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Titanium metal is primarily produced via the Kroll process, which is characterized by a semi-continuous production flow and a lengthy process cycle, resulting in high production costs. Researchers have explored alternative methods for titanium production, including molten salt electrolysis, such as the Fray–Farthing–Chen (FFC), Ono Suzuki (OS), and University of Science and Technology Beijing (USTB) processes, aiming to achieve more economical production. Among these, the USTB process, a representative of soluble anode electrolysis, has shown significant promise. However, controlling oxygen concentration in titanium produced by soluble anode electrolysis remains a challenge. This study proposes a novel approach to enhance deoxidation efficiency in soluble anode electrolysis for titanium production by introducing yttrium chloride (YCl3) into the molten salt electrolyte. Thermodynamic analysis and experimental validation demonstrate that the theoretical deoxidation limit for titanium can reach below 100 ppm under Y/YOCl/YCl3 equilibrium. We report the successful synthesis of titanium powder with an oxygen concentration of 6000 ppm from titanium-carbon-oxygen solid solution. Under optimized conditions, the purity of the titanium powder reached 99.42%, demonstrating a new approach for producing high-purity titanium. This method, based on soluble anode electrolysis, offers a potential alternative to the conventional Kroll process. The research elucidates the fabrication process and analytical methods for titanium-carbon-oxygen solid solution, and employs a combination of analytical techniques, including XRD, SEM-EDS, and ONH Analyzer, for characterization of the electrolytic product, encompassing phase analysis, microstructure, and oxygen concentration testing. [ABSTRACT FROM AUTHOR]

In this work, the asymmetrical rolling of 860 μm thick high-purity titanium (HP-Ti) strips is investigated. HP-Ti ultra-thin strips are produced in thicknesses ranging from 280 μm to 20 μm. The microstructure and texture evolution of HP-Ti ultra-thin strips were analyzed using electron backscattering diffraction (EBSD), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The raw strips have a homogeneous and equiaxed microstructure, containing some face-centered cubic (FCC) Ti laths. With a rise in rolling reduction, equiaxed grains change into deformation structures characterized by a high density of dislocations. The formation of an ultra-fine grained microstructure and the elimination of FCC-Ti laths come next. The influence of grain rotation and slip systems on the development of texture in ultra-thin strips during rolling reduction is illustrated through the analysis of {0002} pole figures and orientation distribution function. The tensile qualities of ultra-thin strips are correlated with their microstructure.

Titanium metal is primarily produced via the Kroll process, which is characterized by a semi-continuous production flow and a lengthy process cycle, resulting in high production costs. Researchers have explored alternative methods for titanium production, including molten salt electrolysis, such as the Fray–Farthing–Chen (FFC), Ono Suzuki (OS), and University of Science and Technology Beijing (USTB) processes, aiming to achieve more economical production. Among these, the USTB process, a representative of soluble anode electrolysis, has shown significant promise. However, controlling oxygen concentration in titanium produced by soluble anode electrolysis remains a challenge. This study proposes a novel approach to enhance deoxidation efficiency in soluble anode electrolysis for titanium production by introducing yttrium chloride (YCl3) into the molten salt electrolyte. Thermodynamic analysis and experimental validation demonstrate that the theoretical deoxidation limit for titanium can reach below 100 ppm under Y/YOCl/YCl3 equilibrium. We report the successful synthesis of titanium powder with an oxygen concentration of 6000 ppm from titanium-carbon-oxygen solid solution. Under optimized conditions, the purity of the titanium powder reached 99.42%, demonstrating a new approach for producing high-purity titanium. This method, based on soluble anode electrolysis, offers a potential alternative to the conventional Kroll process. The research elucidates the fabrication process and analytical methods for titanium-carbon-oxygen solid solution, and employs a combination of analytical techniques, including XRD, SEM-EDS, and ONH Analyzer, for characterization of the electrolytic product, encompassing phase analysis, microstructure, and oxygen concentration testing.

It is practically difficult to find titanium sponges with low and stable aluminum impurities on the market even though it is the precondition to prepare high-purity titanium. Analysis indicates that almost all the aluminum impurities in the titanium sponge are inherited from the magnesium used to reduce titanium tetrachloride. However, it remains elusive for decades why magnesium produced through the silicothermic reduction method contains a high content of aluminum impurities with large fluctuations. By recourse to thermodynamic calculations and comparative experiments, we demonstrate that fluorite, a material used as a catalyst in the silicothermic reduction method to produce magnesium, is the chief culprit for the pest aluminum and propose a mechanism to rationalize the observed phenomena. Our findings indicate that one practical way to produce qualified magnesium for the production of high-purity titanium is to abandon fluorite during the production of magnesium with the silicothermic reduction method.

It is practically difficult to find titanium sponges with low and stable aluminum impurities on the market even though it is the precondition to prepare high-purity titanium. Analysis indicates that almost all the aluminum impurities in the titanium sponge are inherited from the magnesium used to reduce titanium tetrachloride. However, it remains elusive for decades why magnesium produced through the silicothermic reduction method contains a high content of aluminum impurities with large fluctuations. By recourse to thermodynamic calculations and comparative experiments, we demonstrate that fluorite, a material used as a catalyst in the silicothermic reduction method to produce magnesium, is the chief culprit for the pest aluminum and propose a mechanism to rationalize the observed phenomena. Our findings indicate that one practical way to produce qualified magnesium for the production of high-purity titanium is to abandon fluorite during the production of magnesium with the silicothermic reduction method. [ABSTRACT FROM AUTHOR]

Ultrafine-grained (UFG) commercially pure (Ti Grade 2) and high-purity (Ti 99.99%) titanium can be a good alternative to less biocompatible Ti alloys in many biomedical applications. Their severe plastic deformation may lead to a substantial increase of strength, but their highly refined microstructure show a lower thermal stability which may limit their range of applications. The purpose of this study was to investigate the effect of interstitial elements on the thermal stability of UFG Ti Grade 2 and high-purity Ti 99.99% processed by a multi-pass cold rolling to the total thickness reduction of 90%. The severely cold rolled Ti sheets were annealed at temperature in the range of 100–600 °C for 1 h and, subsequently, they were evaluated in terms of microstructure stability, mechanical performance as well as heat effects measured by differential scanning calorimetry (DSC). It was found that the microstructure and mechanical properties were relatively stable up to 200 and 400 °C in the case of UFG Ti 99.99% and Ti Grade 2, respectively. DSC measurements confirmed the aforementioned results about lower temperature of recovery and recrystallization processes in the high-purity titanium. Surprisingly, the discontinuous yielding phenomenon occurred in both investigated materials after annealing above their thermal stability range, which was further discussed based on their microstructural characteristics. Additionally, the so-called hardening by annealing effect was observed within their thermal stability range (i.e., at 100–400 °C for UFG Ti Grade 2 and 100 °C for UFG Ti 99.99%). [ABSTRACT FROM AUTHOR]

High-purity titanium has been subjected to dynamic compression with a strain rate of 103 s−1 to activate { 11 2 - 2 } and { 11 2 - 4 } contraction twins. Electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) were performed to observe the morphologies and twin boundaries of the contraction twins. The results show that { 11 2 - 2 } twins are the predominant twinning mode, as well as the formation of { 11 2 - 4 } twins due to the change in local stress state at the intersection region of { 11 2 - 2 } twin variants or { 11 2 - 2 } twin and grain boundary. The TEM and HRTEM observations reveal that (0001)‖ (11 22 -) facets and (0001)‖ (11 21 -) facets formed along the { 11 2 - 2 } and { 11 2 - 4 } twin boundaries, respectively. According to the theory of interfacial defects, the propagation of the { 11 2 - 2 } twin boundary was discussed with (b3, 3 h { 11 2 - 2 } ) and (b1, h { 11 2 - 2 } ) twinning disconnections, as well as the growth process of the { 11 2 - 4 } twin boundary. [ABSTRACT FROM AUTHOR]

High-purity titanium has been subjected to dynamic compression with a strain rate of 103 s−1 to activate {112-2} and {112-4} contraction twins. Electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) were performed to observe the morphologies and twin boundaries of the contraction twins. The results show that {112-2} twins are the predominant twinning mode, as well as the formation of {112-4} twins due to the change in local stress state at the intersection region of {112-2} twin variants or {112-2} twin and grain boundary. The TEM and HRTEM observations reveal that (0001)‖(1122-) facets and (0001)‖(1121-) facets formed along the {112-2} and {112-4} twin boundaries, respectively. According to the theory of interfacial defects, the propagation of the {112-2} twin boundary was discussed with (b3, 3h{112-2}) and (b1, h{112-2}) twinning disconnections, as well as the growth process of the {112-4} twin boundary.

The results on investigations of mechanical properties of high-purity titanium with grains ranging from tens of nanometers up to a few micrometers subjected to uniaxial tension, compression and microindenting are presented. Different structural states in high-purity titanium were formed by severe plastic deformation according to the scheme «upsetting – extrusion – drawing» in combination with annealing at temperatures of 250–550° C and quasi-hydrostatic extrusion at room and liquid nitrogen temperatures. The values of yield strengths and microhardness for samples of high-purity titanium with grains of different sizes are determined. It was shown that the combination of severe plastic deformation with cryogenic quasi-hydrostatic extrusion allowed to create high-purity nanocrystalline titanium with high mechanical properties. The obtained experimental data were analyzed for the implementation of the Hall-Petch relation and discrepancy between the values of yield strengths in tension and compression (strength differential or S-D effect). Satisfactory fulfillment of the Hall-Petch relation for high-purity titanium in the whole range of the studied grain size values was shown and a noticeable difference in the yield values for compression and tension was found. The values of the coefficients in the Hall-Petch equation for deformation by tension, compression and microindenting were determined. These coefficients are noticeably lower than the corresponding values for the industrial grades of titanium, i.e. in high-purity titanium, the grain boundaries are weaker barriers for moving dislocations than in the industrial titanium, whose boundaries are enriched with impurities. The features of the acoustic waves emission during compression of samples in various structural states were studied. It was concluded that the deformation of titanium in all the investigated structural states was carried out by dislocation slip.

The evolution of microstructure and texture during room temperature compression of high-purity titanium was studied under dynamic loading. X-ray diffraction (XRD) was used to examine the changes in the macrotexture while electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to characterize the microstructural evolution. Dynamic loading was found to enhance the activity of deformation twins; four types of primary twins were activated, including 10 1 ¯ 2 , 11 2 ¯ 1 , 11 2 ¯ 2 and 11 2 ¯ 4 twins. In addition, 11 2 ¯ 2 – 10 1 ¯ 2 and 10 1 ¯ 2 – 11 2 ¯ 2 secondary twins were also formed from a 10% thickness reduction. The newly formed [0001] TD orientation texture component was attributed to the 11 2 ¯ 2 primary twins. Although deformation twinning was the dominant deformation mechanism at the beginning of deformation, slip became dominant with increasing strain. Dislocations with Burgers vectors of ⟨c + a⟩ type character was predicted to accommodate strain along c-axis at higher deformation strain. The ⟨a⟩, pyramidal ⟨c + a⟩ and 11 2 ¯ 2 – 10 1 ¯ 2 secondary twins contributed to the formation of a basal texture at 40% thickness reduction. The twin boundary (TB) thickening resulted from a high density of dislocation interactions with the TB, which destroyed the misorientation relationship of the TB. The TB gradually evolved into TB segments or completely transformed into conventional high angle boundaries. [ABSTRACT FROM AUTHOR]

Abstract: Uniaxial compression tests were carried out at room temperature and at strain rates of 0.001, 0.01, 0.1 and 1s−1 on samples of high-purity titanium. The initial texture was favorably oriented for contraction twinning. The double-differentiation method was employed to detect the initiation of twinning as well as of dynamic recrystallization. Critical strains of about −0.24 and −0.65 were determined, respectively, for these two mechanisms. The relevant mechanisms were identified by means of electron backscatter diffraction (EBSD) techniques. At a true strain of ε =−0.3, two main kinds of primary twins, contraction and extension, were observed and second-generation twins were also identified by means of the EBSD analysis. The presence of low Schmid factor (SF) (<0.2) twins was established as well as the absence of potential high SF (>0.4) twins. The appearance of the low SF twins is explained in terms of the low accommodation work required in the neighboring grains; this involves prismatic glide in the present case. The absence of the potential high SF twins, on the other hand, is justified as requiring the operation of a combination of several difficult deformation modes: basal glide, pyramidal glide, and twinning. [Copyright &y& Elsevier]