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  • 1.
    Ericsson, Torsten
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Larsson, Cecilia
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Studies of residual stress, microcracks, hardness and microstructure of cold compacted metallic green bodies2003In: Materials Research Society Symposium Proceedings, ISSN 0272-9172, E-ISSN 1946-4274, Vol. 759, p. 53-64Article in journal (Refereed)
    Abstract [en]

    The residual stresses have been measured by X-ray and neutron diffraction on PM green bodies manufactured by conventional and high speed compaction of iron powder with and without added copper and brass powder. Compressive residual stresses are present in a thin layer in both top and side surfaces. They are largest in the side surfaces due to plastic deformation of the surface material caused by the friction forces during ejection out of the die. In the interior of the green body residual stresses exist with certain region under compression (periferical regions) and other under tension (more central regions). It is unclear whether mixing iron powder with brass or copper powder leads to considerable phase stresses between the two phases.

  • 2.
    Larsson, Cecilia
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Aspects of residual stress generation in functionally graded WC-Co composites: a literature surveyManuscript (preprint) (Other academic)
    Abstract [en]

    This literature survey provides an introduction to functionally graded materials, WC-Co composites and estimations of residual stresses in such material systems.

    Functionally graded materials feature gradual transitions in microstructure and/or composition. Gradual transitions are preferred over abrupt transitions which introduce local stress concentrations. The various manufacturing methods for functionally graded materials are divided into two classes. Constructive processes (e.g., powder processes) use an appropriate distribution of constituents, often as a precursor to the component, to create the gradient. Transport based processes (e.g., infiltration) rely on natural transport phenomena such as fluid flow, diffusion of atomic species or conduction of heat.

    Liquid phase sintering of mixed and pressed powder is used to produce WC-Co functionally graded composites. The mechanical properties of WC-Cocomposites and their constituent phases are reviewed. A wide range of overall composite behavior can be achieved when the Co content is varied. For example, the hardness is reported to be 1650 HV for WC with 6 wt.% Co and 780 HV for WC with 25 wt.% Co. The corresponding fracture toughness values are 8.5 and 14.5 MPa m1/2, respectively. These values suggest, that WC contributes to the hardness of the composite and Co contributes to the toughness. Therefore, the possibility of tailoring material performance by varying composition in the component arises.

    During cooling from the sintering temperature, thermal residual stresses develop because of the differences between the WC and Co thermal expansion coefficients. It is possible to use X-ray diffraction methods to measure residual stresses in composites. Results from measurements, and finite element (FE) analysis of the residual stresses in WC-Co composites are also reviewed.

  • 3.
    Larsson, Cecilia
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Determination of residual stresses and mechanical properties using neutron, X-ray diffraction, micro- and nanoindentation techniques2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The existence of residual stresses in engineering materials can significantly affect subsequent lifetime by augmenting or impeding failure. Consequently, for an accurate assessment of engineering lifetimes, there is a need to quantify residual stresses. Furthermore, knowledge of the origin of these stresses in conjunction with mechanical properties such as hardness and fracture toughness, among others, can be used to improve functionality by tailoring the microstructure through processing. In this work, neutron, x-ray diffraction, micro- and nanoindentation techniques were used for residual stress determination and mechanical characterization of WC-Co functionally graded composites, a Co-based Haynes® 25 alloy weld, compressed steel and compacted Fe-brass powders. The neutron and x-ray diffraction techniques were used to assess residual strains and stresses while the instrurnented indentation techniques were used to determine hardness, fracture toughness and elastic modulus. In each of these engineering materials, valuable insight relating to the overall mechanical performance was obtained.

    X-ray diffraction was used to determine thermal residual stresses that develop in a functionally graded WC-Co composite, commonly used as tool bits. Microstresses in the graded zone were attributed to the thermal mismatch between WC and the Co phase. The compressive macrostresses were determined to be a result of the compositional gradient. Micro- and nanoindentation experiments were used to determine hardness as a function of depth in two WC-Co functionally graded materials (FGMs). A relationship between hardness and Co phase content was established and explained for the two graded and five homogeneous samples.

    An experimental and simulation study of residual stresses was made in the vicinity of a gas tungsten arc weld in a Co-based Haynes® 25 alloy used in a satellite component. The experimental measurements were made by neutron diffraction on the recently commissioned Spectrometer for Materials Research at Temperature and Stress (SMARTS) at Los Alamos National Laboratory, USA and the simulation used the implicit Marc finite element code. Comparison between experiment and theory showed general agreement.

    Strain pole figures representative of residual intergranular strains were determined from an -2.98 % uniaxially compressed austenitic stainless steel sample. The neutron diffraction measurements were made on SMARTS, using an Euler cradle to obtain spectra over a range of sample orientations. The measurements were compared with predictions from an elasto-plastic self-consistent model and found to be in reasonable agreement. The model was also used to assess the sensitivity of the strain distribution in the deformed sample to the initial texture.

    Neutron diffraction was used to measure residual stresses in a powder metallurgical green body manufactured by high speed compaction from Fe and 15 wt.% brass powders. The tests were performed on SMARTS with the aid of radial collimators configured to measure spatially resolved strains in the axial and radial directions in a cylindrical specimen. Furthermore, sharp (Berkovich) and spherical (Hertzian) indenters were used for instrumented indentation experiments to determine the hardness and elastic modulus.

    List of papers
    1. X-ray diffraction determination of residual stresses in functionally graded WC–Co composites
    Open this publication in new window or tab >>X-ray diffraction determination of residual stresses in functionally graded WC–Co composites
    2004 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 22, no 4-5, p. 177-184Article in journal (Refereed) Published
    Abstract [en]

    X-ray diffraction was used to determine the thermal residual stresses that develop in a functionally graded WC–Co composite. Stresses were measured in both WC and Co phases at various depths. Pole figures were obtained in order to determine optimal sample orientations that provided adequate intensity for measurements in the Co phase. For WC, the in-plane compressive residual stresses varied approximately between −300 and −500 MPa with depth below the surface. For the low volume fraction Co phase, the tensile residual stresses were approximately 600 MPa. The microstresses in the graded zone were attributed to the thermal mismatch between the WC and the Co phase during cooling from the liquid phase sintering temperature (1450 °C). The microstresses determined were in reasonable agreement with a prediction using Eshelby theory. The compressive macrostresses were attributed to the compositional gradient, a result further substantiated by the fact that no significant macrostresses were measured in a comparable homogeneous sample, i.e., without the compositional gradient. Thus, varying compositional gradients in WC–Co composites during fabrication can be expected to directly influence the macrostress component of the overall residual stress state.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-23160 (URN)10.1016/j.ijrmhm.2004.06.002 (DOI)2564 (Local ID)2564 (Archive number)2564 (OAI)
    Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-10-02
    2. Hardness profile measurements in functionally graded WC–Co composites
    Open this publication in new window or tab >>Hardness profile measurements in functionally graded WC–Co composites
    2004 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 382, no 1-2, p. 141-149Article in journal (Refereed) Published
    Abstract [en]

    Micro- and nanoindentation were used to determine hardness as a function of depth in two functionally graded WC–Co composites. The gradients were continuous (extended over ∼70 and ∼40 μm, respectively) and consisted of varying WC and Co phase volume fractions. Five comparable homogeneous samples with different Co contents and different average WC grain sizes were also used for direct comparison. A relationship between hardness and Co content was established for both the graded and the homogeneous samples wherein the hardness decreased with increasing Co content. The magnitude of the hardness was the same (for a given Co content) for the functionally graded and the homogeneous materials. The hardness measurements were also correlated with X-ray diffraction studies of thermal residual stresses and the absence of any major influence explained. It is generally concluded that the hardness values are dominated by the local Co content. Additionally, the examination of surface cracks around indents suggests that compositional gradients in WC–Co composites offer increased toughness.

    Keywords
    hardness, functionally graded composites, WC-Co, nanoindentation, microindentation, residual stress
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46174 (URN)10.1016/j.msea.2004.04.065 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
    3. Measurement and modeling of residual stress in a welded Haynes® 25 cylinder
    Open this publication in new window or tab >>Measurement and modeling of residual stress in a welded Haynes® 25 cylinder
    Show others...
    2005 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 399, no 1-2, p. 49-57Article in journal (Refereed) Published
    Abstract [en]

    An experimental and simulation study of residual stresses was made in the vicinity of a gas tungsten arc weld, used to join a hemispherical end cap to a cylinder. The capped cylinder is used in a satellite application and was fabricated from a Co-based Haynes® 25 alloy. The cylinder was 34.7 mm in outer diameter and 3.3 mm in thickness. The experimental measurements were made by neutron diffraction and the simulation used the implicit Marc finite element code. The experimental resolution was limited to approximately 3 mm parallel to the axis of the cylinder (the weld was 6 mm in the same direction) and comparison over the same volume of the finite element prediction showed general agreement. Subject to the limited spatial resolution, the largest experimentally measured tensile residual stress was 180 MPa, located at the middle of the weld. However, the predictions suggest that there are regions in the weld where average tensile residual stresses as much as 400 MPa exist. One qualitative disparity between the model and the experiments was that the measurement included a larger degree of asymmetry on either side of the weld than predicted by the model.

    Keywords
    Cobalt, Finite element, Haynes® 25, Neutron diffraction, Residual stress, Weld
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-50481 (URN)10.1016/j.msea.2005.02.026 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
    4. Measurements and predictions of strain pole figures for uniaxially compressed stainless steel
    Open this publication in new window or tab >>Measurements and predictions of strain pole figures for uniaxially compressed stainless steel
    2004 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 51, no 6, p. 571-575Article in journal (Refereed) Published
    Abstract [en]

    Strain pole figures representative of residual intergranular strains were determined from an −2.98% uniaxially compressed austenitic stainless steel sample. The measurements were made using neutron diffraction on the recently commissioned Spectrometer for Materials Research at Temperature and Stress (SMARTS) at Los Alamos National Laboratory, USA. The measurements were compared with predictions from an elasto-plastic self-consistent model and found to be in good agreement.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-23147 (URN)10.1016/j.scriptamat.2004.05.030 (DOI)2549 (Local ID)2549 (Archive number)2549 (OAI)
    Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13
    5. Residual stress and mechanical property evaluation of compacted iron-brass powders using neutron diffracation and instrumented indentation
    Open this publication in new window or tab >>Residual stress and mechanical property evaluation of compacted iron-brass powders using neutron diffracation and instrumented indentation
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Neutron diffraction was used to measure residual stresses in a powder metallurgical green body manufactured by high speed compaction of iron and 15 wt.% brass powders. The tests were performed with the aid of radial collimators configured to measure spatially resolved strains in the axial and radial directions in a cylindrical specimen. Compressive residual stresses were present in the iron phase and appear to be larger in the lower to middle sections along the specimen's axis. Furthermore, a combination of sharp (Berkovich) and spherical (Hertzian) indenters were used for instrumented indentation experiments. The results from the spherical indenter were used to determine the elastic modulus, while results from the sharp indenter were used to measure the hardness.

    Keywords
    Iron-Brass Powder, Neutron diffraction, Nanoindentation, Residual Stress, Mechanical Properties
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-86864 (URN)
    Note

    Parts of this manuscript have been published in the following article: http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-30079

    Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2013-01-07
  • 4.
    Larsson, Cecilia
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Thermal residual stresses, hardness and microstructural characterisation of functionally graded WC-Co composites2001Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Functionally graded materials (FGMs) incorporate gradual transitions in their microstructure and/or composition with distance. The gradients provide means to favourably engineer their thermomechanical properties by changing e.g., the local modulus, yield strength, state of residual stress etc. However, prior to optimising such gradients, an understanding of their effect on thermomechanical properties is necessary. WC-Co composites are commonly used as tool bits, where the presence of Co improves the toughness of the wear resistant WC. In this thesis, emphasis has been placed on investigating the thermal residual stresses, hardness, and toughness of functionally graded WC-Co.

    The first paper in this thesis reviews existing literature on the subject while introducing FGMs and WC-Co composites. Additional topics addressed include: fabrication of FGMs, mechanical properties of WC-Co and estimates of residual stresses.

    In the second paper, X-ray diffraction was used to determine thermal residual stresses that develop in a functionally graded WC-Co composite. The gradient was continuous during a distance of about 40 Jlm below the surface and the stresses were measured in both WC and Co phases at various depths. Due to the difference in coefficient of thermal expansion between the two phases, tensile residual stresses where found in the Co phase and balancing compressive stresses in WC. Pole figures were obtained in order to determine optimal sample orientations that provided adequate intensity for measurements in the Co phase. Microstresses in the graded zone were attributed to the thermal mismatch between WC and the Co phase. The compressive macrostresses were determined to be a result of the compositional gradient.

    The third paper reports micro- and nanoindentation experiments to determine hardness as a function of depth in two different WC-Co FGMs. A relationship between hardness and Co phase content was established for the two graded and five homogeneous samples wherein the hardness decreases with increasing Co phase content. For a given Co phase content, no significant differences were observed between the FGMs and homogeneous samples. The measured thermal residual residual stresses did not appear to influence the hardness. Additionally, examination of indents using a Vickers indenter with different loads suggested that larger loads were required to initiate cracks in the FGMs compared to the homogeneous materials. While the investigated WC-Co FGMs did not offer advantages in hardness properties (which seem to be dominated by the local Co content in the graded zone), they appear to offer tribological advantages through increased toughness in terms of crack suppression.

    List of papers
    1. Aspects of residual stress generation in functionally graded WC-Co composites: a literature survey
    Open this publication in new window or tab >>Aspects of residual stress generation in functionally graded WC-Co composites: a literature survey
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    This literature survey provides an introduction to functionally graded materials, WC-Co composites and estimations of residual stresses in such material systems.

    Functionally graded materials feature gradual transitions in microstructure and/or composition. Gradual transitions are preferred over abrupt transitions which introduce local stress concentrations. The various manufacturing methods for functionally graded materials are divided into two classes. Constructive processes (e.g., powder processes) use an appropriate distribution of constituents, often as a precursor to the component, to create the gradient. Transport based processes (e.g., infiltration) rely on natural transport phenomena such as fluid flow, diffusion of atomic species or conduction of heat.

    Liquid phase sintering of mixed and pressed powder is used to produce WC-Co functionally graded composites. The mechanical properties of WC-Cocomposites and their constituent phases are reviewed. A wide range of overall composite behavior can be achieved when the Co content is varied. For example, the hardness is reported to be 1650 HV for WC with 6 wt.% Co and 780 HV for WC with 25 wt.% Co. The corresponding fracture toughness values are 8.5 and 14.5 MPa m1/2, respectively. These values suggest, that WC contributes to the hardness of the composite and Co contributes to the toughness. Therefore, the possibility of tailoring material performance by varying composition in the component arises.

    During cooling from the sintering temperature, thermal residual stresses develop because of the differences between the WC and Co thermal expansion coefficients. It is possible to use X-ray diffraction methods to measure residual stresses in composites. Results from measurements, and finite element (FE) analysis of the residual stresses in WC-Co composites are also reviewed.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-102050 (URN)
    Available from: 2013-11-28 Created: 2013-11-28 Last updated: 2013-11-28
    2. Thermal residues stresses and microstructural characterisation of functionally graded WC-Co composites
    Open this publication in new window or tab >>Thermal residues stresses and microstructural characterisation of functionally graded WC-Co composites
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    X-ray diffraction was used to determine the thermal residual stresses that develop in a functionally graded WC-Co composite. The gradient was continuous within a distance of about 40 Jlm below the surface and consisted of varying WC and Co phase volume fractions. The composite was characterised by scanning electron microscopy, optical microscopy and X-ray diffraction. Thermal residual stresses develop due to the thermal mismatch between the WC and the Co phase during cooling from the liquid-phase sintering temperature (1450°C). Pole figures were obtained in order to determine optimal sample orientations that provided adequate intensity for measurements in the Co phase. Stresses were measured in both WC and Co phases at various depths. For WC, the in-plane compressive residual stresses varied approximately between -300 MPa to -500 MPa with depth below the surface. For the low volume fraction Co phase, the tensile residual stresses were approximately 600 MPa. The changes in the magnitude of the residual stresses can be related to the changes in the Co phase content through the graded zone. Microstresses in the graded zone are attributed to the thermal mismatch between WC and the Co phase. The compressive macrostresses were determined to be a result of the compositional gradient. This conclusion is strongly supported by the result that almost no macrostresses were measured in a similar homogenous sample i.e., without the corresponding compositional gradient. Therefore, varying the composition gradient during fabrication is expected to directly affect the macrostresses.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-102051 (URN)
    Available from: 2013-11-28 Created: 2013-11-28 Last updated: 2013-11-28
    3. Hardness profile measurements in functionally graded WC–Co composites
    Open this publication in new window or tab >>Hardness profile measurements in functionally graded WC–Co composites
    2004 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 382, no 1-2, p. 141-149Article in journal (Refereed) Published
    Abstract [en]

    Micro- and nanoindentation were used to determine hardness as a function of depth in two functionally graded WC–Co composites. The gradients were continuous (extended over ∼70 and ∼40 μm, respectively) and consisted of varying WC and Co phase volume fractions. Five comparable homogeneous samples with different Co contents and different average WC grain sizes were also used for direct comparison. A relationship between hardness and Co content was established for both the graded and the homogeneous samples wherein the hardness decreased with increasing Co content. The magnitude of the hardness was the same (for a given Co content) for the functionally graded and the homogeneous materials. The hardness measurements were also correlated with X-ray diffraction studies of thermal residual stresses and the absence of any major influence explained. It is generally concluded that the hardness values are dominated by the local Co content. Additionally, the examination of surface cracks around indents suggests that compositional gradients in WC–Co composites offer increased toughness.

    Keywords
    hardness, functionally graded composites, WC-Co, nanoindentation, microindentation, residual stress
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46174 (URN)10.1016/j.msea.2004.04.065 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
  • 5.
    Larsson, Cecilia
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Clausen, B.
    Los Alamos National Laboratory, Los Alamos, USA.
    Holden, T.M.
    Los Alamos National Laboratory, Los Alamos, USA.
    Bourke, M.A.M.
    Los Alamos National Laboratory, Los Alamos, USA.
    Measurements and predictions of strain pole figures for uniaxially compressed stainless steel2004In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 51, no 6, p. 571-575Article in journal (Refereed)
    Abstract [en]

    Strain pole figures representative of residual intergranular strains were determined from an −2.98% uniaxially compressed austenitic stainless steel sample. The measurements were made using neutron diffraction on the recently commissioned Spectrometer for Materials Research at Temperature and Stress (SMARTS) at Los Alamos National Laboratory, USA. The measurements were compared with predictions from an elasto-plastic self-consistent model and found to be in good agreement.

  • 6.
    Larsson, Cecilia
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Ericsson, Torsten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Residual stress and mechanical property evaluation of compacted iron-brass powders using neutron diffracation and instrumented indentationManuscript (preprint) (Other academic)
    Abstract [en]

    Neutron diffraction was used to measure residual stresses in a powder metallurgical green body manufactured by high speed compaction of iron and 15 wt.% brass powders. The tests were performed with the aid of radial collimators configured to measure spatially resolved strains in the axial and radial directions in a cylindrical specimen. Compressive residual stresses were present in the iron phase and appear to be larger in the lower to middle sections along the specimen's axis. Furthermore, a combination of sharp (Berkovich) and spherical (Hertzian) indenters were used for instrumented indentation experiments. The results from the spherical indenter were used to determine the elastic modulus, while results from the sharp indenter were used to measure the hardness.

  • 7.
    Larsson, Cecilia
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Holden, T M
    Los Alamos Lab Los Alamos.
    Bourke, M A M
    Los Alamos National Lab Los Alamos.
    Stout, M
    Los Alamos National Lab Los Alamos.
    Residual Stress Measurement in a Co-bsed Haynes -25 Cylinder2002In: American conference on Neutron Scattering ACNS,2002, 2002Conference paper (Refereed)
  • 8.
    Larsson, Cecilia
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Holden, T.M.
    Los Alamos National Laboratory, Los Alamos, USA.
    Bourke, M.A.M.
    Los Alamos National Laboratory, Los Alamos, USA.
    Stout, M.
    Los Alamos National Laboratory, Los Alamos, USA.
    Teague, J.
    Los Alamos National Laboratory, Los Alamos, USA.
    Lindgren, L.-E.
    Div. Comp. Aided Design, Luleå University of Technology and Dalarna University, Luleå, Sweden.
    Measurement and modeling of residual stress in a welded Haynes® 25 cylinder2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 399, no 1-2, p. 49-57Article in journal (Refereed)
    Abstract [en]

    An experimental and simulation study of residual stresses was made in the vicinity of a gas tungsten arc weld, used to join a hemispherical end cap to a cylinder. The capped cylinder is used in a satellite application and was fabricated from a Co-based Haynes® 25 alloy. The cylinder was 34.7 mm in outer diameter and 3.3 mm in thickness. The experimental measurements were made by neutron diffraction and the simulation used the implicit Marc finite element code. The experimental resolution was limited to approximately 3 mm parallel to the axis of the cylinder (the weld was 6 mm in the same direction) and comparison over the same volume of the finite element prediction showed general agreement. Subject to the limited spatial resolution, the largest experimentally measured tensile residual stress was 180 MPa, located at the middle of the weld. However, the predictions suggest that there are regions in the weld where average tensile residual stresses as much as 400 MPa exist. One qualitative disparity between the model and the experiments was that the measurement included a larger degree of asymmetry on either side of the weld than predicted by the model.

  • 9.
    Larsson, Cecilia
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Odén, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Determination of Thermal Residual Stresses in a Functionally Graded WC-Co composite2002In: Denver X-ray Conference,2002, 2002Conference paper (Refereed)
  • 10.
    Larsson, Cecilia
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Odén, Magnus
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hardness profile measurements in functionally graded WC–Co composites2004In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 382, no 1-2, p. 141-149Article in journal (Refereed)
    Abstract [en]

    Micro- and nanoindentation were used to determine hardness as a function of depth in two functionally graded WC–Co composites. The gradients were continuous (extended over ∼70 and ∼40 μm, respectively) and consisted of varying WC and Co phase volume fractions. Five comparable homogeneous samples with different Co contents and different average WC grain sizes were also used for direct comparison. A relationship between hardness and Co content was established for both the graded and the homogeneous samples wherein the hardness decreased with increasing Co content. The magnitude of the hardness was the same (for a given Co content) for the functionally graded and the homogeneous materials. The hardness measurements were also correlated with X-ray diffraction studies of thermal residual stresses and the absence of any major influence explained. It is generally concluded that the hardness values are dominated by the local Co content. Additionally, the examination of surface cracks around indents suggests that compositional gradients in WC–Co composites offer increased toughness.

  • 11.
    Larsson, Cecilia
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Odén, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Thermal Residual Stresses in Functionally Graded WC-Co Composites Determined by X-ray Diffraction2000In: ICRS-6,2000, 2000Conference paper (Refereed)
  • 12.
    Larsson, Cecilia
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Odén, Magnus
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Thermal residues stresses and microstructural characterisation of functionally graded WC-Co compositesManuscript (preprint) (Other academic)
    Abstract [en]

    X-ray diffraction was used to determine the thermal residual stresses that develop in a functionally graded WC-Co composite. The gradient was continuous within a distance of about 40 Jlm below the surface and consisted of varying WC and Co phase volume fractions. The composite was characterised by scanning electron microscopy, optical microscopy and X-ray diffraction. Thermal residual stresses develop due to the thermal mismatch between the WC and the Co phase during cooling from the liquid-phase sintering temperature (1450°C). Pole figures were obtained in order to determine optimal sample orientations that provided adequate intensity for measurements in the Co phase. Stresses were measured in both WC and Co phases at various depths. For WC, the in-plane compressive residual stresses varied approximately between -300 MPa to -500 MPa with depth below the surface. For the low volume fraction Co phase, the tensile residual stresses were approximately 600 MPa. The changes in the magnitude of the residual stresses can be related to the changes in the Co phase content through the graded zone. Microstresses in the graded zone are attributed to the thermal mismatch between WC and the Co phase. The compressive macrostresses were determined to be a result of the compositional gradient. This conclusion is strongly supported by the result that almost no macrostresses were measured in a similar homogenous sample i.e., without the corresponding compositional gradient. Therefore, varying the composition gradient during fabrication is expected to directly affect the macrostresses.

  • 13.
    Larsson, Cecilia
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Odén, Magnus
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    X-ray diffraction determination of residual stresses in functionally graded WC–Co composites2004In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 22, no 4-5, p. 177-184Article in journal (Refereed)
    Abstract [en]

    X-ray diffraction was used to determine the thermal residual stresses that develop in a functionally graded WC–Co composite. Stresses were measured in both WC and Co phases at various depths. Pole figures were obtained in order to determine optimal sample orientations that provided adequate intensity for measurements in the Co phase. For WC, the in-plane compressive residual stresses varied approximately between −300 and −500 MPa with depth below the surface. For the low volume fraction Co phase, the tensile residual stresses were approximately 600 MPa. The microstresses in the graded zone were attributed to the thermal mismatch between the WC and the Co phase during cooling from the liquid phase sintering temperature (1450 °C). The microstresses determined were in reasonable agreement with a prediction using Eshelby theory. The compressive macrostresses were attributed to the compositional gradient, a result further substantiated by the fact that no significant macrostresses were measured in a comparable homogeneous sample, i.e., without the compositional gradient. Thus, varying compositional gradients in WC–Co composites during fabrication can be expected to directly influence the macrostress component of the overall residual stress state.

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