Structure of Ti-40Nb Alloy Formed with High-Energy Methods

Introduction. Ti-40 wt. % Nb (Ti-40 Nb) is a non-conventional material for medical applications as it has low modulus of elasticity (50-60 GPa) which is of great importance for the mechanical compatibility of an implant with bone tissue. The progressive methods productions of finished items on Ti-40Nb alloy are severe plastic deformation (SPD) and selective laser melting (SLM). These methods have different nature and influence on phase composition, structure and properties of finished item. Due to this fact rigorous structural researches arc required. Aim of present study is evaluation of structural characteristics of Ti-40 Nb alloy produced in conditions of high-energy influence via SPD and SLM methods, taking into account heterogeneity of elemental composition, which is caused by the structure formation conditions. Object of research. Alloy ingots were produced via electro-arc melting. SPD of quenched ingots was carried out via combined method including subsequent operations of pressing to symmetric channel, multiaxial forging and rolling. SLM of mechanically alloyed powder was carried out with VARISKAF-100MVS installation. Research methods. Specimens' structure was studied with the methods of optical and scanning electron microscopy, energy-dispersive microanalysis. X-ray diffraction analysis. Elastic modulus and nanohardness were estimated via unrestored print method. Results. It is shown that in the process of ingot's crystallization dendritic structure, consisting of beta-phase with intracrystalline segregation and Nb concentration's difference up to 6 wt. %,is formed. After ingot's quenching alpha ''-phase's martensite structure is formed in Nb-depleted zones. Ingot's SPD leads to the elimination of segregation, to the reverse alpha ''-> beta + alpha transformation and to the formation of ultrafinegrained structure with the optimal complex of physical mechanical properties required for the implants production. SLM forms structure, consisting of beta-phase grains of micron size with interlays of nonequilibrium alpha ''-phase throughout the grains' boundaries. It is proposed to remove the formed in the alloy intracrytalline segregation with the difference of Nb concentrations up to 27 wt. % via subsequent thermal treatment. Conclusion. Two considered high-energy methods of medical implants production, which are SPD and SLM, have significant influence on the structure of Ti-40 Nb alloy. Character of the influence is defined with the method by itself mind with the formed heterogeneity of elemental composition.