Phase Transformations and Microstructural Evolution: Poster Session
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Mohsen Asle Zaeem, Colorado School of Mines; Ramasis Goswami, Naval Research Laboratory; Saurabh Puri, Microstructure Engineering; Eric Payton, University of Cincinnati; Megumi Kawasaki, Oregon State University; Eric Lass, University of Tennessee-Knoxville

Tuesday 5:30 PM
March 1, 2022
Room: Exhibit Hall C
Location: Anaheim Convention Center

Session Chair: Mohsen Asle Zaeem, Colorado School of Mines

O-22: Carbon Transformations in Rapidly Solidified Nickel-carbon Ribbon: Gina Greenidge1; Samuel Price1; Jonah Erlebacher1; 1Johns Hopkins University
    We report the microstructural evolution of rapidly solidified nickel-carbon alloys, as-formed via melt-spinning and after annealing. Via melt spinning, we attained metastable solid solubility of carbon in nickel. Subsequent high-temperature annealing led to the controlled precipitation of carbon from the nickel matrix onto the ribbon free surfaces as well as the growth of spherical precipitates within the bulk of the ribbon. Freestanding carbon was excavated from the alloy via chemical dissolution of the metal and characterized by electron microscopy and Raman spectroscopy. We determined that the microstructure of carbon could be tuned by varying the precursor carbon content from 4 – 12 at. % and annealing the precursor ribbon at temperatures ranging from 400 – 1200 ℃. Via the step-wise variation of these parameters, we sequentially transformed amorphous carbon nanospheres with a BET surface area of 203.4 m2/g into thick, highly crystalline flakes of graphite.

O-24: Coarsening, Dissolution and Re-precipitation in Multimodal Ni Superalloys: An In-situ Study: Muhammad Awais1; Jan Ilavsky2; James Coakley1; 1University of Miami; 2Argonne National Laboratory
    Ni superalloys that operate at intermediate temperatures in gas-turbines are heat-treated to possess a multimodal gamma-prime size distribution. Deducing the influence of the nanoscale precipitates on mechanical properties within the intermediate temperature range is inherently difficult, where coarsening and dissolution of the nanoscale precipitates occurs, and re-precipitation may occur on cooling. Thus the microstructure examined by microscopy may not be representative of the microstructure at elevated temperature. It is similarly difficult to deduce precipitate evolution by in-situ small angle x-ray scattering (SAXS) due to the multiple scattering contributions that form the spectra. Finally, the similar lattice parameters of the different gamma-prime size distributions produce overlaying diffraction peaks, making in-situ wide angle x-ray scattering (WAXS) analysis non-trivial. We present combined in-situ SAXS/WAXS during heating, thermal holds and cooling, along with complementary microscopy, to address the individual technique shortcomings applied to the study of precipitation, dissolution and coarsening of multimodal superalloys.

O-25: Contribution of the Electronic Entropy to Some Congruent and Allotropic Phase Transformations: Jonathan Paras1; Antoine Allanore1; 1Massachusetts Institute of Technology
    Understanding the origin of the entropy in phase transitions opens new avenues for engineering materials. While ubiquitous, both order-disorder and allotropic phase transitions in alloys and transition elements remain difficult to describe quantitatively using conventional thermodynamic and ab-initio modeling techniques. We explore the validity of a formalism that links electronic transport properties and the state electronic entropy in calculating the change in entropy for intermetallics like Cu3Au and transition metals such as Fe and Co. Application of this formalism to additional transition metals that exhibit HCP to BCC transitions suggests a possible electron-driven origin of HCP stability. Comparison of our electronic entropy calculations with some estimates of the vibrational and configurational entropy change in various allotropic and congruent phase transitions yield agreement with calorimetrically measured totals.

O-27: Influence of the Austenitic Grain Size on the Strength in a Medium-carbon and Low-alloy Steel: David Fernández-Sánchez1; Octavio Vázquez-Gómez1; Alexis Gallegos-Pérez1; Pedro Garnica-González1; Héctor Vergara-Hernández1; 1Tecnológico Nacional de México / I.T. Morelia
    The mechanical strength of an experimental steel was evaluated by tensile tests as a function of the austenitic grain size in a medium-carbon steel and low-alloy Fe-1.0Cr-1.0Mo-0.30V. The prior austenitic grain was modified by heat treatment through austenitizing parameters, temperature and time. In turn, the austenitic grain size was determined by the oxidation method and etching to reveal and quantify the boundaries and grain size. To evaluate the effect of the austenitic grain on the strength, the tension test was used under different treatment conditions: normalized, annealing and quenching with brine and oil. Finally, from the results obtained, it was observed that the tensile strength depends on the prior grain size and the treatment condition. In this sense, the strength increased in the specimens with smaller grain size in their respective conditions, while the percentage of elongation decreased with the cooling severity of heat treatment.

O-29: Leveraging Solid-state Phase Transformations to Tailor Residual Stress in Additively Manufactured Metal Components: Aleksandra Vyatskikh1; Xin Wang2; Lorenzo Valdevit2; Enrique Lavernia2; Julie Schoenung2; 1University of California Irvine; 2University of California Irvine
    Residual stress (RS) that forms during additive manufacturing (AM) of metals can cause cracking, delamination and reduced fatigue life of components. Since RS is an inherent consequence of thermal processing, it cannot be fully eliminated through AM process optimization. Here, we demonstrate that RS in AM-fabricated parts can be manipulated through alloy design. We explore Fe and Fe-50Cu (wt.%) parts that were fabricated by directed energy deposition. We find that highly compressive surface RS of ~-190 MPa is present on the top surface of Fe-50Cu parts, while surface RS in pure Fe parts is found to be tensile (~58 MPa). Through transmission electron microscopy and electron backscatter diffraction, we demonstrate that the Cu-rich phase in Fe-50Cu parts exhibits high dislocation density, suggesting preferential plastic deformation of the Cu-rich phase. We attribute the differences in RS to the difference in solid-state phase transformations experienced by the two metals.

O-30: Microstructural and Mechanical Property of Ti-6Al-4V/STS 304 Dissimilar Joints by Diffusion Bonding Using Hierarchical Multilayers Structure: Bo Hun Jang1; Jin Gyu Lee1; Jeong Pyo Lee1; Jin Kyu Lee1; 1Kongju National University
     Recently, there has been an increasing demand for joining dissimilar metals having different properties in various fields. Especially, dissimilar bonding of Ti6Al4V / STS with high specific strength and excellent corrosion resistance expected to increase utilization in the aerospace, nuclear and chemical industries. In dissimilar bonding, it is important to control the formation of intermetallic compounds that are detrimental to mechanical properties at bonding interface.In this study, we report the microstructure and mechanical property of Ti-6Al-4V/STS 304 diffusion bonded joints using multiple interlayers such as V, Cu and Ag, which are introduced to control the formation of intermetallic compounds. Microstructural characterization was carried out by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS). Mechanical properties of the joints were measured using tensile test at room temperature with a strain rate of 8.4x10-4s-1. The surface of fractured specimen was observed by SEM.

O-31: Modeling Phase Transformation and Tensile Properties of Micro-alloyed Structural Steels for Fire Resistance : Fahim Khan Prionto1; Razia Sharme1; H. M. Mamun Rashed2; 1Khulna University of Engineering & Technology; 2Bangladesh University of Engineering and Technology
    Catastrophic heat of fire on steel causes the temperature to rise rapidly due to high thermal conductivity of steel and forms carbide at 650°C. To prevent this, a few steel grades were developed having higher yield strengths at elevated temperatures. This work presents the assessment of presence of different phases; Physical and Mechanical properties at certain temperature and time by adding different composition of Mo (0-0.75% with 0.25% in succession) on EN 10025-2:2004 Grade S355 at elevated temperature using CALPHAD based computational technique. Optimized amount of molybdenum with other alloying elements can intelligently manipulate microstructure to improve strength. It may give some observation about the improvement of common structural steels upon addition of Mo. Besides high temperature strength in addition to Mo on steels, it also provides creep resistance and corrosion resistance. The overall predictions provide observations about the improvement of common structural steels with addition of Molybdenum.

O-32: Phase Evolution of Laser Melted Single Tracks of 316L: Anna Rawlings1; Andrew Birnbaum1; John Steuben1; Athanasios Iliopoulos1; John Michopoulos1; 1U.S. Naval Research Laboratory
    Laser-processed 316L stainless steel single tracks are analyzed for the inverse identification of the solidification and phase transformation sequence upon cooling. The analysis is performed through a parameterized study that couples the effects of the laser parameters with the initial baseplate microstructure. The evidence for the phase evolution is determined through orientation-based grain growth behavior analysis along with identification of microstructural features associated with the solidification modes of austenitic stainless steels. The non-equilibrium conditions and rapid solidification of the selectively laser melted tracks result in significant deviations from the equilibrium phase evolution. The primary solidification phase, that is the first phase to solidify from the molten metal, of 316L showed the strongest dependence on the initial baseplate microstructure, while the processing parameters affect the extent of the characteristic microstructural features within the respective solidification modes.

O-33: Phase Transformations and Microstructural Evolution: George Lindemann1; Paul Chao1; Ashwin Shahani1; 1University of Michigan
    Multi-phase materials often operate under elevated temperatures during which coarsening may cause microstructural changes. Therefore, it is paramount to understand how such materials evolve under these conditions to better predict their longevity in-service. We employ recent advances in 4D (three spatial dimensions with time) synchrotron-based X-ray nano-tomography to investigate the Al-Ag2Al-Al2Cu three-phase eutectic microstructure during isothermal annealing below the eutectic temperature. With the aid of a new, in situ furnace and an innovative total variation regularization reconstruction technique, we visualize the evolution of the eutectic lamellae and identify the coarsening mechanism for the Ag2Al intermetallic phase as 2D Ostwald ripening. An innovative method was also developed to track crystallographic changes of the interphase boundaries in time. Somewhat surprisingly, the data reveal that the microstructure is not self-similar, but instead shows preferential alignment of habit planes as annealing proceeds.

O-34: Polyamorphism in a Solute-lean Al-Ce Metallic Glass: Ziliang Yin1; 1Center for High Pressure Science & Technology Advanced Research
    Polyamorphism is critical to our fundamental understanding of amorphous solids and the corresponding elusive liquid-liquid transitions, an intriguing but controversial topic over the last decades.In our work, by combining in-situ high-pressure x-ray diffraction (XRD), in-situ high-pressure Ce L3-edge x-ray absorption spectroscopy (XAS), and molecular dynamics (MD) simulations, a transition from a low-density amorphous state to a high-density amorphous state is confirmed in a lanthanide-solute metallic glass, Al93Ce7, with an extremely low Ce concentration.Our results provide explicit evidence for the existence of polyamorphism in dilute 4f element-bearing metallic glasses, extending the compositional space from the solvent end to the very dilute solute end for the first time. This finding could provide new insights into the chemical effect on the polyamorphism in MGs and also highlights the critical role of “minor alloying” elements in affecting properties of MGs.

O-35: The Effect of Ni Ion Implantation on the Nanoindentation Response of a Ni 50.5at%-Ti 49.5at% Shape Memory Alloy: Daniel Hong1; Alejandro Hinojos1; Nan Li2; Khalid Hattar3; Jeremy Schaffer4; Taiwu Yu1; Yunzhi Wang1; Michael Mills1; Peter Anderson1; 1Ohio State University; 2Los Alamos National Laboratories; 3Sandia National Laboratories; 4Fort Wayne Metals
    Ion implantation is explored as a novel method to control the superelastic response of a solution-treated Ni50.5-Ti49.5 shape memory alloy, through the creation of irradiation-defects that could serve as nucleation and/or pinning sites for a B2-B19’ phase transformation. Ni ion implantation, at dpa levels typically less than those reported for amorphization, is followed by nanoindentation into a polished cross-sectional surface. A nearly 70% increase in hardness is observed ~3 microns below the implanted surface, while maintaining comparable recoverable displacement. Upon reindentation into existing indents, a more linearized loading/unloading response with reduced hysteresis is observed compared to unimplanted material. The results suggest that Ni ion implantation is a novel avenue to process NiTi shape memory alloys. This work is supported by: the Department of Energy, Basic Energy Sciences (DE-SC0001258) and the Center for Integrated Nanotechnologies (2019BC0126) and The Ohio Supercomputer Center (PAS0676).

O-36: The Influence of Ru Addition on the Precipitation Behavior of Topologically Close-packed Phase in the Ni-based Superalloy: Sangwon Lee1; Kyuseon Jang1; Hosun Jun1; Jeonghyun Do2; Pyuck-Pa Choi1; 1Korea Advanced Institute of Science and Technology; 2Korea Institute of Materials Science
    For Ni-based superalloys, the formation of topologically close-packed (TCP) phase which deteriorates creep life has been considered as one of the main issues during past three decades. To enhance the microstructural instability, Ru has been adopted in the 3rd generation and it has suppressed the formation of TCP phases effectively. However, although many researchers reported about TCP suppression in Ru-containing alloys, its underlying mechanism is still unclear and under debate. In addition, some studies reported that Ru-additions to superalloys caused promotion of TCP phases rather than suppression, such that detailed research on the role of Ru in the formation of TCP is required. In this study, we investigated the TCP precipitation behavior in a Ru-containing Ni-based superalloy from the viewpoints of compositional and crystallographic effects by atom probe tomography (APT) and transmission electron microscopy (TEM).

O-37: The Microstructural Evolution of Ag-39.9at%Cu Eutectic Alloys under Different Cooling Rates: Qingyuan Qin1; 1Shanghai Jiaotong University
     The solidification of most eutectic alloys generally produces two-phase coupled microstructures, which are linked to the intrinsic properties of components and external conditions for solidification. The microstructures of rapidly solidified Ag-39.9at%Cu eutectic alloys have been widely studied, while the research between microstructures and cooling rate is still lacking. We made systematic experiments to study the microstructures of Ag-39.9at%Cu eutectic alloys under different cooling rates by casting into high speed rotating copper wheel and cylindrical copper moulds. SEM and TEM analyses showed the evolution of microstructures from the lamellar structures mixed with abnormal eutectic structures, to the spherical eutectic colonies mixed with abnormal eutectic structures and Ag-rich equiaxed phases, then to the non-segregation solidification structures, as the cooling rate increased. The observed microstructures were very complicated at the intermediate cooling rate, we have tried to explain the formation mechanism on the basis of the SEM images and heat transfer process.

O-38: Thermodynamics of Elinvar Behavior: Pedro Guzman1; Stefan Lohaus1; Camille Bernal1; Brent Fultz1; 1California Institute of Technology
    The bulk modulus of Fe-45%Ni is anomalous in that it remains constant with temperature at ambient pressure; this is the “elinvar effect”. The bulk modulus was assessed with X-ray diffractometry at several conditions of pressure and temperature, confirming that the bulk modulus had no temperature dependence at low pressures. To evaluate the entropic contributions from vibrations and magnetism, we performed nuclear resonant inelastic X-ray scattering and synchrotron Mössbauer experiments to determine the phonon spectrum and the state of magnetization. These measurements were performed at several conditions of pressure and temperature, giving the contributions of phonons and magnetism to the thermal pressure. For elinvar, there appears to be a cancellation of the thermal pressure from phonons and the thermal pressure from magnetization that give the weak temperature dependence of the bulk modulus. Additionally, an anomalous thermal expansion was found between 7 and 13 GPa.

O-39: Transformation-induced Plasticity in Omega Titanium: Amir Hassan Zahiri1; Jamie Ombogo1; Tengfei Ma1; Pranay Chakraborty1; Lei Cao1; 1Universitiy of Nevada Reno
    ω-titanium (Ti) is a high-pressure phase that is conventionally perceived to be brittle and nondeformable, although direct investigations of its deformation process remain scarce. In this work, we perform molecular dynamics simulations to study the deformation process of ω-Ti with initial defects and find that stress-induced ω → α martensitic transformation can cause extensive plasticity in ω-Ti under various loading directions. Moreover, for the first time, we demonstrate that four types of transformation twins— {11-21}, {11-22}, {10-12}, and {10-11} twins—can be formed through the ω → α martensitic phase transformation. This work advances the understanding of plastic deformation in ω-Ti and unveils the essential role of the metastable ω-phase in the formation of transformation twins.