Browsing by Author "Ren, Y"
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- ItemChallenges of measuring residual stresses in large girth welded pipe spools by neutron diffraction(Materials Research Forum LLC, 2016-07-03) Ren, Y; Paradowska, AM; Eren, E; Wang, BIn this paper, welding induced residual stresses in a welded API 5L X65 girth pipe spools are discussed in as-welded and in local post weld heat treated conditions. Stress measurements were carried out non-destructively using the neutron diffraction technique. For such large-scale components residual stress measurements require significant preparation and planning. First of all, a choice of stress free lattice spacing value, discussed extensively, is of great importance for the evaluation of residual strains and stresses correctly. Besides, the use of a virtual instrument (SSCANSS software) can optimize measurements for distorted or undistorted large components with or without complex details. Moreover, the well-planned “window” cut through the thickness greatly reduced measurement time. A number of points were measured across the weld, HAZ and the parent material. Measurement results showed that residual stresses in the as-welded condition was lower than the yield strength of the material, and significant relaxation was also observed in the post weld heat treated samples. © The Authors
- ItemGrain size and structure distortion characterization of α-MgAgSb thermoelectric material by powder diffraction(IOP Publishing, 2020-05-21) Li, XY; Zhang, Z; He, L; Avdeev, M; Ren, Y; Zhao, H; Wang, FNanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg0.97Sb0.99, with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. Here, we report the average grain size of 24–28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron x-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg0.97Sb0.99. © 2020 Chinese Physical Society and IOP Publishing Ltd
- ItemHidden amorphous phase and reentrant supercooled liquid in Pd-Ni-P metallic glasses(International Conference on Neutron Scattering, 2017-07-12) Lan, S; Ren, Y; Wei, X; Wang, B; Gilbert, EP; Shibayama, T; Watanabe, S; Ohnuma, M; Wang, XLAn anomaly in differential scanning calorimetry has been reported in a number of metallic glass materials in which a broad exothermal peak was observed between the glass and crystallization temperatures. The mystery surrounding this calorimetric anomaly is epitomized by half century long studies of Pd-Ni-P metallic glasses, arguably the best glass-forming alloys [1]. Here we show,using a suite of in-situ experimental techniques, including simultaneous small-angle neutron scattering-calorimetry, high-energy X-ray diffraction, and electron microscopy, that Pd-Ni-P alloys have a hidden amorphous phase in the supercooled liquid region. The anomalous exothermal peak is the consequence of a polyamorphous phase transition between two supercooled liquids, involving a change in the packing of atomic clusters over medium-range length scales as large as 18Å. With further temperature increase,the alloy reenters the supercooled liquid phase which forms the room-temperature glass phase upon quenching. The outcome of this study raises a possibility to manipulate the structure and hence the stability of metallic glasses through heat-treatment.
- ItemOn disrupting the Na+-ion/vacancy ordering in P2-type sodium–manganese–nickel oxide cathodes for Na+-ion batteries(American Chemical Society, 2018-09-06) Gutierrez, A; Dose, WM; Borkiewicz, O; Guo, F; Avdeev, M; Kim, SJ; Fister, TT; Ren, Y; Bareño, J; Johnson, CSAn investigation of the electrochemical and structural properties of layered P2–Na0.62Mn0.75Ni0.25O2 is presented. The effect of changing the Mn/Ni ratio (3:1) from what is found in Na0.67Mn0.67Ni0.33O2 (2:1) and consequently the introduction of a third metal center (Mn3+) was investigated. X-ray powder diffraction (in situ and ex situ) revealed the lack of Na+-ion/vacancy ordering at the relevant sodium contents (x = 0.33, 0.5, and 0.67). Mn3+ in Na0.62Mn0.75Ni0.25O2 introduces defects into the Ni–Mn interplane charge order that in turn disrupts the ordering within the Na-plane. The material underwent P2–O2 and P2–P2′ phase transitions at high (4.2 V) and low (∼1.85 V) voltages, respectively. The material was tested at several different voltage ranges to understand the effect of the phase transitions on the capacity retention. Interestingly, the inclusion of both phase transitions demonstrated comparable cycling performance to when both phase transitions were excluded. Last, excellent rate performance was demonstrated between 4.3 and 1.5 V with a specific capacity of 120 mA h/g delivered at 500 mA/g current density. © 2018 American Chemical Society
- ItemPbZr1-xTixO3 by soft synthesis: structural aspects(American Physical Society, 2007-07) Pradhan, SK; Gateshki, M; Niederberger, M; Ren, Y; Petkov, VThe structural aspects of a soft synthetic route employed to obtain fine crystallite PbZr1−xTixO3 (x=0,0.5,1) powders are revealed by total x-ray diffraction and atomic pair distribution function analysis. It is found that the atomic-scale structure of the intermediate, highly disordered phase the route passes through resembles but is not exactly of the targeted, perovskite-type structure. It is suggested that future synthesis efforts are directed toward closing the observed “structure gap” as much as possible. © 2007, American Physical Society
- ItemResidual stress state of X65 pipeline girth welds before and after local and furnace post weld heat treatment(ASME, 2017-08-01) Ren, Y; Paradowska, AM; Wang, B; Eren, E; Janin, YJThis research investigated the effects of global (in other words, furnace-based) and local post weld heat treatment (PWHT) on residual stress (RS) relaxation in API 5L X65 pipe girth welds. All pipe spools were fabricated using identical pipeline production procedures for manufacturing multipass narrow gap welds. Nondestructive neutron diffraction (ND) strain scanning was carried out on girth welded pipe spools and strain-free comb samples for the determination of the lattice spacing. All residual stress measurements were carried out at the KOWARI strain scanning instrument at the Australian Nuclear Science and Technology Organization (ANSTO). Residual stresses were measured on two pipe spools in as-welded condition and two pipe spools after local and furnace PWHT. Measurements were conducted through the thickness in the weld material and adjacent parent metal starting from the weld toes. Besides, three line-scans along pipe length were made 3 mm below outer surface, at pipe wall midthickness, and 3 mm above the inner surface. PWHT was carried out for stress relief; one pipe was conventionally heat treated entirely in an enclosed furnace, and the other was locally heated by a flexible ceramic heating pad. Residual stresses measured after PWHT were at exactly the same locations as those in as-welded condition. Residual stress states of the pipe spools in as-welded condition and after PWHT were compared, and the results were presented in full stress maps. Additionally, through-thickness residual stress profiles and the results of one line scan (3 mm below outer surface) were compared with the respective residual stress profiles advised in British Standard BS 7910 “Guide to methods for assessing the acceptability of flaws in metallic structures” and the UK nuclear industry's R6 procedure. The residual stress profiles in as-welded condition were similar. With the given parameters, local PWHT has effectively reduced residual stresses in the pipe spool to such a level that it prompted the thought that local PWHT can be considered a substitute for global PWHT. © 2021 The American Society of Mechanical Engineers
- ItemUltralow thermal conductivity from transverse acoustic phonon suppression in distorted crystalline α-MgAgSb(Springer Nature, 2020-02-18) Li, XY; Liu, PF; Zhao, EY; Zhang, ZG; Guidi, T; Le, MD; Avdeev, M; Ikeda, K; Otomo, T; Kofu, M; Nakajima, K; Chen, J; He, LH; Ren, Y; Wang, XL; Wang, BT; Ren, ZF; Zhao, HZ; Wang, FWLow thermal conductivity is favorable for preserving the temperature gradient between the two ends of a thermoelectric material, in order to ensure continuous electron current generation. In high-performance thermoelectric materials, there are two main low thermal conductivity mechanisms: the phonon anharmonic in PbTe and SnSe, and phonon scattering resulting from the dynamic disorder in AgCrSe2 and CuCrSe2, which have been successfully revealed by inelastic neutron scattering. Using neutron scattering and ab initio calculations, we report here a mechanism of static local structure distortion combined with phonon-anharmonic-induced ultralow lattice thermal conductivity in α-MgAgSb. Since the transverse acoustic phonons are almost fully scattered by the compound’s intrinsic distorted rocksalt sublattice, the heat is mainly transported by the longitudinal acoustic phonons. The ultralow thermal conductivity in α-MgAgSb is attributed to its atomic dynamics being altered by the structure distortion, which presents a possible microscopic route to enhance the performance of similar thermoelectric materials. © The Author(s) 2020.