Publikationer från Malmö universitet
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  • 1.
    Fisk, Martin
    et al.
    Malmö högskola, Teknik och samhälle (TS).
    Andersson, Joel
    du Rietz, Rickard
    Malmö högskola, Teknik och samhälle (TS).
    Haas, Sylvio
    Hall, Stephen
    Precipitate evolution in the early stages of ageing in Inconel 718 investigated using small-angle x-ray scattering2014Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 612, s. 202-207Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Microstructural evolution during the early stages of ageing (less than one hour) in a Ni–Cr–Fe based superalloy Inconel 718 (IN718) has been investigated using Small-Angle X-ray Scattering (SAXS). The effects of precipitate kinetics on the precipitate size distribution are compared indirectly with SAXS measurements by using Vickers microhardness data. The microhardness increased after 4 min of ageing at a temperature of 760 °C, although the recorded SAXS data did not reveal the precipitate size distribution. This indicates that the precipitates had not evolved enough to be detected, but still a small number of precipitates increased the yield strength. After ageing the alloy for the shortest period for which data were available, 8 min, clear evidence of precipitates could be found from the SAXS data, showing that the γ″-γ″- precipitates are about 6 nm in width and 3 nm in height.

  • 2. Haas, Sylvio
    et al.
    Andersson, Joel
    Fisk, Martin
    Malmö universitet, Fakulteten för teknik och samhälle (TS), Institutionen för materialvetenskap och tillämpad matematik (MTM).
    Park, Jun-Sang
    Lienert, Ulrich
    Correlation of precipitate evolution with Vickers hardness in Haynes® 282® superalloy: In-situ high-energy SAXS/WAXS investigation2018Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 711, s. 250-258Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this work is to characterize the precipitation kinetics in Haynes® 282® superalloys using in-situ high-energy Small Angle X-ray Scattering (SAXS) together with Wide Angle X-ray Scattering (WAXS). The phases identified by WAXS include γ (matrix), γ′ (hardening precipitates), MC (metallic carbides), and M23C6/M6C (secondary metallic carbides). The γ’-precipitates are spheroids with a diameter of several nanometres, depending on the temperature and ageing time. From the SAXS data, quantitative parameters such as volume fraction, number density and inter-particle distance were determined and correlated with ex-situ Vickers microhardness measurements. The strengthening components associated with precipitates and solid solutions are differentiated using the measured Vickers microhardness and SAXS model parameters. A square root dependence between strengthening attributable to the precipitates and the product of volume fraction and mean precipitate radius is found. The solid solution strengthening component correlates with the total volume fraction of precipitates.

  • 3.
    Pederson, R.
    et al.
    Luleå University of Technology, Division of Materials Science, S-97187 Luleå, Sweden; Volvo Aero Corporation, Department of Materials Technology, S-46181 Trollhättan, Sweden.
    Niklasson, F.
    Volvo Aero Corporation, Department of Materials Technology, S-46181 Trollhättan, Sweden.
    Skystedt, F.
    Volvo Aero Corporation, Department of Materials Technology, S-46181 Trollhättan, Sweden.
    Warren, R.
    Malmö högskola, Teknik och samhälle (TS).
    Microstructure and mechanical properties of friction- and electron-beam welded Ti-6Al-4V and Ti-6Al-2Sn-4Zr-6Mo2012Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 552, s. 555-565Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work presents mechanical data and microstructural characterization of friction welded (FRW) and electron beam welded (EBW) post weld heat treated (PWHT) specimens of Ti-6Al-2Sn-4Zr-6Mo and Ti-6Al-4V. PWHT Ti6246/Ti6246 welds and Ti64/Ti6246 welds were evaluated with tensile-, creep-. Charpy-V, and microhardness tests. The PWHT treatments were 593 degrees C/2 h, 640 degrees C/2 h and 704 degrees C/2 h, respectively. The microstructure of the different weld types and alloy combinations where examined and characterized using optical microscope and SEM. Tensile strength and yield strength were within specification for both material combinations. The elongation for Ti6246 welded to Ti6246 is below specification. Only small variations in tensile properties were found for the different PWHTs. Fracture occurred in base material of the Ti64 alloy for the combination of Ti64 welded to Ti6246. Charpy-V tests shows that the welds are more brittle compared with the base material. The largest difference was found in Ti6246 welded to Ti6246. No significant variation in creep properties for the different PWHTs has been found. Ti64 welded to Ti6246 shows poor creep properties due to the high testing temperature for the Ti64 alloy. Ti6246 welded to Ti6246 shows good creep properties compared to the base material. The general trend for the weld microhardness was a decreasing hardness with increasing PWHT temperature. One exception though was the FRW Ti64/Ti6246 combination, were the hardness of the Ti6246 side of the HAZ, close to the interface between the two alloys, was highest after a PWHT temperature of 593 degrees C, then decreasing in hardness for 640 degrees C, not PWHT and being least hard for the PWHT temperature of 704 degrees C. The hardness of the Ti64 base material showed no decrease after the PWHTs, but the hardness of the Ti6246 bulk material decreased after PWHT at 704 degrees C. (c) 2012 Elsevier B.V. All rights reserved.

  • 4. Singh, Ram N.
    et al.
    Khandelwal, HK
    Bind, AK
    Sunil, S.
    Ståhle, Per
    Malmö högskola, Teknik och samhälle (TS).
    Influence of stress field of expanding and contracting plate shaped precipitate on hydride embrittlement of Zr-alloys2013Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 579, s. 157-163Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stress fields of expanding (precipitation) and contracting (dissolution) hydride plates were computed by finite element method using Zr–H solid solution and hydride properties at 25, 200 and 400 °C for fully and semi-constrained hydride plates. For the first time simultaneous hydride expansion and matrix contraction and vice-versa have been considered in a simulation of hydride precipitation and dissolution, respectively. It was observed that a fully constrained expanding hydride plate exerts a tensile stress field in the matrix close to the edge of the hydride plate while a partially contracting hydride plate exerts a tensile stress field in the hydride plate as well as a large compressive stress in the surrounding matrix close to the edge of the hydride plate. It is suggested that a compressive stress component in the matrix acting normal to a partially shrinking hydride plate could possibly explain an enhanced resistance to hydride embrittlement of Zr-alloy at elevated temperature.

  • 5. Singh, Ram N
    et al.
    Ståhle, Per
    Malmö högskola, Teknik och samhälle (TS).
    Chakravartty, JK
    Shmakov, AA
    Threshold stress intensity factor for delayed hydride cracking in Zr-2.5%Nb pressure tube alloy2009Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 523, nr 1-2, s. 112-117Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Delayed hydride cracking (DHC) velocity was determined at 203, 227, 250 and 283 °C using 17 mm width curved compact toughness specimens machined from an unirradiated Zr–2.5 wt.% Nb pressure tube spool, gaseously charged with 60 ppm of hydrogen by weight. Single CT specimen was used to determine DHC velocity at a constant temperature for a range of stress intensity factor (KI) obtained by load drop method. For a given temperature and KI > 15 MPa m1/2, DHC velocity was found to be practically independent of KI. For 15 > KI > 10 MPa m1/2, DHC velocity decreased significantly with decrease in stress intensity factor and extrapolation of the data suggested the threshold stress intensity factor to be about 9–11 MPa m1/2 in the aforementioned temperature range. The activation energy associated with DHC was observed to be 35.1 kJ/mol.

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