Browsing by Author "Ma, Y"

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    Atomic origins of radiation-induced defects and interfacial strengthening in additively manufactured titanium aluminide alloy irradiated with Kr-ions at elevated temperature
    (Elsevier, 2019-04-04) Zhu, HL; Qin, MJ; Aughterson, RD; Wei, T; Lumpkin, GR; Ma, Y; Li, HJ
    The irradiation microstructure of the additively manufactured titanium aluminide (TiAl) alloy subjected to in situ transmission electron microscope (TEM) irradiation with 1 MeV Kr ions at the elevated temperature of 873K was investigated. Triangle and large hexagon shaped volume defects were observed within the γ-TiAl phase in the TEM images of the irradiated microstructure. High resolution TEM images and composition analyses revealed the volume defects were vacancy-type stacking fault tetrahedrals (SFTs). Molecular dynamic simulations showed that the increased diffusion coefficient at the elevated temperature promoted the movement and aggregation of vacancies, leading to the formation and growth of SFTs in the irradiated FCC γ phase. The lamellar interfaces in the irradiation microstructure were more effective for acting as strong sinks to absorb the primary point defects and defect clusters at the elevated temperature. The initial defects at the interfaces of the additively manufactured TiAl alloy enhanced the sink strength of the material and greatly refined SFTs near the lamellar interfaces. © 2019, The Authors.
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    Corrigendum to ‘Atomic origins of radiation-induced defects and the role of lamellar Interfaces in radiation damage of titanium aluminide alloy irradiated with Kr-ions at elevated temperature’ [Acta Mater. 172 (2019) 72–83]
    (Elsevier, 2020-09-15) Zhu, HL; Qin, MJ; Aughterson, RD; Wei, T; Lumpkin, GR; Ma, Y; Li, HJ
    The authors regret that the scale bars in Figure 8(c) BF-STEM and 8(d) HAADF-STEM for volume defects near the γ/γ lamellar interfaces in the Kr-ion irradiated microstructure of the TiAl alloy irradiated at 873 K are mislabelled. The authors would like to apologise for any inconvenience caused. © 2020 Acta Materialia Inc. Published by Elsevier Ltd.
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    Evolution of sandstone peak-forest landscapes – insights from quantifying erosional processes with cosmogenic nuclides
    (Wiley, 2017-10-16) May, JH; Huang, HQ; Fujioka, T; Fink, D; Codilean, AT; Yu, GA; Ma, Y; Wulf, G; Gu, J
    The sandstone peak-forest landscape in Zhangjiajie UNESCO Global Geopark of Hunan Province, China, is characterized by >3000 vertical pillars and peak walls of up to 350 m height, representing a spectacular example of sandstone landform variety. Few studies have addressed the mechanisms and timescales of the longer-term evolution of this landscape, and have focused on fluvial incision. We use in situ cosmogenic nuclides combined with GIS analysis to investigate the erosional processes contributing to the formation of pillars and peak-forests, and discuss their relative roles in the formation and decay of the landscape. Model maximum-limiting bedrock erosion rates are the highest along the narrow fluvial channels and valleys at the base of the sandstone pillars (~83–122 mm kyr−1), and lowest on the peak wall tops (~2.5 mm kyr−1). Erosion rates are highly variable and intermediate along vertical sandstone peak walls and pillars (~30 to 84 mm kyr−1). Catchment-wide denudation rates from river sediment vary between ~26 and 96 mm kyr−1 and are generally consistent with vertical wall retreat rates. This highlights the importance of wall retreat for overall erosion in the sandstone peak-forest. In combination with GIS-derived erosional volumes, our results suggest that the peak-forest formation in Zhangjiajie commenced in the Pliocene, and that the general evolution of the landscape followed our sequential refined model: (i) slow lowering rates following initial uplift; (ii) fast plateau dissection by headward knickpoint propagation along joints and faults followed by; (iii) increasing contribution of wall retreat in the well-developed pillars and peak-forests and a gradual decrease in overall denudation rates, leading to; (iv) the final consumption of pillars and peak-forests. Our study provides an approach for quantifying the complex interplay between multiple geomorphic processes as required to assess the evolutionary pathways of other sandstone peak-forest landscapes across the globe. Copyright © 2017 John Wiley & Sons, Ltd.
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    Neutron diffraction residual stress determinations on Intermetallic alloy components produced by wire-arc additive manufacturing (WAAM)
    (Elsevier, 2019-10-01) Shen, C; Reid, M; Liss, KD; Pan, ZX; Ma, Y; Cuiuri, D; van Duin, S; Li, HJ
    The Wire-Arc Additive Manufacturing (WAAM) process is an increasingly attractive method for producing porosity-free metal components. However, the residual stresses and distortions resulting from the WAAM process are major concerns as they not only influence the part tolerance but can also cause premature failure in the final component during service. The current paper presents a method for using neutron diffraction to measure residual stresses in Fe3Al intermetallic wall components that have been in-situ additively fabricated using the WAAM process with different post-production treatments. By using averaging methods during the experimental setup and data processing, more reliable residual stress results are obtained from the acquired neutron diffraction data. In addition, the present study indicates that the normal residual stresses are significant compared to normal butt/fillet welding samples, which is caused by the large temperature gradient in this direction during the additive layer depositions. © 2019 Elsevier B.V.
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    Neutron diffraction residual stress determinations on Intermetallic alloy components produced by wire-arc additive manufacturing (WAAM)
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-01) Chen, S; Ma, Y; Li, HJ; Mark, R; Paradowska, AM
    Intermetallic alloys such as aluminides of titanium, nickel and iron exhibit an attractive combination of physical and mechanical properties such as high melting point, low density, high strength, good oxidation, and creep resistance, due to their strong internal order and mixed bonding. However, the properties of these materials are often obtained at a cost in terms of ease of manufacturing. In recent years the WAAM process has been successfully applied to in-situ produce TiAl and Fe3Al intermetallic components with designed chemical compositions. One of the major concern is residual stresses (RS) distribution in the WAAM fabricated components as it not only influences the part tolerance but also cause premature failure. The neutron diffraction technique has been recognised as the most precise and reliable method of mapping sub-surface RS in components for both academic and industrial-economic relevance. Considering the outstanding capability of obtaining RS non-destructively deep within the interior of components, our study utilised neutron diffraction technique to conduct RS measurement by the angular scanning instrument KOWARI. Furthermore, an averaging method has been developed for the WAAM multi-bead build up intermetallic alloys with large grain size. With the averaging method applied during experimental setup and data processing, reasonable residual stress results have been obtained from the acquired neutron diffraction data.