Abstract
The element oxygen is expected to be a low-cost, strengthening element of titanium alloys due to its strong solid solution strengthening effect. High cycle fatigue behaviors of Ti-6Al-4V alloys with different oxygen contents (0.17%, 0.20%, 0.23% wt.%) were investigated in this paper. The results illustrated that Ti-6Al-4V-0.20O alloy possesses the highest fatigue strength and the lowest fatigue crack propagation rate. The fatigue fracture morphology verified that the fatigue cracks propagated transgranularly in both Ti-6Al-4V-0.17O and Ti-6Al-4V-0.20O alloys, and the fatigue cracks tended to extend intergranularly in the Ti-6Al-4V-0.23O alloy. The maximum nano-hardness varied from the <0001> direction to the and directions with the increasing oxygen content, which suggested that the dominant slip system varied from prismatic slip to pyramidal slip. The number of the type dislocations increased with the oxygen content, which indicated that the number of the first-order pyramidal and the second-order pyramidal slip systems increased. The oxygen can significantly change the fatigue fracture mechanism of Ti-6Al-4V alloy: From transgranular fracture to intergranular fracture. These results are expected to provide valuable reference for the optimization of the composition and mechanical properties of titanium alloys.
Highlights
Ti-6Al-4V alloy can maintain excellent long-term comprehensive mechanical properties underit has been applied extensively on key components such as turbine disks, compressor disks, aero-engine fan blades, etc. [1,2]
The microstructures consisted of coarser equiaxed alpha phase and transformed beta
With further increase of oxygen content, the volume fraction of the primary equiaxed α phase in Ti-6Al-4V alloy gradually increased to 81.4 ±
Summary
Ti-6Al-4V alloy can maintain excellent long-term comprehensive mechanical properties under. The oxygen variation of the titanium alloy has remarkable effect on the fatigue crack propagation rate, and the testing atmosphere influences the rate significantly [17,18]. Robinson [20] declared that the fatigue crack propagation rate in pure titanium decreased with the increasing oxygen content. The factors, such as alloying element, microstructure features, manufacturing process, etc., have strong influence on the fatigue properties of the titanium alloys, leading to the contradictory conclusions of existing studies.
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