Effects of Ga on the structural, mechanical and electronic properties of ?-Ti-45Nb alloy by experiments and ab initio calculations

This work aims to investigate the structural, mechanical and electronic properties of four novel beta-type (100-x) (Ti-45Nb)-xGa alloys (x = 2, 4, 6, 8 wt%) for implant applications by means of experimental and theoretical (ab initio) methods. All alloys retain the bcc beta phase in the solution-treated and quenched state while the lattice parameter decreases with increase in Ga content. This is due to its smaller atomic radius compared to Ti and Nb, in line with the present density functional theory (DFT) calculations. Tensile and microhardness tests indicate a clear strengthening effect with increasing Ga content, with yield strengths in the range 551 divided by 681 MPa and microhardness in the range 174 divided by 232 HV0.1, mainly attributed to grain refinement and solid solution strengthening. Ga also positively affects ductility, with a maximum value of tensile strain at fracture of 32%. Non-destructive ultrasonic measurements and DFT calculations reveal that the bulk modulus is unaffected by the Ga presence. This phenomenon might be due to the fact that Ga introduced bonding and anti-bonding electron low energy states which balance the average bond strength among the atoms in the metallic matrix. Nevertheless, the introduction of new Ga-Ti super sp-like bonding orbitals along the [110] and [-110] directions in the Ga neighborhood could explain the increase of the Young's modulus upon Ga addition (73 divided by 82.5 GPa) that was found experimentally in the present work. Hence, Ga addition to Ti-45Nb leads to a suitable balance between increased strength and low Young's modulus.

Automated summary

This study explores the properties of four novel beta-type (100-x) (Ti-45Nb)-xGa alloys for implant applications. Experimental and theoretical methods were used to investigate the structural, mechanical, and electronic characteristics of the alloys. The results show that the addition of Ga leads to a decrease in lattice parameter, an increase in strength and ductility, and an unaffected bulk modulus. The introduction of Ga-Ti super sp-like bonding orbitals explains the increase in Young's modulus upon Ga addition.