Low-cost Titanium: 'Affordable Ti': Session II
Sponsored by: TMS Structural Materials Division, TMS: Titanium Committee, TMS: Powder Materials Committee
Program Organizers: Ramana Reddy, University of Alabama; M. Ashraf Imam, George Washington University

Monday 2:30 PM
February 24, 2020
Room: Theater A-8
Location: San Diego Convention Ctr

Session Chair: Ashraf Imam, George Washington University


2:30 PM  Invited
Making Affordable Titanium Alloy with Wrought-like Mechanical Properties from Sintering Low-Cost Titanium Powder: Pei Sun1; Z. Zak Fang1; 1University of Utah
    Although the powder metallurgy (PM) of Ti has shown promise to be a low cost approach, it has not gained significant market acceptance because the performance-to-cost ratio of PM Ti cannot compete with that of wrought Ti. In order to compete, the cost of Ti powder must be drastically reduced and the mechanical properties of PM Ti must be drastically improved. This presentation introduces both a low cost powder production process and a sintering technology that can produce Ti-6Al-4V with wrought-like microstructure and mechanical properties. This talk will present elaborate the design of the hydrogen assisted Mg reduction (HAMR) process and the results that demonstrate HAMR process can produce low oxygen Ti powders. The second part of this presentation introduces the hydrogen sintering and phase transformation (HSPT) process which designed to produce Ti-6Al-4V alloy with wrought-like microstructure and mechanical properties via simple press-&-sintering and heat treatment.

3:10 PM  
A Systematic Experimental Investigation of the Planar-to-wavy Slip Transition in Model Ti-O Alloys: Yan Chong1; Ruopeng Zhang1; Shiteng Zhao1; Mark Asta1; Daryl Chrzan2; Andrew Minor1; 1University of California, Berkeley; 2University of California, Berkeley
    Oxygen can significantly increase the strength of titanium, but also cause planar slip dominant dislocation activity leading to limited work-hardening ability and a loss of ductility. In this study, we proposed a model in which the interstitial oxygen shuffling by screw dislocations and its subsequent reversal determines whether the planar or wavy slip is dominant during tensile deformation. We use tensile deformation at low, room and high temperatures at various strain rates and subsequent microstructural analysis by TEM to experimentally map out the effect of oxygen content, temperature and strain rate on the planar to wavy slip transition in Ti-O model alloys. Our experiments show that not only is planar slip strain rate and temperature dependent, but also effected by the oxygen concentration. We discussed these results in terms of the critical strain rate/temperature for the transition from planar to wavy slip and a proposed theoretical model for this behavior.

3:30 PM  
High Strength and Ductility Titanium Materials with Cheap Alloying Elements Fabricated by Powder Metallurgy: Katsuyoshi Kondoh1; Takayuki Tanaka1; Shota Kariya1; Junko Umeda1; 1Osaka University
    Fe element, one of very cheap β-phase stabilizers, was employed to fabricate powder metallurgy (PM) Ti alloys. Our previous study indicated PM Ti-6wt.%Fe extruded alloy with α and β phases showed 0.2% yield stress (YS) of over 1050MPa and more than 20% elongation at room temperature, which were superior to the commercial Ti-6%Al-4%V alloy. On the other hand, we have already clarified oxygen atoms, one of cheap α-phase stabilizers, was effective to improve the mechanical properties of PM Ti materials due to their solid-solution strengthening effect. In this study, the effect of extrusion conditions on the microstructures formation and mechanical properties of PM Ti-Fe-O alloys was discussed. When the extrusion temperature (Te) was in the temperature range of α+β phases, the extruded Ti-Fe-O alloy showed the equiaxed fine grains (a mean grain size of 2 µm), and revealed 1050 MPa YS and excellent elongation of 30%.

3:50 PM Break

4:05 PM  
Electroplastic Effects in a Dilute Ti-Al Alloy: Shiteng Zhao1; Ruopeng Zhang1; Andrew Minor1; 1University of California, Berkeley
    For decades, it has been known that the application of a high-density direct current pulses can significantly alter the mechanical properties of metals.We performed a series of electrically biased tensile tests using a Ti-7 at. % Al alloy under a current density of 0.5X103 A/cm2. The temperature during the testing was monitored by an infrared camera and only a neglectable temperature rise was observed. It is shown that the tensile ductility of the materials is increased by the electrical pulsing. Postmortem microstructure characterization shows an increased number of {10-12} tensile twins in the electrical-pulsing deformed sample, which is similar to its cryogenic behavior.The twinning induced plasticity, which is most likely to occur during the late stage of deformation, is considered to be responsible for the prolonged ductility of the materials. This work demonstrates that electrical pulsing can potentially be used as a cost-effective way of materials processing for Ti-Al alloys.

4:25 PM  
Machine Learning Assisted Discovery of Affordable Biomedical Ti Alloy: Chunte Wu1; Hsiao-Tzu Chang2; Shi-Wei Chen3; Sih-Ying Huang1; Yeong-Tsuen Pan2; Joshua Chou4; Hung-Wei Yen1; 1National Taiwan University; 2China Steel Corporation; 3National Synchrotron Radiation Research Center; 4University of Technology, Sydney
    In this work, machine learning has led to a revolutionary discovery of biomedical Ti alloy with bone-like modulus and affordable price. Young’s modulus is a critical property for alloy design in orthopedic implant field. However, the present low modulus Ti alloy compositions were constrained in certain intervals with high beta stabilizer content. The constraint prevented discovered alloys from having affordable price. To address this problem, a machine learning based alloy discovery system, named βLow, was developed. It consists of two artificial neural networks for phase stability and Young’s modulus predictions of beta Ti alloys. Following the predictions of βLow, new alloys were produced for model validation and alloy exploration. Surprisingly, βLow not only performed high consistency to experimental results, but also guided the discovery of new alloy with low material price. In conclusion, βLow has opened up a new path for affordable biomedical Ti alloy design.

4:45 PM  
Low-cost Titanium Extraction Process: Molten Salt Electrolysis with Titanium Oxycarbide (TiCxO1-x) as Soluble Anode: Jiusan Xiao1; Hongmin Zhu2; Shuqiang Jiao1; Jun Zhu3; 1Univ of Science and Technology Beijing; 2Tohoku University; 3University of Science and Technology Beijing
    The wider application of titanium is restricted by its expensive price due to high-cost production of Kroll process. The process of molten salt electrolysis with soluble anode is proposed by Zhu and Jiao in 2005, whereas titanium oxycarbide (TiCxO1-x) as soluble anode dissolves into titanium ion in electrolyte of molten chlorides, and metallic titanium with purity of 99.5% and impurity of oxygen lower than 300 ppm deposits in cathode. Moreover, TiCxO1-x can be synthesized through selective carbothermic reduction of ilmenite followed with magnetic separation and acid leaching for concentration. The overall process for titanium production will lead to the cost reduction by half referring to Kroll process.

5:05 PM  Cancelled
Preparation of Ti-6Al-4V Alloy Powder by Aluminothermic Reduction: Tian Wang1; Wang Yaowu1; 1Northeast University
    This work introduces a two-stage aluminothermic reduction process for preparing Ti-6Al-4V using Na2TiF6 and Al-V alloy. The pure Ti-6Al-4V could be prepared directly after the first stage reduction. Ti-containing cryolite is also producted after the first stage. In secondary reduction, Ti3+ and Ti-Al intermetallics in Ti-containing cryolite can be reduced to Al-Ti alloy. In consequence, pure cryolite and Al-Ti alloy were obtained. The Al-Ti alloy used as reducing agent as a raw material for the first stage reduction. Cryolite used in aluminum electrolysis. In this process realizes the recovery and reuse of by-product Ti-containing cryolite. In the two-stage aluminothermic reduction process Ti and Al are almost 100% recyclable. The production cost is reduced and green metallurgy and ecological metallurgy are realized.