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The microstructures, tensile properties, and fatigue lives of the forged Ti-17 using a 1500-ton forging simulator subjected to different solution treatments and a common aging treatment under both load- and strain-controlled conditions to evaluate high cycle fatigue and low cycle fatigue lives, respectively were examined. Then, the tensile properties, microstructures, and relationships between fatigue lives and the microstructural factors were discussed. The fatigue limit under load-controlled conditions increases with increasing solution treatment temperature up to 1143 K, which is in the (α + β) region. However, it decreases with further increase in the solution treatment temperature to 1203 K in the b region. The fatigue ratio at fatigue limit is increasing with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase, and it relates well qualitatively with the volume fraction of the primary α phase when the solution treatment temperature is less than the b transus temperature. The fatigue life under strain-controlled conditions to evaluate the low cycle fatigue life increases with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase. The fatigue life under strain-controlled conditions to evaluate the low cycle fatigue life relates well quantitatively with the tensile true strain at breaking of the specimen and the volume fraction of the primary α phase for each total strain range.

Microstructure dependence on mechanical properties were investigated for Ti-17 forged at temperatures between 700 and 850 ˚C with deformation ratio from 33 to 80 %, and solutiontreated at 800˚C for 4 hours and aged at 620 ˚C for 8 hours. The microstructure was observed after solution and aging treatments. The volume fraction and the size of the primary alpha phase was controlled by solution treatment temperature, not forging temperature and deformation ratio. Forging temperature affected the morphology of grain boundary (GB) alpha phase. Deformation ratio affected the grain size and the aspect ratio of the horizontal and vertical grain size of the prior beta phase. The tensile strength was investigated at room temperature, 450, and 600 ˚C. Forging temperature and deformation ratio did not affect the tensile strength because there is no large difference of the volume fraction of the alphaphase. On the other hand, the elongation and the reduction of area increased with increase of the aspect ratio of the prior beta grains; that means, increase of the deformation ratio. Raising of forging temperature also increased elongation and reduction of area due to the film-like GB alphaphase.

A series of Ti-29Nb-13Ta-4.6Zr(wt.%) {TNTZ} alloys containing either 0.1, 0.3 or 0.7(wt.%) oxygen (O) were room-temperature tensile tested inside a scanning electron microscope to evaluate the effect of O on the deformation evolution. The deformation modes observed for TNTZ-0.1O, which exhibited the largest elongation-to-failure and lowest strength of all the alloys, were deformation-induced α”-martensitic transformation, {332} twinning, and slip. For the other two alloys, slip was the dominant deformation mode, where TNTZ-0.7O exhibited more homogeneous and extensive slip, a higher frequency of cross slip, and a higher work-hardening rate, all of which contributed to both its strength and elongation-to-failure being greater than that for TNTZ-0.3O. TNTZ-0.3O exhibited the greatest tendency for cracking, which generally occurred on grain boundaries perpendicular to the tensile axis, leading to the lowest elongation-to-failure of all the alloys.