2017 Technical Division Student Poster Competition: Functional Materials Division (FMD) Graduate Students
Sponsored by: TMS Extraction and Processing Division, TMS Functional Materials Division, TMS Light Metals Division, TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division
Program Organizers: TMS Administration

Monday 5:00 PM
February 27, 2017
Room: Hall B1
Location: San Diego Convention Ctr

SPG-10: Effect of Different Aging Heat Treatments on Microstructural Evolution and Transformation Temperatures in a NiTiHfAl Shape Memory Alloy: Flávia Gallo1; Hunter Henderson; Michael Kesler; Brittani Maskley; Brandon Saraydar; Michele Manuel; 1Cidade Universitaria
    Shape memory alloys (SMAs) have unique behavior and wide commercial application. A quaternary NiTiHfAl SMA was designed to achieve a good combination of high phase transformation temperature (>100°C) and improved strength, compared to binary NiTi. The addition of Al can produce the strengthening Ni2TiAl Heusler nano precipitate, but depresses the transformation temperature in solution. This drawback can be compensated by Hf addition. Precipitation strengthening improves thermal fatigue life, output force and shape memory effect, increasing critical stress for martensite slip rather than detwinning. In this study, induction melted 50Ni-21Ti-25Hf-4Al alloy aged at different temperatures and mechanical properties were evaluated using Vickers Hardness testing. Microstructural evolution, phase characterization and transformation temperatures were analyzed using SEM, XRD and DSC, respectively. The relationship between chemistry, microstructure, and SMA properties is discussed.

SPG-11: Enhancing Li+ Interfacial Charge-transfer by Highly Oxygen-deficient Lithium Titanate Oxide with Conformal Amorphous Carbon for Lithium-ion Batteries: Ralph Nicolai Nasara1; Shih-kang Lin1; 1National Cheng Kung University
    The lithium titanate defect spinel, Li4Ti5O12, is a promising “zero-strain” anode material for lithium-ion batteries in cycling-demanding applications. However, the low-rate capability limits its range of applications. Surface modifications, e.g., coating and defect engineering, play an intriguing role in interfacial electrochemical processes. Herein, we report a new carbon-coated and oxygen-deficient “defective-Li4Ti5O12” anode material with superior rate performance. It is synthesized using conventional precursors via a one-pot thermal reduction process. A high degree of oxygen vacancies of approximately 6.5 at.% and conformal amorphous carbon coating were achieved simultaneously, resulting in a compounding effect for a high discharge capacity of 123 mAh g-1 with Coulombic efficiency of 99.8% for as high as 10 C-rate. Ab initio calculations foresight that oxygen vacancies increase the electron donor density, while conformal amorphous carbon significantly lowers interfacial charge-transfer resistance. The formation mechanism, as well as the origin of superior electrochemical properties, is elaborated in this paper.

SPG-12: Evaluation on Reliability of Ag-alloy Wire under Cl- environment: Yan Wen Tsau1; Jui-Nung Wang1; Fan Yi Ouyang1; 1National Tsing Hua University
     Recently, people try to replace Au by other materials in wire bonding industry because of the soaring price of Au. Ag alloys, with profound electrical and mechanical properties, become a reliable candidate. In this research, the corrosion and oxidation behavior of Ag-4Pd wires bonded on Al pad under acceleration test is investigated. For acceleration tests, samples were conducted with high temperature storage test (HTST) at 150°C for 500 hours and thermal cycle test (TCT) in the range of -55°C to 125°C for 250 cycles. After that, the samples were further conducted with chlorine corrosion test. For as-bonded samples, Al pad is heavily corroded accelerated by galvanic effect after salt spray test. For samples post HTST, cracks propagated through the IMC layer and separated the IMC layer into two. Finally, samples undergoing TCT exhibited the best corrosion resistance because thin IMC layer acts as a barrier to prevent galvanic corrosion.

SPG-13: Interfacial Reactions in Co/In/Cu Joints by Transient Liquid Phase Bonding in Thermoelectric Modules: Tsu-Ching Yang1; Sinn-Wen Chen1; 1National Tsing Hua University
    There are numerous joints in thermoelectric modules. The joining processes and interfacial reactions are critical to the reliability of the modules. Transient liquid phase bonding technology is a potential joining technology for thermoelectric modules which are used at relative high temperatures but high joining temperatures should be avoided. Barrier layer is introduced at the joints to prevent direct contact of solders with thermoelectric materials. This study examines the interfacial reactions in the Cu/In/Co sandwich samples at 200oC and 500oC, and further verifies the reaction phases and their formation sequences. It has been observed that the Cu11In9 phase is formed at the Cu/In interface after reaction at 200oC for 24 hours; while Cu2In and Cu7In3 phases are formed when reacted at 500oC. Only CoIn3 phase is formed at the Co/In interface for the samples reacted at both 200oC and 500oC. It has also been observed that these reactions are diffusion controlled.

SPG-14: Interfacial Reactions in Transient Liquid Phase Bonding of Cu/Ga/Ni and Cu/Ga/Co: Ji-min Lin1; Sinn-wen Chen1; 1National Tsing Hua University
    The interfacial reactions in the Cu/Ga, Ga/Ni and Ga/Co couples and Cu/Ga/Ni and Cu/Ga/Co sandwich samples were examined at 200oC and 500oC. In the Cu/Ga couples reacted at 200oC, γ3-Cu9Ga4 and CuGa2 phases were formed. The γ1-Cu9Ga4 phase was formed in the couple reacted at 500oC. In the Ga/Ni couples, NiGa4 was formed in those reacted at 200oC while Ni3Ga4 was formed at 500oC. Slight different results were observed in the Cu/Ga/Ni sandwich samples. Both γ3-Cu9Ga4 and CuGa2 phases were formed at 200oC while γ1-Cu9Ga4 and (Ni,Cu)2Ga3 were formed at 500oC. No reaction phase layer was found in the Ga/Co couples reacted at 200oC, but CoGa3 was formed in those at 500oC. In the Cu/Ga/Co sandwich couples, γ3-Cu9Ga4 and CuGa2 were formed at 200oC while γ1-Cu9Ga4 and CoGa3 were formed at 500oC.

SPG-15: The Role of Morphology in the Supercapacitance of Rare Earth Oxides: Aadithya Jeyaranjan1; Tamil Selvan Sakthivel1; Sudipta Seal1; 1University of Central Florida
    Since micro-supercapacitors have very small amounts of active material, it is of primal importance to optimize these materials for maximum charge storage. In this regard, the morphological effects on the supercapacitance of cerium oxide nanostructures has been studied in this work. Three different shapes, nanocubes (NC), nanorods (NR) and nanospheres (NS), were synthesized using a simple hydrothermal process. The physiochemical properties of these nanostructures were evaluated using XRD, TEM, XPS and BET. The electrochemical properties of the materials were evaluated using cyclic voltammetry, chronopotentiometry and impedance spectroscopy in near neutral NaCl solutions. Our results indicate that even though NR had a lower surface area, it exhibits a higher supercapacitance than other morphologies due its rough texture and presence of surface nanopores. This study reemphasizes that there is significant charge storage in the bulk of pseudocapacitive material and careful selection of nanomaterial morphology is necessary for supercapacitor with higher specific capacitance.

SPG-16: The Thermal Stability of Copper Nanotwinned Thin Film with Different Interlayers: Leh-Ping Chang1; Hsin-Yuan Chen1; Fan-Yi Ouyang1; 1National Tsing Hua University
    Highly pure nanotwinned copper thin films applied in semiconductor as interconnects were manufactured by unbalanced magnetron sputtering system (UBMS). To investigate the influence of different interlayers on microstructure and thermal stability of Cu film, CrN and TiN thin film were selected and deposited onto a silicon wafer as an interlayer respectively before coating Cu thin film. After deposition, the Cu thin film was annealed at 250℃ for different time. We observed that Cu texture changed from {111} to {200} with CrN interlayer. However, no texture change was observed with TiN interlayer . The above results suggest that the thermal stability of nanotwinned Cu thin film is strongly related to the interlayer.

SPG-17: Wettability-based Mitigation of Scale Formation: Leonid Rapoport1; Susmita Dash1; Kripa Varanasi1; 1MIT
    Scale formation, due to the presence of dissolved salts and organic impurities, poses serious problems in several practical applications, ranging from household utensils to industrial boilers, and affects industries including desalination, oil and gas, and cooling towers. In particular, salts with inverse solubility with temperature have the tendency to crystallize and adhere to the heat transfer surface and adversely affect the thermal and fluid transport. In the present study, we investigate the mechanism of salt crystallization during pool boiling. The boiling performance parameters, such as, heat transfer coefficient and critical heat flux (CHF) are examined for an under-saturated solution of calcium sulfate. Simultaneous high speed and infrared imaging enables determination of the interdependence between crystallization and bubble dynamics, including, bubble nucleation, growth, and departure. The effect of the three phase contact line during bubble evolution on the crystallization-induced scale formation is demonstrated.

SPG-18: Why and How the Electromigration Effect Occurs?: Yu-chen Liu1; Shih-kang Lin1; Shang-Jui Chiu2; Yen-Ting Liu2; Hsin-Yi Lee2; 1National Cheng Kung University; 2National Synchrotron Radiation Research Center
    The electromigration effect involves atomic diffusion of metals under current stressing. Recent theories of EM are based on the unbalanced electrostatic and electron-wind forces exerted on metal ions. However, none of these models have coupled the EM effect and lattice stability. Here, we performed in situ current-stressing experiments for pure Cu strips using synchrotron X-ray diffractometry and scanning electron microscopy and ab initio calculations based on density functional theory. An intrinsic and non-uniform lattice expansion – larger at the cathode and smaller at the anode, is identified induced by the flow of electrons. If this electron flow-induced strain is small, it causes an elastic deformation; while if it is larger than the yield point, diffusion as local stress relaxation will cause the formation of hillocks and voids as well as EM-induced failure. The fundamental driving force for the electromigration effect is elucidated and validated with experimental observations in the literature.