Mechanical properties and electrochemical behavior of porous Ti-Nb biomaterials

Ti-Nb-based alloys - with their superior mechanical properties and biocompatibility - are attractive biomaterials for orthopedic implants. By producing this alloys with a porous structure, it is possible to achieve mechanical properties similar to that of bone and to facilitate cellular activities. In this study, Ti16Nb (wt%) alloys containing porosity between 4.05-% and 60.79-% were produced by powder metallurgy using different amounts of space holder materials. The samples were sintered at 1200 degrees C for 3 h in a high-level vacuum. The effects of the space holder content - in terms of mechanical properties, amount and morphology of the pores, density and the corrosion behavior of the Ti16Nb alloy - were investigated. It is seen that the addition of 70 vol% space holder materials to the Ti16Nb alloy leads to a decrease in the density value from 4.67 g/cm(3) to 1.91 g/cm(3). Also, it is observed that by producing Ti16Nb with 70 vol% space holder, elastic modulus, compressive and transverse rupture strength values decreased from 96 GPa to 15 GPa, from 1450 MPa to 100 MPa, and from 1173 MPa to 97 MPa, respectively. Although Ti16Nb porous alloys are designed by imitating the properties of the cortical bone for use in the production of load-bearing implants, it is seen that increasing the amount of pores causes, an increase in the corrosion rate and the corrosion current density and a decrease in the polarization resistance

Processing of hydroxyapatite and its composites using ceramic fused filament fabrication (CF3)

In this article, we report the fabrication of hydroxyapatite (HAp) and its composites with 7.75 vol% Si3N4 (HAp10SN) using ceramic fused filament fabrication (CF3). Homogeneous feedstock with 40 vol% ceramic powder was prepared and used to extrude filaments for further printing using a desktop printer. Our results showed that the addition of Si3N4 to HAp increases the feedstock viscosity. However, the filaments and CF3 parts made using HAp and HAp10SN feedstocks exhibited comparable densities without gross defects. We have obtained relatively smoother CF3 parts with HAp10SN than pure HAp, which is attributed to their high feedstock viscosity and formation of liquid phase during sintering. Sintering at 1250 degrees C for 4 h in air, after thermal debinding, resulted in a relative density of-85% with HAp and tricalcium phosphate (TCP) as major constituents. Sintered HAp10SN samples also revealed almost 70% reduction in the grain size and 4-fold increase in the hardness compared to pure HAp. Our results indicate that the CF3 processed HAp10SN samples containing-15% porosity, Si3N4 particles and Si-substituted HAp/TCP have strong potential as bone replacements

Laser powder bed fusion of in-situ composites using dry-mixed Ti6Al4V and Si3N4 powder

Herein, we report laser powder bed fusion (L-PBF) of dry-mixed Ti6Al4V + Si3N4 powder to create in-situ titanium matrix composites. The dry-mixed Ti6Al4V powder with 5 wt.% Si3N4 was processed using L-PBF at varying laser energy densities, between 44 and 133 J/mm(3), by changing the laser scan speed (400-1200 mm/s) at constant laser power of 96 W, layer thickness of 20 mu m and scan spacing of 90 mu m. The selected samples were examined for microstructural evolution, in-situ reaction products and hardness. The results showed that the in situ reaction between liquid titanium and Si3N4 forms fine TiN and Ti5Si3 reinforcements in these L-PBF processed samples. However, the irregular shape and fine size of Si3N4 reduced the feedstock flowability, and the composites could not be processed with laser energy density (E) < 89 J/mm(3). The amount, distribution and size of the reinforcements were found to depend on the laser energy density. These in-situ composites exhibited high hardness of 860 +/- 49 KHN, which is 110 % higher than that of Ti6Al4V and ex-situ processed Ti-TiN and Ti-TiC composites. Our results show that the dry-mixed Ti6Al4V-Si3N4 feedstock can be processed using L-PBF but further improvement is required through adjusting Si3N4 powder attributes (size, shape) and concentration

Properties of Water Atomized 25Cr7Ni Stainless Steel Processed by Laser-Powder Bed Fusion

The 25Cr7Ni stainless steel is characterized by its two-phase microstructure consisting of ferrite and austenite, contributing to an excellent combination of mechanical and corrosion properties. The present study examined the effects of laser energy density and laser powder bed fusion (L-PBF) process parameters on the physical, mechanical and corrosion properties of a water atomized 25Cr7Ni stainless steel powder processed through L-PBF. The results from the study saw that a combination of L-PBF process parameters (laser scan speed and laser scan spacing at a constant layer thickness) as critical factors affecting the mechanical and corrosion properties of the printed samples. The Archimedes density, mechanical and corrosion properties of samples improved with increase in energy density. The as-printed samples displayed single-phase ferritic microstructure and higher mechanical strength (1050 MPa) compared to wrought, metal injection molded (MIM), powder metallurgically sintered (PM) 25Cr7Ni stainless steel (super duplex stainless steel) alloys. The samples exhibited comparable corrosion resistance to that of a wrought 25Cr7Ni stainless steel despite the presence of only ferritic microstructure