bluuebunny/crossref_metadata_2025 huggingface dataset:
Developments in Titanium Research and Applications in Germany
Authors: Siemers Carsten , Stöcker Christian
Published: October 2020

Since the Ti-2015 World Conference on Titanium held in San Diego, USA, research, development and applications of commercially pure titanium, titanium alloys and titanium aluminides have advanced considerably. In this plenary paper, information is provided on important achievements in the German titanium industry, governmental and non-governmental research organisations and universities from the last four years.
Recent activities of titanium research and development in Japan
Authors: Narushima Takayuki , Sugizaki Yasuaki
Published: October 2020

The research and development of Ti and its alloys as well as progress in Japan’s Ti industries and markets are described. Academic and industrial advances and activities over the past four years, since the 13th World Conference on Titanium held in San Diego, USA, are overviewed.
Opportunities and Challenges for the Industrial Titanium Market
Authors: Henson Hershel Robert
Published: October 2020

The industrial titanium market is the second largest segment of the titanium industry and currently comprises less than 20 % of the overall titanium market. In spite of a more than 50 year history of successful application in corrosive environments myths about availability, fabrication, pricing and corrosion resistance are still part of the conversation and culture with many potential customers. The author will discuss these issues and present comparisons with other common materials of construction to demonstrate the business case for titanium.

With seawater/brackish water being the most common corrosive environment where titanium is applied examples of current applications will be presented. By highlighting the characteristics of titanium that led to the material choice in these examples potential new applications can be identified. These examples will come from application on offshore platforms, LNG liquefaction plants, power generation, desalination and petroleum refining operations.

Against the backdrop of the application analysis the author will also explore regulatory, market influences and new technology impacting the industrial titanium market segment. Drawing on statistics from the Titanium Association and other resources a projection for industrial growth will be presented for the next decade.
Topology optimisation of an aircraft nose-wheel fork for production in Ti6Al4V by the Aeroswift high-speed laser powder bed fusion machine
Authors: Monaheng L F , du Preez W B , Kotze N , Vermeulen M
Published: October 2020

Recent levels of structural integrity of components built in the Aeroswift high-speed laser powder bed fusion machine have led to the decision to produce a structural aircraft component through this technology. The Aeroswift machine is capable of building larger Ti6Al4V parts at a more rapid pace than current commercial laser metal powder bed fusion systems. As prototype component, the nose-wheel fork of the AHRLAC aircraft, which was conventionally machined in aluminum alloy 7050, was selected. This paper describes the design, topology optimisation and the manufacturing approach taken in this project.

Given the design space, loads, strength requirements and boundary conditions prescribed by the AHRLAC engineers, topology optimisation was performed on the nose-wheel fork to design a lightweight component for production in Ti6Al4V. Different topology optimisation software suites were used, to establish their capabilities and fit-for-purpose features. The optimised design and percentage of weight saving are presented. An assessment based on the experience with the different software suites is offered.
Microstructure and Properties of 3D Ti-6Al-4V Articles Produced with Advanced Co-axial Electron Beam & Wire Additive Manufacturing Technology
Authors: Kovalchuk Dmytro , Ivasishin Orest , Savvakin Dmytro
Published: October 2020

Ti-6Al-4V articles were produced with advanced additive manufacturing technology of Direct Energy Deposition (DED) type using profile electron beam and wire as feedstock material. The key distinctive feature of this additive manufacturing process is the applying of the hollow conical electron beam generated by low-voltage (<20kV) gas-discharge EB gun for heating and melting of the substrate and co-axially fed wire. Such configuration ensures precisely controllable liquid metal transfer from the wire end to the substrate, specific temperature gradients at the fusion area and heat flow from liquid metal pool. Such conditions of heating, melting and cooling during 3D manufacturing processing provide the ability for controllable microstructure formation, including grain size and material texture.

Influence of processing parameters and cooling conditions on crystallization, grain formation and intragrain structure of solidified material is discussed. Optimization of processing parameters allowed production of 3D Ti-6Al- 4V articles with isotropic microstructure and mechanical properties which met standard requirements for Ti-6Al-4V alloy.
On the advances to obtain excellent and repeatable mechanical properties and build quality of LaserForm® Ti gr23 (A) across whole build platform
Authors: Beckers Anthony , Muralidharan Gokula Krishna , Lietaert Karel , Ray Nachiketa , Van Cauwenbergh Pierre , Vanacken Koen , Thijs Lore , Van Vaerenbergh Jonas
Published: October 2020

Direct Metal Printing (DMP) or Laser Based Powder Bed Fusion (L-BPF) enables manufacturing of highly complex geometries which are used in a wide range of applications - healthcare to aerospace. Producing these products with excellent and consistent part quality in terms of density and mechanical properties is key. DMP ProX® 320 machine has been used for over 10 years for this purpose. In this study, the key improvements made on the process stability for targeting consistent build quality across build platform and repeatability have been evaluated. The quality is assessed by determining the density, mechanical properties and surface roughness of direct metal printed LaserForm® Ti gr23 (A). The main finding from the study is that the use of the optimized gas flow enables production of LaserForm® Ti gr23 (A) with consistent and improved mechanical properties across the whole build platform. Moreover, there is no need any more for hot isostatic pressing to ensure good fatigue properties. The elongation strain to failure increased by 15 % to 20 %, which is 4-5 % higher than ASTM F3001 specifications. The axial fatigue limit (5x106 loading cycles) was 637 MPa (R=0.1), which is as good as or even better than annealed wrought Ti6Al4V.
Microstructural Stability of Ti based Composites Fabricated by Spark Plasma Sintering
Authors: Watanabe Yoshimi , Hattori Miwa , Chiba Tadachika , Sato Hisashi
Published: October 2020

In our previous study, the effects of TiC heterogeneous nucleation site particles on formability and microstructure of additive manufactured (AMed) Ti-6Al-4V products were studied. It was found that the addition of TiC particles decreased the grain size of primary β phase in AMed Ti-6Al-4V samples, since TiC particles act as heterogeneous nucleation sites. It is also found that the density of AMed Ti-6Al-4V samples could be increased by addition of TiC particles. It is expected that solid-state β-grain growth by the high temperature thermal cycles associated with layer-by-layer manufacturing can be suppressed by the pinning effect of TiC heterogeneous nucleation site particles. In this study, the pinning effect of heterogeneous nucleation site particles on microstructure of Ti at elevated temperatures is studied. For this purpose, Ti-0.3vol%TiC samples fabricated by spark plasma sintering (SPS) are used as the model materials, and microstructure and hardness of the samples heat treated at elevated temperatures are studied.
Effect of Heat Treatments on Fatigue Properties of Ti-6Al-4V Alloy Fabricated by EBM Additive Manufacturing
Authors: Lee Dong-Geun , Choi Youngsin
Published: October 2020

The powder bed fusion method using a heat source for 3D printing can be applied to fabricate the geometrical shapes of some parts, and enables rapid melting and cooling. 3D EBM additive manufacturing can supply a near-net-shape or net-shape and precise parts better than micro scale casting and precision casting. Casting parts have residual stress in the matrix and their microstructure, which can affect the dynamic properties, but if they are heat-treated under the optimal conditions, the residual stress can be reduced to enhance the dynamic-mechanical properties of 3D printed parts. In this study, Ti-6Al-4V bulk bars were fabricated by EBM additive manufacturing, and the microstructures, residual stress, and various interior defects of the specimens were analyzed. The residual stress and surface tension were measured and calculated in different specimens heat-treated at 850~950 ℃ . The relationship between the residual stress and surface tension was explained using the related equations and the influence on the high cycle fatigue properties was evaluated.
Improving the high temperature oxidation resistance of Ti-β21S by mechanical surface treatment
Authors: Lavisse L. , Kanjer A. , Cheveau K. , Optasanu V. , Peyre P. , Gorny C. , François M. , Tidu A. , Schuman C. , Herbst F. , Saint-Jean M. , Montesin T. , Marco de Lucas M. C.
Published: October 2020

The improvement of the high temperature oxidation resistance of titanium alloys is currently a technological challenge. Mechanical surface treatments as shot-peening (SP) have shown their ability to improve the behaviour of pure zirconium and titanium. However, shot-peening treatments can induce a significant surface contamination. Laser shock peening (LSP) appears as a good alternative. Here, we have investigated the effect of SP and LSP treatments on the HT oxidation behavior of Ti-β21S. Samples treated by these methods have been compared to untreated ones for long exposures (3000 h) at 700 °C in dry air. The samples placed in a furnace at 700 °C were periodically extracted to be weighed. The results have been compared to that of pure commercial titanium (Ti-α) samples studied in the same conditions. The higher performances of the Ti-β21S alloy, and the beneficial effect of the SP treatment, and even more of the LSP one, on the HT oxidation resistance of Ti-β21S have been clearly shown. The effect of the mechanical treatments on the microstructure of the Ti-β21S samples and the changes induced by the long duration exposure at high temperature have been mainly studied by scanning electron microscopy combined with energy and wavelength dispersive spectrometry.
Effect of oxygen contents on strain rate sensitivity of commercially pure titanium
Authors: Lee Min-Su , Hyun Yong-Taek , Jun Tea-Sung
Published: October 2020

In this study, we have investigated the effect of oxygen contents on strain rate senstivitiy (SRS) within Gr. 1 and 4 commercially pure titanium (CP-Ti). The SRS was evaluated in multi-scales using macro-scopic tensile test with constant strain rate (CSR) method and strain rate jump (SRJ) method, and nanoindentation test with SRJ method. Electron backscatter diffraction (EBSD) has been used to characterise crystallographic texture and individual grain orientation of samples. Slip and twin activities of each CP-Ti were compared by EBSD measurements and the associated Schmid factor (SF) analysis. The active slip system is anticipated to be different in each relation between loading directions and textures, but twin activity is much similar. The texture dependent global SRS is thus thought to be resulted from the different slip activity. Local SRS was dependent not only on the grain orientation but also on the oxygen contents, leading to the fact that the impact of oxygen contents is closely correlated in macro- and micro-scopic level.
High temperature oxidation and mechanical behavior of β21s and Ti6242S Ti-based alloys
Authors: Put Aurelie Vande , Thouron Carole , Emile Philippe , Peraldi Raphaëlle , Dod Benjamin , Monceau Daniel
Published: October 2020

Aircraft industry always looks for higher in-service temperatures and lighter structures. With a high specific strength, Ti-based alloys are good candidates for such applications. However, when exposed to oxidizing environments at high temperatures, they undergo large oxygen dissolution while forming an oxide scale, which can greatly affect their mechanical properties. Then, evaluating the oxidation resistance and mechanical behavior of such alloys is essential. In this aim, long term oxidation tests were performed under laboratory air between 500 °C and 625 °C on two Ti-based alloys: β21s, exhibiting a fully β microstructure supposed to dissolve lower amount of oxygen and nitrogen, and Ti6242S, with an α/β microstructure. The oxidized samples were characterized using XRD, Raman spectroscopy, SEM-EDS and micro-durometer. As for the mechanical behavior, tensile tests were performed at room temperature on not aged and on oxidized samples. While larger mass variations were obtained at 500 and 560 °C and up to 997 h at 625 °C for β21s, its mass variations became lower than those of Ti6242S for longer durations at 625 °C. Nevertheless, β21s exhibited thicker micro-hardness affected depths and underwent larger mechanical property modifications compared to Ti6242S.
Tensile properties of α-titanium alloys at elevated temperatures
Authors: Nawaya Tarik , Beck Werner , von Hehl Axel
Published: October 2020

Hot-deep drawing is an innovative processing technology to produce complex shaped sheet metal components with constant wall thickness from high-strength lightweight materials. For some aerospace and automotive applications oxidation resistance at medium to high temperatures is an important aspect. In terms of this titanium α-alloys are often used due to their balanced relation of strength and oxidation resistance. In the presented study the stress-strain characteristics of several α-titanium alloys were determined at ambient and elevated temperatures by means of hot tensile tests. Besides the commercially pure Titanium alloy ASTM-Grade 4, two novel α-titanium alloys were investigated. Regarding the hot forming properties a comparison with α-β Ti-6Al-4V alloy was conducted. The hot tensile tests were carried out by means of a particular forming dilatometer type “Gleeble 3500” at 400, 500, 600, 650, 700 and 800 °C. The test showed favorable peak plasticity for all α-alloys at the temperature range between 600 and 650 °C in contrast to lower or higher temperatures. All samples were metallographically characterized.

Key words: titanium α-alloys, hot tensile properties, elevated temperatures, Gleeble 3500.
Effect of Edge Conditions on the Formability of Commercially Pure Titanium Sheet (Grade 2) at Room Temperature
Authors: Kwame J.S. , Yakushina E. , Blackwell P.
Published: October 2020

Titanium and its alloys are difficult to form, particularly at room temperature, due to their crystallographic structure and limited availability of slip systems. Such limited formability could be exacerbated by virtue of the technique used to cut the sheet. Forming limit diagrams will not necessarily recognize such effects, which can lead to failures during forming trials. An example of a situation where this could be demonstrated is in sheet with pre-fabricated holes. This work used a hemispherical punch to stretch in-plane a 20mm diameter hole prepared with laser, EDM and AWJ cutting techniques in order to quantify the edge formability of the material. It was identified that, the edge surface conditions have a major impact on the edge formability of the material. The edges of the material prepared with EDM showed very high formability tendencies compared with AWJ and laser cutting. The work proposed an alternative characterization method that could be adopted for edge formability assessment.
Evolution of mechanical properties of Ti6242S alloy after oxidation in air at 560°C: influence of solid salts deposits
Authors: POPA Ioana , BERTHAUD Maxime , CISZAK Clément , BROSSARD Jean-Michel , MONCEAU Daniel , CHEVALIER Sébastien
Published: October 2020

Titanium alloys are widely used in aerospace applications due to their good ratio of weight versus mechanical properties. When exposed to air at 560°C, Ti6242S titanium alloy presents very good oxidation resistance: a very thin oxide layer forms at its surface and oxygen dissolution inside the metallic material is rather limited. However, in real functioning conditions of the plane, near seas or oceans, the atmosphere contains NaCl, that can crystallise at the surface of hot parts. An active corrosion mechanism is established in these conditions, with catastrophic effect on the material behaviour at high temperature: very thick and brittle oxide scales and very important damaging of the metal outer part. Another issue is the formation of Na2SO4 specie by reaction of NaCl with kerosene combustion gases (SO2/SO3), leading to mixed NaCl/Na2SO4 deposits. The effect of exposure conditions on the mechanical properties of titanium alloy Ti6242S was evaluated through tensile tests performed on the raw alloy and after oxidation in air at 560°C of the specimens: without any deposit, with NaCl solid deposit, with NaCl/Na2SO4 solid deposit. The evolution of mechanical properties was interpreted in connexion with the microstructural modifications that occur during the high temperature ageing.
Influences of Mo addition on mechanical properties and deformation behavior of β-type Ti alloys
Authors: Cho K. , Morioka R. , Yasuda H.Y.
Published: October 2020

The influences of Mo addition on the tensile properties and deformation behavior of β-type Ti-Mn alloys were investigated with particular focus on {332}<113> deformation twinning. We found that Ti-7Mn and Ti-5Mo-3Mo alloys exhibit completely different tensile properties, despite having the same microstructure and stability of the β phase. The Ti-5Mn-3Mo alloy demonstrates higher tensile strength and larger ductility than the Ti-7Mn alloy due to its strong work hardening, caused by {332} <113> deformation twinning. The critical resolved shear stress (CRSS) for {332}<113> deformation twinning in these alloys was measured by compression tests using single crystals. It was thereby found that Mo addition is effective in decreasing the CRSS for {332}<113> deformation twinning in Ti-Mn alloys.
Development of elastically graded titanium alloys for biomedical applications
Authors: DELANNOY Stéphanie , BAÏZ Sarah , LAHEURTE Pascal , JORDAN Laurence , PRIMA Frédéric
Published: October 2020

Recent works have shown that the elastic mismatch observed at the bone / implant interface could be responsible for stress shielding issues causing bone resorption phenomena and potentially implant failures. In the present study, new advanced thermomechanical approaches leading to titanium alloys with graded elastic properties are proposed. The underlying philosophy and the whole methodology is detailed here, from the selection of candidates with large elastic variability to the creation of gradients, involving the identification of microstructure-properties relationships and the use of appropriate thermo-mechanical treatments. Applied on Ti-Nb-Zr alloys, these original routes enabled to get the following graded properties: elastic modulus from 85 to 65GPa over 400μm for TNZ alloy by surface deformation, and from 130 to 75GPa over 100μm for Ti-13-13 by preferential dissolution. These promising results thus validated the previously designed material-strategy-process combinations.
Corrosion of titanium alloys in pressurized water at 300 °C and 15 MPa
Authors: Quentin BIGNON , Quentin AUZOUX , Frantz MARTIN , Amandine RAYNAL , Frédéric MISERQUE , Michel TABARANT , Laurence LATU-ROMAIN , Yves WOUTERS
Published: October 2020

Commercially pure titanium (Ti CP) and two titanium alloys (Ti 64 and Ti10-2-3) representative of different metallurgical classes were exposed to pressurized water at 300 °C, 15 MPa in a dedicated stainless steel corrosion loop up to 1632 h.

Mass uptake measurements as well as extensive characterization of the oxides formed on the polished samples using scanning and transmission electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, photoelectrochemistry and glow discharge optical emission spectroscopy led to the following main conclusions:

• The oxide scale was made of a thin and continuous TiO2 layer topped by small TiO2 anatase crystallites and large FeTiO3 ilmenite crystallites.

• The interface tortuosity increased with exposure duration, as well as the amount of crystallites. From 217 h exposure, the thickness of the thin continuous TiO2 layer remained constant with exposure duration.

• The mass uptake increased approximately linearly with exposure duration.

These observations were consistent with a corrosion mechanism involving simultaneous oxide growth, dissolution and precipitation. The corrosion rate of the three studied materials was estimated to be around 3 µm/year.
Development of Method for Direct Deoxidation of Titanium using Mixtures of Magnesium Chloride and Rare-Earth Chlorides
Authors: Ouchi Takanari , Zheng Chenyi , Kong Lingxin , Okabe Toru H.
Published: October 2020

To decrease the cost of Ti sponge, Ti scrap is added during the remelting process to produce an ingot. However, the use of Ti scrap as an additive during this process is limited because Ti scrap is contaminated by oxygen (O) and iron (Fe), which are not removable during the remelting process. Here we introduce a new electrochemical deoxidation process for Ti scrap using a mixture of magnesium chloride (MgCl2) and rare-earth chlorides (RECl3, RE: Y and Ho) as a flux. Ti and carbon were used as the cathode and anode, respectively. Mg is deposited on the Ti cathode and reduces the oxygen in the Ti to oxide ions (O2). The activity of the generated O2” in the system,aQi-, is maintained at a low level through the formation of rare-earth oxy chloride (REOCl), and is further decreased by the formation of carbon oxides on the anode. During this process, the concentration of oxygen in the Ti is effectively decreased to 100 mass ppm in the MgCl2-YCl3flux at 1,200 K. This new deoxidation method is considered applicable to the recycling process of Ti scrap containing large amounts of oxygen.
The production of Titanium Powder via Hydrogen Reduction of Titanium Tetrachloride by Inductively Coupled RF plasma
Authors: Park Sung-hun , Lee So-yeong , Lee Ho-seong , Son Ho-sang
Published: October 2020

In this study, the production of titanium powder via hydrogen reduction of titanium tetrachloride by inductively coupled radio frequency plasma was investigated. While titanium tetrachloride is hard to be reduced by hydrogen thermodynamically, dissociated hydrogen radical which formed from hydrogen gas passing through the plasma can react with titanium tetrachloride to form hydrochloric acid and subsequently produce titanium. The frequency of generator used in this experiment was 13.56 MHz and input power was varied. The characteristics of the powder such as powder size, size distribution, and phases were analyzed with x-ray diffractometer, field emission scanning electron microscope, energy dispersive x-ray spectrometer and transmission electron microscope. The deposited height of titanium powders, after 4 minutes reaction, were 4.004 μm and loosely attached that could be easily collected. The morphology of powders was found to be more spherical with the increase in applied input power. Most of the powders were composed of titanium and oxygen. The average diameter of powders was approximately 200 nm.
Integrated Computational Materials Engineering of Gamma Titanium Aluminides for Aerospace Applications
Authors: Dahar Matthew S. , Tamirisakandala Sesh A. , Lewandowski John J.
Published: October 2020

Although the benefits of titanium aluminides for intermediate service temperature applications were well conceived and significant research and development activities were conducted in the past four decades, they remained as developmental materials due to barriers associated with melting, processing, scale-up, and cost. Demanding requirements of efficient aero-engines and extensive risk reduction demonstrations paved the path for commercial introduction of gamma titanium aluminides. The single most attractive current application is for low pressure turbine blades (LPTBs) in advanced aero-engines replacing conventionally cast nickel superalloys. This paper provides an overview of recent progress, producibility challenges, and opportunities. The successful journey of gamma (γ) TiAl LPTB development from laboratory demonstrations to production insertions in mass-produced commercial jet engines will be described. Collaboration and integrated product development were identified as the most critical needs for rapid maturation and implementation of γ-TiAl into aerospace applications. An integrated computational materials engineering modeling framework and toolsets developed under a collaborative US Air Force Metals Affordability Initiative project between industry, government, and academia will be illustrated. Model-based optimization of material and processing for achieving desired performance goals will be highlighted.
Multi-scale reinforcements stimulated dynamic recrystallization and mechanical behavior of as-extruded titanium matrix composites
Authors: Qiu Peikun , Han Yuanfei , Huang Guangfa , Le Jianwen , Du Lihua , Lu Weijie
Published: October 2020

Different volume fraction of TiB, TiC and La2O3 multiple-reinforced Ti6Al4V composites were fabricated by casting and followed by forging and hot extrusion. The microstructural evolution and mechanical behavior of (TiB+TiC+La2O3)/Ti6Al4V composites during hot extrusion were investigated. The microstructural observations showed that the TiBw and TiCp agglomeration disappeared and distributed more homogeneously in the Ti matrix after hot extrusion. Besides, TiBw exhibited highly preferred alignment along the extrusion direction and TiCp distributed along the same direction. Besides, two kinds of microstructure bands with distinctive spatial distributions of reinforcements were formed after hot extrusion: equiaxial bands embedded with fairly substantial reinforcements and finer basket-weave bands containing few reinforcements, in which the micron-scale TiBw, TiCp and submicron-scale La2O3 particle stimulating nucleation occurred and resulting dynamic recrystallization were the main mechanisms responsible for grain refinement. The tensile tests revealed that hot extrusion significantly increased elongation of (TiB+TiC+La2O3)/Ti6Al4V composites from 2.71% to 13.2% accompanied by slightly decreasing ultimate tensile strength from 954MPa to 903MPa, compared with that of the as-forged composites, which due to a complex process of reinforcements/matrix interaction during extrusion and dynamic recrystallization.
Effect of Melting Interruption on Composition and Microstructure of BT22 Ingot in VAR
Authors: Hua Zhengli , Luo Wenzhong , He Tao , Lei Qiang , Wang Longzhou , Liu Xianghong
Published: October 2020

BT22 ingot was remelted by vacuum arc remelting (VAR) furnace with a melting rate of 20kg/min. The power of VA R was interrupted for five minutes when the weight of the remelted ingot is approximately 4000 kg. The melting process was then resumed at the same melting rate after the five minutes interruption. Optical microscopy (OM), inductively coupled plasma-mass spectrometry (ICP-MS) and electron probe micro analyzer (EPMA) were utilized to analyze the microstructure, composition and distribution of elements. No significant microstructural difference was oberved at the remelting interrupted region. The variation of Al, Mo, V, Cr, Fe contents between the melting interruption region and normal region is within 0.23 wt%. The distribution of elements in equiaxed grains of the melting interruption region and the normal regions were compared by EPMA analysis. The contents of Al, V, Fe and Cr increase from the center of equiaxed grains to their grain boundaries. The content of Mo decreases from the center of equiaxed grains to their grain boundaries. The trend of element content in the normal region is similar to that of the melting interrupted region.

Key words: BT22; ingot; composition; microstructure
Ti and TiAl melting with a semi-industrial PAMCHR
Authors: Ruby-Meyer Fabienne , Doridot Emiliane , Delfosse Jérôme , Hans Stéphane
Published: October 2020

Upscaling from laboratory trials to industrialization is a critical step in the development of new metallurgical processes and products. Pilot trials are an important way to provide data that can be used to better understand and model the industrial-scale process.

MetaFensch has invested in a semi-industrial Plasma Arc Melter Cold Hearth Refiner (PAMCHR) in order to support the development of the recycling of titanium scraps into aeronautical grade titanium alloy ingots.

This pilot supports the industrial scale PAMCHR of the company Ecotitanium in the frame of a collaborative project with Aubert & Duval and Safran as industrial partners.

The work done on the pilot scale PAMCHR consists in studying the influence of various parameters like the type of melting feedstock, plasma arc parameters, operating pressure on the final quality of the cast ingot. The goal is to understand the physico-chemical mechanisms involved in the plasma arc interacting with the liquid metal in order to optimize the melting and refining parameters for the industrial scale furnace Ecotitanium (Ti64 alloy).

Ti64 and TiAl ingots were cast in 150 mm and 100 mm diameter. Chemical composition and solidification structure were characterized. The effect of the different process parameters on the titanium melt and on the ingot quality are studied. Examples of exploitation of the thermograms obtained with the thermal camera situated above the refining cold hearth will also be presented in this paper.
Microstructures and tensile properties of a high strength β titanium alloy Ti5Al4Zr8Mo7V by near β forging and β-transus forging
Authors: Zhu Wenguang , Lei Jia , Sun Qiaoyan , Xiao Lin , Sun Jun
Published: October 2020

A novel high-strength metastable β-Ti alloy Ti-5Al-4Zr-8Mo-7V has been successfully developed by improved Bo-Md map combined with critical Mo equivalent criteria. Near β forging combined with different heat treatments was introduced to tailor the Bi-modal structure. The alloy exhibits good strength-ductility combination with UTS~1390 MPa and El~10% after solution treated (ST) at 800°C followed by 570°C aging. After β-transus forging combined with subsequent heat treatment, an excellent combination of strength UTS~1460MPa and El~10% is achieved which is attributed to the Tri-modal structure consisting of primary α (αp), sub-micro α rods (αr) and nano-scale α platelets (αs). Plastic strain is effectively partitioned in both αp, αr and β matrix during deformation, which results in a more homogeneously strain distribution and improved ductility. Nano-scale distribution of αs effectively block the dislocation motion in β matrix and strengthen the alloy.
A Surrogate Approach to Reveal Microstructural Mechanisms Controlling the 3D Short Crack Growth in a Ti-6Al-4V Alloy
Authors: Hassanipour Meysam , Watanabe Shinta , Li Han , Hirayama Kyosuke , Toda Hiroyuki , Takeuchi Akihisa , Uesugi Kentaro
Published: October 2020

Microstructural features and short crack growth behavior were characterized and linked in a Ti-6Al-4V by employing X-ray micro-tomography combined with EBSD serial sectioning. Statistical analysis was used to rank the contributing features to the crack behavior. Afterwards, by creating surrogate models, the microstructural mechanism controlling the short crack behavior were revealed. Short crack preferably grows inside the predominant α phase above the average microstructural fraction. A high number of grains in contact with cracked α grains elongated in the loading direction may impose a constraint on the crack opening resulting in low crack growth rates. As the crack front becomes larger, the increase in the shear stress field away from the cracked grain leads to crack bifurcations, resulting in a decrease in crack driving forces with low crack growth rates. This leads to a preferable growth in α+β phase and along the interface above the average microstructural fractions.
Local lattice strain around alloying element and martensitic transformation in titanium alloys
Authors: Morinaga M. , Yukawa H. , Yoshino M.
Published: October 2020

Local strain is introduced into the lattice around solute atom due to the size mismatch between solute and solvent atoms in alloy. In this study, local lattice strains are calculated for the first time in titanium alloys, using the plane-wave pseudopotential method. As an extreme case, the local lattice strain around a vacancy is also calculated in various bcc, fcc and hcp metals. It is found that the local strain energy is very high in both bcc Ti and bcc Fe, where the martensitic transformation takes place. From a series of calculations, it is shown that the magnitude of the strain energy stored in the local lattice is comparable to the thermal energy, kBT, where kB is the Boltzmann constant and T is the absolute temperature. Therefore, the presence of local lattice strains in alloy could influence the phase stability that varies largely depending on temperatures. For example, the local lattice strain correlates with the martensitic transformation start temperature, Ms, in binary titanium alloys.
A study on the micromechanical behavior of Ti-55531 titanium alloy with lamellar microstructure by in-situ neutron diffraction
Authors: Cui Yimin , Li Chaohua , Harjo Stefanus , Zhang Changsheng , Li Runguang , Zheng Weiwei , Wang Yandong
Published: October 2020

High strength titanium alloys are promising materials for heavy component parts in the aviation industry. The limited combination of strength and ductility requires an understanding of deformation and stress partitioning between constituent phases. The micromechanical behaviors of Ti-55531 titanium alloy with lamellar microstructure are investigated by in-situ neutron diffraction. The phase strain and lattice strain evolution of α and β phase at loading direction and transverse direction are determined. The results show that the micromechanical behaviors of oriented grains of α and β phase are obviously different. Furthermore, the stress partitioning between α and β phase during the deformation is clearly illustrated. It is found that the β matrix is subjected to higher stress than α precipitates. In addition, the intergranular and interphase microstress is quantitatively characterized. It is found that the intergranular microstress in the β phase grains is predominant among these microstresses. Combining the in-situ neutron diffraction with microstructure characterization, the present work provides a guide for further microstructure optimization.
Design and development of a dual-phase TRIP-TWIP alloy for enhanced mechanical properties
Authors: Lilensten Lola , Danard Yolaine , Sun Fan , Vermaut Philippe , Perrière Loïc , Joubert Jean-Marc , Prima Frédéric
Published: October 2020

Triggering transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) mechanisms in metastable β titanium alloys (bcc, body centered cubic) have helped reaching unprecedented mechanical properties for Ti-alloys, including high ductility and work-hardening. Yet the yield strength of such alloys generally remains rather low. So far, mostly single-phase metastable bcc alloys have been developed. In this study, a dual phase TRIP/TWIP alloy is designed and investigated. While the β-matrix is expected to display TRIP/TWIP deformation mechanisms, the addition of a second phase, α in the present study, aims at increasing the yield strength. The composition was designed in the Ti-Cr-Sn system, based on Calphad prediction and on the semi-empirical d-electron alloy design approach. Results were compared to the published full β Ti – 8.5Cr – 1.5Sn (wt%) TRIP/TWIP alloy. The dual-phase alloy was prepared and processed to reach the desired microstructure containing about 20% α. It displays remarkable mechanical properties such as a ductility of 29%, an ultimate tensile strength of 1200 MPa and a yield strength of 760 MPa, 200MPa higher than the Reference single-phase β alloy. Analysis of the mechanical properties and deformation microstructures confirm the TRIP and TWIP effects, validating the proposed approach.
Quantitative relationship between microstructural factors and fatigue life of Ti-5Al-2Sn-2Zr-4Cr-4 Mo (Ti-17) fabricated using a 1500-ton forging simulator
Authors: Niinomi M. , Akahori T. , Nakai M. , Koizumi Y. , Chiba A. , Nakano T. , Kakeshita T. , Yamabe-Mitarai Y. , Kuroda S. , Motohashi N. , Itsumi Y. , Choda T.
Published: October 2020

The microstructures, tensile properties, and fatigue lives of the forged Ti-17 using a 1500-ton forging simulator subjected to different solution treatments and a common aging treatment under both load- and strain-controlled conditions to evaluate high cycle fatigue and low cycle fatigue lives, respectively were examined. Then, the tensile properties, microstructures, and relationships between fatigue lives and the microstructural factors were discussed.

The fatigue limit under load-controlled conditions increases with increasing solution treatment temperature up to 1143 K, which is in the (α + β) region. However, it decreases with further increase in the solution treatment temperature to 1203 K in the b region. The fatigue ratio at fatigue limit is increasing with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase, and it relates well qualitatively with the volume fraction of the primary α phase when the solution treatment temperature is less than the b transus temperature. The fatigue life under strain-controlled conditions to evaluate the low cycle fatigue life increases with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase. The fatigue life under strain-controlled conditions to evaluate the low cycle fatigue life relates well quantitatively with the tensile true strain at breaking of the specimen and the volume fraction of the primary α phase for each total strain range.
Effects of Heat Treatment on Mechanical Properties and Microstructure Evolutions of Ti-5321 Alloy
Authors: Niu Jingzhe , Gub Yulei , Guo Yanhua , Wuc Wenjun , Wu Cong , Xinc Shewei , Changb Hui , Zhou Lian
Published: October 2020

This work presents a comprehensive study on the microstructure evolution and mechanical property under different heat treatment procedures of a new near β type titanium Ti-5321(Ti-5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe). Two solution temperatures(830°C and 900°C) and a group of aging temperatures(300-650°C) were carried out to investigate the influence of heat treatment on this new alloy. The strengthening mechanism of Ti-5321 after solution and aging treatment was discussed by analyzing the microstructure and its mechanical properties. The best ultimate tensile strength can be achieved to 1564 MPa with 5% on elongation when solution treated at 830°C and aging at 450°C for this new alloy. The lamellar and globular α grains can be found in all 830°C solution treated specimens which contribute to a better ductility. Ultra-fine α phase can be found in all low aging temperature treated specimens but will coarsen significantly when raising the aging temperature and thus increase the tensile strength and lower the ductility. All these results can provide a comprehensive guidance on heat treatment for this new near β type titanium in the future.
Fine-tuning of stress-induced martensite in TRIP/TWIP Ti alloys
Authors: QIAN Bingnan , SUN Fan , VERMAUT Philippe , PRIMA Frédéric
Published: October 2020

Fine-tuning of stress-induced martensitic (SIM) transformation was studied in Ti-Mo based β metastable alloys, showing combined Transformation Induced Plasticity (TRIP) and Twinning Induced Plasticity effects (TWIP) effects. The work aimed to clarify the transition and interaction between the two deformation mechanisms and their influences on the mechanical properties of Ti-Mo based alloys. Electron parameter design methods (Bo-Md and e/a ratio) were cross-used to increase the β phase stability from near-TRIP to near-TWIP by adding third alloying elements. SIM α″ transformation and mechanical twinning were traced by in-situ EBSD (Electron backscatter diffraction) mapping under cyclic tension. The deformation modes of β phase exhibited significant changes when shifting its metastability via chemical composition modifications. In near-TRIP conditions (dominated by the growth of SIM α″ in plastic regime), SIM α″ transformation and internal twinning of martensite were the main mechanisms to accommodate the local stress-strain conditions. In near-TWIP ones (dominated by the growth of {332}<113>β twinning in plastic regime), SIM α″ was observed only at twinning interface during strain process and disappeared after stress release.
Assessment of 3D Short Crack Closure in Ti-6Al-4V Alloy Utilizing Synchrotron X-ray Microtomography
Authors: TUBEI Valary , HASSANIPOUR Meysam , HIRAYAMA Kyosuke , TODA Hiroyuki , TAKEUCHI Akihisa , UESUGI Kentaro
Published: October 2020

Synchrotron X-ray microtomography was utilized to observe the complex 3D crack morphology and the closure behavior of a short crack in Ti-6Al-4V alloy. The aim of the study was to investigate the effect of the crack path evolution on the 3D short crack closure behavior. In situ fatigue tests at R = 0.1 were carried out using microtomography with a spatial resolution of 1 μm. The 3D crack morphology was observed in detail consisting of non-facets (zigzag), branching, and facets with deflection angles indicating the presence of mode II and mode III displacements. The crack grows with facet-like paths mainly in α grains as compared to the non-facet paths in the α+β grains. The change in the crack path from facet-like paths to non-facet-like paths in the larger crack front induces an increase in the fractional area of closed patches.
Effect of microstructure on fatigue crack propagation in a titanium-aluminide alloy under thermomechanical fatigue conditions - Current activities in the subcommittee of Titanium-Aluminide alloys in the Society of Materials Science, Japan (JSMS) -
Authors: Yamazaki Yasuhiro , Sugaya Ryota , Tooyama Fumio
Published: October 2020

Titanium aluminide (TiAl) alloys have attracted to considerable interest as a material of blade in the low-pressure turbine section of aero engines since their superior specific strength. The mechanical properties and strengths of TiAl alloys are strongly sensitive to their microstructure controlled with thermo-mechanical processing. The collaborative research has been started from 2017 by the subcommittee on Titanium-Aluminide alloys, JSMS Committee on High Temperature Strength of Materials, in order to get basic information about the influence of microstructure on the high-temperature strength. This paper is a part of the collaborative research. The crack propagation tests were carried out under the load controlled out-of-phase type TMF (OP-TMF) loading condition with temperature range 400 ℃ -760 ℃ . The effect of microstructure on fatigue crack propagation behavior in was discussed.
Study of oxygen content in titanium alloys after exposure at elevated temperature
Authors: Kalienko M. , Volkov A. , Leder M. , Zhelnina A.
Published: October 2020

Isothermal oxidation testing of near α titanium alloys VT18U, VT20, Ti6Al7Nb and Ti6242S was performed in air at 560 °С for 1000 hours. Parameters of diffusion layer on the alloy surfaces were studied by microhardness indentations, optical microscopy, X-ray diffraction analysis and nuclear microanalysis. It was established that concentration of oxygen in diffusion layer of tested alloys after oxidation differs significantly. An approach was demonstrated and validated by nuclear microanalysis data that allows comparative evaluation of the total concentration of interstitial impurities in the diffusion layer by the X-ray diffraction method.
Deformation processes near a crack initiation site under dwell-fatigue loading of Ti-6Al-4V
Authors: Lavogiez C. , Hémery S. , Villechaise P.
Published: October 2020

The present article reports an investigation of the mechanism of surface crack initiation of a dwell fatigue tested Ti-6Al-4V alloy with a bi-modal microstructure. Interactions between slip bands and grain boundaries were characterized in order to obtain insights into the crack initiation process and discuss the similarities with models described in the literature. Twinning and local lattice rotation occurred as a result of the slip band blocking at the interface and suggests high local stress concentrations. Nevertheless, crack initiation happened to be intergranular and not transgranular. The crack opened up the basal plane that was located at the interface between two nodules poorly oriented for slip and having a common c axis of the hexagonal unit cell.
Modeling and Verification of Stress Relaxation Behavior of Ti-6Al-4V
Authors: Zhang Xingzhen , Deng Ying , Liang Tian , Jin Shihan , Li Weidong
Published: October 2020

The phenomenon of gradual decrease of internal stress with the deformation of material maintained under the precondition of certain temperature and initial stress or pre-strain is called stress relaxation. Due to that, the flow stress of the metal material falls rapidly when the hot forming process pauses, and then the required forming load. In this paper, the experiment was carried out to study the stress relaxation property of Ti-6Al-4V, in the temperature range of 1023K~1123K and with the pre-tension strain 0.7%, 4% and 10%. The quartic delay function was used to describe the stress relaxation behavior. The predicted value of stress relaxation equation is in good agreement with the experimental data, and the correlation coefficient is above 0.99. Arrhenius creep constitutive equation embedded in CAE software was derived. The finite element model of stress relaxation process of test bar was builded, and the tensile-relaxation experiment was performed under the loading condition of 1:1 part forming process. The forming force results agree well, and the validity and accuracy of the constitutive model are verified, laying a foundation for the subsequent process simulation and optimization.
Predicting the tensile properties of additively manufactured Ti-6Al-4V via electron beam deposition
Authors: Ales Thomas , Ghamarian Iman , Hayes Brian , Welk Brian , Baker Andrew , Kenney Matthew , Harlow D Gary , Fraser Hamish , Li Wenqi , Collins Peter
Published: October 2020

Additively manufactured materials are gaining wide attention owing to the manufacturing benefits as it results in near net shape components. It is well known that the manufacturing processes affects the performance of the components via microstructural features and the mechanical properties. There is an urgent need to understand the processing-structure-property-performance relationship for the materials manufactures via such innovative techniques. Strategies are needed to quantify and modify the mechanical properties. This study assists to design and tailor the process parameters based on the final properties required. Current work predicts the yield strength of additively manufactured Ti-6Al-4V with different post heat treatments. A thermal model predicted by ABAQUS is fed into an implementation of Langmuir equation that predicts the chemistry which is then used in a phenomenological equation predicting the yield strength. The model is confirmed via experiments showing less than 2% deviation from the predicated properties. A statistical model gives design allowables that have an uncertainty of less than 1 ksi.