| 1. |
- Lazar, Isac, et al.
(author)
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Characterisation of worn WC tool using STEM-EDS aided by principal component analysis
- 2021
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In: Journal of Microscopy. - : Wiley. - 0022-2720 .- 1365-2818. ; 283:1, s. 64-73
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Journal article (peer-reviewed)abstract
- Interdiffusion and chemical reactions contribute to tool wear in metal machining. Increased understanding of these processes, through characterisation of worn tools, can facilitate design of more resilient materials through chemical and diffusional passivation. However, the unknown reaction conditions, the large number of elements, and the formation of interspersed phases makes for a complex analysis. Here, we demonstrate the use of scanning transmission electron microscopy and energy dispersive X-ray spectroscopy for characterising the interaction layer between a titanium alloy and a cemented carbide tool. Principal component analysis is used to find chemical correlations and help separate signals from embedded phases. Crucially, we evaluate the required X-ray count statistics from simulated spectrum images and theory prior to the experiment. We find no indications of intermediate phases between the original WC and the metallic W interaction layer. Furthermore, we find enrichment of minor constituents in the titanium alloy closest to the tool which alter the solubility of out-diffusing species, suggesting strong interrelations between the diffusion processes.
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| 2. |
- Lazar, Isac, et al.
(author)
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Diffusion Bonding 321-Grade Stainless Steel : Failure and Multimodal Characterization
- 2024
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In: Microscopy and Microanalysis. - : Oxford University Press. - 1431-9276 .- 1435-8115. ; 30:2, s. 192-199
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Journal article (peer-reviewed)abstract
- Vacuum diffusion-bonded printed circuit heat exchangers are an attractive choice for the high-temperature, high-pressure demands of next-generation energy applications. However, early reports show that the high-temperature materials desired for these applications suffer from poor bond strengths due to precipitation at the bond line, preventing grain boundary migration. In this study, a diffusion bond of the high-temperature stainless steel grade 321H is investigated, and poor mechanical properties are found to be caused by Ti(C, N) precipitation at the bond line. Through in situ studies, it is found that Ti diffuses from the bulk to the mating surfaces at high temperatures. The Ti subsequently precipitates and, for the first time, an interaction between Ti(C, N) and Al/Mg-oxide precipitates at the bond line is observed, where Ti(C, N) nucleates on the oxides forming a core-shell structure. The results indicate that small amounts of particular alloying elements can greatly impact diffusion bond quality, prompting further research into the microstructural evolution that occurs during bonding conditions.
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| 3. |
- Lazar, Isac, et al.
(author)
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In situ imaging of precipitate formation in additively manufactured al-alloys by scanning X-ray fluorescence
- 2024
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In: European Journal of Materials. - 2688-9277. ; 4:1
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Journal article (peer-reviewed)abstract
- Al-alloys incorporating Mn, Cr and Zr, tailored for powder bed fusion-laser beam processes with solubilities three times equilibrium have recently been developed that yield a high strength. Mn and Cr-enriched precipitates that form during printing and heat treatment influence the material’s mechanical properties hence making it important to understand their kinetics. In this study, direct imaging of these precipitates was accomplished through the utilisation of in situ synchrotron-based scanning X-ray fluorescence. During heat treatment, a selective accumulation of Cr and Mn in two distinct types of precipitates at grain boundaries was observed. Additionally, the microstructure at the melt-pool boundary, containing precipitates found in the as-printed state, remains thermally stable during the heat treatment. Both these results shed light on the active role Cr plays in the precipitation kinetics of the material. The study also demonstrates the significant value of employing high-sensitivity in-situ X-ray fluorescence microscopy in exploring the kinetics of sub-micrometre scale precipitation.
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| 4. |
- Yue, Xiaoqi, et al.
(author)
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Unveiling nano-scale chemical inhomogeneity in surface oxide films formed on V- and N-containing martensite stainless steel by synchrotron X-ray photoelectron emission spectroscopy/microscopy and microscopic X-ray absorption spectroscopy
- 2025
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In: Journal of Materials Science & Technology. - : Chinese Society of Metals. - 1005-0302. ; 205, s. 191-203
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Journal article (peer-reviewed)abstract
- Nano-scale chemical inhomogeneity in surface oxide films formed on a V- and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron- based hard X-ray Photoelectron emission spectroscopy (HAXPES) and microscopy (HAXPEEM) as well as microscopic X-ray absorption spectroscopy (μ-XAS) techniques. The results reveal the inhomogeneity in the oxide films on the micron-sized Cr2N- and VN-type particles, while the inhomogeneity on the martensite matrix phase exists due to localised formation of nano-sized tempering nitride particles at 600 °C. The oxide film formed on Cr2N-type particles is rich in Cr2O3 compared with that on the martensite matrix and VN-type particles. With the increase of tempering temperature, Cr2O3 formation is faster for the oxidation of Cr in the martensite matrix than the oxidation of Cr nitride-rich particles.
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