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Publications (10 of 15) Show all publications
Hedström, P., Han, T.-S., Lienert, U., Almer, J. & Odén, M. (2010). Load partitioning between single bulk grains in a two-phase duplex stainless steel during tensile loading (ed.). Paper presented at . Acta Materialia, 58(2), 734-744
Open this publication in new window or tab >>Load partitioning between single bulk grains in a two-phase duplex stainless steel during tensile loading
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2010 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 58, no 2, p. 734-744Article in journal (Refereed) Published
Abstract [en]

The lattice strain tensor evolution for single bulk grains of austenite and ferrite in a duplex stainless steel during tensile loading to 0.02 applied strain has been investigated using in situ high-energy X-ray measurements and finite-element modeling. Single-grain X-ray diffraction lattice strain data for the eight austenite and seven ferrite grains measured show a large variation of residual lattice strains, which evolves upon deformation to the point where some grains with comparable crystallographic orientations have lattice strains different by 1.5 × 10-3, corresponding to a stress of ≈300 MPa. The finite-element simulations of the 15 measured grains in three different spatial arrangements confirmed the complex deformation constraint and importance of local grain environment.

National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-4403 (URN)10.1016/j.actamat.2009.09.053 (DOI)000272917000041 ()2-s2.0-70449487414 (Scopus ID)259d7510-bf18-11de-b769-000ea68e967b (Local ID)259d7510-bf18-11de-b769-000ea68e967b (Archive number)259d7510-bf18-11de-b769-000ea68e967b (OAI)
Note
Validerad; 2010; 20091022 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2020-01-31Bibliographically approved
Odén, M., Rogström, L., Terner, M., Hedström, P., Almer, J. & llavsky, J. (2009). In situ small-angle x-ray scattering study of nanostructure evolution during decomposition of arc evaporated TiAlN coatings (ed.). Paper presented at . Applied Physics Letters, 94(5), 53114
Open this publication in new window or tab >>In situ small-angle x-ray scattering study of nanostructure evolution during decomposition of arc evaporated TiAlN coatings
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2009 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, no 5, p. 53114-Article in journal (Refereed) Published
Abstract [en]

Small-angle x-ray scattering was used to study in situ decomposition of an arc evaporated TiAlN coating into cubic-TiN and cubic-AlN particles at elevated temperature. At the early stages of decomposition particles with ellipsoidal shape form, which grow and change shape to spherical particles at higher temperatures. The spherical particles grow at a rate of 0.18 Å/°C while coalescing

National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-4974 (URN)10.1063/1.3078283 (DOI)000263167000062 ()2-s2.0-59849098305 (Scopus ID)2fc91f20-049d-11de-802a-000ea68e967b (Local ID)2fc91f20-049d-11de-802a-000ea68e967b (Archive number)2fc91f20-049d-11de-802a-000ea68e967b (OAI)
Note
Validerad; 2009; 20090227 (bajo)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2020-01-31Bibliographically approved
Hedström, P., Lindgren, L.-E., Almer, J., Lienert, U., Bernier, J., Terner, M. & Odén, M. (2009). Load partitioning and strain-induced martensite formation during tensile loading of a metastable austenitic stainless steel (ed.). Paper presented at . Metallurgical and Materials Transactions. A, 40(5), 1039-1048
Open this publication in new window or tab >>Load partitioning and strain-induced martensite formation during tensile loading of a metastable austenitic stainless steel
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2009 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 40, no 5, p. 1039-1048Article in journal (Refereed) Published
Abstract [en]

In-situ high-energy X-ray diffraction and material modeling are used to investigate the strain-rate dependence of the strain-induced martensitic transformation and the stress partitioning between austenite and α′ martensite in a metastable austenitic stainless steel during tensile loading. Moderate changes of the strain rate alter the strain-induced martensitic transformation, with a significantly lower α′ martensite fraction observed at fracture for a strain rate of 10-2 s-1, as compared to 10-3 s-1. This strain-rate sensitivity is attributed to the adiabatic heating of the samples and is found to be well predicted by the combination of an extended Olson-Cohen strain-induced martensite model and finite-element simulations for the evolving temperature distribution in the samples. In addition, the strain-rate sensitivity affects the deformation behavior of the steel. The α′ martensite transformation at high strains provides local strengthening and extends the time to neck formation. This reinforcement is witnessed by a load transfer from austenite to α′ martensite during loading.

National Category
Other Materials Engineering Other Materials Engineering
Research subject
Material Mechanics; Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-10754 (URN)10.1007/s11661-009-9807-3 (DOI)000264886400008 ()99c9ba70-34d0-11de-98cd-000ea68e967b (Local ID)99c9ba70-34d0-11de-98cd-000ea68e967b (Archive number)99c9ba70-34d0-11de-98cd-000ea68e967b (OAI)
Note
Validerad; 2009; 20090429 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2020-01-31Bibliographically approved
Mangalaraja, R., Mouzon, J., Hedström, P., Camurri, C., Ananthakumar, S. & Odén, M. (2009). Microwave assisted combustion synthesis of nanocrystalline yttria and its powder characteristics (ed.). Paper presented at . Powder Technology, 191(3), 309-314
Open this publication in new window or tab >>Microwave assisted combustion synthesis of nanocrystalline yttria and its powder characteristics
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2009 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 191, no 3, p. 309-314Article in journal (Refereed) Published
Abstract [en]

Microwave assisted combustion synthesis is used for fast and controlled processing of advanced ceramics. Single phase and sinter active nanocrystalline cubic yttria powders were successfully synthesized by microwave assisted combustion using the organic fuels urea, citric acid and glycine as reducing agents. The precursor powders were investigated by thermogravimetry (TG) and differential scanning colorimetry (DSC) analyses. The as-prepared precursors and the resulting oxide powders calcined at 1100 °C in oxygen atmosphere were characterized for their structure, particle size and morphology. The thermal analyses (TG/DSC), X-ray diffraction (XRD) and Fourier transform infra red (FT-IR) results demonstrate the effectiveness of the microwave assisted combustion synthesis. The scanning electron microscopy (SEM) observations show the different morphologies of as-prepared powders and transmission electron microscopy (TEM) shows the particle sizes in the range of 30-100 nm for calcined powders for different fuels. The results confirm that the homogeneous, nano scale yttria powders derived by microwave assisted combustion have high crystalline quality and the morphology of the as-prepared precursor powders depends on the nature of organic fuel used.

National Category
Chemical Process Engineering Other Materials Engineering
Research subject
Chemical Technology; Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-9777 (URN)10.1016/j.powtec.2008.10.019 (DOI)000264689900012 ()2-s2.0-60849121705 (Scopus ID)8758e140-e246-11dd-981b-000ea68e967b (Local ID)8758e140-e246-11dd-981b-000ea68e967b (Archive number)8758e140-e246-11dd-981b-000ea68e967b (OAI)
Note
Validerad; 2009; 20090114 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2020-01-31Bibliographically approved
Mangalaraja, R., Mouzon, J., Hedström, P., Kero, I., Ramam, K., Camurri, C. & Odén, M. (2008). Combustion synthesis of Y2O3 and Yb-Y2O3: Part 1: Nanopowders and their characterization (ed.). Paper presented at . Journal of Materials Processing Technology, 208(1-3), 415-422
Open this publication in new window or tab >>Combustion synthesis of Y2O3 and Yb-Y2O3: Part 1: Nanopowders and their characterization
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2008 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 208, no 1-3, p. 415-422Article in journal (Refereed) Published
Abstract [en]

Nanosized yttrium oxide and ytterbium doped yttrium oxide powders were prepared by ceramic combustion techniques such as flash combustion, citrate gel decomposition and glycine combustion using urea, citric acid and glycine respectively as fuels. As synthesized precursors and calcined powders were characterized for their structural, particle size and morphology, and the optimization of calcination process by differential scanning calorimetry and thermal gravimetry. The thermal analyses together with XRD results demonstrate the effectiveness of the combustion process for the synthesis of pure phase nanocrystalline powders. Nanocrystalline pure yttria powders were obtained by the calcination of as-prepared precursors at 1100 °C for 4 h.

National Category
Chemical Process Engineering Other Materials Engineering
Research subject
Chemical Technology; Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-15082 (URN)10.1016/j.jmatprotec.2008.01.023 (DOI)000260690500055 ()2-s2.0-52949119509 (Scopus ID)e8bfe080-7380-11dd-a60f-000ea68e967b (Local ID)e8bfe080-7380-11dd-a60f-000ea68e967b (Archive number)e8bfe080-7380-11dd-a60f-000ea68e967b (OAI)
Note
Validerad; 2008; 20080826 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2020-01-31Bibliographically approved
Hedström, P., Lienert, U., Almer, J. & Odén, M. (2008). Elastic strain evolution and ε-martensite formation in individual austenite grains during in situ loading of a metastable stainless steel (ed.). Paper presented at . Materials letters (General ed.), 62(2), 338-340
Open this publication in new window or tab >>Elastic strain evolution and ε-martensite formation in individual austenite grains during in situ loading of a metastable stainless steel
2008 (English)In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 62, no 2, p. 338-340Article in journal (Refereed) Published
Abstract [en]

The (hcp) ε-martensite formation and the elastic strain evolution of individual (fcc) austenite grains in metastable austenitic stainless steel AISI 301 has been investigated during in situ tensile loading up to 5% applied strain. The experiment was conducted using high-energy X-rays and the 3DXRD technique, enabling studies of individual grains embedded in the bulk of the steel. Out of the 47 probed austenite grains, one could be coupled with the formation of ε-martensite, using the reported orientation relationship between the two phases. The formation of ε-martensite occurred in the austenite grain with the highest Schmid factor for the active {111}b12¯1N slip system.

National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-16083 (URN)10.1016/j.matlet.2007.05.054 (DOI)000251870400045 ()2-s2.0-36249008533 (Scopus ID)faa627a0-9dca-11dc-9810-000ea68e967b (Local ID)faa627a0-9dca-11dc-9810-000ea68e967b (Archive number)faa627a0-9dca-11dc-9810-000ea68e967b (OAI)
Note
Validerad; 2008; 20071128 (cira)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2020-01-31Bibliographically approved
Knutsson, A., Hedström, P. & Odén, M. (2008). Reverse martensitic transformation and resulting microstructure in a cold rolled metastable austenitic stainless steel (ed.). Paper presented at . Steel Research International, 79(6), 433-439
Open this publication in new window or tab >>Reverse martensitic transformation and resulting microstructure in a cold rolled metastable austenitic stainless steel
2008 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 79, no 6, p. 433-439Article in journal (Refereed) Published
Abstract [en]

The reverse martensitic transformation in cold-rolled metastable austenitic stainless steel has been investigated via heat treatments performed for various temperatures and times. The microstructural evolution was evaluated by differential scanning calorimetry, X-ray diffraction and microscopy. Upon heat treatment, both diffusionless and diffusion-controlled mechanisms determine the final microstructure. The diffusion reversion from α′-martensite to austenite was found to be activated at about 450°C and the shear reversion is activated at higher temperatures with Af′ ∼600°C. The resulting microstructure for isothermal heat treatment at 650°C was austenitic, which inherits the α′-martensite lath morphology and is highly faulted. For isothermal heat treatments at temperatures above 700°C the faulted austenite was able to recrystallize and new austenite grains with a low defect density were formed. In addition, carbo-nitride precipitation was observed for samples heat treated at these temperatures, which leads to an increasing Ms-temperature and new α′-martensite formation upon cooling.

National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-10957 (URN)10.2374/SRI08SP039-79-2008-433 (DOI)000257357500005 ()2-s2.0-47349118099 (Scopus ID)9da81870-7375-11dd-a60f-000ea68e967b (Local ID)9da81870-7375-11dd-a60f-000ea68e967b (Archive number)9da81870-7375-11dd-a60f-000ea68e967b (OAI)
Note
Validerad; 2008; 20080826 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2020-01-31Bibliographically approved
Ukonsaari, J., McCarthy, D., Prakash, B. & Hedström, P. (2008). Tribological studies on an EAL lubricated bearing bronze - steel pair under reciprocating sliding conditions (ed.). Paper presented at . Tribologia : Finnish Journal of Tribology, 27(1), 3-18
Open this publication in new window or tab >>Tribological studies on an EAL lubricated bearing bronze - steel pair under reciprocating sliding conditions
2008 (English)In: Tribologia : Finnish Journal of Tribology, ISSN 0780-2285, Vol. 27, no 1, p. 3-18Article in journal (Refereed) Published
Abstract [en]

Boundary lubricated journal bearings are found in various applications involving oscillatory sliding conditions. Environmental adaptation of hydraulic systems includes the introduction of synthetic esters. These new environmentally adapted lubricants (EALs) have shown very good boundary lubrication performance but also condition sensitivity. This study examines an oil lubricated bronze pin on hardened steel configuration in a reciprocating friction and wear test machine. Three synthetic esters were tested with a 1 mm stroke length. Results were compared with those for a mineral oil. The tribological performance with synthetic ester lubricant can, under certain conditions, be very good. SEM-EDS and XRD surface sensitive studies indicate the formation of a soft, copper enriched outer contact layer. The layer's nature and contact mechanisms clearly affect the performance of the different lubricants. (17 refs.)

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Other Materials Engineering
Research subject
Machine Elements; Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-12512 (URN)babe09a0-3311-11dd-b113-000ea68e967b (Local ID)babe09a0-3311-11dd-b113-000ea68e967b (Archive number)babe09a0-3311-11dd-b113-000ea68e967b (OAI)
Note
Godkänd; 2008; 20080605 (brap)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2020-01-31Bibliographically approved
Hedström, P. (2007). Deformation and martensitic phase transformation in stainless steels (ed.). (Doctoral dissertation). Paper presented at . Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Deformation and martensitic phase transformation in stainless steels
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of high-energy synchrotron x-rays which has enabled three- dimensional structural characterization from the nano- to the macroscopic scale, and now to the meso-scale, such as individual grains and dislocation structures, is a major scientific advance. This is the first technique with sufficient spatial resolution and penetration power to probe the local structure embedded deep within the material. This, together with good time resolution makes it suitable for investigations of e.g. phase transformations kinetics, stress-strain behaviour, and texture evolution in stainless steels. The micromechanical response of a metastable austenitic stainless steel and a duplex stainless steel during loading has been investigated by a series of high-energy x-ray diffraction experiments at the Advanced Photon Source (APS) in Argonne, IL, USA. Different measurement scales of the steels are tested, ranging from the behaviour of individual grains up to the macroscopic material behaviour. The experimental data is used as input to material models to validate and improve existing models for strain-induced martensite and mechanical properties. The x-ray investigations have revealed that autocatalytic Ü-martensite transformation is triggered by strains induced by the transformation itself in 301 and this was evidenced as bursts of Ü-martensite transformation during tensile loading. To the author's knowledge this behaviour has not been previously reported, and is of significant importance for the mechanical properties of the metastable stainless steels, since it provides strong local hardening and increases the time to neck formation. The å-martensite formation was investigated for 45 individual austenite bulk grains in 301 and the resolved shear stress was determined. Out of the 45 austenite grains probed one was observed to form å-martensite. The grain that formed å-martensite had the highest Schmid factor for the active slip system during fcc to hcp transformation. The behaviour of 301 during tensile loading at different strain rates was also investigated and it was concluded that even moderate strain rates produce adiabatic heating sufficient to suppress the martensite formation. The strain-induced martensitic transformation and the stress-strain behaviour was predicted by an extended Olson-Cohen model, finite element simulations for the temperature evolution and a radial return algorithm for the stress-strain behaviour. The measured and modelled results were in fair agreement. In addition, the phase specific stresses were measured during the experiments and these were in good agreement with the predicted results from the finite element model. Thus, it was concluded that the employed iso- work principle was a good assumption for the stress distribution between the phases. One way of tailoring the metastable austenitic stainless steels' microstructure with different phase fractions and deformation structures is by the reverse transformation from martensite to austenite. This was investigated for the cold rolled 301 steel, and the reverse transformation was observed to occur via two different mechanisms, one diffusion controlled and the other a diffusionless transformation. The onset of the diffusion reversion was about 450°C and the shear reversion became active at higher temperatures. The microstructure of shear reversed austenite consists of highly faulted austenite with an inherited lath like structure. The stress response of 15 individual austenite and ferrite grains deeply embedded in the bulk of a duplex stainless steel was measured during tensile loading. These results showed large intergranular stresses acting between grains due to grain interaction. The large intergranular stresses will have a significant effect on the two-phase behaviour during loading.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2007. p. 158
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544 ; 2007:67
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-18455 (URN)8b330fb0-9c48-11dc-97ff-000ea68e967b (Local ID)8b330fb0-9c48-11dc-97ff-000ea68e967b (Archive number)8b330fb0-9c48-11dc-97ff-000ea68e967b (OAI)
Note
Godkänd; 2007; 20071126 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2020-01-31Bibliographically approved
Hedström, P., Lienert, U., Almer, J. & Odén, M. (2007). Stepwise transformation behavior of the strain-induced martensitic transformation in a metastable stainless steel (ed.). Paper presented at . Scripta Materialia, 56(3), 213-216
Open this publication in new window or tab >>Stepwise transformation behavior of the strain-induced martensitic transformation in a metastable stainless steel
2007 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 56, no 3, p. 213-216Article in journal (Refereed) Published
Abstract [en]

In situ high-energy X-ray diffraction during tensile loading has been used to investigate the evolution of lattice strains and the accompanying strain-induced martensitic transformation in cold-rolled sheets of a metastable stainless steel. At high applied strains the transformation to α-martensite occurs in stepwise bursts. These stepwise transformation events are correlated with stepwise increased lattice strains and peak broadening in the austenite phase. The stepwise transformation arises from growth of α-martensite embryos by autocatalytic transformation.

National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-7512 (URN)10.1016/j.scriptamat.2006.10.009 (DOI)000242726500009 ()2-s2.0-33751183061 (Scopus ID)5e7cfb20-7a6b-11db-8824-000ea68e967b (Local ID)5e7cfb20-7a6b-11db-8824-000ea68e967b (Archive number)5e7cfb20-7a6b-11db-8824-000ea68e967b (OAI)
Note
Validerad; 2007; 20061122 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2020-01-31Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1102-4342

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