Abstract
In this work, theoretical composition design and thermo-mechanical treatments were combined in order to improve the mechanical compatibility of a biomedical β-type titanium alloy. By applying a composition design theory, cold rolling and low temperature aging, a metastable β-type Ti-35Nb-7Zr-5Ta (wt%) alloy with an elastic modulus of 47 GPa and a yield strength of 730 MPa was successfully fabricated. This combination of high yield strength and low elastic modulus resulted in enhanced elastic recoverable strain of 1.7%, which is much higher than that of the conventional metallic biomaterials. The microstructure responsible for the much sought-after mechanical properties was observed to be mainly consisted of a homogeneous distribution of nanometer-sized ω- and α-precipitates in a β-phase matrix obtained via cold rolling plus short-time aging at low temperature, i.e. aging at 673 K for 20 min. These precipitates increase the strength of the material by hindering the motion of dislocations while the β-matrix with relatively low content of β-stabilizers gives rise to the observed low elastic modulus. By extending aging time, a higher strength is reached at the expense of an undesirable increasing in elastic modulus.
Highlights
Titanium and its alloys are normally considered to be the most suitable biomaterials for implant applications due to their excellent biocompatibility and high corrosion resistance[1]
Zr does not follow the general feature of a neutral element, but instead it behaves as β-stabilizer when alloyed with other β-type elements, such as Nb and Ta9,10
A metastable β-type Ti-35Nb-7Zr-5Ta alloy with ultralow elastic modulus and high strength was fabricated by combining composition design theory and an appropriate thermo-mechanical treatment
Summary
Titanium and its alloys are normally considered to be the most suitable biomaterials for implant applications due to their excellent biocompatibility and high corrosion resistance[1]. V and Al ions released from Ti-6Al-4V might induce longterm health problems including Alzheimers disease[3] In this scenario, non-toxic metastable β-type Ti alloys with lower modulus have currently become the hotspots in the field of metallic biomaterials. The design strategy of β-type Ti alloys is usually based on the “d-electron alloy design method” proposed by Morinaga[4] This approach provides a physical background to the phase stability and to the elastic modulus of titanium alloys by connecting the values of two electronic parameters, Bo (the covalent bond strength between Ti and alloying elements) and Md (the mean “d” electron-orbital energy level concerning electronegativity and elements radius) to the chemical stability of the phases. The second phase precipitates introduced by heat treatments (e.g. annealing) usually exhibit high values of elastic modulus[5]. Several studies have been currently carried out with the purpose of finding a method able to strengthen metastable β-Ti alloys without substantially modifying their elastic modulus[6,7,8]
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