Influence of in situ TiB reinforcements and role of heat treatment on mechanical properties and biocompatibility of ββ Ti-alloys

The effect of heat treatment on the mechanical properties of Ti–35Nb–5.7Ta–7.2Zr (TNZT) and Ti–35Nb–5.7Ta–7.2Zr–0.5B (TNZTB) alloys has been investigated. In the case of TNZT alloy, the presence of ωω phase in the matrix has a greater effect on strength and hardness than the presence of secondary αα precipitates. The TNZTB alloy shows higher hardness and tensile strength than the TNZT alloy due to the formation of hard TiB precipitates in the matrix of the former. However, the boron free alloy offers higher ductility than the boron containing alloy. Presence of TiB precipitates in the matrix increases the strength of the TNZTB alloy when ωω precipitates are present in the matrix. However, the boride precipitates have no substantial influence on the strength of the TNZTB alloy when ωω phase in the matrix is replaced by the αα phase. The elastic modulus of the TNZT samples shows a very small variation with different heat treatment conditions. The TNZT alloy samples containing ββ and ωω phases show higher elastic modulus than the samples containing ββ and αα phases. The elastic modulus of the TNZTB alloy is higher than that of the TNZT alloy due to the formation of high modulus TiB particles in the matrix. Both the alloys show better cell adhesion and spreading than the control material (polystyrene). However, the boron free Ti-alloy shows better cell attachment than the boron containing Ti-alloy.

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► Effect of heat treatment on the mechanical properties of ββ Ti-alloys.
► TiB precipitate has a major influence on the mechanical properties of ββ Ti-alloys.
► Presence of ωω or αα phase also determines the mechanical properties of ββ Ti-alloys.
► ωω phase in the matrix has a greater effect on strength and hardness than αα phase.
► The BB free Ti-alloy shows better biocompatibility than the BB containing Ti-alloy.