Development of Solidification Microstructure in Boron-Modified Alloy Ti–6Al–4V–0.1B

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Hypoeutectic boron addition (0.1 wt.%) to Ti–6Al–4V is known to cause significant refinement of the cast microstructure. In the present investigation, it has been observed that trace boron addition to Ti–6Al–4V alloy also ensures excellent microstructural homogeneity throughout the ingot. A subdued thermal gradient, related to the basic grain refinement mechanism by constitutional undercooling, persists during solidification for the boron-containing alloy and maintains equivalent β grain growth kinetics at different locations in the ingot. The Ti–6Al–4V alloy shows relatively strong texture with preferred components (e.g. ingot axis||[0 0 0 1] or [1 0 1 0]) over the entire ingot and gradual transition of texture components along the radius. For Ti–6Al–4V–0.1B alloy, significant weakening characterizes both the high-temperature β and room-temperature α texture. In addition to solidification factors that are responsible for weak β texture development, microstructural differences due to boron addition, e.g. the absence of grain boundary α phase and presence of TiB particles, strongly affects the mechanism of β → α phase transformation and consequently weakens the α phase texture. Based on the understanding developed for the boron-modified alloy, a novel mechanism has been proposed for the microstructure and texture formation during solidification and phase transformation.



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