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Phase Transformations and Microstructural Evolution: On-Demand 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, VulcanForms Inc; Eric Payton, University of Cincinnati; Megumi Kawasaki, Oregon State University; Eric Lass, University of Tennessee-Knoxville

Monday 8:00 AM
March 14, 2022
Room: Physical Metallurgy
Location: On-Demand Poster Hall

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Microstructure Evolution of HK40 and HP40 Heat Resistant Steels after Isothermal Aging: Victor Lopez-Hirata¹; Eduardo Perez-Badillo¹; Maribel Saucedo-Muñoz¹; Hector Dorantes-Rosales¹; Carlos Ferreira-Palma¹; Diego Rivas-Lopez¹; ¹Instituto Politecnico Nacional-ESIQIE
    Thermo-Calc and experimental analyses were carried out for the as-cast and heat-treated HK40 and steel. The as-cast steels were aged at 800 and 900 °C for times up to 1000 h. As-cast and heat-treated specimens were characterized by XRD, HR-SEM, and Vickers hardness. Thermo-Calc Scheil analysis indicated the presence of an austenite matrix with the presence of Cr-rich M7C3, and M7C3 and (Nb,Ti)C carbides in the as-cast HK40 and HP40 steels, respectively, which is in agreement with experimental results. The aging at 800 and 900 °C produces the precipitation of M23C6 carbides, and M23C6 and (Nb,Ti)C carbides in the austenite matrix of the as-cast HK40 and HP40 steels, respectively. This precipitation process promotes an increase in hardness. Themo-Calc Prisma also predicted the precipitation of the same phases and the fastest growth kinetics of precipitation was at 900 °C for the as-cast HK40 and 1200 °C for the as-cast HP40 steel.

Coupled Effects of Shear and Temperature on Intermixing in Cu-Ni Multilayers: Qin Pang¹; Jenna Bilbrey¹; Arun Devaraj¹; Suveen Mathaudhu²; Peter Sushko¹; ¹Pacific Northwest National Laboratory; ²Colorado School of Mines
    Epitaxial films represent a convenient model for studies of initial stages of mechanically induced deformations. Here, we discuss atomic-scale pathways of shear-induced intermixing across epitaxial Cu-Ni heterojunction at finite temperatures. Using first principles simulations, we found that the orientation of shear vector with respect to the interface determines whether shear leads to intermixing between Cu and Ni or interface reorientation. The isolated vacancies were found to reduce the magnitude of the shear corresponding to the onset of plastic deformation, facilitating the intermixing process. There is a preferential vacancy diffusion across the interface from Ni into Cu, corresponding to the diffusion of Cu atoms into the Ni host. The energy barrier for this process (0.6 eV) decreases under applied shear by as much as 8.3 % for shear strain of 0.08 at 0K. This effect is enhanced at elevated temperature; spontaneous diffusion is observed at simulated temperature of 1000 K.

Precipitation Process during Isothermal Aging of an Austenitic Stainless Fe-12Cr-10Mn-12Ni-5Mo-0.24N-0.03C Steel and Its Effect on the Mechanical Properties: Maribel Saucedo-Muñoz¹; Victor Lopez-Hirata¹; Erika Avila-Davila¹; Felipe Hernandez-Santiago¹; Jose Villegas-Cardenas¹; ¹Instituto Politecnico Nacional-ESIQIE
    The precipitation process was studied during the isothermal aging at temperatures between 600 and 900 °C for times up to 1000 min. The aged specimens were characterized by SEM, XRD analysis, CVN impact test at –196 °C, and hardness test. Thermo-Calc analysis indicated that the Mo-rich M6C carbide precedes the precipitation of M2N nitrides in the austenite matrix at aging temperatures lower than 700 °C. The fastest growth kinetics takes place at about 800 °C for the M6C carbide and 850 °C for the M2N nitride. The CVN impact energy shows a decrease with aging time and temperature, while the Vickers harness indicates an increase with aging time. The intergranular precipitation was the main responsible for the decrease of cryogenic toughness.

Microstructure Rearrangements in Magnesium Alloys upon Thermo-mechanical Processing Studied by Advanced In-situ Synchrotron X-ray Diffraction: Xiaojing Liu¹; Emil Zolotoyabko²; Klaus-Dieter Liss¹; ¹Guangdong Technion – Israel Institute of Technology; ²Technion – Israel Institute of Technology
    In the present paper, we describe in-situ heating experiments on rolled AZ31 and AZ91 Mg alloys and analyze experimental results obtained using both synchrotron and laboratory X-ray diffraction methods. We found that X-ray diffraction provides rich information on heat-mediated transformation processes, which lead to the formation of different intermetallic phases. The growth and decay of intermetallic inclusions can be monitored via respective diffraction intensities. Measurements of chemical strain in the matrix solid solution allow us to shed light on atomic diffusion of Al from the Mg-Al matrix into intermetallic inclusions and vice versa. Combined effects of temperature and Al content on the c/a ratio in magnesium-aluminum alloys are investigated and discussed. In addition, the thermal expansion coefficients of the intermetallic phases and the matrix are determined. Important information on the recovery and recrystallization processes can be extracted from azimuthal distributions of diffraction intensity within the two-dimensional diffractograms.

Elastic Inhomogeneity Effects on Spinodal Decomposition in Ternary Alloys: Jitin Nair¹; Abinandanan T A¹; ¹Indian Institute of Science
    The effects of elastic inhomogeneity (i.e., differences in elastic moduli of phases in a microstructure) on microstructural evolution are well-documented in binary systems. Examples of these effects include rafting (microstructural evolution in inhomogeneous systems under applied stress),  phase inversion (in which a softer phase with a lower volume fraction changes its morphology from a precipitate to a matrix, with the harder phase doing the reverse), and instabilities in thin-film instabilities leading to their break-up. However, the effects of modulus mismatch in ternary systems remain largely unexplored. This study examines ternary spinodal decomposition leading to two-phase microstructures; more specifically, this paper will present our results from ongoing work on the effect of elastic inhomogeneity on early-stage decomposition and its possible role in altering the course of microstructural evolution.

Overview of the Non-isothermal Recrystallization in Cold-rolled Low-carbon Steels during Low-rate Annealing: Ivon Alanis-Fuerte¹; Octavio Vázquez-Gómez¹; Pedro Garnica-González¹; Edgar López-Martínez²; Héctor Vergara-Hernández¹; ¹Tecnológico Nacional de México / I.T. Morelia; ²Universidad del Istmo
    The non-isothermal recrystallization kinetics of two cold-rolled low-carbon steels, one alloyed and the other unalloyed, were analyzed by optical and scanning electron microscopy to characterize the microstructure. The grade of recrystallization was determined as a function of the heating rate and Vickers microhardness measurements at different annealing temperatures, established below the critical austenite formation temperature start. From the annealing conditions, the start and end of recrystallization were determined in a range between 500-700 °C. The results do not show a significant effect of the low-heating rate on the recrystallization kinetics, however, microstructural changes are evidenced with respect to the composition. Alloy steel shows a spheroidized cementite due to the fracture of previously cold-rolled pearlite, while unalloyed steel shows deformed pearlite grains without spheroidization compared to the same annealing temperature.

Morphological Evolution of Internally Twinned Martensite in Laser Additively Manufactured Ti6Al4V: Mangesh Pantawane¹; Shashank Sharma¹; Abhishek Sharma¹; Sriswaroop Dasari¹; Srikumar Banerjee¹; Rajarshi Banerjee¹; Narendra Dahotre¹; ¹University of North Texas
    The multiple thermal cycles during laser powder bed fusion additive manufacturing (LPBF-AM) of Ti6Al4V evolved the morphological features of the martensite phase and twins within them. The separate experiments involving laser surface melting with single, double, triple laser tracks and solutionization of wrought Ti6Al4V were conducted. The significant martensite laths were thinner in the water-quenched Ti6Al4V compared to LPBF-AM Ti6Al4V. The gradual coarsening of martensite lath occurred with successive thermal cycles of single, double, and triple laser track treatments. In addition, multiple generations of twins with distinct morphology were detected in LPBF-Ti6Al4V, which were rarely observed in solutionized and water quenched wrought Ti6Al4V. The multiple generations of twins were also distinctive features of the single laser track treated wrought Ti6Al4V. The evolution of these morphologically and crystallographically diverse martensite phase structures was linked to the computationally predicted thermokinetic and thermomechanical conditions during thermal treatments experienced during the LBPF-AM process.

The Effect of Irradiation Induced Defects on Martensitic Transformation in NiTi Shape Memory Alloys: Taiwu Yu¹; Alejandro Hinojos¹; Daniel Hong¹; Peter Anderson¹; Michael Mills¹; Yunzhi Wang¹; ¹Ohio State University
    Under the impact of radiation with high energy electrons, defects may be induced in the form of metastable clusters of amorphous phase. Consequently, suppression of thermally induced martensitic transformations (MTs) has been observed in irradiated NiTi, but with an enhancement in the reversible strain. On the other hand, linearized stress-strain responses have been observed in irradiated NiTi during stress-induced MTs, with considerable reversible strains. In this study we employ a phase field model to simulate the B2 to R MT under the effects of irradiation defects. The defect microstructures from the irradiation damage characterized by experiments, in terms of their type, size, number density and spatial distribution, are used directly as model inputs. The simulation results show that such defect clusters are promising to produce quasi-linear pseudoelasticity with ultra-low apparent elastic modulus. This study will inspire the design of shape memory alloys with desired properties by defect engineering using radiation.

Phase Transformation upon Low Temperature Nitriding of Co-Cr Alloys: Maryam Akhlaghi¹; Stefan Martin²; Johannes Dallmann¹; Rainer Hock¹; Carolin Körner¹; Andreas Leineweber²; ¹Friedrich-Alexander University Erlangen-Nuremberg (FAU); ²TU Bergakademie Freiberg
    Nitriding of Co- 15 at.% Cr alloy with an initial hexagonal close-packed (hcp) crystal structure was applied using gaseous nitriding medium at low temperatures of 400 °C and 450 °C. By diffusion of atomic nitrogen into the hcp lattice of substrate at low nitriding temperature of 400 °C, nitrogen supersaturated hcp phase has been developed. Formation of this expanded hcp phase results in the development of self-equilibrating residual macrostress throughout the nitrided layer and the corresponding substrate. Upon further diffusion of nitrogen, transformation from hcp to face-centered cubic (fcc) lattice is favored within the nitrided layer. However, owing to the developed macrostress, the progress of this phase transformation dependents on the initial orientation of hcp variants with respect to nitriding direction. The expanded phase takes up around 20 at.% N at the surface, which has a significant impact on enhancement of hardness in nitrided layer.

Advanced Characterization of High-temperature Oxygen-induced Phase Evolution in NbTiZr: David Beaudry¹; Daniel Foley¹; Elaf Anber¹; Jean-Philippe Couzinié²; Loïc Perrière²; Keith Knipling³; Christopher Pasco¹; Tyrel McQueen¹; Michael Waters⁴; James Rondinelli⁴; Mitra Taheri¹; ¹Johns Hopkins University; ²University Paris-Est Créteil; ³U.S. Naval Research Laboratory; ⁴Northwestern University
    Refractory High Entropy Alloys (RHEAs) offer a potential alternative to Ni-based superalloys in high-temperature applications because of their specific strength at elevated temperatures. These alloys often exhibit detrimental oxidation behavior due to their constituent refractory elements. Some RHEA compositions exhibit phase transformations that can both influence and be influenced by oxygen content. NbTiZr, a common derivative of studied RHEAs, was selected to better understand the fundamental oxide formation and evolution in these systems. Annealing heat treatments were performed at 900°C, 1050°C, and 1250°C followed by oxidation treatments at the same temperatures. A multi-layered surface microstructure formed. High Resolution TEM and APT revealed that the high-temperature oxygen influx stabilized a low-temperature phase transformation, resulting in a suboxide layer of two metallic phases with distinct oxygen content. The interplay of these oxygen-stabilized phases with oxide precipitation offers a novel “bottom-up” approach to tune phase transformations at the bulk-oxide interface.

Kinetic Monte Carlo Simulations of Solute Clustering in Multicomponent Al Alloys: Zhucong Xi¹; Louis Hector²; Amit Misra¹; Liang Qi¹; ¹University of Michigan; ²GM Global Technical Center
    High-strength Al-Mg-Zn-based alloys have severe formability limitations due to fast precipitate kinetics at room temperature (natural aging). This is primarily a result of the nucleation and growth of solute clusters and Guinier-Preston (GP) zones. Here, solute clustering kinetics in multicomponent Al alloys is simulated with a newly developed kinetic Monte Carlo (kMC) simulation framework. First-principles calculations demonstrate that the Kinetic Ising Model, which assumes a linear relationship between vacancy migration barriers and vacancy migration driving forces, is inaccurate for Al-Mg-Zn-based alloys due to lattice distortion effects. A surrogate model is therefore constructed to accurately predict vacancy migration barriers. This model was implemented in a kMC simulation package to study solute clustering kinetics in Al-Mg-Zn-based alloys as a function of temperature, vacancy concentration, and chemical composition. Simulation results on solute cluster evolution are used to identify effective strategies to trap vacancies and hence slow natural aging.

Coarsening Behavior of Hierarchical B2 Precipitates in a High Entropy Alloy: Subhashish Meher¹; Thomas Lillo¹; ¹Idaho National Laboratory
    An experimental approach has been used to explore a hierarchical structure at nanoscale for enhanced coarsening resistance of ordered B2 precipitates in a high entropy alloy. The hierarchical microstructure formed in this alloy is composed of a body centric cubic (BCC) matrix with B2 precipitates that contain embedded, spherical BCC precipitates, which coarsen during high-temperature annealing but do delay coarsening of the larger B2 precipitates. The experimental results uniquely demonstrated the pathways of precipitate coalescence that were captured on electron microscopy results. Chemical mapping via atom probe tomography suggests the possible routes of origin of such structural hierarchy that can give insights to future hierarchical materials fabrication.

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