Structure and Properties of High‑Strength Ti Grade 4 Prepared by Severe Plastic Deformation and Subsequent Heat Treatment.

Alena Michalcová,Jan Drahokoupil,Kristína Bartha,Jan Džugan,Jaroslav Vavřík,Přemysl Beran,Pavel Lejček,Jan Palán,Dalibor Vojtěch,Jakub Čížek

doi:10.3390/ma13051116

Abstract

Severe plastic deformation represented by three passes in Conform SPD and subsequent rotary swaging was applied on Ti grade 4. This process caused extreme strengthening of material, accompanied by reduction of ductility. Mechanical properties of such material were then tuned by a suitable heat treatment. Measurements of in situ electrical resistance, in situ XRD and hardness indicated the appropriate temperature to be 450 °C for the heat treatment required to obtain desired mechanical properties. The optimal duration of annealing was stated to be 3 h. As was verified by neutron diffraction, SEM and TEM microstructure observation, the material underwent recrystallization during this heat treatment. That was documented by changes of the grain shape and evaluation of crystallite size, as well as of the reduction of internal stresses. In annealed state, the yield stress and ultimate tensile stress decreased form 1205 to 871 MPa and 1224 to 950 MPa, respectively, while the ductility increased from 7.8% to 25.1%. This study also shows that mechanical properties of Ti grade 4 processed by continual industrially applicable process (Conform SPD) are comparable with those obtained by ECAP.

Highlights

Titanium and its alloys exhibit frequent utilization in a wide range of application fields, from aircraft industry [1,2,3] to medicine [2,3,4]
In situ electrical resistance and in situ XRD proved substantial microstructural changes in the material at the temperature of 450 ◦ C. These changes can be attributed to the relaxation of internal stresses at higher temperatures, followed by recrystallization and grain coarsening
This study showed that it is possible to tune mechanical properties of this material by appropriate annealing

Summary

Introduction

Titanium and its alloys exhibit frequent utilization in a wide range of application fields, from aircraft industry [1,2,3] to medicine [2,3,4]. Titanium with commercial purity has been very popular for structural applications [4,5,6,7]. The main reason is that the impurities present in commercially pure titanium (mainly oxygen and iron) do not limit the possibility of medical application, unlike some other potentially harmful alloying elements. Pure titanium is differentiated on the basis of the amount of impurities by grades, where grade 1 means the lowest content of impurities. Among titanium with different commercial purities, one of the most studied is Ti grade 4, with maximal allowed content of O 0.4% and maximal allowed content of Fe 0.5% [8].

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