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In-situ synchrotron radiation study of the aging response of Ti-6Al-4V alloy with different starting microstructures
No full textThe aging behavior of a Ti-6Al-4V alloy with different starting microstructures was evaluated by means ofsynchrotron X-ray diffraction, scanning-transmission electron microscopy and micro-hardness measurements.Initial microstructures were produced by thermal and thermomechanical treatments and comprised differentmorphologies of α phase (martensitic, lamellar, bimodal and globular), as well as the presence or absence of theβ phase. Results show that one or more of the following phenomena can take place during aging and contributeto the hardening of the alloy: β decomposition into fine secondary α laths; transformation of the metastablemartensitic α′ into the equilibrium α phase; and precipitation of the intermetallic TiAl. The composition anddistribution of the β phase was shown to affect the precipitation of secondary α during aging, while the compositionof the α phase plays a key role on the formation of TiAl. In situ X-ray diffraction studies of the earlystages of aging show the kinetics of the α′→α conversion by the reduction in FWHM of XRD reflections, indicatethe contribution to hardening by the increase of the c/a ratio and the consequent limitation of active slip systemsand depict the chemical homogenization and decomposition of the β phase
Ruthenium under ultrafast laser excitation: Model and dataset for equation of state, conductivity, and electron-ion coupling
No full textInteraction of ultrashort laser pulses with materials can bring the latter to highly non-equilibrium states, where the electronic temperature strongly differs from the ionic one. The properties of such excited material can be considerably different from those in a hot, but equilibrium state. The reliable modeling of laser-irradiated target requires careful analysis of its properties in both regimes. This paper reports a procedure which provides the equations of state of ruthenium using density functional theory calculations. The obtained data are fitted with analytical functions. The constructed equations of state are applicable in the one- and two-temperature regimes and in a wide range of densities, temperatures and pressures. The electron thermal conductivity and electron-phonon coupling factor are also calculated. The obtained analytical expressions can be used in two-temperature hydrodynamics modeling of Ru targets pumped by ultrashort laser pulses. The data is related to the research article “Similarity in ruthenium damage induced by photons with different energies: From visible light to hard X-rays” [1]
In situ observations of continuous cooling transformations in low alloy steels
No full textA typical heat treatment for a low alloy steel will often involve a quenching heat treatment step, in which the steel is cooled from high temperatures to trigger austenite decomposition. The particular cooling rate during the quenching step can have a marked influence on the phase transformations taking place, and the resulting steel microstructure and mechanical properties. Although methods such as dilatometry have been available for many decades to characterise continuous-cooling transformation (CCT) behaviour in steels, the use of in situ synchrotron X-ray diffraction (SXRD) to elucidate CCT behaviour in a systematic way has not been reported.In this work, we measure the CCT behaviours of two pressure vessel steels in situ using simultaneous dilatometry and SXRD. Both steels are subject to austenitisation followed by quenching at a range of cooling rates. On comparing results from SXRD and dilatometry, it is found that recorded starts of transformations appear to be in good agreement. However, calculations of phase fractions derived from dilatometry data significantly overestimate the fraction of ferrite that forms in comparison to SXRD when the formation involves the partitioning of carbon. This happens for two reasons: first, because the method to extract ferrite volume fractions from dilatometry data generally ignores the presence of any retained austenite at low temperatures, and second, because analyses of dilatometry data do not account for the expansion of the austenite during transformation due to enrichment in carbon. This enrichment leads to an increase in strain, and the standard analysis method falsely attributes this increase to ferrite formation, thereby overestimating it. The results highlight that caution must be exercised when interpreting the results of dilatometry, since levels of ferrite (especially diffusively-formed) and retained austenite are important quantities for the prediction of mechanical behaviour, and they are not readily quantified by the analysis of dilatometry data alone
Equivalence of Gouy and Courant-Snyder Phase
No full textThe generation of electron vortex beams and the conversion of these beams into beams without angular momentum by means of astigmatic optical systems, or vice versa, has been pursued in the optical and the electron microscopy community, but also in the accelerator community in the past decades. Despite different conceptual approaches similar results have been achieved. By adapting the Courant-Snyder theory, which was originally developed for the description of optical properties of accelerators, to the description of laser modes, it is shown that identical mode converters have been developed for charged particle and for light beams, and that the Courant-Snyder phase and the Gouy phase are equivalent
Enabling time-resolved 2D spatial-coherence measurements using the Fourier-analysis method with an integrated curved-grating beam monitor
No full textDirect 2D spatial-coherence measurements are increasingly gaining importance at synchrotron beamlines, especially due to present and future upgrades of synchrotron facilities to diffraction-limited storage rings. We present a method to determine the 2D spatial coherence of synchrotron radiation in a direct and particularly simple way by using the Fourier-analysis method in conjunction with curved gratings. Direct photon-beam monitoring provided by a curved grating circumvents the otherwise necessary separate determination of the illuminating intensity distribution required for the Fourier-analysis method. Hence, combining these two methods allows for time-resolved spatial-coherence measurements. As a consequence, spatial-coherence degradation effects caused by beamline optics vibrations, which is one of the key issues of state-of-the-art X-ray imaging and scattering beamlines, can be identified and analyzed
Model-independent energy budget of gravitational waves from a cosmological phase transition
No full textCosmological first-order phase transitions are predicted by many new physics models and could have facilitated the generation of the baryon asymmetry. Gravitational waves are a promising tool to study phase transitions in the early universe. In this talk, I focus on the energy budget of such phase transitions, which is an important factor in the prediction of the gravitational wave spectrum. Formerly, this analysis was based mostly on simplified models, such as the bag equation of state. In this talk, I'll present a model-independent computation of the energy budget, which only depends on the speed of sound in the broken phase and a newly defined phase transition strength parameter. I compare our new approach to approximations found in the literature and show that the new, model-independent analysis is accurate to the percent level, whereas the former approaches give at best the right order of magnitude
Determination of Temperature-Dependent Elastic Constants of Steel AISI 4140 by Use of In Situ X-ray Dilatometry Experiments
No full textIn situ dilatometry experiments using high energy synchrotron X-ray diffraction in transmission mode were carried out at the high energy material science beamline P07@PETRAIII atDESY (Deutsches Elektronen Synchrotron) for the tempering steel AISI 4140 at defined mechanical loading. The focus of this study was on the initial tempering state ( f errite) and the hardened state (martensite). Lattice strains were calculated from the 2D diffraction data for different hkl planes and from those temperature-dependent lattice plane specific diffraction elastic constants (DECs) were determined. The resulting coupling terms allow for precise stress analysis for typical hypoeutectoid steels using diffraction data during heat treatment processes, that is, for in situ diffraction studies during thermal exposure. In addition, by averaging hkl specific Young's moduli and Poisson ratios macroscopic temperature-dependent elastic constants were determined. In conclusion a novel approach for the determination of phase-specific temperature-dependent DECs was suggested using diffraction based dilatometry that provides more reliable data in comparison to conventional experimental procedures. Moreover, the averaging of lattice plane specific results from in situ diffraction analysis supply robust temperature-dependent macroscopic elastic constants for martensite and ferrite as input data for heat treatment process simulations
Novel intermetallic-reinforced near-α Ti alloys manufactured by spark plasma sintering
No full textNear- Ti alloys are ideal candidates for high-temperature aerospace, automotive and nautical propulsion systems due to their high strength, low density and good corrosion resistance. However, the maximum service temperature of the well-known near- alloy Ti6242S is limited to about 540 °C. By adding, for example, intermetallic -TiAl based alloy particles to Ti6242S powder a significant increase in yield strength up to 650 °C can be achieved by means of spark plasma sintering, along with sufficient room temperature ductility. In this study, investigations on the underlying strengthening mechanisms were carried out. For this purpose, mechanical tests and detailed microstructural characterization were performed.Spark plasma sintering at 1150 °C of powder blends with 10 m.% spherical -TiAl based powder (<20 μm) leads to a homogeneous dissolution of the TiAl particles in the matrix material and a refinement of the lamellar microstructure. Due to the formation of ordered intermetallic α-TiAl precipitates, which are completely stable up to 670 °C in the newly evolved Ti-8.3Al-1.8Sn-3.7Zr-2.0Mo-0.9Nb-0.08Si alloy (m.%), the creep resistance at 600 °C has been increased significantly. In the B containing variant, it was found that finely distributed titanium borides TiB formed in the Ti6242 matrix and led to an even more pronounced refinement of the microstructure. For B additions of 1 m.%, however, the creep resistance at 600 °C is reduced compared to the other alloys, but the strength is increased up to 500 °C
Giant electrochemical actuation in a nanoporous silicon-polypyrrole hybrid material
No full textThe absence of piezoelectricity in silicon makes direct electromechanical applications of this mainstream semiconductorimpossible. Integrated electrical control of the silicon mechanics, however, would open up new perspectivesfor on-chip actuorics. Here, we combine wafer-scale nanoporosity in single-crystalline silicon withpolymerization of an artificial muscle material inside pore space to synthesize a composite that shows macroscopicelectrostrain in aqueous electrolyte. The voltage-strain coupling is three orders of magnitude larger than the best-performingceramics in terms of piezoelectric actuation. We trace this huge electroactuation to the concerted actionof 100 billions of nanopores per square centimeter cross section and to potential-dependent pressures of up to150 atmospheres at the single-pore scale. The exceptionally small operation voltages (0.4 to 0.9 volts), along withthe sustainable and biocompatible base materials, make this hybrid promising for bioactuator applications
In situ X-ray measurements over large Q-space to study the evolution of oxide thin films prepared by RF sputter deposition
No full textSputter deposition is a versatile and industrially important deposition technique for thin films, with increasing demand for matching the characteristics of thin film materials to specific requirements. The actual film properties are largely determined by sputtering parameters such as pressure conditions, temperature and power settings. By means of various X-ray diffraction and scattering techniques, it is shown that the characterization of film formation and growth is feasible in real time at synchrotron sources, thus adding an important dimension to the fundamental understanding of the evolution of thin film microstructure. In particular, grazing incidence small-angle X-ray scattering, grazing incidence X-ray powder diffraction and X-ray reflectometry are used in a complementary manner to study the influence of deposition temperature and substrate choice on the crystallization kinetics and growth of polycrystalline BaTiO films