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H J Rack - One of the best experts on this subject based on the ideXlab platform.
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Phase Transformations in ti nb ta and ti nb ta zr alloys
Journal of Materials Science, 2000Co-Authors: X Tang, T Ahmed, H J RackAbstract:Phase Transformations in solution treated and quenched Ti-(13-26) Nb-(22-38) Ta (wt.%) and Ti-(13-35.5) Nb-(5-22) Ta-(4-7.2) Zr alloys have been studied. It has been observed that Phase Transformations in these alloys are sensitive to both composition and cooling rate. In ternary alloys, water and oil quenching resulted in the formation of orthorhombic martensite (α′′) in a retained β + ωathermal matrix, whereas slower cooling showed evidence of fine α and ωisothermal formation within the β matrix. Increase of Nb + Ta content decreases the volume percentage of martensite. Moreover, addition of Zr stabilized the β Phase, lowered the martensite start temperature and suppressed ω formation. Finally, dynamic moduli of air cooled quaternary alloys showed that the modulus was sensitive to the composition, a minima at Nb/Ta ratio of 12.0 and 5 at% Zr being observed, this minimum in dynamic modulus being consistent with ω Phase suppression.
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Phase Transformations during cooling in α β titanium alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1998Co-Authors: T Ahmed, H J RackAbstract:Abstract A simplified methodology for investigating the effects of cooling rate from elevated temperature on Phase Transformations observed in α+β titanium alloys is described. It involves adaptation and refinement of a circumferentially insulated and instrumented Jominy end quench bar, time–temperature profiles obtained during cooling at locations along the bar length providing a complete thermal history. The ability of this procedure to examine the Phase transformation for α+β titanium alloys has been demonstrated in Ti–6Al–4V where varying cooling rates from 525 to 1.5°C s−1 are shown to result in a series of martensitic, massive and diffusional Phase Transformations. Cooling rates above 410°C s−1 result in a fully martensitic microstructure, a massive transformation being observed between 410 and 20°C s−1, this transformation being gradually replaced by diffusion controlled Widmanstatten α formation with decreasing cooling rate.
Yury Gogotsi - One of the best experts on this subject based on the ideXlab platform.
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Phase Transformations in silicon under contact loading
2002Co-Authors: Vladislav Domnich, Yury GogotsiAbstract:This review provides an analysis of the state of the art in the emerging research area of high-pressure surface science of silicon. Phase Transformations and amorphization that occur in silicon under contact loading, such as indentation with hard indenters, scratching or machining, will be described. Contact loading is one of the most common mechanical impacts that materials can experience during processing or use. Examples are dicing, slicing, grinding, polishing and other machining operations. This kind of loading may be accommodated by such competing processes as dislocation-induced plasticity, microfracture, mechanochemical interactions with the environment and/or counterbody, and changes in the material's structure (Phase Transformations). The former ones have been studied by mechanical engineers and tribologists, but the processes of Phase Transformations at the sharp contact have only been investigated for a very few materials (silicon is one of them) and further research is necessary. One of the reasons for the lack of information may be the fact that the problem is at the interface between at least three scientific fields, that is, materials science, mechanics, and solid state physics. Thus, an interdisciplinary approach is required to solve this problem and understand how and why a hydrostatic or shear stress in the two-body contact can drive Phase Transformations in materials.
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cyclic nanoindentation and raman microspectroscopy study of Phase Transformations in semiconductors
Journal of Materials Research, 2000Co-Authors: Yury Gogotsi, Vladislav Domnich, S N Dub, Andreas Kailer, Klaus G. NickelAbstract:This paper supplies new interpretation of nanoindentation data for silicon, germanium, and gallium arsenide based on Raman microanalysis of indentations. For the first time, Raman microspectroscopy analysis of semiconductors within nanoindentations is reported. The given analysis of the load-displacement curves shows that depth-sensing indentation can be used as a tool for identification of pressure-induced Phase Transformations. Volume change upon reverse Phase transformation of metallic Phases results either in a pop-out (or a kink-back) or in a slope change (elbow) of the unloading part of the load-displacement curve. Broad and asymmetric hysteresis loops of changing width, as well as changing slope of the elastic part of the loading curve in cyclic indentation can be used for confirmation of a Phase transformation during indentation. Metallization pressure can be determined as average contact pressure (Meyer's hardness) for the yield point on the loading part of the load-displacement curve. The pressure of the reverse transformation of the metallic Phase can be measured from pop-out or elbow on the unloading part of the diagram. For materials with Phase Transformations less pronounced than in Si, replotting of the loaddisplacement curves as average contact pressure versus relative indentation depth is required to determine the transformation pressures and/or improve the accuracy of data interpretation.
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raman microspectroscopy study of processing induced Phase Transformations and residual stress in silicon
Semiconductor Science and Technology, 1999Co-Authors: Yury Gogotsi, C Baek, F KirschtAbstract:Raman spectroscopy was used for analysis of Phase Transformations and residual stress in machined silicon. Wear debris from dicing of silicon was scanned with a Raman spectrometer. Recorded spectra manifest the presence of amorphous Si, hexagonal Phase (Si-IV), bc8 Phase (Si-III) and pristine Si-I under residual stress. On surfaces of diced wafers as well as lapped silicon wafers, the r8 Phase (Si-XII) was detected in addition to the above Phases. The composition of Phases in diced cross sections of silicon wafers differs dramatically between high and low speed cuts. The quantification of these Phases was attempted by curve fitting each spectrum with corresponding peaks of each Phase. Subsequently, relative intensity maps of specific Phases were generated. Thus, Raman spectroscopy studies of machined surfaces demonstrated metallization of Si under a variety of machining conditions including lapping, grinding, scratching, dicing and slicing. All metastable Phases of silicon disappear after etching and polishing of respective wafers. No evidence of Phase Transformations was found on a quartz-damaged silicon wafer surface. Residual stress having a characteristic distribution was observed in this case.
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pressure induced Phase Transformations in diamond
Journal of Applied Physics, 1998Co-Authors: Yury Gogotsi, Andreas Kailer, Klaus G. NickelAbstract:The stability of diamond under pressure and the structure of hypothetical high-pressure Phases have been a controversial issue for a long time. “Will diamond transform under megabar pressures?” asked Yin and Cohen in the title of their paper [Phys. Rev. Lett. 50, 2006 (1983)] which attempted to predict an answer to this question 15 years ago. Before and after that, many other scientists tried to find the answer doing both modeling and experiments. However, the cubic structure of diamond seems to be experimentally stable up to the highest static pressures that the modern high-pressure technology can achieve. We addressed the problem by decreasing the contact area of pressurization instead of increasing the total load. Experimentally this can be easily done in indentation tests using a sharp diamond indenter. In addition to hydrostatic stresses, such a test creates shear stresses as well. Here deformations may be realized, which are either impossible or would require much higher pressures when utilizing only hydrostatic stresses. By coupling the indentation loading with micro-Raman spectroscopy, we were able to drive and monitor Phase Transformations in diamond. A very similar phenomenon can be observed by scratching a diamond with another diamond. Thus, Phase Transformations in diamond may in fact be a very common feature of wear.
Philip Ryan - One of the best experts on this subject based on the ideXlab platform.
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self assembled periodic nanostructures using martensitic Phase Transformations
Nano Letters, 2020Co-Authors: Abhinav Prakash, Tianqi Wang, Ashley Bucsek, Tristan Truttmann, Alireza Fali, Michele Cotrufo, Hwanhui Yun, Jongwoo Kim, Philip RyanAbstract:We describe a novel approach for the rational design and synthesis of self-assembled periodic nanostructures using martensitic Phase Transformations. We demonstrate this approach in a thin film of ...
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self assembled periodic nanostructures using martensitic Phase Transformations
arXiv: Materials Science, 2020Co-Authors: Abhinav Prakash, Tianqi Wang, Ashley Bucsek, Tristan Truttmann, Alireza Fali, Michele Cotrufo, Hwanhui Yun, Jongwoo Kim, Philip RyanAbstract:We describe a novel approach for the rational design and synthesis of self-assembled periodic nanostructures using martensitic Phase Transformations. We demonstrate this approach in a thin film of perovskite SrSnO3 with reconfigurable periodic nanostructures consisting of regularly spaced regions of sharply contrasted dielectric properties. The films can be designed to have different periodicities and relative Phase fractions via chemical doping or strain engineering. The dielectric contrast within a single film can be tuned using temperature and laser wavelength, effectively creating a variable photonic crystal. Our results show the realistic possibility of designing large-area self-assembled periodic structures using martensitic Phase Transformations with the potential of implementing "built-to-order" nanostructures for tailored optoelectronic functionalities.
Y Mishin - One of the best experts on this subject based on the ideXlab platform.
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segregation induced Phase Transformations in grain boundaries
Physical Review B, 2015Co-Authors: Timofey Frolov, Mark Asta, Y MishinAbstract:Phase Transformations in metallic grain boundaries (GBs) present significant fundamental interest in the context of thermodynamics of low-dimensional physical systems. We report on atomistic computer simulations of the Cu-Ag system that provide direct evidence that GB Phase Transformations in a single-component GB can continue to exist in a binary alloy. This gives rise to segregation-induced Phase Transformations with varying chemical composition at a fixed temperature. Furthermore, for such Transformations we propose an approach to calculations of free-energy differences between different GB Phases by thermodynamic integration along a segregation isotherm. This opens the possibility of developing quantitative thermodynamics of GB Phases, their Transformations to each other, and critical phenomena in the future.
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structural Phase Transformations in metallic grain boundaries
Nature Communications, 2013Co-Authors: Timofey Frolov, Mark Asta, David L Olmsted, Y MishinAbstract:Structural Transformations at interfaces are of profound fundamental interest as complex examples of Phase transitions in low-dimensional systems. Despite decades of extensive research, no compelling evidence exists for structural Transformations in high-angle grain boundaries in elemental systems. Here we show that the critical impediment to observations of such Phase Transformations in atomistic modelling has been rooted in inadequate simulation methodology. The proposed new methodology allows variations in atomic density inside the grain boundary and reveals multiple grain boundary Phases with different atomic structures. Reversible first-order Transformations between such Phases are observed by varying temperature or injecting point defects into the boundary region. Owing to the presence of multiple metastable Phases, grain boundaries can absorb significant amounts of point defects created inside the material by processes such as irradiation. We propose a novel mechanism of radiation damage healing in metals, which may guide further improvements in radiation resistance of metallic materials through grain boundary engineering.
Ashley Bucsek - One of the best experts on this subject based on the ideXlab platform.
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self assembled periodic nanostructures using martensitic Phase Transformations
Nano Letters, 2020Co-Authors: Abhinav Prakash, Tianqi Wang, Ashley Bucsek, Tristan Truttmann, Alireza Fali, Michele Cotrufo, Hwanhui Yun, Jongwoo Kim, Philip RyanAbstract:We describe a novel approach for the rational design and synthesis of self-assembled periodic nanostructures using martensitic Phase Transformations. We demonstrate this approach in a thin film of ...
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self assembled periodic nanostructures using martensitic Phase Transformations
arXiv: Materials Science, 2020Co-Authors: Abhinav Prakash, Tianqi Wang, Ashley Bucsek, Tristan Truttmann, Alireza Fali, Michele Cotrufo, Hwanhui Yun, Jongwoo Kim, Philip RyanAbstract:We describe a novel approach for the rational design and synthesis of self-assembled periodic nanostructures using martensitic Phase Transformations. We demonstrate this approach in a thin film of perovskite SrSnO3 with reconfigurable periodic nanostructures consisting of regularly spaced regions of sharply contrasted dielectric properties. The films can be designed to have different periodicities and relative Phase fractions via chemical doping or strain engineering. The dielectric contrast within a single film can be tuned using temperature and laser wavelength, effectively creating a variable photonic crystal. Our results show the realistic possibility of designing large-area self-assembled periodic structures using martensitic Phase Transformations with the potential of implementing "built-to-order" nanostructures for tailored optoelectronic functionalities.
