Phase Transformations and Microstructural Evolution: General Topics I
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 8:30 AM
February 27, 2020
Room: 33B
Location: San Diego Convention Ctr
Session Chair: Pankaj Kumar, University of Nevada, Reno; Fulin Wang, University of California, Santa Barbara
8:30 AM
Precipitation Kinetics and Evaluation of the Interfacial Mobility of Precipitates in an AlSi7Cu0.5Mg0.3 Cast Alloy: Pierre Heugue1; Daniel Larouche1; Francis Breton2; Rémi Martinez3; X Grant Chen4; Denis Massinon5; 1Laval University; 2Rio Tinto; 3Linamar Corporation; 4University of Quebec at Chicoutimi; 5Montupet Laigneville
Heat treatment of cast Aluminum alloys parts enables the formation and distribution of nano-sized precipitates through an optimum sequence including solutionizing, quenching and artificial aging. Quaternary alloys are particularly challenging and the present study aims to understand and outline the precipitation kinetics in the foundry AlSi7Cu0.5Mg0.3 alloy. Using techniques like differential scanning calorimetry (DSC), transmission electron microscopy (TEM), LKSZ kinetic equations and micro-hardness testing, the precipitation kinetics was quantitatively characterized. Activation energies of the phase transformations were extracted using the Kissinger analysis of non-isothermal DSC runs conducted at different stationary heating rates. Finally, a first evaluation of the interfacial mobility of precipitates in this alloy was made using the developed methodology.
8:50 AM
Neutron Diffraction-based Assessment of Eutectoid Phase Transformation Kinetics in U-10Mo Alloys with Minor Ternary Alloying Additions of Cr, Co, and Ni: Nathan Peterson1; Daniel Malta1; Saumyadeep Jana2; Vineet Joshi2; Sean Agnew1; 1University of Virginia; 2Pacific Northwest National Laboratory
U-10Mo alloys are proposed for replacement of highly enriched uranium fuels in research reactors. Below the eutectoid temperature of 560°C, the U(Mo) γ-phase (body centered cubic) solid solution decomposes into orthorhombic α-U and tetragonal γ’-U2Mo phases. The anisotropy of these phases is detrimental to in-reactor fuel performance. Thus, it is critical to develop an understanding of the γ-U(Mo) phase stability at sub-eutectoid temperatures. Here, minor (0.2wt%) ternary alloying additions (Cr, Ni, Co) have been examined using neutron diffraction to quantify the time and temperature dependence of the eutectoid transformation at 450, 500, and 525°C. The effect of the ternary additions on the reaction kinetics will be discussed, as well as the importance of the Debye-Waller factor in Rietveld refinement on the interpretation of the neutron scattering data in this study.
9:10 AM
Thermodynamic and Kinetic Study of the fcc-B2 Phase Transformation and Consecutive Microstructural Evolution in the Ag-Cu-Pd System: Solene Iruela1; Yannick Champion1; Annie Antoni-Zdziobek1; Fabien Volpi1; Christine Bourda2; Vincent Jarry2; 1SIMaP; 2Metalor Technologies Electrotechnics France
Ag-Cu-Pd alloys are key materials for intermittent electrical contact applications due to their large hardness and low resistivity. However, the further improvement of their physical properties is highly challenging: the traditional strategies of mechanical strengthening generally lead to antagonist effects on electrical conductivity. Ag-Cu-Pd system presents the B2-type ordered phase, which combines high conductivity and hardness, formed by fcc transformation. In this work, domains of stable B2-phase in the Ag-Cu-Pd ternary system have been established experimentally by heat treatments. The nanometric microstructures have then been characterized by Scanning Electron Microscopy, Transmission Electron Microscopy and Atom Probe Tomography. Phase-equilibrium calculations based on a consistent set of thermodynamic parameters are performed to define new interesting compositions. In situ X-Ray Diffraction is employed to follow the fcc-B2 transformation and the ordering rate has been specified at selected temperatures. This approach can be used as a guideline to select appropriate heat treatment conditions.
9:30 AM
Fabrication of Gamma Prime Strengthened Ni-Cr-Al-Ti Microtubes via Gas-phase Deposition and the Kirkendall Effect: Haozhi Zhang1; Ashley Paz y Puente1; 1University of Cincinnati
Metallic Ni-based superalloy lattice structures have garnered significant interest recently since they provide low density, high surface area and improved heating/cooling efficiency compared to their traditional bulk counterparts. Here Ni-Cr-Al-Ti wires, which fundamentally represent the struts of a lattice structure, have been fabricated using a gas-phase deposition technique called pack cementation. By taking advantage of the short diffusion distances and radial symmetry in lattice structures, this method can also be used to harness the Kirkendall effect to create hollow struts leading to a secondary level of porosity. In this talk, the influence of various alloying additions on the Kirkendall pore formation and evolution will be discussed. The final composition of the hollowed wires can be further optimized by de-alloying via reversing the pack cementation process to get the target composition and the desired gamma prime strengthened microstructure.
9:50 AM
Exploring Phase Transformations in the Au-Zn-Al System: Taylor Jacobs1; Seth Imhoff1; Meghan Gibbs1; Clarissa Yablinsky1; 1Los Alamos National Laboratory
The Au-Zn-Al system is being utilized to study phase transformation behaviors in high density metal alloys. A combined effort involving differential scanning calorimetry, dilatometry, microscopy, x-ray diffraction, and neutron diffraction were utilized to explore microstructure evolution after casting and heat treating. Microstructures often consist of multiple phases of complex morphologies observed on vastly different length scales. Depending on alloy composition, up to four phase transformations were observed after solidification. The results of the present study are combined with mechanical behavior studies and modeling efforts to improve fundamental understandings of processing high density metal alloys.
10:10 AM Break
10:30 AM
Barrier-free Nucleation at Grain-boundary Triple Junctions during Solid-state Phase Transformations: Huajing Song1; Jeff.J. Hoyt2; 1Los Alamos National Laboratory; 2McMaster University
Molecular dynamics simulations are used to provide strong evidence for barrier-free nucleation events in a heterogeneous solid-solid system. The barrier-free events are characterized by an absence of an incubation time and a growth rate of the emerging phase that is independent of the system size. Furthermore, an analysis of the size and shape of the critical nucleus using the Winterbottom construction indicates that no solution exists for these barrier-free cases. We propose that barrier-free nucleation, which will have a profound effect on phase transformation kinetics, may be a general phenomenon for any polycrystalline material.
10:50 AM
Formation and Stability of Ni-Y Clusters in Mg85Y9Ni6 Alloys: Hiroshi Okuda1; Mikito Ito1; Michiaki Yamasaki2; Yoshihito Kawamura2; 1Kyoto University; 2Kumamoto University
Formation and growth of Y-Ni clusters in Mg85Y9Ni6 alloys have been examined by in-situ small- and wide-angle X-ray scattering measurements and EXAFS. Amorphous ribbons have been heated in-situ from room temperature to the melting at the heating rate of 10 K/min. Small clusters were found even in the amorphous state, as is the same for Mg85Y9Zn6 alloys. The distribution of clusters change even in the amorphous region, and then after crystallization, the growth of the cluster became more apparent and reached the size of Y8TM6+interstitial ‘L12 cluster’ as demonstrated for MgYZn alloys. EXAFS measurements showed that the size of the L12 clusters is slightly smaller than that of MgYZn, but still the atomic configurations are the same. These results suggested that the kinetics of LPSO formation in MgYNi alloys are characterized as hierarchical phase transformations as proposed for MgYZn alloys. Difference appeared at the relative stability at higher temperatures.
11:10 AM
Dislocation or Twinning Formation in Inorganic Semiconductors from Light Irradiation: Yidi Shen1; Hongwei Wang1; Qi An1; 1University of Nevada–Reno
Inorganic semiconductors have widespread applications in electronic devices, but they suffer from the brittle failure because of their strong ionic and directional covalent bonding which suppress the mobile dislocations. Therefore, it is essential to improve their ductility for the extended engineering applications. Here, we employed quantum mechanics (QM) simulations to investigate how the photonic excitation affect the plastic deformation in sphalerite ZnS and related II-IV semiconductors. We found that in ZnS the dislocation dominated deformation mode transforms to a twin dominated deformation mode when the electron-hole pair are excited, leading to a brittle failure. While the dislocation dominated mechanism leads to a ductile mechanical behavior under the ground state. These simulation results agree very well with the recent mechanical experiments on single crystal ZnS in which the ductile ZnS under darkness becomes brittle with light illumination. Our results provide the theoretical basis to investigate the photon-mechanical behaviors of semiconductors.