Caracterização microestrutural e mecânica da liga Ti-35Nb-7Zr-5Ta produzida por fusão seletiva à laser
Resumo
Selective Laser Melting (SLM) is an additive manufacturing technique that
consists of a layer-by-layer fusion of a powder bed by scanning a laser enabling
the production of full density parts accordingly to a 3D CAD model with complex
geometry. Biocompatible beta-TiNb alloys have been specially considered as
promising to replace the more conventional Ni-Ti and Ti-6Al-4V alloys to be used
in prostheses because their low Young’s modulus and their excellent
biocompatibility. In this study, the main objective is to investigate and compare
the microstructure and mechanical properties of a beta Ti-35Nb-7Zr-5Ta (TNZT)
alloy processed by SLM using three different scanning strategies: unidirectional
(Y); bi-directional, 79° rotating between layers (R79°); and checkboard (CHB).
We produced samples in a SLM Realizer 50 with a laser power of 129W,
scanning speed of 0,57 m/s, layer thickness of 40μm, in argon atmosphere, using
those three different strategies. We analyzed these samples in terms of density
and porosity using Archimedes’ principle and micro X-ray computerized
tomography. Moreover, we characterized the samples by X-ray diffraction, optical
microscopy, scanning electron microscopy, energy-dispersive X-ray
spectroscopy, electron backscattered diffraction, and compression and
microhardness tests. All samples presented columnar dendritic and equiaxial
grains of beta Ti phase, preferably oriented in the building direction. The oxygen
percentage increased in relation to the starting powder, indicating oxygen
absorption during the process. The samples showed greater than 99.5% relative
density with pores of different shapes, sizes and distribution among the
strategies. The EBSD showed samples with different textures. The samples
showed high ductility under compression, without premature failure. The yield
limit ranged between σ = 436 and 466 MPa and elastic modulus between E = 47
and 50 GPa. The Vickers microhardness values kept constant along the building
direction (190 HV) for both samples.
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