Phase Transformations and Microstructural Evolution: Phase Transformations in Non-Ferrous Alloys
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
Wednesday 2:00 PM
February 26, 2020
Room: 33B
Location: San Diego Convention Ctr
Session Chair: Yufeng Zheng, University of Nevada, Reno; Leslie Mushongera, University of Nevada, Reno
2:00 PM
Defect Assisted Growth of Fine Scale Alpha in Titanium Alloys: Abigail Ackerman1; Benjamin Savitzky2; Colin Ophus2; Mohsen Danaie3; Phani Karamched4; Angus Wilkinson4; David Rugg5; David Dye1; 1Imperial College, London; 2National Center for Electron Microscopy; 3Electron Physical Sciences Imaging Centre (ePSIC); 4University of Oxford; 5Rolls-Royce plc.
Ti-6246 is a titanium alloy used in the intermediate pressure compressor of a gas turbine engine, due to its high strength to weight ratio and specific fatigue strength. Its strength benefit is thought to be due to its microstructure; multi orientated primary alpha laths within a beta matrix, with finer secondary alpha laths between. By increasing the dislocation content via processing, secondary alpha can be encouraged to nucleate from dislocations within the beta matrix, forming finer laths. Here, tensile, low cycle fatigue, high cycle fatigue and corner crack testing is used to show that this finer microstructure is superior to the as received material. Additionally, in situ heating in the TEM is used to show that nucleation is occurring within the beta matrix, with TKD showing that all 12 alpha variants are still present. Finally, CBED is used to show the evolving strain as this phase grows.
2:20 PM
Structural Phase Transformation in Single Crystal Titanium during Dynamic Loading: Curt Bronkhorst1; Biao Feng2; Benjamin Morrow3; Ellen Cerreta3; 1University of Wisconsin, Madison; 2Kimberly-Clark Corporation; 3Los Alamos National Laboratory
The mechanical loading of metallic materials to high pressures and over short time durations remains a technically challenging arena of research. We will present a study of structural phase transformation of high-purity titanium single crystals loaded by SHPB and plate-impact. Some sample material from these experiments was also soft-recovered and metallographically examined for structural evolution information. A thermodynamically consistent theory describing the finite elastic, dislocation slip, deformation twin, and phase transformation response of single crystals is presented. This theory presents physics coupling within both the energetic and structural components of the model for general high deformation rate loading conditions. The SHPB and shock loading along the [0 0 0 1] and [1 0 -1 1] directions of single crystal high purity Ti is investigated computationally. Multiple experimental phenomena are interpreted based upon the progression of dislocation slip, deformation twinning, and phase transformation.
2:40 PM
Effect of Heat Treatments on Microstructures and Mechanical Properties of Ti-5553 Alloy: Ritupurna Sahoo1; Abu Syed Kabir1; 1Carleton University
The mechanical properties of near-β Ti-alloys are highly dependent on their microstructures, which often is composed of multiple phases and precipitates. The volume fraction, size, morphology, and distribution of these precipitates can significantly influence the final mechanical properties. Therefore, a complete and detailed understanding on phase transformations and microstructural evolution are crucial to optimize the mechanical properties for various applications. In this study, Ti-5Al-5Mo-5V-3Cr (Ti-5553) a near-β titanium alloy has been solution treated at two temperatures above and below the β-transus followed by series of artificial aging treatments at various times and temperatures to study the microstructural evolutions. Different phases were identified, and phase quantity were measured using X-Ray Diffraction and Scanning Electron Microscope. Micro-indentation hardness was measured and finally, an effort has been taken to correlate that with the associated microstructures.
3:00 PM
(Al,Zn)3Zr Dispersoid-assisted η′ Precipitation in a Model Al-Zn-Mg-Cu-Zr Alloy: Huan Zhao1; Yiqiang Chen1; Surendra K. Makineni1; Baptiste Gault1; Dirk Ponge1; Dierk Raabe1; 1Max-Planck-Institut Fur Eisenforschung G
A small amount (0.05-0.16 wt.%) of zirconium is commonly added to Al-Zn-Mg-Cu alloys with the aim to reduce the grain size. Zr acts on grain refinement by forming nano-sized Al3Zr dispersoids during homogenization, hampering grain boundary motion through Zener pinning during downstream processing. In this talk, I will show microstructural evidence on the evolution of strengthening ηʹ precipitates during aging on prior presentL12-(Al,Zn)3Zr dispersoids in an Al-Zn-Mg-Cu-Zr alloy. A combination of atom probe tomography and aberration-corrected scanning transmission electron microscopy techniques were utilized for atomic scale compositional and structural characterization. Our findings explicitly provide a fundamental understanding on the formation mechanism of L12 structured composite dispersoids that coexist with η' precipitates.
3:20 PM Break
3:40 PM
The Impact of the Cooling Rate on Controlling the Grain Boundary Morphology and the Mechanical Properties of Nickel-based Superalloys: Bader Alabbad1; Sammy Tin1; 1Illinois Institute of Technology
For polycrystalline Ni-base superalloys, meso-scale engineering for grain boundary structures can be utilized through the development of serrated grain boundaries via controlling cooling process as the precipitation of γ′ precipitates is highly sensitive to the cooling rate. Controlled two-step cooling process was proposed to introduce small volume fraction of coarse γ′ along the grain boundaries to serrate the grain boundaries and to produce fine intragranular γ′ precipitates that are necessary to provide strength. Maintaining a slow initial cooling rate through the γ′ solvus-temperature enables the formation of large grain boundary γ′ precipitates that grow and serrate the grain boundary before the nucleation of the secondary γ′ precipitates. Transitioning to a faster cooling rate can be used to control the size and density of the secondary γ′ precipitates. The microstructure evolution and mechanical properties of the two-step cooling processes were compared and benchmarked to those produced via conventional continuous cooling processes.
4:00 PM Cancelled
In-situ Investigation of Phase Transformation in Ti-Mo Alloy: Xiaoqian Fu1; Qian Yu1; 1Zhejiang University
Phase transformation is the fundamental theory to guide the heat treatments and to regulate the microstructures and properties of Ti alloys. Since alloying elements used to stabilize certain phases may influence the phase transformation pathways dramatically at elevated temperature through diffusion, which cannot be predicted by thermodynamics. By using in situ TEM annealing experiment on a dual-phase Ti-Mo alloy, we found that diffusion of Mo could tune the phase transformation pathways at a wide range of annealing temperatures. At ~600°C, Mo diffused in HCP alpha phase to form nano-sized intermetallic compound as a precursor to facilitate martensitic-type alpha-to-beta transformation. At ~900°C, spinodal-type decomposition of beta phase led to concentration gradient in beta phase. Consequently, beta-to-alpha transformation proceeded at Mo-depleted interface by ledge mechanism and alpha-to-beta transformation occurred at Mo-enriched interface by creating new ledges. Overall, the concurrent beta-to-alpha and alpha-to-beta transformations caused increase of volume fraction of alpha phase.