Laser metal fusion of beta Ti 21S alloy

Abstract

Motivation: We propose the Beta-Ti 21S alloy processed by laser metal fusion (LMF) as a viable alternative to Ti6Al4V for biomedical applications. The expected benefits of the beta alloy are i) a lower elastic modulus, leading to an improved mechanical compatibility with the bone, ii) an improved biocompatibility due to the lack of Vanadium and iii) suppression of the martensitic transformation responsible for hard and brittle solidification structures.

Materials and Methods: The prealloyed Beta-Ti 21S (D10 = 25 ?m, D50 = 41 ?m D90 = 60 ?m) was used in this work. Chemical analysis on the powder revealed 14.6 % Mo, 2.8 % Al, 2.8 % Nb and 0.3 % Si, 0.11 % O and 0.004 % N. Tensile test samples with the main axis parallel to the building direction were fabricated using a SISMA MYSINT100 printer with a laser spot of 55 ?m. Density measurements, microstructural analysis by OM/SEM, XRD analysis and tensile test measurements were carried out for the microstructural characterization of LMF materials.

Results and Discussion: The as built samples show near full density (>99.7 %) and a ? phase constitution. The tensile test curve evidences good mechanical properties, i.e. YS of 710 MPa, UTS of 830 MPa, e_R close to 20%. The elastic modulus is 54 GPa, much lower that standard Ti-grade 23 (about 110 GPa) and closer to the that of the bone. Results are particularly promising, considering that these could be obtained for the AB material, i.e. with no need of any post heat treatment.

Conclusion: A beta Ti alloy could be produced by LMF. High density, full beta structure and good mechanical properties cold be observed in as built state, i.e. without any post heat treatment.