Fatigue Properties Of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Alloy Produced By Laser Melting Deposition

The microstructure, tensile properties and fatigue properties of the Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy produced by Laser melting deposition have been investigated using optical microscopy, X-ray diffraction, scanning electron microscopy and electron backscattered diffraction, micro-hardness, tensile and fatigue test. The effect of last heating history on the microstructure of laser melting deposition was analyzed. The effects of microstructure on tensile properties and fatigue properties were discussed.The columnar grains of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy by directional solidification during laser melting deposition, which is roughly parallel to the deposition direction, had been found by optical microscopy; strongly (1012)a crystallographic texture has been confirmed by X-ray diffraction and electron backscattered diffraction. According to the last heating history, the microstructure of alloy presents martensitic α□in the layer bands; coarsened lenticular a with martensitic α□below layer bands; thick a laths with small equiaxed a microstructure by recrystallization annealing; annealed martensitic α□with the average a lath width of0.9μm below recrystallization annealing temperature.The average Vickers micro-hardness value is364HV. No discernable differences in hardness had been found on the varied microstructure. The ultimate tensile strength of specimen parallel to the deposition direction is925MPa, less than1025MPa of the specimen vertical to the deposition direction, but the former’s plastic elongation is18.8%higher than the latter’s8.2%, which is related to its columnar microstructure by directional solidification of laser melting deposition.The fatigue limit of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy produced by Laser melting deposition Fatigue Properties is365MPa, which is lower than the traditional titanium alloy made by forging. The most significantly reason for leading to fatigue strength decrease of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy produced by Laser melting deposition is micropores, which is introduced by the process of laser preparation. The fatigue crack fountains are on the pores, foreign substance or other defects at surface/subsurface. Two factors most significantly affecting the fatigue performance of the present material are the presence of pore size and the location of the pores; the fatigue strength increase with the decrease of pore size and the increase of distance from the pore location to the specimen surface. The main way of fatigue crack propagation is transgranular.