al–4V was systematically studied as a function of microstructural modifications and the associated crystallographic texture. Uniaxial fatigue tests, fractographic analysis and thorough EBSD analysis were performed on an extruded blended elemental PM Ti–6Al–4V alloy to reveal the relationship between crystallographic texture and fatigue properties. We demonstrate that the fatigue crack initiation mechanism is related to the microstructural features of the alloy (colonies in the lamellar microstructure, colony-like primary α plates in the acicular microstructure, and strongly textured primary α grains in the bimodal microstructure) and not to porosity. Through in-depth crystallographic analysis, we demonstrate that the highest fatigue strength achieved with the bimodal microstructure is due to the sharp [10$\overline{1}$0]//extrusion direction crystal texture of the primary α grains which require higher applied stresses in order to induce deformation along basal systems as well as crack opening along basal planes. The crystallographic texture of the alloy thermomechanically processed in the β field is not favourable for fatigue and the resulting lamellar microstructure has the lowest fatigue strength as grains are easily deformed along basal systems. The grain refinement typical of the solution and aged acicular microstructure increases the fatigue resistance with respect to the lamellar microstructure as fatigue strength increases with the reduction of the slip length.

系统地研究了热机械加工的PM Ti-6Al-4V的裂纹萌生机理和疲劳行为，作为微观组织修饰和相关的晶体织构的函数。对挤压混合元素PM Ti-6Al-4V合金进行了单轴疲劳试验，分形分析和全面EBSD分析，以揭示晶体织构与疲劳性能之间的关系。我们证明了疲劳裂纹的萌生机理与合金的微观结构特征（层状微观结构中的菌落，针状微观结构中的菌落状原生α板以及双峰微观结构中的强烈织构化的原生α晶粒）有关，而与孔隙率无关。通过深入的晶体学分析，$\overline{\mathrm{1个}}$0] //初生α晶粒的挤压方向晶体织构，需要更高的施加应力，以引起沿基体系统的形变以及沿基体平面的开裂。在β场中热机械加工的合金的晶体结构不利于疲劳，并且由于晶粒容易沿基体系统变形，因此所得的层状微结构的疲劳强度最低。随着疲劳强度随着滑移长度的减小而增加，溶液的典型晶粒细化和老化的针状微结构相对于层状微结构提高了抗疲劳性。