| 1. |
- Shvab, Ruslan, 1985, et al.
(författare)
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Prediction, Formation and Analysis of Microstructure of High Chromium-Alloyed PM Stainless Steel Sintered in Different Atmospheres
- 2014
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Ingår i: Powder Metallurgy Progress. - 1339-4533. ; 14:2, s. 99-107
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of the microstructure of high chromium alloyed PM stainless steel was performed in several stages. The equilibrium phase diagrams and mass fractions of phases for alloy Fe-20%Cr-17%(Ni,Si,Mn)-C were calculated using Thermo-Calc and JMatPro software. All calculations were done for two nitrogen content levels, which correspond to compositions of material sintered in N2-H2 and atmosphere without nitrogen (pure H2 and argon), respectively. According to calculations, austenite and chromium carbides are in equilibrium if sintering is an in atmosphere without nitrogen, and austenite with chromium carbonitrides and carbides for material sintered in N2-H2 atmosphere. The microstructure of the materials is affected by the sintering atmosphere, especially at the surface. The influence of sintering atmospheres on microstructure was analyzed. The results showed that the predicted microstructure is in good agreement with observed real microstructure.
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| 2. |
- Cialone, Matteo, et al.
(författare)
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Tailoring magnetic properties of multicomponent layered structure via current annealing in FePd thin films
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Multicomponent layered systems with tailored magnetic properties were fabricated via current annealing from homogeneous Fe67Pd33 thin films, deposited via radio frequency sputtering on Si/SiO2 substrates from composite target. To promote spontaneous nano-structuring and phase separation, selected samples were subjected to current annealing in vacuum, with a controlled oxygen pressure, using various current densities for a fixed time and, as a consequence, different phases and microstructures were obtained. In particular, the formation of magnetite in different amount was observed beside other iron oxides and metallic phases. Microstructures and magnetic properties evolution as a function of annealing current were studied and interpreted with different techniques. Moreover, the temperature profile across the film thickness was modelled and its role in the selective oxidation of iron was analysed. Results show that is possible to topologically control the phases formation across the film thickness and simultaneously tailor the magnetic properties of the system.
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| 3. |
- Hryha, Eduard, 1980, et al.
(författare)
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Surface chemical state of Ti powders and its alloys: Effect of storage conditions and alloy composition
- 2016
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 388, s. 294-303
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Tidskriftsartikel (refereegranskat)abstract
- High affinity of titanium to oxygen in combination with the high surface area of the powder results in tremendous powder reactivity and almost inevitable presence of passivation oxide film on the powder surface. Oxide film is formed during the short exposure of the powder to the environment at even a trace amount of oxygen. Hence, surface state of the powder determines its usefulness for powder metallurgy processing. Present study is focused on the evaluation of the surface oxide state of the Ti, NiTi and Ti6Al4V powders in as-atomized state and after storage under air or Ar for up to eight years.Powder surface oxide state was studied by X-ray photoelectron spectroscopy (XPS) and high resolution scanning electron microscopy (HR SEM). Results indicate that powder in as-atomized state is covered by homogeneous Ti-oxide layer with the thickness of ∼2.9 nm for Ti, ∼3.2 nm and ∼4.2 nm in case of Ti6Al4V and NiTi powders, respectively. Exposure to the air results in oxide growth of about 30% in case of Ti and only about 10% in case of NiTi and Ti6Al4V. After the storage under the dry air for two years oxide growth of only about 3-4% was detected in case of both, Ti and NiTi powders. NiTi powder, stored under the dry air for eight years, indicates oxide thickness of about 5.3 nm, which is about 30% thicker in comparison with the as-atomized powder. Oxide thickness increase of only ∼15% during the storage for eight years in comparison with the powder, shortly exposed to the air after manufacturing, was detected.Results indicate a high passivation of the Ti, Ti6Al4V and NiTi powder surface by homogeneous layer of Ti-oxide formed even during short exposure of the powder to the air.
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| 4. |
- Hryha, Eduard, 1980, et al.
(författare)
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Surface Oxide State on Metal Powder and its Changes during Additive Manufacturing: an Overview
- 2018
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Ingår i: Metallurgia Italiana. - 0026-0843. ; 110:3, s. 34-39
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Quality and usefulness of the powder for additive manufacturing (AM) are strongly determined by the surface composition of the powder. In addition, taking into account harsh conditions during AM process, significant changes in the powder surface chemical composition are taking place, limiting powder recyclability. Hence, knowledge concerning amount of oxides, their composition and spatial distribution on the powder surface determines further powder recycling. This communication summarizes possibilities of qualitative and quantitative analysis of powder surface chemistry by surface-sensitive chemical analyses using XPS and HR SEM coupled with EDX. The effect of alloy composition, AM process applied and powder handling on the surface composition of the powder are addressed. Results indicate significant enrichment in the thermodynamically stable surface oxides in case of high-alloyed powder for both, EBM and LS processes. A generic model for the oxide distribution, depending on the alloy composition and powder surface degradation during AM manufacturing, is proposed.
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| 5. |
- Krajňáková, P.G., et al.
(författare)
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Effect of double electron beam remelting on microstructure of HVOF and CGDS bond coat
- 2017
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Ingår i: Materials Science Forum. - 1662-9752 .- 0255-5476. - 9783035710182 ; 891, s. 574-578
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Konferensbidrag (refereegranskat)abstract
- This work focuses to investigate the influence of the parameters used in electron beam (EB) remelting including the effect of double remelting of CoNiCrAlY coatings fabricated on Nickel based super alloy substrates by using the high velocity oxygen-fuel (HVOF) and cold gas dynamic spraying (CGDS) methods. The microstructure of as sprayed and remelted coatings were investigated by scanning electron microscopy and the phase analysis by X-ray diffraction (XRD). The results obtained show that there are advantages at using the pulsed EB surface modification technique. Double EB treatment provides a smooth surface and low porosity level and at last but not least this study demonstrate that low-temperature processing of CoNiCrAlY bond coat represents an interesting and promising alternative for their manufacturing.
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| 6. |
- Leicht, Alexander, 1987, et al.
(författare)
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Characterization of virgin and recycled 316L powder used in additive manufacturing
- 2016
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Ingår i: SPS16, Lund, Sweden 2016.
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Konferensbidrag (refereegranskat)abstract
- Gas atomized 316L powder used in electron beam melting was investigated in virgin and recycled stateto indicate the influence of recycling on the powder properties. A cross sectional investigation of thepowder microstructure was performed by means of light optical microscopy and the phase compositionwas determined by means of X-ray diffraction analysis. The powder surface characterization was doneby using X-ray photoelectron spectroscopy and high resolution scanning electron microscopy equippedwith an energy dispersive X-ray analyser. Results showed that evenly distributed oxide particles in thesubmicron range can be observed on the surface of both virgin and recycled powder. The size of theseoxide features on the surface of recycled powder is on average around 200 nm which is four times largerin comparison to virgin powder which is around 50 nm. The EDX analysis indicated enrichment of Si,Cr and Mn in the oxides. According to XPS, both powders are covered by homogenous Fe-oxide layerwith particulate oxide features rich in Cr and Mn. Significantly higher amount of Cr oxide was detectedon the surface of recycled powder compared to the surface of the virgin powder. The recycled powderalso had lower Mn content on the surface. The reason for this is proposed to be the sublimation of Mn,which drives the decomposition of Mn-oxide. The powder cross-section showed that the microstructureof the recycled powder had a tendency to change towards cellular structure, while the microstructure ofvirgin powder is fully dendritic.
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| 7. |
- Manchili, Swathi Kiranmayee, 1987, et al.
(författare)
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Surface analysis of iron and steel nanopowder
- 2018
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Ingår i: Surface and Interface Analysis. - : Wiley. - 1096-9918 .- 0142-2421. ; 50:11, s. 1083-1088-10886
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Tidskriftsartikel (refereegranskat)abstract
- High sinter density is desired in powder metallurgy components as the requirement for performance is increasing day‐by‐day. One of the promising ways to achieve improved densification during sintering is through the addition of nanopowder to the conventional micrometer sized metal powder. It is well known that the surface chemistry of the powder has a decisive effect on sintering and consequently the properties of the components produced. Extensive research has hence been conducted to elucidate the surface chemistry and its influence on sintering for powder used in conventional powder metallurgy. Nanopowder, owing to high surface to volume ratio, can contribute to the activation of sintering at lower temperatures and enhance the sinter density. In this context, the surface chemistry of the nanopowder is also expected to exhibit substantial influence on sintering. The present investigation is aimed at establishing a methodology to study the surface chemistry and oxide thickness of nanopowder. For this purpose, iron nanopowder of 3 different size fractions: 35 to 45, 40 to 60, and 60 to 80 nm with core‐shell structure were studied. Different approaches were adopted to evaluate the shell thickness of the iron nanoparticles. The methodology was developed and tried on low alloy steel nanopowder to measure oxide thickness. X‐ray photoelectron spectroscopy, thermogravimetry, and high‐resolution scanning electron microscopy techniques were used to study the nanopowder. Results from different core‐shell models for iron nanopowder were found to be consistent except in the case where depth profiling was taken into account. The results were in agreement with the values obtained from thermogavimetry‐surface area correlation.
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| 8. |
- Mellin, Pelle, et al.
(författare)
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COPGLOW and XPS investigation of recycled metal powder for selective laser melting
- 2017
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Ingår i: Powder Metallurgy. - : Informa UK Limited. - 0032-5899 .- 1743-2901. ; 60:3, s. 223-231
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this paper is to compare, in terms of depth composition profile, a recycled hastelloy X powder and a virgin powder of the same alloy. We compare also the COPGLOW (compacted powder glow discharge analysis) method to the more established XPS (X-ray photoelectron spectroscopy) technique, in terms of similarity in reported elemental contents. A good match between the two methods was obtained on the surface of the powder particles (using an etching depth of 1 nm). Similar oxide layer thickness, of about 0.5–1 nm, was found on both powders by COPGLOW. Oxidation sensitive elements, such as Cr, were found on the surfaces by both XPS and COPGLOW on both powders. Surface content of Si appears to have decreased during use in selective laser melting. Finally, the two methods did not otherwise reveal any unexpected features in the depth profiles.
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| 9. |
- Shvab, Ruslan, 1985, et al.
(författare)
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Characterization of the virgin and recycled nickel alloy hx powder used for selective laser melting
- 2016
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Ingår i: World PM 2016 Congress and Exhibition.
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Konferensbidrag (refereegranskat)abstract
- Taking to account high specific surface area of the powder, its surface state becomes one of the most important aspects of usability of the powder in PM process and particularly in additive manufacturing. Powder surface characterization of the two HX Ni-based superalloy powders sampled during selective laser melting-namely virgin and re-cycled powders was performed by means of XPS and high-resolution SEM combined with EDX. Results showed slight difference in surface chemical composition between the powders. The most sensitive to oxidation alloying elements in the powder-Al and Cr-segregate to the surface to form more stable oxides in case of re-cycled powder. Loss of silicon due to sublimation was also detected on the surface of re-cycled powder. Ni, as a base element, was presented in the form of hydroxide on the as-received surface of both investigated powders.
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| 10. |
- Shvab, Ruslan, 1985, et al.
(författare)
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Copper Bronze Powder Surface Studied by XPS and HR SEM
- 2016
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Ingår i: Powder Metallurgy Progress. - : Walter de Gruyter GmbH. - 1339-4533. ; 16:1, s. 40-47
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Tidskriftsartikel (refereegranskat)abstract
- The state of the powder surface represents one of the main interests in the whole cycle of components’ production using powder metallurgy (PM) route. Large specific surface area of the powder in combination with often alloying with oxygen sensitive elements results in oxidation of the powder surface in most of the cases. The information about surface chemistry of the powder is of vital importance for further consolidation and sintering steps. Surface sensitive analytical techniques – X-ray photoelectron spectroscopy (XPS) and high-resolution scanning electron microscopy combined with energy dispersive X-ray analysis (HR SEM+EDX) were used for surface chemical analysis of the 60Cu-40Sn bronze powder. Determination of the compositional profiles and estimation of the surface oxide layer thickness was done by altering of ion etching and XPS analysis. The results showed tin oxide enrichment and presence of copper hydroxide on the surface of the powder particles. The impurities of P, Zn and Ca were also detected on the top surface of the powder in trace amounts.
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