| 1. |
- Adegoke, Olutayo, et al.
(författare)
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Scanning electron microscopy and atom probe tomography characterization of laser powder bed fusion precipitation strengthening nickel-based superalloy
- 2023
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Ingår i: Micron. - 0968-4328 .- 1878-4291. ; 171
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Tidskriftsartikel (refereegranskat)abstract
- Atom probe tomography (APT) was utilized to supplement scanning electron microscopy (SEM) characterizationof a precipitation strengthening nickel-based superalloy, Alloy 247LC, processed by laser powder bed fusion (LPBF). It was observed that the material in the as-built condition had a relatively high strength. Using both SEMand APT, it was concluded that the high strength was not attributed to the typical precipitation strengtheningeffect of γ’. In the absence of γ’ it could be reasonably inferred that the numerous black dots observed in thecells/grains with SEM were dislocations and as such should be contributing significantly to the strengthening.Thus, the current investigation demonstrated that relatively high strengthening can be attained in L-PBF even inthe absence of precipitated γ’. Even though γ’ was not precipitated, the APT analysis displayed a nanometer scalepartitioning of Cr that could be contributing to the strengthening. After heat-treatment, γ’ was precipitated and itdemonstrated the expected high strengthening behavior. Al, Ta and Ti partitioned to γ’. The strong partitioningof Ta in γ’ is indicative that the element, together with Al and Ti, was contributing to the strain-age crackingoccurring during heat-treatment. Cr, Mo and Co partitioned to the matrix γ phase. Hf, Ta, Ti and W were found inthe carbides corroborating previous reports that they are MC.
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| 2. |
- Deirmina, Faraz, et al.
(författare)
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Heat Treatment And Mechanical Properties Of A Novel Ultrahigh Strength Co-free Maraging Steel Fabricated By Additive Manufacturing
- 2021
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Ingår i: Euro PM2021 Congress Proceedings. - : European Powder Metallurgy Association (EPMA).
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Konferensbidrag (refereegranskat)abstract
- We report on the fabrication of a Co-free ultra-high strength maraging steel designed for the laser-powder bed fusion (L-PBF) process using computational approaches. The aim was to obtain an essentially martensitic microstructure after the L-PBF process, and to achieve an ultimate tensile strength (UTS) of minimum 1700 MPa after direct ageing of the as-built microstructure. Microstructural characterization, dilatometry, and tensile and impact toughness tests were used to evaluate the employed approach.
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| 3. |
- Deirmina, Faraz, et al.
(författare)
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Influence of boron on the stress-rupture behavior of an additively manufactured Hastelloy X
- 2023
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 863
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Tidskriftsartikel (refereegranskat)abstract
- The influence of minor additions of boron and the as-built (AB) microstructure on stress-rupture behavior of a modified crack-free Hastelloy X fabricated by laser powder bed fusion (L-PBF) was investigated. Isothermal stress rupture tests were performed at 816 degrees C under a static tensile load of 103 MPa. Micro-void formation in the vicinity of carbide precipitates and their coalescence was only observed at chevron-like high-angle grain boundaries, characteristic of L-PBF process. These grain boundaries, laying on the planes with maximum resolved shear stress with respect to the loading direction, directly governed the intergranular crack propagation. In view of the fracture mechanism and the time to rupture, increasing boron content significantly improves timeto-rupture through a diffusion-controlled mechanism by hindering the carbon diffusion to the grain boundaries. Adequate additions of boron (>10 ppm) guarantee the stress-rupture properties (strength) of the AB components without the need for additional post-thermal treatments. Further increase in boron content (i.e., 30 ppm), led to about five times increase in time to rupture (500 h vs. 110 h), and significantly improved creep elongation (30% vs. 9%) compared with the low boron alloy.
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