Produção e caracterização de ligas de Ti-Nb sinterizados em sal fundido

Abstract

Titanium and its alloys have unique characteristics when compared to other metals, such as low density, high mechanical strength, high corrosion resistance and biocompatibility. Titanium alloys have properties varying over a wide range, which makes them interesting for different applications, especially for the aerospace sector and biomedical implants. Ti-Nb alloys have been studied as an alternative to replace of biomedical implants, made of Ti6Al4V or stainless steel currently used,because their mechanical properties are close to those of human bone. Ti-Nb alloys are considered non-toxic and have a lower elastic modulus, which favors osseointegration. The metal injection molding (MIM) process is an established technology for producing parts without loss of material by conventional machine processes, an attractive feature of powder metallurgy. However, the binder’s choice, the high melting point and reactivity of titanium with interstitial elements add another issues for its processing, such as the need to use high vacuum furnaces. The present work investigated an alternative to conventional sintering, with lower cost and shorter processing time. In this work, the sintering in molten salt of Ti-Nb alloys samples produced by warm compaction of MIM feedstocks was investigated. MIM feedstocks were produced with three different compositions: Ti-10Nb, Ti-16Nb and Ti-22Nb using Ti and Nb elementary powders. Subsequently, the feedstocks were warm compacted and underwent the extraction of binders. Sintering was carried out in a molten salt atmosphere and in a vacuum for comparison. TiNb parts sintered using a molten salt shield showed properties similar to alloys used in biomedical implants. However, they have a lower densification when compared to samples sintered in vacuum. Microstructural and mechanical properties of Ti-xNb parts were evaluated. Ti-10Nb and Ti-16Nb samples showed a porosity of 7.0 and 10.5% when sintered in salt and 1.7 and 1.8% when sintered in vacuum. Samples with a higher amount of niobium require higher sintering temperatures for complete diffusion of niobium into titanium. Hardness values increase with increasing amount of niobium. Mechanical analyzes showed that the samples sintered in salt have a static elastic modulus of 13 to 17 GPa and a dynamic elastic modulus of 30 to 43 GPa, while the samples sintered in vacuum showed a static elastic modulus of 19 to 26 GPa and dynamic elastic modulus in range from 31 to 51 GPa. Therefore, the mechanical tests show a reduction in the Static and Dynamic Elastic Modulus in the samples sintered in molten salt, as well as a reduction in the compressive strength, approaching the values found for human bone. The results obtained in this work demonstrate that molten salt sintering is an alternative route for manufacturing porous titanium alloys.