Ti-10Mo has been quite studied in relation their microstructure and mechanical properties. It alloy has predominately body-centered cubic crystalline (β phase), but other secondary phases may occur, like as α and α’’[1]-[3]. It has knew that zirconium is a neutral element when added in pure titanium but when zirconium is restrained as substitutional element in alloys with beta phase stabilizers elements, it can assist the stabilization of that phase. In this work, it was verified the effect of zirconium in Ti-10Mo-xZr alloys (x = 5, 10, 15, 20 wt%) on Vickers microhardness and elastic modulus.
The alloys were melted by arc-furnace with non-consumable tungsten electrodes and water-cooled copper crucible, in argon atmosphere to avoid sample contamination. After, the produced alloys were submitted to homogeneity heat treatment (for 86400 s and 1273 K), in a vacuum of 10-6 Torr, with slow cooling. Subsequently, hot rolling was performed at 1273 K, followed by air cooling. The alloys were characterized by chemical analysis, structural, microstructural, mechanical properties and biocompatibility tests. The chemical analysis was determined by energy dispersive x-ray (EDX) and density. The structure and microstructure of the alloys were evaluated by x-ray diffraction (XRD), optical and scanning electronic microscopic. The mechanical properties were evaluated by Vickers microhardnessand for the elastic modulus, the impulse excitation method was used.
The results of chemical composition showed that stoichiometry of the produced alloys were obtained satisfactorily with relation the nominal composition. The structure and microstructure of the alloys have predominance of β phase with the presence of small amount of α phase, as can be observed in Fig. 1. The addition of zirconium helped stabilize the β phase[4].
Figure 1: X-ray diffraction (a) and SEM – EBSD (b), for the Ti-10Mo alloys after the homogeneity heat treatment.
The Vickers microhardness obtained for these alloys present solid solution hardening and phase precipitation hardening, suffering influence of processing, as can observed in part (a) of Fig. 2[2][5]. The obtained values for elastic modulus showed that the alloys suffered strong influence of the addition of substitutional elements, as can observed in part (b) of Fig. 2. The alloys with 5 and 10 wt% percent have elastic modulus closer to Ti-10Mo (95 GPa), verifying that the zirconium decrease significantly the elastic modulus of the alloys from 102 GPa (Ti-10Mo-5Zr) to 78 GPa (Ti-10Mo-20Zr).
Figure 2: Microhardness after homogeneity heat treatment (a) and Elastic modulus after hot rolling (b), for Ti-10Mo-Zr alloys.
The results of cytotoxicity tests showed that alloys have no cytotoxicity effects, as can be observed in Fig. 3.
Figure 3: Cytotoxicity tests for Ti-10Mo-Zr alloy.
CNPq (grants #481.313/2012-5 and #307.279/2013-8); FAPESP (grants #2013/09.063-5 and #2015/08.462-9)
References:
[1] MARTINS JÚNIOR, J. R. S. et al. Preparation and characterization of Ti-15Mo alloy used as biomaterial. Materials Research, v. 14, n. 1, p. 107-112, 2011.
[2] CORREA, D. R. N.; KURODA, P. A. B.; GRANDINI, C. R. Structure, Microstructure, and Selected Mechanical Properties of Ti-Zr-Mo Alloys for Biomedical Applications. Advanced Materials Research, v. 922, p. 75-80, 2014.
[3] ZHANG, W.-D. et al. Elastic modulus of phases in Ti–Mo alloys. Materials Characterization, v. 106, p. 302-307, 2015.
[4] HO, W.-F. et al. Effects of molybdenum content on the structure and mechanical properties of as-cast Ti–10Zr-based alloys for biomedical applications. Materials Science and Engineering: C, v. 32, n. 3, p. 517-522, 2012.
[5] CORREA, D. R. N. et al. Effect of the substitutional elements on the microstructure of the Ti-15Mo-Zr and Ti-15Zr-Mo systems alloys. Journal of Materials Research and Technology, v. 4, n. 2, p. 180-185, 2015.