Hans-Olof Andrén's research projects

Materials research programme CROX:  Mechanisms of creep and oxidation of high-performance alloys (2003-2007)

Programme leader: Prof. Hans-Olof  Andrén, Chalmers
Project leaders: Profs. John Ågren and Rolf Sandström, Department of Materials Science, Royal Institute of Technology, Stockholm; Prof. Göran Wahnström, Surface and Materials Theory, Chalmers; Prof. Krystyna Stiller and Dr Mats Halvarsson, Microscopy and Microanalysis, Chalmers; Prof. Lars-Gunnar Johansson, Dept. of Chemical and Biological Engineering, Chalmers.
Financing: Swedish Foundation for Strategic Research. 5 year programme, 2003-2007.
   The microstructure development during creep of primarily martensitic alloys and oxidation of primarily austenitic stainless steels and aluminium-rich coatings on nickel-based superalloys are characterised and modelled. The aim is to improve knowledge of the rate determining mechanisms, to predict the creep and oxidation behaviour (life assessment), and to decrease the time and effort needed to develop new alloys. Our vision for the future is to reliably predict the creep and oxidation behaviour of high temperature alloys at given load and temperature an a given environment, based on a detailed understanding of how microstructure develops.
   Oxidation studies are made with thermobalance, low vacuum SEM, and thin film XRD. Characterisation of the microstructure is made primarily with electron microscopy (FEG-SEM, TEM/EDS/ EFTEM), atom probe techniques (1DAP and 3DAP), and SIMS. For the preparation of thin foils and tips also a FIB-SEM instrument is used. Quantitative microstructural data (EFTEM) are important to support creep modelling, whereas oxidation studies focus on finding and understanding mechanisms of oxide growth. Both chromia and alumina formers are studied.
   Modelling of microstructure development, both during creep and oxidation, is done with Thermo- Calc and DICTRA software. Interfacial energies are needed e. g. for coarsening modelling, and interfacial work of separation is needed to estimate the adhesion of oxide layers. Atomistic modelling of interfaces using the density functional method is used to study precipitate/matrix as well as oxide/metal interfaces. In addition, the diffusion of boron in ferrite is stuidied using atomistic modelling. Creep strain modelling is made using fundamentally derived relations for microstructure evolution. In particular, a new model for the climb of dislocations past precipitates has been developed, which includes the effect of solid solution on climb velocity.
 

Creep behaviour and life assessment of modified 12% chromium steels (2001-2007)

Participants: Dr Ardeshir ("Ash") Golpayegani and Prof. Hans-Olof Andrén, Chalmers; MSc Johan Jeppsson, Prof. John Ågren, Division of Physical Metallurgy, Royal Institute of Technology, Stockholm.
Collaboration with: Hilmar Danielsen and John Hald, Technical University of Denmark; COST 536; MSc Dan Fors and Prof. Göran Wahnström, Chalmers.
In-kind work: Siemens, Finspång (Lennart Johansson); DONG Energy, Denmark (John Hald).
Financing: KME (Consortium for Materials Technology for Thermal Energy Processes), Research Foundation of VGB (Technical Association of Large Power Plant Operators, Essen, Germany), CROX (see above).
    9-12% chromium steels are being developed for use in power plants with a steam temperature of 600-650°C. There is a  need for reliable methods to predict the creep behaviour (100,000 hours) without relying on actual creep data. The coarsening of MX and M23C6 precipitates and growth of Laves phase are important microstructural changes that occur during service, and these have been extensively studied in several steels using EFTEM, APFIM and thermodynamical modelling (DICTRA). In particular the mechanisms behind the beneficial effects of  high boron additions are being studied, as well as the nucleation of the complex nitride Z-phase, which is detrimental to creep strength.


Atomistic modelling and microanalysis with atomic resolution of interfaces in cemented carbide systems (2005-2009)

Participants: MSc Jonathan Weidow and Prof. Hans-Olof Andrén (project leader and supervisor), Microscopy and Microanalysis, Chalmers; MSc Sven Johansson and Prof. Göran Wahnström (supervisor), Materials and Surface Theory, Chalmers; Dr Mattias Elfwing and Dr Susanne Norgren, Sandvik Tooling, Stockholm; and Dr Jenni Zackrisson and Dr Bo Jansson (assistant supervisor), Seco Tools.
Collaboration with: MSc Valerie Bounhoure, Prof. Sabine Lay and Prof. Jean-Michel Missiaen, LTPCM (Laboratoire de Thermodynamique et Physico-chemie Métallurgiques), INPG (Institut National Polytechnique de Grenoble-Université Joseph Fourier); Emmanuel Pauty, Sandvik Grenoble.
In-kind work: Sandvik Tooling, Seco Tools AB.
Financing: Swedish Research Council, AB Sandvik Tooling, Seco Tools.
     The structure and chemistry of grain and phase boundaries in WC-MC-Co is studied with SEM-EBSD, 3DAP and DFT modelling. Results are compared with HREM data from Grenoble.
DFT has predicted half-monolayer segregation of Co, Cr, V, Mn and Ti to WC-WC boundaries. 3DAP has confirmed segregation of Co and, to a lesser extent, Cr and V but not Mn.
At the phase boundary in WC-VC-Co small volumes of (V,W)C have been found, in accordance with HREM data.


New hot-work tool steels (2006-2010)

Participants: BTech Jörgen Andersson, Uddeholm Tooling (industrial PhD student), Prof. Hans-Olof  Andrén, Chalmers (supervisor), Prof. Lars-Erik Svensson, Volvo Powertrain (assistant supervisor), MSc Henrik Jesperson, Uddeholm (mentor)
Collaboration with: Dr Karin Carling and Prof. Jens Bergström, Materials and Mechanical Technology, University of Karlstad
In-kind work and financing: Uddeholm Tooling AB
   The maximum service temperature of hot-work tool steels is around 650°C. The project aims first at understanding the detailed microstructure of existing steels and its development during heat treatment and service. Then possible ways to increase the service temperature will be explored, by producing trial materials, measuring mechanical properties and characterising the microstructure of the materials. Strengthening with various carbide, nitride and/or intermetallic precipitates will be studied.
 

 

Microstructure and degradation mechanisms of boron nitride based cutting tool materials (2006-2010)

Participants: MSc Jenny Angseryd, Sandvik Tooling (industrial PhD student),  Profs. Hans-Olof Andrén (supervisor) and Eva Olsson (assistant supervisor), Chalmers; Dr Mattias Elfwing, Leif Dahl, Alexandra Kusoffsky and Dr Per Gustafson, Sandvik Tooling.
Collaboration with:  Sandvik Tooling, Stockholm.
In-kind work: Sandvik Tooling.
Financing: Swedish Research Council, Sandvik Tooling.
     Cutting tools based on polycristalline cubic boron nitride (PCBN) have excellent properties for working of chill cast irons and hardened steels. High loads and a high temperature give rise of tool degradation, which limits tool life. The project aims at characterising the microsturcture of materials with different biner phases in detail using SEM and TEM techniques, and at characterise degradation using cross-sections of worn materials.
 
 


Mechanisms for oxidation of zirconium alloys (2006-2011)

Participants: MSc Pia Söderberg (PhD student),  Profs. Hans-Olof Andrén (supervisor) and Lars-Gunnar Johansson (assistant supervisor), Chalmers
Collaboration with:  Sandvik Materials Technology (Mats Hättestrand), Sandviken; Westinghouse Electric Sweden AB (Björn Andersson), Västerås; Vattenfall Bränsle AB (Håkan Pettersson), Stockholm; OKG AB (Gunnar Rönberg), Oskarshamn; Swedish Nuclear Power Inspectorate (SKI) (Jan-Erik Lindbäck), Stockholm; OECD Halden Reactor Project (Erik Kolstad).
In-kind work: Sandvik and Westinghouse
Financing: Sandvik, Westinghouse, Vattenfall, OKG, SKI.
     The oxidation of fuel cladding tubes in light water nuclear reactors may limit the burn-up of the fuel, both due to loss of cross-section (strength) and because of hydrogen pickup (embrittlement). Cladding tubes are made from zirconium alloys, and empirically it is known that the oxidation behaviour depends on the heat treatment of the tubes during manufacture. The heat treatment affects the size and number density of second phase precipitates, but the mechanisms by which precpitate distributions affect oxide growth are not known. In this project, TEM/EDS/EFTEM of thin foil cross sections of metal-oxide interface is used to follow the oxidation  process. The cross sections are made using the FIB-SEM technique. As a first step some autoclave tested  Zircaloy-2 materials are being studied.


 
 
 

updated November 30, 2006
andren@fy.chalmers.se