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Determination of residual stresses and mechanical properties using neutron, X-ray diffraction, micro- and nanoindentation techniques
Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
2003 (English)Doctoral 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.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2003. , 24 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 856
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-30056Local ID: 15516ISBN: 91-7373-786-0 (print)OAI: oai:DiVA.org:liu-30056DiVA: diva2:250877
Public defence
2003-12-19, Kvalitetstekniks seminarierum, Linköpings Universitet, Linköping, 10:15 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-01-07
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, 177-184 p.Article 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, 141-149 p.Article 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.

Keyword
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, 49-57 p.Article 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.

Keyword
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, 571-575 p.Article 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: 2013-01-07
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.

Keyword
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

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