| 1. |
- Frisk, Karin, et al.
(författare)
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Studies of oxide reduction during sintering of Cr alloyed PM steel by coupled experimental and diffusion simulations
- 2016
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Ingår i: World PM 2016 Congress and Exhibition. - : European Powder Metallurgy Association (EPMA). - 9781899072484
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Konferensbidrag (refereegranskat)abstract
- Oxide reduction in Cr alloyed PM steel has been simulated experimentally by measuring the oxygen loss from powders when exposed to a heating cycle, by photo acoustic spectroscopy (PAS) and by thermogravimetric analysis (TGA). Pressed samples were heated in dry hydrogen gas using a defined, slow, heating rate up to 1300oC. The oxides in the powder are reduced by the hydrogen gas. From the PAS curves distinct reduction temperatures are observed, that can be correlated to the type of oxide by comparing with thermodynamic calculations of the oxide stabilities. The experimental results were analyzed by diffusion simulations that involve a description of the diffusion controlled oxide reduction. It is shown how the calculated rate of oxygen diffusion in the samples, compared with the experimental results, has been applied as a tool for increased understanding of the reduction during sintering.
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| 2. |
- Heikkilä, Irma, et al.
(författare)
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First experiences on characterization of surface oxide films in powder particles by gd-oes
- 2015
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Ingår i: Proceedings Euro PM 2015. - : European Powder Metallurgy Association (EPMA). - 9781899072477
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Konferensbidrag (refereegranskat)abstract
- The surface characteristics of the powder particles play a key role on the processing of the powders to consolidated products and on the final properties achieved for the material. Characterization of surface oxide films by techniques like XPS and TEM EDS provide reliable information on the surface films, but they are time-consuming methods and the analyzed areas are extremely limited. In this evaluation, the potential of the depth profile analysis by Glow Discharge Optical Emission Spectroscopy (GD-OES) is experimented for Astaloy CrM and 316L powders. The conducted experiments show that the chemical composition and thickness of the surface oxides can be analyzed by GD-OES even for powder materials. Thus, the first results indicate that GD-OES provides a fast method to analyze the surface characteristics of a large number of powder particles during a single measurement.
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| 3. |
- Magnusson, Hans, et al.
(författare)
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Carbon reactions at sintering of chromium alloyed PM steels
- 2015
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Ingår i: Proceedings Euro PM 2015. - : European Powder Metallurgy Association (EPMA). - 9781899072477
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Konferensbidrag (refereegranskat)abstract
- Carbon has a strong influence on oxide stability. It assists the sintering process by the reduction of oxides on the surface of the powder. Carbon as a small interstitial atom has also a high mobility and can easily diffuse in the material already at relatively low temperature. Due to its high mobility and its influence on oxide reduction it is of interest to predict how carbon is distributed in the sintered body. The carbon distribution in the microstructure will also determine the mechanical properties of the sintered product. Sintering trials have been made for water atomised powder pre-Alloyed with 3wt% chromium and 0.5wt% Mo. These experimental simulations have been made in different N2/H2 atmospheres. The surface reactions during sintering are monitored using photoacoustic spectroscopy, measuring the outgoing gases from the furnace. Computational methods using Thermo-Calc are used to verify the gas reactions taking place in the furnace. By applying kinetic simulations with the Dictra software the carbon diffusion can be modelled for the sintering trials. The computational methods describe the experimentally observed reactions, and contribute to a better understanding of the reduction process.
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| 4. |
- Tahir, Abdul Malik, et al.
(författare)
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Behaviour of master alloy during sintering of PM steels : redistribution and dimensional variations
- 2015
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Ingår i: Powder Metallurgy. - 0032-5899 .- 1743-2901. ; 58:2, s. 133-141
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Tidskriftsartikel (refereegranskat)abstract
- The addition of alloying elements in low alloyed PM steels in the form of a master alloy gives the advantage of introducing oxidation sensitive but less expensive elements and also allows manipulation in composition adjustment to achieve desired properties. In this work, interrupted sintering trials of the Fe-2MA-0.5C (%) (MA = Cu based master alloy) are performed. The behaviour of the liquid forming master alloy, for instance in terms of liquid phase formation, alloying element redistribution and effect on the dimensional changes, is investigated. The results show that master alloy particles melt over a range of temperature, which is also supported by the thermodynamic calculations. The low swelling in the master alloy system, compared to a reference system of Fe-2Cu-0.5C, is attributed to the progressive melting of the master alloy. The mean diffusion distance of Cu in Fe at the interparticle boundaries is 5.8 mu m after 34 min of isothermal holding.
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