Commercial Purity Research Articles

Uncovering the Intrinsic High Fracture Toughness of Titanium via Lowered Oxygen Impurity Content.

Titanium (Ti) and its alloys are known to exhibit room-temperature fracture toughness below 130 MPa m1/2, only about one half of the best austenitic stainless steels. It is purported that this is not the best possible fracture resistance of Ti, but a result of oxygen impurities that sensitively retard the activities of plasticity carriers in this hexagonal close-packed metal. By a reduction of oxygen content from the 0.14wt% in commercial purity Ti to 0.02wt%, the mode-Ι fracture toughness of the low-oxygen Ti is measured to be as high as KJ Ic ≈ 255 MPa m1/2, corresponding to J-integral-based crack-initiation toughness of up to JIc ≈ 537kJ m-2. This extraordinary toughness, reported here for the first time for pure Ti, places Ti among the toughest known materials. The intrinsic high fracture resistance is attributed to the profuse plastic deformation in a significantly enlarged plastic zone, rendered by the pronounced deformation twinning ahead of the crack tip along with ample twin-stimulated 〈c+a〉 dislocation activities, in the absence of impeding oxygen. Controlling the content of a property-controlling impurity thus holds the promise to be a readily applicable strategy to reach for unprecedented damage tolerance in some other structural alloys.

Impact of Chemical Dynamics of Commercial PURE Systems on Malachite Green Aptamer Fluorescence.

The malachite green aptamer (MGapt) is known for its utility in RNA measurement in vivo and in lysate-based cell-free protein systems. However, MGapt fluorescence dynamics do not accurately reflect RNA concentration. Our study finds that MGapt fluorescence is unstable in commercial PURE systems. We discovered that the chemical composition of the cell-free reaction strongly influences MGapt fluorescence, which leads to inaccurate RNA calculations. Specific to the commercial system, we posit that MGapt fluorescence is significantly affected by the system's chemical properties, governed notably by the presence of dithiothreitol (DTT). We propose a model that, on average, accurately predicts MGapt measurement within a 10% margin, leveraging DTT concentration as a critical factor. This model sheds light on the complex dynamics of MGapt in cell-free systems and underscores the importance of considering environmental factors in RNA measurements using aptamers.

An Experimental and Simulation Study on the Formability of Commercial Pure Titanium Foil.

In order to understand the formability of as-received tempered commercial pure titanium grade 2 foils (CP Ti Gr2) with a thickness of 38 µm, a series of micro limited dome height (µ-LDH) tests were conducted in quasi-static speed (0.01 mm/s) at room temperature without the use of a lubricant. A technique developed at NIU was also used to create micro-circular grids (ϕ50 μm) on the as-received material. The forming limit curve (FLC) of the CP Ti Gr2 foils was obtained through the proposed µ-LDH test. For having mechanical properties of the CP Ti Gr2 foils for LS-Dyna FEA (Finite Element Analysis) simulations, a series of tensile tests in three directions were also conducted at room temperature with the same speed. The obtained FLC has been validated using a micro deep drawing case study in which both FEA simulations and experiments were conducted and compared. It has been proven in this study that the FLC obtained using the proposed µ-LDH test can be used for an extremely thin sheet-metal-forming process by the automotive, aerospace, medical, energy, and electronic industries, etc., right away for product design, forming process development, tool and die designs, and simulations, etc.

Effect of CSET processing on a commercial purity polycrystalline Al sample and numerical simulation of induced plastic deformation

A commercial purity Al sample was processed using complex shearing of the extruded tube (CSET) technique, which enables the preparation of tubes from bulk samples in one step by combining extrusion and two Equal Chanel Angular Pressing - like passes. In the present paper, the CSET process was simulated and analysed using Finite Element Method. The results of the simulations were compared with the experimental findings. Both modelling and experiment revealed a gradual increase in plastic deformation in the material during CSET processing. Simultaneously, microscopic investigations confirmed concurrent grain refinement. Moreover, a slight gradient of plastic deformation predicted by FEM in the main deformation zone was confirmed by microhardness measurements. In the resulting tube wall, electron backscattered diffraction experiments revealed the presence of fine grains and a partially recovered microstructure. The Vickers microhardness was found to be doubled by the CSET processing.

Characterization of Electrochemical and Biocompatibility of Zinc Oxide Coating Electrodeposited on Commercial Pure Titanium Alloy

This study examines how the duration of electrodeposition affects the morphology and electrochemical characteristics of zinc oxide coatings applied to a pure titanium substrate. The morphology of the coating and the phases present within it are analyzed using a scanning electron microscope and the X‐ray diffraction technique. The coating's resistance to corrosion in a phosphate‐buffered saline solution is evaluated using two electrochemical methods: impedance spectroscopy and potentiodynamic polarization tests. The surface roughness of the coated samples is assessed using interferometry. The results demonstrate that an increase in electrodeposition time, ranging from 150 to 1200 s, leads to an enhanced texture intensity in the (0002) and (010) planes of the ZnO coating. Furthermore, the thickness of the ZnO crystals and surface roughness increases by factors of 3.25 and 2.79, respectively, as the deposition time is extended. This extended duration results in the formation of larger needle‐shaped and flower‐like ZnO crystals, leading to a significantly nonuniform structure. Correspondingly, the corrosion rate also increases as the electrodeposition time is extended from 150 to 1200 s, rising from 0.001951 to 9.117 μm year−1. The lowest corrosion rate (1.654 μm year−1) is achieved in coatings deposited for 300 s using a potential of 3 V.

Evaluating the thermal, mechanical and swelling behavior of novel silicone and polyurethane additively manufactured O-rings in the presence of organic liquids and military fuels

This work investigates the physical properties and swelling behavior of additively manufactured (AM) and traditionally manufactured (TM) polyurethane (PU) and silicone O-rings when exposed to organic liquids and military fuels. Polymer properties were explored using differential scanning calorimetry, thermal gravimetric analysis, and tensile testing, and two AM print orientations (vertical and horizontal) were investigated. The AM polyurethane vertical and horizontal O-rings formed from a selective laser sintering (SLS) process had similar thermal features to each other and differed slightly from the un-sintered polymer in the temperature at which the greatest rate of mass loss occurred in the TGA analysis. The thermal features of the AM silicone O-rings formed using stereolithography (SLA) were more similar to those of a commercial soft silicone than to those of a commercial high purity silicone. The horizontal print orientation for each polymer had a higher tensile strength than its respective vertically oriented print. A 1-week exposure of the AM O-rings to the various organic liquids reduced the tensile strength of AM O-rings by as much as 80% (tensile strength exposed/tensile strength unexposed = 0.2). Polyurethane AM O-rings swelled from 3 to 74% with the greatest swelling occurring from exposure to acetone. Silicone AM O-rings swelled from 13 to 258% with the greatest swelling occurring from exposure to iso-octane. In general, the commercial O-rings swelled less than their AM counterparts, had higher tensile strengths, and had smoother surfaces. The maximum swelling for the PU O-rings occurred at an overall Hansen solubility parameter (HSP) between 18 and 20 MPa1/2, while the maximum for silicone occurred at an HSP of 14.3 MPa1/2. These values are consistent with literature values, which can vary widely.

Experimental study of two-phase cryogenic cooling of aluminum stator conductors using a single slot test configuration

An important goal to enable widespread adoption of electric aircraft propulsion is to develop higher power density motors and generators which are at the same time highly efficient. One way to do this is to use conductors that can carry higher currents and/or generate lower losses. One approach to this is the use of superconducting windings. However, here we focus on very low resistance normal state conductors operating at cryogenic temperatures. The resistivity of both aluminum and copper drops quickly with decreasing temperature, such that the resistivity of Cu drops by about a factor of 7, and that of aluminum by 10, by the time we reach 77 K (LN2). OSU and Hyper Tech have teamed to develop a motor with liquid cryogen cooled aluminum windings (LN2 or LNG cooled). It includes a multi-slot stator with direct cryogen cooling. Here we present the results of a simple “single slot” test which explores the temperature rise of a pair of conductors in a slot directly cooled by LN2. These two aluminum bars are made of 1100 commercial purity Al alloy were placed in parallel with a 1.6 mm gap, which behaved as 120 mm long cryogenic flow channel. Current densities up to 75 A/mm2 were explored, with LN2 flow rates ranging from 1.9 g/s to 6.4 g/s. Thermocouples and voltage taps were used to capture temperature and voltage data during the experiment. As a result, we found stable cooling and operation at these flow rates and current densities, and we characterized the temperature gradient which developed along the conductor bars.

Characterizing Surface Morphological and Chemical Properties of Commonly Used Orthopedic Implant Materials and Determining Their Clinical Significance.

The goal of the study was to compare the surface characteristics of typical implant materials used in orthopedic surgery and traumatology, as these determine their successful biointegration. The morphological and chemical structure of Vortex plate anodized titanium from commercially pure (CP) Grade 2 Titanium (Ti2) is generally used in the following; non-cemented total hip replacement (THR) stem and cup Ti alloy (Ti6Al4V) with titanium plasma spray (TPS) coating; cemented THR stem Stainless steel (SS); total knee replacement (TKR) femoral component CoCrMo alloy (CoCr); cemented acetabular component from highly cross-linked ultrahigh molecular weight polyethylene (HXL); and cementless acetabular liner from ultrahigh molecular weight polyethylene (UHMWPE) (Sanatmetal, Ltd., Eger, Hungary) discs, all of which were examined. Visualization and elemental analysis were carried out by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Surface roughness was determined by atomic force microscopy (AFM) and profilometry. TPS Ti presented the highest Ra value (25 ± 2 μm), followed by CoCr (535 ± 19 nm), Ti2 (227 ± 15 nm) and SS (170 ± 11 nm). The roughness measured in the HXL and UHMWPE surfaces was in the same range, 147 ± 13 nm and 144 ± 15 nm, respectively. EDS confirmed typical elements regarding the investigated prosthesis materials. XPS results supported the EDS results and revealed a high % of Ti4+ on Ti2 and TPS surfaces. The results indicate that the surfaces of prosthesis materials have significantly different features, and a detailed characterization is needed to successfully apply them in orthopedic surgery and traumatology.

Microstructural evolution of ion-irradiated commercially pure titanium

Radiation-induced dislocation loop evolution in ion-irradiated commercially pure (CP) Ti was investigated through both ex situ 4 MeV Ar beams and by in situ TEM irradiation with 1 MeV Kr ion beams at different temperatures. The dominant mechanism for dislocation loop growth was loop coalescence. Both <a>- and c-component loops exhibited an increase in size and density with increased irradiation dose and temperature. C-component loops were observed only after reaching a threshold incubation dose (TID). In CP Ti, these loops initiated at lower doses compared to previous observations in Zr, and the TID decreased with increasing temperature.

Indentation of Commercial Pure Titanium Processed by Cold Rolling

Indentation of Commercial Pure Titanium Processed by Cold Rolling

The Influence of the Shielding-Gas Flow Rate on the Mechanical Properties of TIG-Welded Butt Joints of Commercially Pure Grade 1 Titanium.

This article proposes as a novelty the differentiation of shielding-gas flow rates from both sides of the tungsten inert gas (TIG)-welded butt joints of commercially pure (CP) grade 1 titanium tubes. Such an approach is aimed at economically reducing the amount of protective gas used in TIG closed butt welding. The effect of the shielding-gas flow rate on the properties of CP grade 1 titanium butt-welded joints made using the tungsten inert gas (TIG)-welding method. Butt-welded joints were made for different values of the shielding-gas flow from the side of the root of the weld. Argon 5.0 was used as the shielding gas in the welding process. As part of the research, the welded joints obtained were analysed using optical and scanning electron microscopy. The microstructural characteristics of the joints were examined using an optical microscope, and the mechanical properties were determined using hardness and tensile tests. It was observed that as the flow of the shielding gas decreases, the hardness of the weld material increases and its brittleness also increases. A similar trend related to the amount of gas flow was also noticeable for the tensile strength of the joints. The increase in the hardness of the weld and the heat-affected zone compared to the base metal is mainly related to the increase in the amount of acicular structure (α' phase). The optimal gas flow rates from the side of the root of weld were found at the values of 12 dm3/min.

C.P titanium/Ti–6Al–4V joint by spark plasma welding: Microstructure and mechanical properties

The welding ability of Ti–6Al–4V alloy is weak due to their two-phase microstructure. On the other hand, friction welding methods lead to significant microstructural changes. In this research, for the first time, pure titanium was successfully joined to the Ti–6Al–4V alloy, without any change in the microstructure and mechanical properties of both alloys, by applying the SPW method. Further, the effects of temperature, pressure, and time of the SPW process on the microstructure and mechanical properties of commercial pure (C.P) titanium joined to the Ti–6Al–4V alloy were investigated. The results indicated that the effect of temperature and pressure on the SPW process was greater than that of time. Further, mechanical properties investigations showed that the yield strength of the joint interface was larger than that of the substrate metal, following which necking and fracture occurred in the pure titanium substrate metal. The alloy (Ti–Ti64) bonded at 800 °C, with a time of 10 min and pressure of 20 MPa, exhibited the superior bonding of 7–9 μm interface thickness, and excellent tensile strength (534 ± 13 MPa) and Vickers micro-hardness (190 ± 5 HV0.1). Investigation of the effect of pressure (normal stress) also showed that with an increase in pressure, because of the reduction of the chemical potential of diffusing species, the joint temperature would drop, and the joint could be created at a temperature below 800 °C.

Evaluation of biocompatibility of Commercial Pure Titanium / Bioactive Glass Ceramic Functionally Graded Material as Dental Implant Material In-Vivo study

Background: the ultimate goal of modern implantology is fine and fast osseointegration which is a major factor influencing the success of dental implantation, and the optimum circumstances of it the biointegration which is the occurrence of continuity of ceramic implant to bone without intervening space. &#x0D; Material and method: Two groups of cylindrical implant specimens were prepared from functionally graded material and commercial pure titanium. Each group composed of 40 implant specimens. The femur of 20 white male New Zealand rabbits, were chosen as implantation sites. Push out test was performed to measure bone bonding strength between implant specimen and bone after 2 and 4 weeks healing periods (10 rabbits for each periods). For each time interval 20 implant specimens for each group, which implanted in rabbits. Histological study for evaluation of tissue response and histomorphometric analysis was performed for measurement of new bone area at two time intervals.&#x0D; Result: the results of push out force and new bone formation area appeared that mean values of functionally graded material implant specimens were a statistically highly significant more than that of commercial pure titanium implant specimens after 2 weeks and 4 weeks of implantation. In histological examination, there was an active osteoid tissue around functionally graded material implants and hematopoietic tissues around commercial pure titanium implants after 2 weeks, and there was an osteoid maturation with observation of reversal lines around functionally graded material implants and new bone formation with osteocyte around commercial pure titanium implants after 4 weeks of implantation.

Combined severe plastic deformation processing of commercial purity titanium enables superior fatigue resistance for next generation implants

Commercial purity titanium (cp-Ti) is considered for replacing Ti64 as an implant material in various applications, due to the potential toxicity associated with the release of Al and V ions. However, the mechanical properties of cp-Ti, particularly fatigue resistance, are inadequate for this purpose. In this study, cp-Ti grade 4 rods were processed using a combination of equal channel angular pressing and rotary swaging (ECAP/RS). Tensile and fatigue tests were conducted, along with detailed microscopy and evaluation of corrosion resistance and biocompatibility. An average yield strength of 1383 MPa was obtained while maintaining moderate ductility of 10 %. This represents the highest strength ever recorded for cp-Ti, even exceeding that of Ti64. Additionally, fatigue endurance limit increased by 43 % up to 600 MPa, almost obtaining that of Ti64. Strengthening mechanisms were attributed to the ultrafine-grained (UFG) microstructure generated by ECAP/RS, along with strong crystallographic texture and formation of sub-grain structure. Furthermore, the corrosion resistance and biocompatibility of cp-Ti were largely unaffected, potentially easing regulatory transition in future medical devices. Thus, these results demonstrate high potential of combined ECAP/RS processing to manufacture UFG cp-Ti grade 4 materials that prospectively allow for the substitution of questionable alloys and downsizing of medical implants.

Contribution of Oxygen Reduction to Mg Corrosion: Experimental Evidence By Electrochemical Microprobes

Unravelling the mechanisms of magnesium corrosion is vital for establishing reliable research methodologies, developing new alloys and predicting magnesium degradation behaviour. Hydrogen evolution reaction is widely regarded as by far the main cathodic process during corrosion of magnesium. Hence, tracing the amount of released hydrogen was thought to be a reliable measure of magnesium degradation rate. Recently, experimental evidences obtained by different methods have been presented by several groups that oxygen reduction (ORR) is important secondary cathodic reaction during Mg corrosion [1-8]. For model galvanic couple Al-Cu-Mg, oxygen consumption on the surface of Mg along with that on Cu was observed by using oxygen sensing microoptode [1]. A simultaneous measurement of local current density by scanning vibrating electrode technique (SVET) and local oxygen concentration by oxygen sensing microoptode found a strong oxygen consumption at the active corrosion sites on the surface of commercially pure Mg in NaCl electrolyte [2]. Then, the evidence for the varying contributions of ORR to the total cathodic process on Mg alloys during atmospheric and aqueous corrosion was presented based on newly developed respirometric methods [3-5]. While around 10% of the total cathodic current was ascribed to ORR during aqueous corrosion, up to 60% of the total corrosion process was shown to be due to the ORR contribution during simulated atmospheric corrosion with wet-dry cycles. Nanoparticle-based O2 imaging was used to map decreased O2 concentration at the interface of several Mg alloys exposed to simulated body fluids [6].High ORR rate on a slowly corroding ultra-high-purity Mg (UHP-Mg) in NaCl electrolyte was shown in our recent work [7]. Comparing that with lower ORR rate for faster corroding commercial purity Mg (CP-Mg), the rate of ORR was found to depend on the growth rate of Mg(OH)2 , which is the main corrosion product of Mg in the simple saline solution. The formation of Mg(OH)2 impeded the diffusion of oxygen from bulk electrolyte to metal interface, preventing metallic Mg substrate from the interaction with oxygen. The distribution of local concentration of dissolved gaseous H2 and O2 assessed by amperometric Clark-type micorprobes at the interface of UHP-Mg and CP-Mg demonstrated the inverse relationship between HER and ORR, and supports the finding that diffusion-controlled ORR highly depends on the barrier property of corrosion products on the surface [8]. The contribution of ORR current to total cathodic current reached 29.1% for UHP-Mg, while only 0.9% for CP-Mg after 1 hour of immersion in NaCl solution. The contribution of ORR decreases with immersion time, due to the impeded access of dissolved O2 to Mg interface caused by thickening of Mg(OH)2 layer. A numerical model was developed considering the mixed potential diagram and measured local oxygen concentration. REFERENCES: [1] D. Snihirova, M. Taryba, S.V. Lamaka, M.F. Montemor, Corrosion inhibition synergies on a model Al-Cu-Mg sample studied by localized scanning electrochemical techniques, Corrosion Science, 112 (2016) 408-417.[2] E.L. Silva, S.V. Lamaka, D. Mei, M.L. Zheludkevich, The Reduction of Dissolved Oxygen During Magnesium Corrosion, ChemistryOpen, 7 (2018) 664-668.[3] M. Strebl, S. Virtanen, Real-Time Monitoring of Atmospheric Magnesium Alloy Corrosion, Journal of The Electrochemical Society, 166 (2019) C3001-C3009.[4] M. Strebl, M. Bruns, S. Virtanen, Editors’ Choice—Respirometric in Situ Methods for Real-Time Monitoring of Corrosion Rates: Part I. Atmospheric Corrosion, Journal of The Electrochemical Society, 167 (2020) 021510.[5] M. Strebl, M.P. Bruns, G. Schulze, S. Virtanen, Respirometric In Situ Methods for Real-Time Monitoring of Corrosion Rates: Part II. Immersion, Journal of the Electrochemical Society, (2021).[6] B. Zeller-Plumhoff, A.R. Akkineni, H. Helmholz, D. Orlov, M. Mosshammer, M. Kühl, R. Willumeit-Römer, M. Gelinsky, Oxygen-sensitive nanoparticles reveal the spatiotemporal dynamics of oxygen reduction during magnesium implant biodegradation, NPJ Materials Degradation, 6 (2022) 95.[7] C. Wang, D. Mei, G. Wiese, L.Q. Wang, M. Deng, S.V. Lamaka, M.L. Zheludkevich, High rate oxygen reduction reaction during corrosion of ultra-high-purity magnesium, NPJ Materials Degradation, 4 (2020) 42.[8] C. Wang, W. Xu, D. Höche, M.L. Zheludkevich, S.V. Lamaka, Exploring the contribution of oxygen reduction reaction to Mg corrosion by modeling assisted local analysis, Journal of Magnesium and Alloys, 11 (2023) 100-109. ACKNOWLEDGEMENTS: C. Wang, Wen Xu, thank China Scholarship Council for the funding, grants no. 201806310128 and 201908510177

Using Taguchi Design to Compare the Corrosion Behavior of Commercial Pure Ti Alloys Coated by Dip and Electrophoretic Deposition with YSZ

Using Taguchi Design to Compare the Corrosion Behavior of Commercial Pure Ti Alloys Coated by Dip and Electrophoretic Deposition with YSZ

Ceramic Conversion Treatment of Commercial Pure Titanium with a Pre-Deposited Vanadium Layer

Titanium is characterized by poor wear resistance which restricts its application. Ceramic conversion treatment (CCT) is used to modify the surface; however, it is a time-consuming process. In this work, a thin vanadium layer was pre-deposited on the commercial pure titanium (CPTi) samples’ surface, and it increased the oxygen absorption significantly and assisted in obtaining a much thicker oxide layer than those samples without a V layer at the treatment temperatures of 620 °C and 660 °C. The oxidation of the samples pre-deposited with the V layer had a much higher oxidation rate, and V was evenly distributed in the oxide layer. After CCT, all samples had a low wear volume and stable coefficient of friction in comparison to the untreated CPTi sample. A slightly higher wear area in the wear track was observed on the V pre-deposited samples than those samples without vanadium, especially those with a thicker oxide layer (&gt;4 µm). This might be associated with defects in a thicker oxide layer and insufficient support from a shallower oxygen diffusion zone or hard debris created at the initial stage. Vanadium in the oxide layer reduced the contact angles of the surface and increased the wettability significantly.

Residual Stress and Dimensional Deviation in a Commercially Pure Titanium Thin Bipolar Plate for a Fuel Cell Using Laser Power Bed Fusion

In this study, the feasibility of commercially pure (CP)-Ti bipolar plates for fuel cells were assessed by designing, manufacturing, and evaluating thin plates fabricated through the laser powder bed fusion (L-PBF) technique. The width, height, and thickness of thin CP-Ti plates were carefully considered in its design to ensure comprehensive evaluation. The maximum displacement was measured through blue light scanning in accordance with the building direction. The finite element model and experimental results showed that the building layer per volume has a linear relationship with the maximum displacement and maximum residual tensile stress along the building direction. Thin plates with a high aspect ratio (198 × 53 × 1.5 mm) had the lowest maximum displacement (0.205 mm) when building in the height direction and had a high correlation coefficient with the finite element model (0.936). Proper aspect ratio design and building strategy enable highly accurate manufacturing of CP-Ti thin plates for fuel cell systems.

Influence of ultrafine-grained structure parameters on the annealing-induced hardening and deformation-induced softening effects in pure Al

This work investigates the influence of parameters of initial ultrafine-grained (UFG) structure in commercially pure (CP) Al on annealing-induced hardening (AIH) and deformation-induced softening (DIS) effects. UFG structures were formed via processing CP Al by various methods of severe plastic deformation (high pressure torsion (HPT), equal channel angular pressing (ECAP) and combination of ECAP and cold rolling (CR)). AIH and DIS effects are observed in all the studied UFG structures. However, HPT Al demonstrates large increase of strength due to annealing and drastic gain of ductility after subsequent additional deformation whereas in ECAP Al and ECAP + CR Al both effects are much less pronounced. Microstructure characterization by X-ray diffraction (XRD) analysis, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) was performed for HPT Al and ECAP + CR Al in the three studied states: before and after annealing and after annealing and subsequent additional deformation. Analysis of microstructure evolution during annealing and subsequent additional deformation shows that the key microstructure parameter which is responsible for AIH and DIS effect is the change of dislocation density in grain interior in ECAP + CR Al, whereas in HPT Al the effects are related to the change of dislocation density at/near grain boundaries. In addition, outstanding combination of high strength (∼210 MPa), high electrical conductivity (∼62 %IACS) with sufficiently good ductility (7–10 %) and thermal stability (up to 150°С, at least) was achieved for ECAP + CR Al after annealing at 150 °C, 1h.

Creation of a heterogeneous grain structure is a condition for increasing the low-temperature ductility of nanocrystalline hcp metals

The paper considers the influence of a heterogeneous (bimodal) grain structure on the ductility characteristics of commercial purity titanium in a wide range of low temperatures (4.2–395 K) as a strategy for optimizing mechanical properties within the framework of the “strength–plasticity” ratio. Using titanium as an example, the physical mechanism for increasing the low-temperature ductility of hcp nanocrystalline metals with a heterogeneous grain size distribution is explained by a combination of several processes: an increase in the activity of intragrain dislocation slip, dynamic grain growth under tensile stresses, and activation of nanotwinning in submicron-sized grains.