Simultaneously enhancing strength and ductility of Ti-6Al-4V alloy with the hierarchical structure via a novel thermal annealing treatment

A novel solution and aging (STA) heat treatment was proposed to improve the strength and ductility of Ti-6Al-4V alloy simultaneously. Effects of the novel heat treatment on microstructure and mechanical properties of the Ti6Al-4V alloy prepared by spark plasma sintering (SPS) were studied in this work. The crystalline structure and microstructure of both the as-fabricated Ti-6Al-4V alloy and the STA Ti-6Al-4V alloy were observed using X-ray diffraction (XRD) technique, optical microscope (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The XRD patterns indicated that the two Ti-6Al-4V samples have the similar crystalline structure with alpha phase and beta phase. However, the results of OM images suggested that the microstructure of Ti-6Al-4V alloy was transformed from the Widmansta center dot tten structure to a hierarchical structure which included the basket-weave structure and the Widmansta center dot tten structure after the STA heat treatment. Apart from the above-mentioned microstructure, the hierarchical structure also exhibited specifically some fine dispersed beta surrounded by some equiaxed alpha. Moreover, the results of the room temperature tensile tests revealed that the STA heat treatment could improve the strength and ductility of the Ti-6Al-4V alloy simultaneously. Based on the observation of TEM images, the increment of the elongation of the STA Ti-6Al-4V alloy can be attributed to the effect of annealing twins and equiaxed alpha, and the total strength increments should be caused by the dispersion strengthening effect of the dispersed beta.

Automated summary

The novel STA heat treatment improved the microstructure of the Ti-6Al-4V alloy, transforming it into a hierarchical structure and enhancing both strength and ductility. The dispersion strengthening effect of the dispersed beta and the presence of annealing twins and equiaxed alpha contributed to the increased elongation and total strength of the alloy after the heat treatment.