Phase Transformations and Microstructural Evolution: General Topics II
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Yufeng Zheng, University of North Texas; Rongpei Shi, Harbin Institute of Technology; Stoichko Antonov, University of Science and Technology Beijing; Yipeng Gao, Jilin University; Rajarshi Banerjee, University of North Texas; Yongmei Jin, Michigan Technological University
Thursday 2:00 PM
February 27, 2020
Room: 33B
Location: San Diego Convention Ctr
Session Chair: Bharat Gwalani, Pacific Northwest National Laboratory; Zhi Liang, National Institute of Standards and Technology
2:00 PM
Molecular Dynamic Study the Role of the Kinetic Factor during Nucleation of Stoichiometric Compounds from Liquid: Huajing Song1; Y Sun2; F Zhang2; C.Z. Wang2; K.M. Ho3; M.I. Mendelev2; 1Los Alamos National Laboratory; 2Ames Laboratory; 3Iowa State University
We applied the molecular dynamics (MD) simulations to study the liquid-solid nucleation of the pure Ni and the Ni50Al50 alloys. We also innovated a persistent-embryo method (PEM) to drive a metallic glass Cu50Zr50 to overcome its high activation energy barrier and nucleate in the MD time scale. Combined the mean first-passage time (MFPT) method with the Fokker-Planck (FP) equation, the free-energy and kinetic factor were directly calculated from the MD data. Usually, the nucleation rate is related to the energy barrier, higher the barrier lower the nucleation rate. However, our obtained data show that the nucleation free-energy barrier is in order of Ni > Cu50Zr50 > Ni50Al50, but the nucleation rate is opposite Cu50Zr50 < Ni50Al50 < Ni. This result can be explained by the slow attachment kinetics in the CuZr and NiAl alloy which was related to the ordered nature of the atom in the B2 phase.
2:20 PM
Predictably Tuning Transformation Temperatures in Thin Epitaxial Films: Ashley Bucsek1; Ananya Renuka Balakrishna2; Abhinav Prakash2; Bharat Jalan2; Richard James2; 1University of Michigan; 2University of Minnesota
For the majority of functional material applications involving phase transformations, it is necessary to tune the transformation temperature for the specific operating conditions of the application. Here, we focus on the ability to tune the transformation temperature using stress. Because the magnitudes of the biaxial stress states in epitaxially grown films can be relatively large (1–2%) while also resisting the formation of dislocations, we focus on thin epitaxial films where the change in transformation temperature can be quite dramatic. For example, we have observed a transformation temperature depression of roughly 1000°C, bringing a normally inaccessible phase transformation to room temperature. Here, we present a free energy approach to predicting transformation temperatures in thin epitaxial films. This approach builds on theory describing compatibility requirements in thin films versus bulk materials. The result is a straightforward approach for engineering phase-transforming films with desired transformation temperatures.
2:40 PM
(S)TEM Investigation of a Passivating Alumina Layer Formed During Air Annealing of CVD-Grown Hf(1-x)AlxB2 Coatings: Carly Romnes1; Kinsey Canova1; Zoë Tucker1; Zhejun Zhang1; John Abelson1; Jessica Krogstad1; 1University of Illinois at Urbana-Champaign
Transition metal diboride protective coatings are of interest in automotive, aerospace, and manufacturing industries due to the potential to improve hardness, chemical inertness, and increase wear resistance. Currently, use of diboride coatings is limited due to the onset of oxidation above 700°C. We report an innovative, low temperature, chemical vapor deposition process that results in a metal diboride film with improved oxidation resistance and is well-adherent and conformal. The coatings consist of mixed-metal alloy diborides in which the second metal is an effective oxide former. During annealing, a dense and protective surface oxide evolves to afford oxidation resistance, while the bulk transforms into a nanocrystalline phase. To better understand the annealing behavior, these coatings were investigated at various time stages during isothermal annealing using transmission electron microscopy (TEM), scanning TEM, and energy dispersive x-ray spectroscopy. We report key insights on the relationship between microstructural evolution and oxidation resistance.
3:00 PM Cancelled
Analysis of the Grain Growth Rate on the Voxel-based Microstructural Representation: Hyeonho Kim1; Kunok Chang1; 1Kyung Hee University
Predicting grain growth rate from the grain boundary network morphology has been important task in the material science. Von Neumann-Mullins theorem assumed equilibrium of triple junction is always 120° which means the force balance at the triple junction is achieved. However, during the grain growth, the triple junction migrates, it means the net force applied to the triple junction should not be 0. General way to represent the microstructure is the voxel based microstructure representation. However, since the dihedral angle is the property evaluated by the line differential of the grain boundary, more in-depth discussion is needed to obtain the value. In this talk, we introduced the reliable way to measure the dihedral angle of the grain structure obtained by the phase-field modeling, which adopts the voxel based microstructure representation and the obtained angle was used to predict the grain growth rate proposed by R. Kirchheim [Acta Materialia 173(2019) 327-331].
3:20 PM
Comparison of Phase Transformations in Binary Ti-Mo and Zr-Nb Alloys: Anna Veverkova1; Petr Harcuba1; Jana Šmilauerová1; Josef Stráský1; 1Charles University
Titanium and zirconium are both allotropic materials – they occur in more crystallographic phases. They can be found in the same group of periodic table of elements, they both occur in HCP structure at room temperature and in BCC structure above beta-transus temperature. While Ti alloys are used in aircraft industry or biomedicine, Zr is primarily applied in nuclear reactors. Phase transformations in metastable beta titanium alloys have been thoroughly explored. On the other hand, metastable beta Zr alloys are almost unexplored. This study aims on using knowledge of phase transitions in Ti alloys for description of phase transformations in similar Zr based alloys. Binary Ti-(12-18)Mo and Zr-(12-15)Nb alloys were manufactured by vacuum arc melting and investigated by in-situ methods such as electrical resistivity measurement, DSC and dilatometry. Observed results were confirmed by ex-situ SEM observations.
3:40 PM Break
4:00 PM
The Validity of Additivity Rule for Pearlite Transformation in Eutectoid Steels: Jeong Min Kim1; Kyung Jong Lee1; 1Hanyang University
The additivity rule has been widely used to predict the phase transformation behavior during continuous cooling (CCT) from the experimental isothermal phase transformation data (TTT). The calculated result of the additivity rule is the temperature (TCCT) which satisfies the summation of Δt/tTTT equals unity under specific continuous cooling rate. The tTTT represents the time required to obtain the fraction X at temperature(TTTT), which is usually fitted by the curve. Since the TTT experiment can be performed only in a limited temperature range, the extrapolated tTTT values between equilibrium and maximum measured temperature significantly affect TCCT. The extrapolated tTTT are discussed in terms of fitting curves originated from the transformation model, and the upper and lower bound concept. In this study, a proper method of the extrapolated tTTT is proposed. The method is applied to pearlite transformation. It is confirmed that additivity rule is quite possible to apply to pearlite transformation.
4:20 PM Cancelled
XRD and Synchrotron-based XRD Study of Chalcopyrite Leaching Catalyzed by Silver Ions: Rui Liao1; Jun Wang1; Shitong Liu1; Hao Lin1; Mo Lin1; Shichao Yu1; 1Central South University
Silver ion can effectively improve the bioleaching efficiency of chalcopyrite, and the mechanism of the process is still in controversy. In this study, leaching experiments, X-ray diffraction (XRD) and synchrotron radiation X-ray diffraction (SR-XRD) were conducted to investigate the intermediate of chalcopyrite in chemical leaching and bioleaching system. In the chemical leaching system, different ratio of ferric ions to ferrous ion was adopted as the leaching reagent. L. ferriphilum was used in the bioleaching system. The leaching behaviors showed that the copper extraction was significant promoted from 39% to 96% and from 60% to 95% inchemical leaching and bioleaching system, respectively. The X-ray diffraction results showed that jarosite was the main intermediate during the leaching process. By using synchrotron radiation X-ray diffraction, idaite was also detected. Even though much jarosite still formed in the presence of silver ions, this passivation film would not hinder the leaching of chalcopyrite.