Research

Linking scales: Diffraction contrast tomography, three-dimensional synchrotron X-ray diffraction, and high resolution EBSD

By: Hamid Abdolvand,  Jonathan Wright1, Angus Wilkinson2 
1European Synchrotron Radiation Facility, Grenoble, France
2Department of Materials, University of Oxford, Oxford, UK
 
 
This research aimed to combine Three-Dimensional X-Ray Diffraction (3DXRD), Diffraction Contrast Tomography (DCT), to High Resolution Electron BackScatter Diffraction (HREBSD). This was to bridge between the two sides of a wide spectrum, i.e. local type-III stresses measured by HREBSD to type-II stresses measured by 3DXRD, and to those applied (Type-I). The 3DXRD experiments were conducted on commercially pure zirconium (CPZr) and titanium (CPTi) samples. Sample textures were engineered so that effects of deformation twinning can be minimized. The 3D measured microstructures were imported into our CPFE model.

 

Results (Part I):

(I) The results of both measurements and modeling revealed an interesting phenomenon in HCP polycrystals, ie, significant grain stress relaxation while macroscopic stress increases. This is surprising as it happened in the absence of twinning. 

(II) Experimental and modeling results both revealed the significant effects of grain neighbourhood on the load-sharing and stress relaxation at the grain level.

(III) Results show that accurate modeling of polycrystals demands the use of full-filed models that can capture localized effects of grain-grain interactions.

 

This is discussed in:

Abdolvand, H.*, Wright, J., Wilkinson, A.J., “Strong Grain Neighbour Effects in Polycrystals”, Nature Communications, 2018, 9, 171, DOI: 10.1038/s41467-017-02213-9

 

Data set:  3D-XRD and HR-EBSD data in support of this article are openly available at DOI: 10.5281/zenodo.1042139

CPFE results are also included in the data set.

 

Results (Part II):

(I) A series of codes were developed to read lattice strains and rotations from CPFE models and forward simulate diffraction peaks in 3D. 

(II) A method was developed to compare the simulated diffraction peaks to the measured ones and determine the activity of various deformation mechanisms in polycrystals.

(III) With using (II), it was shown that Pyramidal <a> slip system is hardly active at the room temperature and for the investigated strain levels.

 

This is discussed in:

Abdolvand, H.*, Wright, J., Wilkinson, A.J., “On the state of deformation in a polycrystalline material in three-dimension: elastic strains, lattice rotations, and deformation mechanisms”, International Journal of Plasticity, 2018.

Deformation twinning in 3D

By: Hamid Abdolvand1,4, Marta Majkut1,2, Jette Oddershede2, Jonathan Wright3, Mark Daymond1
1Department of Mechanical and Materials Engineering, Queen’s University, Kingston, Canada
2NEXMAP, Department of Physics, Technical University of Denmark, Fysikvej, 2800 Kgs. Lyngby, Denmark
3European Synchrotron Radiation Facility, Grenoble, France
4Department of Materials, University of Oxford, Oxford, UK
 
High anisotropy in the elastic and plastic properties of hexagonal close-packed (hcp) structured metals not only results in drastic stress variation across grain boundaries, but also heterogeneous distributions within grains. Understanding the mechanism of load sharing between different grains becomes more complicated when deformation twinning plays a significant role in accommodating an externally applied load. In this work, a comprehensive study of stress development in a coarse grained strongly textured hcp polycrystal Zircaloy-2 and MgAZ31B, was given using three-dimensional X-ray diffraction (3DXRD) microscopy. In-situ uniaxial straining was carried out at seven steps up to 2.7% in the macroscopic direction that favors twin formation, while center-of-mass position, crystallographic orientation, elastic strain, stress, and relative volume of each grain were measured. This information was used to reconstruct the 3D microstructure  using he weighted Voronoi tessellation method  which was subsequently imported into the ABAQUS finite element solver for further analysis.  It is shown that upon considering the stress variations within each grain, stresses in the parent and twin are quite different if they are plotted in the global coordinate system. However, if the stress tensor is rotated into the local coordinate system of the twin habit plane, all the stress components averaged over the presented population are close, except for the shear acting on the twin plane and the transverse stress. This result is significant as it provides information needed to model such parent-twin interactions in crystal plasticity codes.
 
The results of this research are published in the following articles:
 
  • Abdolvand, H., Majkut, M., Oddershede, J., Wright, J., Daymond, M. R., “Study of 3-D Stress Development in Parent and Twin Pairs of a Hexagonal Close-Packed Polycrystal: Part I- In situ Three-Dimensional X-ray Diffraction Measurement”, Acta Materialia, July 2015, Vol 93, Page 246-255, DOI: 10.1016/j.actamat.2015.04.020.
  • Abdolvand, H., Majkut, M., Oddershede, J., Wright, J., Daymond, M. R., “Study of 3-D Stress Development in Parent and Twin Pairs of a Hexagonal Close-Packed Polycrystal: Part II- Crystal Plasticity Finite Element Modeling”, Acta Materialia, July 2015, Vol 93, Page 235-245, DOI: 10.1016/j.actamat.2015.04.025.
  • Abdolvand, H., Majkut, M., Oddershede, J., Schmidt, S., Lienert, U., Diak, B., Withers, P. J., Daymond, M. R., “On the Deformation Twinning of MgAZ31B: a Three-Dimensional X-ray Diffraction Experiment and Crystal Plasticity Finite Element Model”, International Journal of Plasticity, July 2015, Vol 70, Page 77-97, DOI: 10.1016/j.ijplas.2015.03.001.

Deformation twinning in 2D

CPFE and DIC part by: Hamid Abdolvand1,  Mark Daymond1
HREBSD part by: Hamid Abdolvand2, Yi Guo2, Ben Britton3, Angus Wilkinson2 
1Department of Mechanical and Materials Engineering, Queen’s University, Kingston, Canada
2Department of Materials, University of Oxford, Oxford, UK
2Department of Materials, Royal School of Mines, Imperial College London, London, UK
 
 
This project was started at Queen's university, Canada, with the aim of developing a crystal plasticity finite element code that can model grain-grain interaction close to the crack tip in hydrided zirconium alloys. As many fundamental aspects of deformation mechanisms of hexagonal close-packed materials are still unknown, this project was redirected toward understanding deformation twinning. In this research, a crystal plasticity finite element code was developed by Hamid Abdolvand. The code is capable of modeling slip and twinning in HCP, BCC, and FCC polycrystals. The CPFE code was initially validated against in-situ neutron diffraction experiments that were conducted to measure texture and lattice strain development in Zircaloy-2 and MgAZ31. In-situ tensile experiments were also performed in an Scanning Electron Microscope (SEM) to study twin variant selection and strain development during uniaxial loading of Zircalloy-2 samples. EBSD maps from pre-load and unload steps were used to study twin nucleation and propagation while Digital Image Correlation technique (DIC) was used to examine the capability of the CPFE code in predicting localized strains.   
 
In the second part of this research, a newly installed Merlin (FEG-SEM) with a Bruker EBSD was calibrated and characterized for measuring localized lattice rotations, "relative" elastic strains, and Geometrically Necessary Dislocation (GND) densities in polycrystalline materials. As a part of this process, the system was used to measure GND and stress concentration close to twin tips. In parallel to this, the CPFE code was updated for incorporating the effects of the transformation strain into the materials' constitutive equations. 
 
The results of this research are published in the following articles:
 
  • Abdolvand, H.*, Wilkinson, A. J., “On the effects of Reorientation and Shear Transfer during Twin Formation: Comparison between High Resolution Backscatter Diffraction Experiments and a Crystal Plasticity Finite Element Model”, International Journal of Plasticity, 2016, In Press, DOI: 10.1016/j.ijplas.2016.05.006. Open Access. 
 
  • Abdolvand, H.*, Wilkinson, A. J., “Assessment of Residual Stress Fields at Deformation Twin Tips and the Surrounding Environment”, Acta Materialia, February 2016, Vol 105, Page 219-231, DOI: 10.1016/j.actamat.2015.11.036. Open Access.
  • Abdolvand, H.*, Daymond, M. R., “Multi-Scale Modeling and Experimental Study of Twin Inception and Propagation in Hexagonal Close-Packed Materials Using a Crystal Plasticity Finite Element Approach; Part I: Average Behavior”, Journal of The Mechanics and Physics of Solids, 2013, Vol 61 (3), Page 783-802, DOI: 10.1016/j.jmps.2012.10.013.
  • Abdolvand, H.*, Daymond, M. R., “Multi-Scale Modeling and Experimental Study of Twin Inception and Propagation in Hexagonal Close-Packed Materials Using a Crystal Plasticity Finite Element Approach; Part II: Local Behavior”, Journal of The Mechanics and Physics of Solids, 2013, Vol 61 (3), Page 803-818, DOI: 10.1016/j.jmps.2012.10.017.
  • Abdolvand, H.*, Daymond, M. R., “Internal Strain and Texture Development during Twinning: Comparing Neutron Diffraction Measurements with Crystal Plasticity Finite Element Approaches”, Acta Materialia, 2012, Vol 60 (5), Page 2240-2248, DOI: 10.1016/j.actmat.2012.01.016.
  • Abdolvand, H., Daymond, M. R.*, Mareau, C., “Incorporation of Twinning into a Crystal Plasticity Finite Element Model: Evolution of Lattice Strains and Texture in Zircaloy-2” International Journal of Plasticity, 2011, Vol 27 (11), Page 1721-1738, DOI:10.1016/j.ijplas.2011.04.005.

Transformation plasticity during thermo-mechanical cycles

By: Hamid Abdolvand1, Nicholas O'Meara1, Joanna Walsh1, John A. Francis1, Ben Pellereau2, and Philip Withers1
1School of Materials, The University of Manchester, Manchester, UK
2Rolls-Royce Plc, Raynesway, Derby, UK
 
 
 

The manufacturing of thick-walled pressure vessels as encountered in the nuclear industry generally requires multipass welding techniques, for which the measurement of residual stresses development in the vicinity of thick-section welds can be costly or impractical. SA508 grade 3 and grade 4 are nuclear pressure vessel steels that undergo phase transformation during welding. The development of residual stress during the welding of these steels depends not only on key phase transformations, but also on the mechanical properties of the individual phases (ferrite, bainite, or martensite, or a mixture) that form. In this work, key thermo-mechanical properties of SA508 Grade 3 & 4 steels were investigated to enable more reliable materials models to be established for weld simulation. For this purpose, samples were heated to different peak temperatures and held for different time intervals in order to allow for changes in the austenite grain size. These samples were subsequently quenched and their PAGSs were measured. Free dilatometry experiments were also performed using a Gleeble 3500 weld simulator to investigate the effects of cooling rate on the formation of the final phase. Further, the evolution of the transformation strain as a function of applied load during the martensitic phase transformation was measured. In parallel to this, variant selection during martensitic phase transformation was studied in-situ by the use of an electro-thermo-mechanical testing machine that was installed at Diamond Synchrotron X-ray facility.

The results of this research are published in the following articles:

  • Abdolvand, H.*, Francis, J. A., Azough F., Walsh, J., Gill, M. C., Withers, P. J., “On the Thermo-mechanical Behaviour of SA508 Grade 4 Ferritic Steel”, Proceedings of ASME 2014 Pressure Vessels and Piping Conference, 2014, PVP2014-28972, DOI:10.1115/PVP2014-28972. 
  • O’Meara, N.*, Abdolvand, H., Francis, J. A., Smith, S. D., Withers, P. J., “Quantifying the Metallurgical Response of a Nuclear Steel to Welding Thermal Cycles”, Materials Science and Technology, 2016, In Press, DOI: 10.1080/02670836.2015.1132529.
  • Mark, A. F.*,  Moat, R., Forsey, A., Abdolvand, H., Withers, P. J., “A New Method for Quantifying Anisotropic Martensitic Transformation Strains Accumulated During Constrained Cooling”, Materials Science and Engineering A, 2014, Vol 611, Page 354-361, DOI:10.1016/j.msea.2014.06.012.
  • Francis, J. A.*, Moat, R. J., Abdolvand, H., Forsey, A., “An Assessment of the Mechanism of Transformation Plasticity in SA508 Grade 3 Steel during Simulated Welding Thermal Cycles”, Materials Science Forum, 2014, Vol 777, Page 188-193, DOI:10.4028/www.scientific.net/MSF.777.188.

Residual stress in autogenous and narrow gap laser welding of 316L stainless steel

By: A. S. Elmesalamy1, H. Abdolvand1, J. N. Walsh1, J. A. Francis1, L. Li1
1School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester, UK
 
Thick-section austenitic stainless steels have widespread industrial applications, especially in nuclear power plants, where stress-corrosion cracking is often of major concern. Problems tend to arise in the vicinity of welds, where substantial residual stresses often reside. In this research, the residual stresses in autogenous high power laser welds and narrow gap laser welds (NGLW) in 10 mm thick AISI grade 316L steel plates were studied by the use of both neutron diffraction and the contour method. The element birth & death technique was used to model torch traveling and to simulate the laying of the filler materials onto the parent substrates.   

The results of this research is published in the following article:

  • Elmesalamy, A. S*, Abdolvand, H., Walsh, J. N., Francis, J. A., Suder, W., Williams, S., Li, L., “Measurement and modelling of the residual stresses in autogenous and narrow gap laser welded AISI grade 316L stainless steel plates”, International Journal of Pressure Vessels and Piping, 2016, DOI: 10.1016/j.ijpvp.2016.09.007

Thermo-mechanical response of polymer matrix composites

By Hamid Abdolvand and M. Shokrieh
Iran University of Sciene and Technology
 
Spatial distributions of temperatures in different glass/epoxy composite laminates were extracted experimentally and were compared with 3D mathematical models. A finite difference approach was used to solve the 3D equations considering changes in the physical properties of the samples with temperature. Experiments were conducted on both unidirectional and woven laminates with different thicknesses. The results of the modeling and experiments in unidirectional laminates show that heat transfer occurs more in the longitudinal direction than in the transverse direction. Experimentally, it was observed that this behavior influences the morphology of the delamination where an elliptical delamination was observed in unidirectional laminates and a circular delamination was observed in woven laminates. 
 
The results of this research are published in the following article:
  • Shokrieh, M., Abdolvand, H., “Three Dimensional Modeling and Experimental Validation of Heat Transfer in Polymer Matrix Composites”, Journal of Composite Materials, 2011, Vol 45 (19), Page 1953-1965, DOI: 10.1177/0021998310393295.