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1. Role of Aluminum rejection from isothermal ω precipitates on the formation of α precipitates in the metastable β-titanium alloy Ti-10V-2Fe-3Al

   https://doi.org/10.1016/j.scriptamat.2023.115565  

   Mantri, SA; Dasari, S; Sharma, A; Zheng, Y; Fraser, HL; Banerjee, R (September 2023, Scripta Materialia)

   The formation of isothermal ω phase precipitates and its influence on subsequent fine-scale α precipitation is investigated in a metastable β-titanium alloy, Ti-10V-2Fe-3Al. Atom-probe tomography and high-resolution transmission electron microscopy reveal that the rejection of Al, a potent α stabilizer, from the growing isothermal ω precipitates at 330°C, aids in the formation of α precipitates. Additionally, the presence of α/ω and α/β interfaces conclusively establish that these α precipitates form at the β/ω interface. Interestingly, the local Al pile-up at this interface results in a substantially higher than equilibrium Al content within the α precipitates at the early stages of formation. This can be rationalized based on a novel three-phase β+ω+α metastable equilibrium at a lower annealing temperature (330°C, below the ω solvus). Subsequent annealing at a higher temperature (600°C, above the ω solvus), dissolves the ω precipitates and re-establishes the two-phase β+α equilibrium in concurrence with solution thermodynamic predictions. 

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2. In Situ X-ray Radiography and Computational Modeling to Predict Grain Morphology in β-Titanium during Simulated Additive Manufacturing

   https://doi.org/10.3390/met12071217  

   Jasien, Chris; Saville, Alec; Becker, Chandler Gus; Klemm-Toole, Jonah; Fezzaa, Kamel; Sun, Tao; Pollock, Tresa; Clarke, Amy J. (July 2022, Metals)

   The continued development of metal additive manufacturing (AM) has expanded the engineering metallic alloys for which these processes may be applied, including beta-titanium alloys with desirable strength-to-density ratios. To understand the response of beta-titanium alloys to AM processing, solidification and microstructure evolution needs to be investigated. In particular, thermal gradients (Gs) and solidification velocities (Vs) experienced during AM are needed to link processing to microstructure development, including the columnar-to-equiaxed transition (CET). In this work, in situ synchrotron X-ray radiography of the beta-titanium alloy Ti-10V-2Fe-3Al (wt.%) (Ti-1023) during simulated laser-powder bed fusion (L-PBF) was performed at the Advanced Photon Source at Argonne National Laboratory, allowing for direct determination of Vs. Two different computational modeling tools, SYSWELD and FLOW-3D, were utilized to investigate the solidification conditions of spot and raster melt scenarios. The predicted Vs obtained from both pieces of computational software exhibited good agreement with those obtained from in situ synchrotron X-ray radiography measurements. The model that accounted for fluid flow also showed the ability to predict trends unobservable in the in situ synchrotron X-ray radiography, but are known to occur during rapid solidification. A CET model for Ti-1023 was also developed using the Kurz–Giovanola–Trivedi model, which allowed modeled Gs and Vs to be compared in the context of predicted grain morphologies. Both pieces of software were in agreement for morphology predictions of spot-melts, but drastically differed for raster predictions. The discrepancy is attributable to the difference in accounting for fluid flow, resulting in magnitude-different values of Gs for similar Vs. 

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3. In situ design of advanced titanium alloy with concentration modulations by additive manufacturing

   https://doi.org/10.1126/science.abj3770  

   Zhang, Tianlong; Huang, Zhenghua; Yang, Tao; Kong, Haojie; Luan, Junhua; Wang, Anding; Wang, Dong; Kuo, Way; Wang, Yunzhi; Liu, Chain-Tsuan (October 2021, Science)

   Additive manufacturing is a revolutionary technology that offers a different pathway for material processing and design. However, innovations in either new materials or new processing technologies can seldom be successful without a synergistic combination. We demonstrate an in situ design approach to make alloys spatially modulated in concentration by using laser-powder bed fusion. We show that the partial homogenization of two dissimilar alloy melts—Ti-6Al-4V and a small amount of 316L stainless steel—allows us to produce micrometer-scale concentration modulations of the elements that are contained in 316L in the Ti-6Al-4V matrix. The corresponding phase stability modulation creates a fine scale–modulated β + α′ dual-phase microstructure that exhibits a progressive transformation-induced plasticity effect, which leads to a high tensile strength of ~1.3 gigapascals with a uniform elongation of ~9% and an excellent work-hardening capacity of >300 megapascals. This approach creates a pathway for concentration-modulated heterogeneous alloy design for structural and functional applications. 

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4. Lattice Parameter Evolution during the β-to-α and β-to-ω Transformations of Iron- and Aluminum-Modified Ti-11Cr(at.%)

   https://doi.org/10.3390/cryst14020145  

   Ballor, JoAnn; Poplawsky, Jonathan D.; Devaraj, Arun; Misture, Scott; Boehlert, Carl J. (February 2024, Crystals)

   β-titanium (β-Ti) alloys are useful in diverse industries because their mechanical properties can be tuned by transforming the metastable β phase into other metastable and stable phases. Relationships between lattice parameter and β-Ti alloy concentrations have been explored, but the lattice parameter evolution during β-phase transformations is not well understood. In this work, the β-Ti alloys, Ti-11Cr, Ti-11Cr-0.85Fe, Ti-11Cr-5.3Al, and Ti-11Cr-0.85Fe-5.3Al (all in at.%), underwent a 400 °C aging treatment for up to 12 h to induce the β-to-ω and β-to-α phase transformations. Phase identification and lattice parameters were measured in situ using high-temperature X-ray diffraction. Phase compositions were measured ex situ using atom probe tomography. During the phase transformations, Cr and Fe diffused from the ω and α phases into the β matrix, and the β-phase lattice parameter exhibited a corresponding decrease. The decrease in β-phase lattice parameter affected the α- and ω-phase lattice parameters. The α phase in the Fe-free alloys exhibited α-phase c/a ratios close to those of pure Ti. A larger β-phase composition change in Ti-11Cr resulted in larger ω-phase lattice parameter changes than in Ti-11Cr-0.85Fe. This work illuminates the complex relationship between diffusion, composition, and structure for these diffusive/displacive transformations. 

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5. Role of deformation twinning in fatigue of CrCoNi medium-entropy alloy at room temperature

   https://doi.org/10.1016/j.scriptamat.2021.113985  

   Heczko, Milan; Mazánová, Veronika; Slone, Connor E.; Shih, Mulaine; George, Easo P.; Ghazisaeidi, Maryam; Polák, Jaroslav; Mills, Michael J. (September 2021, Scripta materialia)

   Cylindrical specimens of CrCoNi alloy with electropolished surfaces were subjected to constant total strain amplitude low cycle fatigue. The alloy exhibited an initial period of cyclic hardening followed by cyclic softening until failure occurred. At the end of hardening stage at the peak of cyclic stress, well-developed persistent slip markings (PSMs) consisting of extrusions and intrusions were associated with thin deformation twins. A sophisticated experimental workflow was designed to extract information from the surface and the bulk of tested material. A combination of SEM, EBSD, ECCI, FIB and HR-STEM was used to study the internal structure and the surface profiles around the deformation twins, which were produced during the initial period of cyclic loading. Furthermore, localized cyclic plastic strain and stress concentrations near deformation twins led not only to early, well-developed PSMs, but also to the activation of TWIP and TRIP plasticity even at low macroscopic stress amplitudes. 

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