Page 157 - MSAM-4-3

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

A

B

Figure 7. X-ray diffraction patterns of the Ti-10Ta-2Nb-2Zr alloy. (A) As-built condition; (B) After heat treatment

patterns obtained from the samples: Figure 7A corresponds processing, the cooling rates far exceed those used in
to the as-built condition, while Figure 7B shows the results DSC analysis, further promoting the formation of a non-
after heat treatment. equilibrium martensitic phase instead of the equilibrium
The XRD pattern reveals that the as-built microstructure α + β structure.
consists predominantly of α’ martensitic phase with 3.4. Mechanical properties of Ti-10Ta-2Nb-2Zr alloy
HCP crystal structure. The most intense diffraction peak
appears at approximately 40° (2θ), corresponding to the 3.4.1. Tensile properties
α-Ti (101) plane. Other characteristic α-Ti reflections The tensile properties of the Ti-10Ta-2Nb-2Zr alloy in the
are observed at approximately 35° (100), 38° (002), 53°, as-built condition and after heat treatment are summarized
63°, 70°, and 76 – 77° (doublet). The peaks exhibit some in Table 3. Each value represents the average of multiple
broadening, indicative of high levels of internal stress and specimens, with standard deviations provided to indicate
small crystallite size typical of rapid solidification during the variability of the measurements.
L-PBF.
The as-built Ti-10Ta-2Nb-2Zr specimens exhibited
No distinct peaks associated with β-phase BCC are high strength characteristics of a yield strength of 551.8
visible in the pattern, suggesting that the high cooling ± 8.4 MPa and an ultimate tensile strength of 641.2 ±
rates during L-PBF processing promoted almost complete 5.7 MPa, combined with a good ductility indicated by
transformation to α’ martensite. The slight shifts in an elongation of 19.0 ± 1.8% and a reduction in area of
peak positions compared to pure Ti result from lattice 58.0 ± 2.3%. The elastic modulus in the as-built condition
distortion caused by the incorporation of alloying elements was 89.0 ± 2.4 GPa, which is significantly lower than
(Ta, Nb, Zr). that typically reported for conventional Ti alloys such as
These XRD results align with the SEM observations Ti-6Al-4V (110 – 120 GPa).
of acicular microstructure characteristic of martensitic The application of heat treatment (vacuum annealing
transformation. The dominant martensitic structure at 900°C for 1 h) resulted in a notable decrease in strength
is consistent with the phase transformation behavior properties (Figure 8), with the yield strength reduced by
identified in the DSC analysis (Section 3.2), where the 18.0% – 452.3 ± 14.7 MPa and the ultimate tensile strength
β → α + β transformation during cooling was detected reduced by 15.0% – 545.0 ± 3.6 MPa. Interestingly, the
in the temperature range of 804 – 743°C. During L-PBF elongation slightly increased to 20.2 ± 3.6%, while the

Volume 4 Issue 3 (2025) 9 doi: 10.36922/MSAM025220044