Abstract
The effect of Nb content on microstructure, mechanical properties and superelasticity was investigated for a series of Ti-xNb alloys, fabricated by the laser engineered net shaping method, using elemental Ti and Nb powders. The microstructure of as-deposited materials consisted of columnar β-phase grains, elongated in the built direction. However, due to the presence of undissolved Nb particles during the deposition process, an additional heat treatment was necessary. The observed changes in mechanical properties were explained in relation to the phase constituents and deformation mechanisms. Due to the elevated oxygen content in the investigated materials (2 at.%), the specific deformation mechanisms were observed at lower Nb content in comparison to the conventionally fabricated materials. This made it possible to conclude that oxygen increases the stability of the β phase in β–Ti alloys. For the first time, superelasticity was observed in Ti–Nb-based alloys fabricated by the additive manufacturing method. The highest recoverable strain of 3% was observed in Ti–19Nb alloy as a result of high elasticity and reverse martensitic transformation stress-induced during the loading.
Highlights
Ti–Nb-based metastable β titanium alloys are among the most promising candidates for long-term implantation due to their excellent corrosion resistance, biocompatibility and superior mechanical properties [1,2]
In our previous work [12], we showed that Ti-Nb alloys obtained using mechanical alloying (MA) and spark plasma sintering (SPS) possess a much higher strength in comparison to cast alloys; e.g., the yield strength (YS) of the cast and solution-treated Ti-26Nb alloy reaches about 300 MPa, while, typically, for alloys obtained using the powder metallurgy (PM)
The influence of Nb content on microstructure, mechanical properties and superelastic behavior was studied for a series of Ti-xNb alloys fabricated using the laser engineered net shaping process
Summary
Ti–Nb-based metastable β titanium alloys are among the most promising candidates for long-term implantation due to their excellent corrosion resistance, biocompatibility and superior mechanical properties [1,2]. Materials for bone implants should fulfill several requirements, among which the most important are appropriate composition, without any toxic elements, and mechanical behavior similar to the bone [3] These requirements are only partially satisfied with Ti–6Al–4V alloy, commercially used in implantology, in which the alloying elements Al and V can cause allergic reactions and Alzheimer’s disease [3,4]. Ni is well known as an allergic and toxic element [3] The advantages of these two materials (the superior mechanical properties of the Ti–6Al–4V alloy and low elastic modulus and superelastic behavior of Ni–Ti alloys) could be combined in metastable β-titanium alloys while eliminating toxic elements [7,8]
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