Periodic Reporting for period 3 - PMP (The Physics of Metal Plasticity)
Période du rapport: 2023-10-01 au 2025-03-31
The societal need to conserve raw materials and energy and reduce CO2 emissions calls for lighter and stronger metal components. The advantage of metals is their unique combination of plasticity (i.e. formability) and strength, which is governed by their complex structure. This structure is organized hierarchically on several length scales, from grains over domains to defects (dislocations). This complexity has led to the common theoretical framework not being physics, but an engineering science: metallurgy. As a result, phenomenological models prevail. So far, these have failed in a rather spectacular sense with respect to predicting how the structural self-organization takes place during deformation and how this leads to increased strength and affects failure and corrosion properties.
The biggest obstacle to advance our understanding of the mechanisms underlying self-organization has been a lack of methods to visualize the dynamics of the structure under realistic conditions. Prior to the start of the proejct the PI developed a hard x-ray microscope for high-resolution 3D studies of mm thick samples at the European Synchrotron Radiation Facility, ESRF. Uniquely, this allows us to zoom into materials and map the interior structure during processing.
The overall objective of PMP is to use this new tool to unravel the science of how metals deform and become stronger. For the first time, we can directly see the processes involved. This will provide the answer to fundamental questions at the core of metal science. The aim is that the PMP data will not only guide theory, but allow for unprecedented testing of quantitative 3D models by direct comparison with 3D experiment at all relevant scales. Based on these results, we will construct a physically based, multiscale model of plasticity that can predict which patterns evolve when and where in the metal and what the associated strengthening is.
On a broader perspective, the consensus in the materials community is that “materials design in a computer” is the future. However this requires a new generation of materials models that can predict structural evolution during processing, at all scales. PMP introduces a new approach to performing materials science with the promise to facilitate the establishment of such physics based models.
The biggest obstacle to advance our understanding of the mechanisms underlying self-organization has been a lack of methods to visualize the dynamics of the structure under realistic conditions. Prior to the start of the proejct the PI developed a hard x-ray microscope for high-resolution 3D studies of mm thick samples at the European Synchrotron Radiation Facility, ESRF. Uniquely, this allows us to zoom into materials and map the interior structure during processing.
The overall objective of PMP is to use this new tool to unravel the science of how metals deform and become stronger. For the first time, we can directly see the processes involved. This will provide the answer to fundamental questions at the core of metal science. The aim is that the PMP data will not only guide theory, but allow for unprecedented testing of quantitative 3D models by direct comparison with 3D experiment at all relevant scales. Based on these results, we will construct a physically based, multiscale model of plasticity that can predict which patterns evolve when and where in the metal and what the associated strengthening is.
On a broader perspective, the consensus in the materials community is that “materials design in a computer” is the future. However this requires a new generation of materials models that can predict structural evolution during processing, at all scales. PMP introduces a new approach to performing materials science with the promise to facilitate the establishment of such physics based models.
The overall goal of direct three-dimensional visualisation of the creation of dislocations, their self-organization into boundaries, and the subsequent creation of ever more complex patterns has been successfully demonstrated experimentally – as well as the ability to monitor the mechanical fields around the dislocations/patterns. We have also developed most of the algorithms and tools needed to compare the experimental data from the x-ray microscope with dislocation dynamics simulations.
In the short period left by the COVID pandemic and a one year shut down at ESRF for an upgrade, we had five beamtimes. During these beamtimes we have acquired 3D movies of the two major physical processes taken place: pattern initiation and pattern refinement.
The goal of first set of experiments was to understand why and how patterning is initiated and its relation to mechanical work-hardening in samples deformed up to 4% elongation. This deformation regime has essentially been uncovered ground due to previous lack of proper characterization techniques. A major finding from our work is that features resembling the dislocation patterns at higher strains are observed already at 0.5%. This reveals that patterning starts at the early stages of plastic deformation and that some of the fundamental mechanisms are the same at all loadsteps. Next, we have obtained two experimental 3D movies from in-situ tensile testing showing how the individual dislocations move and interact at the very onset of plastic deformation.
The goal of second set of experiments was to understand how and why the structures established get continuously smaller at larger deformation (4-30%). Here very comprehensive ex situ and in situ data sets have been acquired. Initial visualisation of the data clearly shows the evolution in the patterns. Procedures to characterise the patterns quantitatively are currently being tested with inspiration from the methods used in electron microscopy.
The collaboration with the CDD modelling group of El-Azab in Purdue has been strengthened via a sabbatical by Prof Purdue at DTU and joint papers that makes the foundation for combining experimental data and modelling. A new collaboration with Stanford has been stablished. Jointly we have used the PMP methodology to unravel the role of dislocations in the melting of pure metals.
In the short period left by the COVID pandemic and a one year shut down at ESRF for an upgrade, we had five beamtimes. During these beamtimes we have acquired 3D movies of the two major physical processes taken place: pattern initiation and pattern refinement.
The goal of first set of experiments was to understand why and how patterning is initiated and its relation to mechanical work-hardening in samples deformed up to 4% elongation. This deformation regime has essentially been uncovered ground due to previous lack of proper characterization techniques. A major finding from our work is that features resembling the dislocation patterns at higher strains are observed already at 0.5%. This reveals that patterning starts at the early stages of plastic deformation and that some of the fundamental mechanisms are the same at all loadsteps. Next, we have obtained two experimental 3D movies from in-situ tensile testing showing how the individual dislocations move and interact at the very onset of plastic deformation.
The goal of second set of experiments was to understand how and why the structures established get continuously smaller at larger deformation (4-30%). Here very comprehensive ex situ and in situ data sets have been acquired. Initial visualisation of the data clearly shows the evolution in the patterns. Procedures to characterise the patterns quantitatively are currently being tested with inspiration from the methods used in electron microscopy.
The collaboration with the CDD modelling group of El-Azab in Purdue has been strengthened via a sabbatical by Prof Purdue at DTU and joint papers that makes the foundation for combining experimental data and modelling. A new collaboration with Stanford has been stablished. Jointly we have used the PMP methodology to unravel the role of dislocations in the melting of pure metals.
The x-ray dark field microscope, the data analysis method and the interfacing to mechanical modelling are all novel concepts. To illustrate the impact, we mention that the methodological work undertaken in PMP has not only led to the design of a dedicated flagship instrument at ESRF: the new microscopy Beamline ID03 - the concept is also being copied at 6 other synchrotrons and Xray Free-electron Lasers. In particular an implementation at XFEL at LCLS at Stanford demonstrated how one can acquire movies of structural evolution deeply within mm sized samples on the ns time scale. This was used to visualize the transmission and reflection of sound waves, with the outlook to study dislocation dynamics at the relevant time scale (an ambition level that is beyond the scope of the original proposal.)
The methods and first results for plasticity are reeky novel and have been well received by the community, in terms of invitations to give lectures, but perhaps more importantly in setting up a future international user community. This is backed by a new Commission of Diffraction Microstructure Imaging within the IUCr.
A new and upgraded microscope will be commissioned by early 2024. At the same time most of the data analysis software has been validated. Hence, we are in a strong position to move ahead with developing PMP and addressing the science questions outlined in the project proposal. With the constraint of the slow start due to the unfortunate timing of COVID and the ESRF shut down we anticipate delivering on the project as proposed
The methods and first results for plasticity are reeky novel and have been well received by the community, in terms of invitations to give lectures, but perhaps more importantly in setting up a future international user community. This is backed by a new Commission of Diffraction Microstructure Imaging within the IUCr.
A new and upgraded microscope will be commissioned by early 2024. At the same time most of the data analysis software has been validated. Hence, we are in a strong position to move ahead with developing PMP and addressing the science questions outlined in the project proposal. With the constraint of the slow start due to the unfortunate timing of COVID and the ESRF shut down we anticipate delivering on the project as proposed