Morphology evolution and growth mechanism of the secondary Widmanstatten α phase in the TA15 Ti-alloy

• Growth models for grain boundary and intragranular Widmanstatten α were proposed.
• Clustered lamellar αWGB grows via adjacent lamellae merging and subsequent coarsening.
• Holes in thick lamellae expand and further fracture result in forked αWI.
• Merger of residual thick αWI with thin tertiary parallel αWI results in double forked αWI.

The morphology evolution and growth mechanism of secondary Widmanstatten α phase in the TA15 Ti-alloy, including the clustered grain boundary Widmanstatten α (αWGB), and forked intragranular Widmanstatten α (αWI), were investigated and the growth model were proposed. Results indicate that the clustered lamellar αWGB grows via the merger of adjacent thin lamellae and subsequent coarsening. Two types of forked αWI exist: a forked αWI with short and thick branches, and a forked αWI with thin and long branches. They results of the fracture of thick lamellar αWI and merger of residual thick αWI with the newly precipitated thin lamellar αWI, which showed a clustered distribution and paralleled the residual thick αWI, respectively.