Grain refinement of cast titanium alloys via trace boron addition

Microstructures and Grain Refinement of Additive-Manufactured Ti-xW Alloys

“…[11][12][13][14][15] In addition, the growth restriction factor is equivalent to the rate of development of constitutional undercooling (DT c ) relative to the rate of development of solid (f s ). [16] Recent work includes the work of Tamirisakandala et al who reported the effect of boron on the grain refinement of as-cast Ti-6Al-4V and Ti-6242 [17] and Bermingham et al who studied the same effect for as-cast commercially pure titanium. [18] In these studies, an interpretation of the factor Q is that the boron solute is rejected in front of the solid-liquid interface, forming a boron rich undercooled region that restricts the growth of preexistent nuclei and necessarily increases the probability to activate new nuclei.…”

“…For example, while B and Si both have an ability to reduce the grain size, [17,25] these two elements will form intermetallic compounds that may have secondary (perhaps deleterious) effects on the microstructural evolution [24] or the mechanical properties [26] beyond a certain composition limit c 0 . While the overall design of new alloy composition is well beyond this paper, multiple activities are underway [27] to provide tools that can be used in parallel with the emphasis of this paper-affecting grain size.…”

“…It is useful to present a brief review and analysis of previous results on grain refinement for the Ti-Si [24,25] and Ti-B [17,18] systems to understand the applicability and interpretation of the Easton and St. John equation [13,22] for the Ti-W system results presented here. In their study, Bermingham et al observed significant grain refinement of Ti (i.e., average grain diameters dropping from 600 to 200 lm) upon the addition of small quantities of Si (i.e.…”

“…[24] In a subsequent study performed by Bermingham et al [18] they discussed the refinement of titanium alloys by boron additions and applied the previous model that takes into account the nuclei effect that was ignored in the Ti-B study made by Tamirisakandala et al [17] Considering that the nuclei effect should be always taken into account, Bermingham et al found that the addition of boron is not introducing a significant amount of nuclei, so the refining mechanism in this specific case is mainly governed by solute additions and this results confirms the initial assumptions made by Tamirisakandala et al [18] In a more generic analysis of titanium alloys refined by solute additions, performed by Bermingham et al, two possible scenarios are posed to explain the grain refinement. [11] The first scenario is a solute-based mechanism where the grain refinement is increasing with solute content until reaching a saturation point that depends upon a preestablished nuclei population available (see Figure 7(a)).…”

Effect of the Boron Addition on the Structure of the Ni-Mn-Co-In Alloys

“…Significant grain refinement was achieved through addition a small amount of boron to e.g. Ti-alloys [10], Ni-Mn-Ga [11], furthermore improvement in mechanical properties was achieved e.g. in steel [12].…”