Phase Transformations upon Ageing in Ti15Mo Alloy Subjected to Two Different Deformation Methods

Kristína Bartha,Irina Semenova,Anna Veverková,Veronika Polyakova,Jozef Veselý,Miloš Janeček,Josef Stráský,Jaroslav Málek,Jakub Čížek

doi:10.3390/met11081230

Kristína Bartha, Irina Semenova + Show 7 more

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https://doi.org/10.3390/met11081230

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Abstract

Ti15Mo alloy was subjected to two techniques of intensive plastic deformation, namely high pressure torsion and rotary swaging at room temperature. The imposed strain resulted in the formation of an ultrafine-grained structure in both deformed conditions. Detailed inspection of the microstructure revealed the presence of grains with a size of around 100 nm in both conditions. The microstructure after rotary swaging also contained elongated grains with a length up to 1 µm. Isothermal ageing at 400 °C and 500 °C up to 16 h was applied to both conditions to investigate the kinetics of precipitation of the α phase and the recovery of lattice defects. Positron annihilation spectroscopy indicated that the recovery of lattice defects in the β matrix had already occurred at 400 °C and, in terms of positron trapping, was partly compensated by the precipitation of incoherent α particles. At 500 °C the recovery was fully offset by the formation of incoherent α/β interfaces. Contrary to common coarse-grained material, in which the α phase precipitates in the form of lamellae, precipitation of small and equiaxed α particles occurred in the deformed condition. A refined two-phase equiaxed microstructure with α particles and β grain sizes below 1 μm is achievable by simple rotary swaging followed by ageing.

Highlights

Thanks to their excellent mechanical properties, titanium alloys have extensive use in the aerospace as well as in the biomedical industry [1,2]
This study aims to investigate the precipitation of α particles in the two deformed conditions, i.e., high pressure torsion (HPT) and rotary swaging (RS), and in particular, the effect of different types of lattice defects on the nucleation of α particles
Ti15Mo, a metastable β-Ti alloy was deformed by two techniques, namely, high pressure torsion (HPT) and rotary swaging (RS)

Summary

Introduction

Thanks to their excellent mechanical properties, titanium alloys have extensive use in the aerospace as well as in the biomedical industry [1,2]. Ti-6Al-4V alloy still belongs to the most used alloy in the biomedical field. In recent years, biological safety has become a crucial issue in the development of biomedical metallic materials [3]. Small amounts of harmful elements, such Al or V can trigger an allergic reaction [4]. Metastable β-Ti alloys, which have comparable mechanical properties to Ti-6Al-4V alloy but contain only nontoxic elements, are considered to be appropriate candidates for surgical and orthopaedic implant manufacturing [5]. Current research focuses on the development of biocompatible metastable β-Ti alloys and the improvement of their mechanical properties

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