The fatigue properties of the Ti-6.5Al-3.5Mo-l.5Zr-0.3Si alloy produced by direct laser deposition (DLD) have been investigated. The fatigue limit of the alloy perpendicular to and parallel to the deposition direction at specified life of 10⁷ and stress ration of 0.1 is 337 MPa and 365 MPa, respectively. The porosities of specimens are among 0.014–0.028%, averaged porosity is 0.02%. The fatigue cracks initiate at the pores near the surface, which are located mostly at the column grain boundary during solidification. The size of pore and its distance from the surface are two important factors to control the fatigue life of specimen, i.e., bigger the pore or nearer to the surface, shorter the fatigue life. The fatigue fracture consists of fatigue source, radial slow crack growth and rough fast fracture region. The columnar grains boundaries of Ti-6.5Al-3.5Mo-l.5Zr-0.3Si alloy by epitaxial growth from the underlying template grains layer-by-layer during direct laser deposition are the weak joints under the cyclic stress and crack formed propagates preferentially along the grain boundaries, which should be a key factor leading to the difference of fracture morphology in the region of fatigue source and final fast fracture, and also the lower fatigue limit of specimen perpendicular to the deposition direction than that parallel to the deposition direction.

研究了通过直接激光沉积（DLD）生产的Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金的疲劳性能。在规定的寿命10 ^7内，垂直于和平行于沉积方向的合金的疲劳极限0.1的应力比分别为337 MPa和365 MPa。试样的孔隙率在0.014–0.028％之间，平均孔隙率为0.02％。疲劳裂纹始于表面附近的孔，这些孔在凝固过程中主要位于圆柱晶界处。孔的大小及其与表面的距离是控制试样疲劳寿命的两个重要因素，即孔越大或越靠近表面，疲劳寿命越短。疲劳断裂包括疲劳源，径向缓慢裂纹扩展和粗糙快速断裂区。Ti-6.5Al-3.5Mo-1.5Zr-0的柱状晶界。