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

chosen to ensure complete transformation to the β-phase The design of TPMS architectures took into
field, as it is approximately 40°C above the measured consideration the technological limitations and capabilities
β-transus finish temperature (862°C). This temperature of the L-PBF process. The sample dimensions were selected
was selected to promote full recrystallization of the according to the work of Soro et al., whereas the unit cell
28
as-built microstructure while minimizing grain growth. size was adapted to account for the technical specifications
Furnace cooling was selected to promote the formation of of the printer used. The chosen parameters ensure that
a stable lamellar α + β microstructure, balancing strength key structural elements comply with the minimum
and ductility, which is critical for load-bearing orthopedic permissible dimensions for our L-PBF equipment while
implants. maintaining the required mechanical properties. The
selected TPMS architecture types (Schwarz, gyroid,
2.4. TPMS structures and split) represent designs whose feasibility in L-PBF
As part of the investigation into the effects of cellular processes has been confirmed by previous studies. 29,30
structures on the mechanical properties of alloys, Nevertheless, the geometric features of these structures
experimental samples with three different TPMS lead to variations in manufacturing accuracy. Among
architecture types were designed and fabricated: Schwarz, the considered variants, the split structure, characterized
gyroid, and split (Figure 2). Computer-aided design of by the smallest constructive elements, demonstrates an
the TPMS architectures was performed using nTopology increased susceptibility to manufacturing imperfections
software (Version 3.0, nTopology Inc., USA). To ensure compared to gyroid and Schwarz structures, which is
an optimal balance between mechanical characteristics reflected in the variability of mechanical properties. To
and L-PBF manufacturing capabilities, a unit cell size ensure uniformity in production conditions and resulting
of 1.5 mm was established for all architecture types. mechanical characteristics, all experimental samples were
Adjustment of the wall thickness was performed to manufactured with the longitudinal axis of the cylinder
achieve the target volumetric porosity of 50%. For oriented along the build direction. The positioning strategy
mechanical compression testing, cylindrical specimens and technological parameters were optimized based on
with TPMS architecture were constructed with published data on the successful fabrication of TPMS
dimensions of 6 mm in diameter and 12 mm in height. structures from Ti alloys. In addition, an investigation
During manufacturing, the samples were positioned so of the printed gyroid lattice structure was conducted to
that the longitudinal axis of the cylinder aligned with the evaluate the influence of lattice geometry on the resulting
build direction. microstructure, which established a relationship between
the topological features of the cellular construction and
A B C microstructural parameters in various regions of the
Ti-10Ta-2Nb-2Zr alloy specimen.

2.5. Characterization methods
2.5.1. Density analysis
The density of the fabricated samples was measured using
the Archimedes method (hydrostatic weighing) with an
analytical balance (XS205, Mettler Toledo, Switzerland)
equipped with a density measurement kit. Distilled water
was used as the immersion medium, and measurements
were conducted at 22 ± 0.5°C. Four measurements were
taken for each sample to ensure statistical reliability.
The theoretical density of the Ti-10Ta-2Nb-2Zr alloy was
calculated using thermodynamic calculations in JMatPro
11 software (11.0, Sente Software Ltd., United Kingdom),
which provides accurate density predictions based on the
chemical composition and phase equilibria of the alloy
system.
The relative density was determined as the ratio of the
Figure 2. Designs of triply periodic minimal surface samples. (A) Schwarz; measured density (obtained using Archimedes’ method) to
(B) gyroid; (C) split the theoretical density (calculated using JMatPro 11).

Volume 4 Issue 3 (2025) 5 doi: 10.36922/MSAM025220044