Microstructure evolution and globularization mechanism of lamellar phases in Ti6.5Al2Zr1Mo1V produced by electron beam melting

Electron beam melting (EBM) was adopted to produce Ti6.5Al2Zr1Mo1V titanium alloy, and the microstructure of as-built samples was characterized to illustrate the effect of complex thermal history on microstructure evolution. Under the combined action of cyclic heating and powder bed preheating, lamellar phases were globularized simultaneously during the EBM process. Boundary splitting, lamellar termination migration and epitaxial growth were involved in the globularization process of lamellar phases. Sub-grain boundaries were formed according to the climbing or recombination of dislocations, and then lamellas were segmented through boundary splitting and the edge globularization. As the cooling rate decreased, some globular phases were formed by epitaxial growth on the split segments, and then the microstructure was coarsened through terminating migration and Ostwald ripening.