Abstract
Direct Metal Laser Sintering (DMLS) technology was used to produce tensile and flexural samples based on the Ti-6Al-4V biomedical composition. Tensile samples were produced in three different orientations in order to investigate the effect of building direction on the mechanical behavior. On the other hand, flexural samples were submitted to thermal treatments to simulate the firing cycle commonly used to veneer metallic devices with ceramics in dental applications. Roughness and hardness measurements as well as tensile and flexural mechanical tests were performed to study the mechanical response of the alloy while X-ray diffraction (XRD), electron microscopy (SEM, TEM, STEM) techniques and microanalysis (EDX) were used to investigate sample microstructure. Results evidenced a difference in the mechanical response of tensile samples built in orthogonal directions. In terms of microstructure, samples not submitted to the firing cycle show a single phase acicular α’ (hcp) structure typical of metal parts subject to high cooling rates. After the firing cycle, samples show a reduction of hardness and strength due to the formation of laths of the β (bcc) phase at the boundaries of the primary formed α’ plates as well as to lattice parameters variation of the hcp phase. Element partitioning during the firing cycle gives rise to high concentration of V atoms (up to 20wt%) at the plate boundaries where the β phase preferentially forms.
Highlights
Material and methods 2.1 Sintering parameters, material composition and properties Starting from EOS Ti64 powder, supplied by EOS GmbH Electro Optical System, flexural and tensile specimens were produced by Direct Metal Laser Sintering (DMLS)
A Philips CM200 and a JEOL JEM-2010 ARP equipped with an Oxford Inca energy dispersive Xray microanalysis, both operating at 200 kV, were used for transmission electron microscopy (TEM) observations and energy dispersive X-ray microanalysis (EDX) analysis
For the FLEXFC sample, scanning transmission electron microscopy (STEM) observations performed in high angle annular dark field (HAADF) mode and EDX elemental mapping showed segregation of V at the plate boundaries in correspondence of the β phase
Summary
In order to investigate possible variations of the mechanical properties with the sample building orientation, three different groups of tensile (TENS) specimens were produced. In order to investigate possible variations of mechanical properties and microstructure of the Ti-6Al-4V alloy due to the firing cycle (FC), a five-step thermal treatment was adopted in this work The standard deviations (SD) associated to the roughness value were estimated from the five measurements
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