Modification of Ti-6Al-4V alloy element and phase composition by compression plasma flows impact

N.N Cherenda,A.V Basalai,V.I Shymanski,V.V Uglov,V.M Astashynski,A.M Kuzmitski,A.P Laskovnev,G.E Remnev

doi:10.1016/j.surfcoat.2018.02.048

Abstract

Phase and element composition, microhardness of Ti-6Al-4V titanium alloy, Ti/Ti-6Al-4V and Zr/Ti-6Al-4V systems treated by compression plasma flows have been investigated in this work. X-ray diffraction, scanning electron microscopy, energy-dispersion X-ray microanalysis and Vickers microhardness measurements were used for samples characterization. The findings showed that treatment of the “coating/titanium alloy” system by compression plasma flows allowed decreasing the toxic elements (Al, V) concentration in the surface layer of Ti-6Al-4V titanium alloy. The variation of the energy absorbed by the surface layer resulted in the change of the element concentration and the formation of a number of phases in the modified layer: a solid solution on the basis of α′ phase in Ti-6Al-4V and Ti/Ti-6Al-4V systems and β phase in Zr/Ti-6Al-4V system. The formation of δ-TiNx at the surface due to interaction of surface layer atoms with nitrogen atmosphere in the vacuum chamber was also found. The change of phase composition and quenching effects resulted in the microhardness increase.

Highlights

Being a good material with a high specific strength-to-weight ratio and excellent corrosion resistance pure titanium has a limited practical application due to low mechanical, tribological properties, a high oxidation rate at elevated temperatures
The findings showed that compression plasma flows (CPF) generated by quasi-stationary plasma accelerators could be effectively used for modification of the material surface properties [10, 11]
CPF treatment resulted in the surface layer melting, homogenization of its structure and elements distribution (Fig. 1 a, b)

Summary

Introduction

Being a good material with a high specific strength-to-weight ratio and excellent corrosion resistance pure titanium has a limited practical application due to low mechanical, tribological properties, a high oxidation rate at elevated temperatures This problem is usually solved by producing composite alloys with different additional elements. Modification is aimed at producing a barrier sub-surface layer with a lower vanadium content In this case such mechanical properties as hardness, strength, etc., should be similar to those of the unmodified alloy. This will prevent the formation of a high mechanical stress gradient in the surface layer that causes cracks formation and destruction of the implant Another wide-spread technique of vanadium-tissue contact limitation is protective coating deposition on the surface of Ti-6Al-4V alloy, e.g. deposition of a coating based on transition metals nitrides [6] or a graphite coating [7]. In this case a thin coating serves as a barrier layer between the implant and the tissue

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Conclusion