Abstract
The effect of Nb content on microstructure, mechanical properties and superelasticity was studied in Ti-Nb alloys fabricated by powder metallurgy route using mechanical alloying and spark plasma sintering. In the microstructure of the as-sintered materials, undissolved Nb particles as well as precipitations of α-phase at grain boundaries of β-grains were observed. In order to improve the homogeneity of the materials, additional heat treatment at 1250 °C for 24 h was performed. As a result, Nb particles were dissolved in the matrix and the amount of α-phase was reduced to 0.5 vol.%. Yield strength of the as-sintered alloys decreased with Nb content from 949 MPa for Ti-14Nb to 656 MPa for Ti-26Nb, as a result of the decreasing amount of α-phase precipitations. Heat treatment did not have a significant effect on mechanical properties of the alloys. A maximum recoverable strain of 3% was obtained for heat-treated Ti-14Nb, for which As and Af temperatures were − 12.4 and 2.2 °C, respectively.
Highlights
Ti-Nb-based alloys are considered as materials for orthopedic implants due to their excellent biocompatibility (Ref 1), low elastic modulus (Ref 2) and good superelastic properties (Ref 3)
In order to determine the influence of Nb content on the microstructure, mechanical properties and superelastic behavior of b-type Ti-Nb alloys, mechanical alloying followed by spark plasma sintering techniques were used to prepare Ti-xNb alloys
The obtained results are as follows: (1) The applied sintering conditions allow to obtain dense samples, with porosity below 0.5 vol.%; additional annealing at 1250 °C for 24 h had to be applied in order to increase the homogeneity of the as-sintered materials
Summary
Ti-Nb-based alloys are considered as materials for orthopedic implants due to their excellent biocompatibility (Ref 1), low elastic modulus (Ref 2) and good superelastic properties (Ref 3). Ical calculation shows that alloys which contain 26 at.% of Nb maximum strain transformation along [011] direction can reach about 3% (Ref 3) This value can be increased by reducing the concentration of Nb or by replacing Nb by other elements such as Ta, Mo, Zr (Ref [3, 6]). Lai et al (Ref 10) show that stable RT superelastic properties can be obtained in binary TiNb alloys prepared by powder metallurgy route by reducing Nb content to about 13%. In order to obtain superelastic properties in binary Ti-Nb alloys obtained by powder metallurgy route, the Nb concentration has to be reduced to compensate the effect of interstitial atoms on the Ms temperature. Tests were performed using Shimadzu Autograph AG–X plus testing machine at strain rate 10À3 1/s
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