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Materials Science in Additive Manufacturing L-PBF Ti-10Ta-2Nb-2Zr: Microstructure and Strength

1. Introduction This characteristic makes β-Ti alloys particularly attractive
for load-bearing orthopedic applications where modulus
Titanium (Ti) and its alloys have gained widespread matching with bone tissue is critical. Recent advances in
recognition as biomaterials due to their unique β-Ti alloys have enabled the development of compositions
combination of high specific strength, excellent corrosion with elastic moduli as low as 40 – 80 GPa, which is
1,2
resistance, and superior biocompatibility. However, the substantially closer to natural bone properties compared
traditional Ti-6Al-4V alloy, which dominates biomedical to traditional implant alloys. 11,12
applications, has two significant limitations: a relatively
high elastic modulus (~110 – 120 GPa) compared to Several β-stabilizing elements, including niobium (Nb),
human bone tissue (10 – 30 GPa for cortical bone), and tantalum (Ta), molybdenum (Mo), and zirconium (Zr),
concerns regarding the potential long-term toxicity of have been thoroughly investigated for biomedical Ti alloys
aluminum (Al) and vanadium (V) ions released into due to their superior biocompatibility and ability to reduce
3,4
surrounding tissues. These limitations have stimulated elastic modulus while maintaining adequate mechanical
13
extensive research efforts aimed at developing novel Ti strength. Among these elements, Ta has attracted
alloys specifically designed for biomedical applications, significant attention due to its exceptional biocompatibility,
with particular emphasis on reducing the elastic modulus outstanding corrosion resistance, and strong tendency
to minimize stress shielding effects while maintaining to stabilize the β-phase in Ti. 14-16 When alloyed with Ti,
adequate mechanical strength and biocompatibility. even at relatively modest concentrations, Ta promotes the
formation of the BCC crystal structure, which exhibits a
Stress shielding represents a critical clinical problem in lower elastic modulus than the HCP structure of pure Ti or
orthopedic implants, arising from a significant mismatch predominantly α-alloys.
between the elastic moduli of the implant material and
surrounding bone tissue. This mechanical incompatibility Notable developments in this field include the Ti-Nb
results in the stiffer implant bearing a greater portion of alloy family, with compositions such as Ti-35Nb-7Zr-
applied loads, leading to reduced mechanical stimulation 5Ta demonstrating promising combinations of low elastic
of adjacent bone. Consequently, bone remodeling is modulus and good biocompatibility. 17,18 Similarly, Ti-24Nb-
disrupted, resulting in bone resorption, osteoporosis, and 4Zr-8Sn has shown excellent superelasticity with an elastic
19
4,5
potential implant loosening over time. The risk of stress modulus of only 53 GPa. Other β-alloys, such as Ti-29Nb-
shielding increases proportionally with the difference 13Ta-4.6Zr and Ti-35Nb-5Ta-7Zr, have also demonstrated
between implant and bone elastic moduli, making the favorable combinations of mechanical properties and
development of low-modulus implants a paramount biocompatibility for orthopedic implants. 20,21 However,
objective in orthopedic biomaterial research. many of these compositions contain relatively high
concentrations of expensive elements, such as Nb and Ta,
Beyond developing new alloys, researchers have paid potentially limiting their widespread clinical application.
significant attention to a structural approach for addressing
elastic modulus mismatch through the application of Binary Ti-Ta alloys, particularly those containing 20 –
lattice structures based on triply periodic minimal surfaces 40 wt.% of Ta, have demonstrated promising combinations
6
(TPMS). These biomimetic structures enable a significant of relatively low elastic modulus (65 – 70 GPa) and good
22
reduction in the effective elastic modulus of implants to biocompatibility. However, these binary alloys often suffer
values comparable to those of bone tissue, regardless of the from processing issues due to the high melting point of Ta
7
base material. A key advantage of TPMS structures is the (3,017°C) and its significant density difference compared to
ability to control mechanical properties through variation Ti. In addition, the high cost of Ta makes high-Ta content
of parameters such as relative density, unit cell type (gyroid, alloys economically less attractive for widespread clinical
Schwarz, split, etc.), and their geometric characteristics. application. To address these limitations while retaining
Moreover, the porous architecture of lattice structures the beneficial properties of Ta, the development of multi-
promotes enhanced osteointegration by providing optimal component Ti-Ta alloys with reduced Ta content and the
pore sizes for bone tissue ingrowth and efficient nutrient addition of other β-stabilizing elements has attracted
transport. 8,9 attention. 23,24
Beta-Ti alloys have emerged as promising candidates The Ti-10Ta-2Nb-2Zr alloy represents a strategic
for addressing these issues due to their inherently lower design approach that utilizes synergistic effects between
25
elastic modulus compared to α and α + β Ti alloys. The different alloying elements. Ta provides primary
β-phase has a body-centered cubic (BCC) crystal structure, β-stabilization and biocompatibility, while Nb contributes
which fundamentally exhibits lower stiffness than the additional β-stabilization and may enhance mechanical
10
hexagonal close-packed (HCP) structure of the α-phase. properties through solid solution strengthening. Zr, as a

Volume 4 Issue 3 (2025) 2 doi: 10.36922/MSAM025220044