Dissertação
Produção e caracterização de ligas de Ti-Nb sinterizados em sal fundido
Fecha
2022-09-16Autor
Signor, Fernanda
Institución
Resumen
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.