Phase Transformations and Microstructural Evolution: Microstructure and Precipitation 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
Tuesday 2:00 PM
February 25, 2020
Room: 33B
Location: San Diego Convention Ctr
Session Chair: Yipeng Gao, Idaho National Laboratory; Yijia Gu, Missouri University of Science and Technology
2:00 PM
Linear Complexion Formation and their Effect on the Strength of Metallic Alloys: Vladyslav Turlo1; Timothy Rupert1; 1University of California, Irvine
Linear complexions are phase-like features that are thermodynamically stable only near dislocations and are analogous to grain boundary complexions (phase-like interfacial structures). In this talk, we discuss how different types of linear complexions can be formed at dislocations, with a special focus on structural materials and their mechanical properties. By using atomistic simulations, we first explore a large number of alloys at different compositions and temperatures to construct “linear complexion phase diagrams”, showing the appropriate conditions for complexion formation while also providing an information about their expected size and makeup. Next, we perform shear deformation simulations of the samples with nanoscale-size linear complexions and demonstrate that such complexions are able to significantly improve the strength of metallic alloys by pinning moving dislocations or modifying their local atomic structure. Taken as a whole, our findings allow for the possibility of a tunable alloy microstructure and properties, advancing the materials design toolbox.
2:20 PM Cancelled
Understanding the Role of Microwave Heating on the Crystallization Behavior, Microstructure Formation and Mechanical Response of ZrO2-Containing SiO2 – MgO - Al2O3 – K2O – B2O3 – F mica Glass-ceramics: Shibayan Roy1; Mrinmoy Garai1; 1Indian Institute of Technology (IIT) Kharagpur
Microwave heat-treatment was carried out on mica-based boro-alumino-silicate glass (Si-O-Si/B/Al), containing varying amounts of nucleating agent, ZrO2 (2, 5 and 10 wt.%). Base glasses were heat-treated, first at 700°C and later at 780°C in a microwave furnace at a rate of 40°C/min. Microwave heating produces fluorophlogopite, KMg3(AlSi3O10)F2 with interlocked card-like and rod-like microstructure. With increasing ZrO2 content, average crystal width increases, whereas average crystal length decreases due to the availability of nucleation sites. Microhardness of these glass-ceramics increases from 5.68 GPa for 2 wt.% ZrO2 to 6.17 and 6.64 GPa for 5 and 10 wt.%, respectively. Machinability studies involving scratch tests at 40N load indicate that the resistance to deformation is inversely proportional to strength of matrix in the order 2 wt.% ZrO2 > 5 wt.% ZrO2 > 10 wt.% ZrO2. Scratch induced lateral crack propagation increases with higher width of the crystalline phase following the same order.
2:40 PM
Interphase Boundary Anisotropy Effects on the Microstructure Evolution in Three Phase β(In) – In2Bi – γ(Sn) Eutectic System: Samira Mohagheghi1; Melis Serefoglu1; 1Koc University
Anisotropy in the crystal/crystal surface energy strongly affects the microstructure evolution in eutectics. Accordingly, four different classes of three-phase eutectic grains (EG) as a function of interphase anisotropy, namely, quasi-isotropic, nearly-locked, locked, and rod-within-lamellae (RL3), were recently identified by the authors. In this work, we address the origins of observing substantially different microstructures in these three-phase EG by performing real-time rotating directional solidification (RDS) experiments on In-Bi-Sn model alloy system. We identified that the morphology of phases changes substantially in RL3 grains during RDS although they remain to be lamellae in all other EG types. More specifically, while the morphology of β(In) phases change between rod and lamellar, major axis of γ(Sn) lamella becomes parallel and perpendicular to the sample plane in every half rotation of the sample. Complimentary EBSD and XRD studies show the strong influence of crystals orientation with respect to the sample plane on the microstructures.
3:00 PM Cancelled
Mechanical Property Variation and Microstructure Evolution of
Inconel Alloy Induced by Electric Current Stressing: Wen-Jung Li1; Kwang-Lung Lin1; 1Department of Materials Science and Engineering,National Cheng Kung University
Electromigration refers to atoms movement due to the momentum transfer from the electron wind force induced by electric current. Previous studies reported that electromigration could induce recrystallization and verify the mechanical properties of materials with appropriate control of current stressing parameters. The present study investigated the recrystallization and thus mechanical property variation behavior of Inconel-600 alloy, a γ-phase nickel-chromium alloy, with electric current stressing at 7000 A/cm2 under ambient condition. The combinations of current stressing time (tD ) and stressing cycles (N) were found to reduce or enhance the micro hardness, ranging 180Hv~220 Hv, of the annealed alloy depending on the tD/N parameters. A maximum peak value of micro hardness was achieved in the range of log(tD/N) from -3 to 1.4. The study investigated the microstructure variation with EBSDand TEM to understand the property variation. An interpretation of the recrystallization behavior induced by current stressing will be presented.
3:20 PM
Effect of Zirconium Addition to Wrought Al-Mg-Si Alloys on Microstructure: Florian Schmid1; Thomas Ebner2; Peter J. Uggowitzer3; Stefan Pogatscher1; 1Christian Doppler Laboratory for Advanced Aluminum Alloys; 2AMAG rolling GmbH; 3Montanuiversitaet Leoben
Increasing the recycling rates as a key action to reduce global CO2 emissions, alloy manufacturers are confronted with a wider variation of elements, that can act either positively or negatively. During thermo-mechanical production, manganese, iron or chromium are common to control the microstructure evolution by forming stable precipitates that can effectively hinder grain boundary motion via Zener-pinning. In a similar way, Zr forms Al3Zr-precipitates, which show an even increased potential to stabilize the microstructure and act resistively against recrystallization. However, Zr tends to increase cast grain size. This study evaluates the impact of Zr on conventional grain refiner in combination with different amounts of Fe and Mn. Microstructure evolution during thermo-mechanical treatment is examined by optical and electron microscopy. Results are discussed in terms of grain size, recrystallization tendency and Al3Zr precipitate density.
3:40 PM Break
4:00 PM
Nitride Precipitation Induced by Nitrogen-solute Clustering in Ferrous Alloys: Goro Miyamoto1; Meng Zhu1; Yasuhiro Tateyama1; Tadashi Furuhara1; 1Tohoku University
Nitriding treatment is commonly used for surface hardening of machinery parts for improvement of fatigue strength and wear resistivity. In the nitriding of ferrous alloys containing strong nitride forming element (M), surface hardening occurs by precipitation of fine nitrides. The present authors directly observed that surface hardening in the nitriding of Ti or V-added specimens occurs not by the precipitation of stable alloy nitrides but by meta-stable mono-layer M-nitrogen(N) clusters by means of high resolution transmission electron microscopy. On the other hand, clustering was not observed in Al or Cr-added specimens. Furthermore, in nitriding of ternary alloys containing cluster-forming and non-forming elements, such as Fe-Al-(V, Ti) alloys, V-N or Ti-N clustering induces nucleation of fine AlN particles, which results in significant surface hardening. This indicates pre-cursor solute clustering can be used to control precipitation reaction in ferrous alloys.
4:20 PM Cancelled
Precipitate Nucleation Enhanced by Deformation through Dislocations in Mg-Al Alloys: Peng Yi1; Michael Falk1; 1Johns Hopkins University
Magnesium has great potential as a lightweight material. Deformation processing experiments demonstrate the ability to enhance nanoscale precipitation to achieve a higher precipitation strengthening effect in Mg alloys. We study the fundamentals of precipitate nucleation enhanced by deformation through dislocations. Nucleation of gamma-Mg17Al12 precipitates in alpha Mg-Al solid solution is simulated using molecular dynamics to calculate the critical nucleus size. Solute segregation and non-hydrostatic stress generated by dislocations reduces the critical nucleus size. The Gibbs free energy is calculated for solids under non-hydrostatic stress to estimate the interfacial free energy using the classical nucleation theory. Local amorphization/melting is observed at the matrix-precipitate interface, and was confirmed by an anisotropic melting temperature calculation. The tension stress significantly reduces the interfacial free energy and the nucleation barrier, and increases the nucleation rate and growth velocity. Interfacial free energy increases parabolically with composition difference between the alpha and gamma phases.