Surface grain formation mechanism in the laser remelting molten pool of a near-β titanium alloy

Near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) was treated by laser surface rapid remelting. Solidification surface grains generated at the free surface were observed. The surface grains consist of a layer of crystal film and inward growth cells. Because of the high supercooling of molten pool surface, crystal film is formed through two-dimensional growth and covers the molten pool surface. Small-scale inward growth cells form on the lower interface of crystal film. Surface grains and epitaxially grown columnar grains have competitive growth relationships.