S.A. Mantri

The effect of boron on the grain size and texture in additively manufactured β-Ti alloys

AbstractOne of the critical microstructural attributes affecting the properties of additively manufactured (AM) alloys is the growth of large columnar grains along the build direction. While most of the work in the reported literature is focused on Ti–6Al–4V and other α/β alloys, there are rather limited investigations on grain growth and texture development in AM β-Ti alloys. The addition of trace amounts of boron to these AM β-Ti alloys resulted in significant changes in the microstructure. Depending on the alloy system, a grain refinement of 50–100 times was noted. The change in the grain size has been attributed to a combined effect of constitutional supercooling, caused by boron rejection from the growing β grains, and the growth restriction factor (Q) of the grains caused by the solute elements. The addition of boron also changed the morphology of the grains from being columnar to more equiaxed, a much more pronounced change than observed in traditional α/β alloys such as Ti–6Al–4V. A change in texture of the β grains along the build direction was also noted, wherein the addition of boron randomized the texture from the typically observed strong (001)β oriented grains in AM Ti alloys. Finally, the addition of boron changed the morphology of the α precipitates in the Ti–Mo system from lath-like to more equiaxed, while preserving the Burgers orientation relationship between the α and β phases.

Strengthening strategy for a ductile metastable β-titanium alloy using low-temperature aging

ABSTRACT While ω precipitates in metastable β titanium alloys are typically considered embrittling and consequently deleterious to the mechanical properties, this paper demonstrates that low-temperature aging (LTA) treatments for short time periods can in fact enhance the yield strength while preserving substantial elongation-to-failure in ω containing β titanium alloys. LTA treatments, carried out on a ductile β metastable Ti–12Mo alloy, significantly improve the yield strength of the material (∼55% increase as compared to solution-treated samples) while keeping both TRIP/TWIP effects and a large elongation-to-failure (ϵ = 0.4 in true strain), resulting in a balance of mechanical properties. IMPACT STATEMENT Employing a novel low-temperature annealing strategy, omega precipitates, typically considered embrittling in beta titanium alloys, can effectively increase the yield strength by 50% while preserving 40% tensile ductility. GRAPHICAL ABSTRACT

Effect of Boron Addition on the Mechanical Wear Resistance of Additively Manufactured Biomedical Titanium Alloy

The effect of the addition of boron to the biomedical alloy Ti-13Nb-13Zr (TNZ) has been studied. A noticeable change between TNZ and TNZ-0.5B has been observed both in terms of morphology, and size scale of the α precipitates along with the in situ formation of TiB precipitates during laser processing. These contrasting microstructures are responsible for differences in mechanical hardness and sliding wear properties and mechanisms.