Rogelio Macias

The present study shows the effect of Nb on a Ti matrix to fabricate composites via the conventional powder metallurgy for medical applications. Ti powder mixture compacts with different Nb contents were obtained from the conventional pressing and sintering technique. The sintering behavior was evaluated using the dilatometry technique, and the microstructure was studied using scanning electron microscopy (SEM) and X-ray diffraction (XDR). The mechanical properties were obtained from simple compression tests, and the corrosion resistance was determined from a standard three-electrode arrangement in Hank’s solution. The results showed that the Nb in the Ti matrix limits the evolution of sintering depending on the Nb content. Nb slightly accelerates the phase transition temperature. The microstructure and X-rays revealed that biphasic α + β-Ti structures can be obtained, in addition to retaining the β-Ti phase and forming the martensitic phases α′ and α″ of Ti. Likewise, the mechanical behavior showed a Young’s modulus of 10–45 GPa, which is close to that reported for human bones. Furthermore, the circuit analysis revealed that the Ti-Nb sintered systems were conditioned by the surface oxide layer and that the oxide layer formed within the residual pores of the sintering process. Finally, it was demonstrated that adding Nb to the Ti matrix increases the corrosion resistance and that contents close to 15 wt.% of this element have the best results.

This study presents a methodology to fabricate Ti6Al4V cylindrical compacts with a highly porous core and dense shell with the aim to mimic the bone microstructure. Compacts with different core diameters were obtained via conventional pressing and sintering. Large pores were created with the aid of pore formers. Dilatometry was used to determine the sintering kinetics, while X-ray computed tomography was used for characterization. Also, the permeability was evaluated on the 3D microstructure, and the mechanical strength was evaluated via compression tests. The results indicated that sintering was constrained by the different densification rates of the porous and dense layers. However, defect-free compacts were obtained due to neck bonding between the Ti6Al4V particles. Large pores were located in the designed core with a similar pore size distribution. The permeability increased following a power law as a function of the pore volume fraction. The porous core drove the stiffness of the bilayer components, while the combination of both layers increased their strength. The bilayer materials showed permeability (1.36 × 10⁻¹⁰ m²), mechanical properties (E = 6.83 GPa and σ_y = 299 MPa), and admissible strain (σ_y/E = 43 × 10⁻³) similar to those of human bones.

This study presents a methodology to fabricate Ti6Al4V cylindrical compacts with a highly porous core and dense shell with the purpose to mimic the bone microstructure. Compacts with different core diameters were obtained by conventionally press and sintering. Large pores were created with the aid of pore formers. Sintering kinetics was determined by dilatometry, whereas characterization was performed by X-ray computed tomography. Also, permeability was evaluated on the 3D microstructure and the mechanical strength was evaluated by compression tests. Results indicated that sintering is constraint by the different densification rates of the porous and dense layers. Nonetheless, defectless compacts were obtained due to neck bonding between Ti6Al4V particles. Large pores were located in the designed core with similar pore size distribution. Permeability increased following a power law as a function of the pore volume fraction. Stiffness of bilayer components was driven by the porous core, meanwhile, the strength resulted from the combination of both layers. Bilayer materials obtained showed a permeability and mechanical properties, as well as admissible strain (σy /E) similar to those of human bones.

This work reports on the fabrication of a novel two-layer material composed of a porous tantalum core and a dense Ti6Al4V (Ti64) shell by powder metallurgy. The porous core was obtained by mixing Ta particles and salt space-holders to create large pores, the green compact was obtained by pressing. The sintering behavior of the two-layer sample was studied by dilatometry. The interface bonding between the Ti64 and Ta layers was analyzed by SEM, and the pore characteristics were analyzed by computed microtomography. Images showed that two distinct layers were obtained with a bonding achieved by the solid-state diffusion of Ta particles into Ti64 during sintering. The formation of β-Ti and α′ martensitic phases confirmed the diffusion of Ta. The pore size distribution was in the size range of 80 to 500 µm, and a permeability value of 6 × 10⁻¹⁰ m² was close to the trabecular bones one. The mechanical properties of the component were dominated mainly by the porous layer, and Young’s modulus of 16 GPa was in the range of bones. Additionally, the density of this material (6 g/cm³) was much lower than the one of pure Ta, which helps to reduce the weight for the desired applications. These results indicate that structurally hybridized materials, also known as composites, with specific property profiles can improve the response to osseointegration for bone implant applications.

The focus of this work is to analyze the sintering kinetics of Ti12.5Ta12.5Nb alloy by dilatometry. The mixture of powders was achieved by mixing individual powders of Ti, Ta and Nb, which were then axially pressed. Sintering was performed at 1260 °C using different heating rates. The microstructure was determined by X-ray diffraction and scanning electron microscopy. Results show that densification is achieved by solid state diffusion and that the relative density increased as the heating rate was slow. Due to the full solubility of Ta and Nb in Ti, the relative density reached was up to 93% for all samples. Activation energy was estimated from the densification rate and it was determined that two main diffusion mechanisms were predominant: grain boundary and lattice self-diffusion. This suggests that Ta and Nb diffusion did not affect the atomic diffusion to form the necks between particles. The microstructure shows a combination of α, β and α′, and α″ martensitic phases as a result of the diffusion of Ta and Nb into the Ti unit cell. It was concluded that the heating rate plays a major role in the diffusion of Ta and Nb during sintering, which affects the resulting microstructure.

This works proposes a methodology for fabricating materials with specific characteristics mimicking human bones. A Ti64 alloy powder was used as the base material and it was mixed with Ag, Ta, TiN and salt particles to obtain different features. A hip-bone like component was fabricated, including a highly porous core of Ti64/25Ta/5Ag and a compact outer shell of Ti64/5Ag that is supposed to improve corrosion and osseointegration. Besides, a harder cover surface in Ti64/10TiN composite should increase the wear resistance. The green component was sintered at 1260°C in argon. Its Young’s modulus was close to the one of bones due to the added porosity, which also provided a permeability close to the one reported for trabecular bones. Tribocorrosion behaviour in simulated body fluid was improved by TiN addition. In conclusion, the proposed processing route was able to produce complex components fulfilling specific features required for human bone replacement.

The present work is focused on developing Ti-xTa porous alloys processed by the space holder method and solid-state sintering. The volume fraction of Ta ranged between 20 and 30 wt.%. The sintering kinetics was evaluated by dilatometry tests. Sintered materials were characterized by SEM, XRD and computed tomography. Porosity features and permeability were determined from 3D images, and their mechanical properties were evaluated from microhardness and compression tests. The sintering behavior and the final microstructure are driven by the Ta diffusion into the Ti, slowing down the densification and modifying the transition temperature of α-to-β. Due to β-stabilization, martensite α′ was obtained after sintering. Mechanical properties are reduced because of the β-stabilization and pore addition, being predominantly the pore effect. Permeability depended on the pore characteristics, finding values close to the human bones. It was concluded that powder metallurgy generates highly TixTa alloys with a combination of α, β and α′ Ti phases as well as remaining Ta particles that are beneficial to improve the biocompatibility and osseointegration of such materials. Being the Ti25Ta40salt alloy the most suitable for orthopedic implants because of its characteristics and properties.