Dynamic and meta-dynamic recrystallization of Ni-based superalloy Haynes 282
Doctoral thesis, 2022
Thermomechanical processes are a crucial manufacturing step because they can “reset” the microstructure, and set the starting point for all following steps. In turn, the microstructure can be used to tailor the mechanical properties of the material. It is therefore of great importance to understand how deformation parameters affect the resulting microstructure. The mechanism responsible for this “reset” of microstructures is recrystallization, where the thermal energy and internal stored energy drive the creation of new, deformation-free, grains at the expense of the deformed ones. However, recrystallization is a complex phenomenon affected by alloy composition, temperature, strain, strain rate etc.
In the work presented here, the dynamic, and meta-dynamic recrystallization mechanisms occurring in Ni-base superalloy Haynes 282 are investigated, both below and above the secondary carbide solvus temperature (1100 \C) at various strains, strain rates and post-deformation holding times. Discontinuous dynamic recrystallization, with a clear nucleation of grains at grain boundaries, was observed to be the dominating recrystallization mechanism. For strains up to 0.8 the increase in recrystallized fractions stemmed from nucleation of new grains, whereas for larger strains continued increase in recrystallized fractions was caused by grain growth. Particle stimulated nucleation, where MC carbides acted as nucleation sites, was also observed. Carbides located at grain boundaries did not affect the recrystallization progression significantly. During deformation, the strain rate was seen as the governing factor on the final microstructure, while temperature, strain and holding times were the dominating parameters affecting the meta-dynamic recrystallization. Larger strains led to shorter times to reach a fully recrystallized microstructure during a post-deformation hold. The average grain size also decreased with higher strains applied prior to a static hold.
In the work presented here, the dynamic, and meta-dynamic recrystallization mechanisms occurring in Ni-base superalloy Haynes 282 are investigated, both below and above the secondary carbide solvus temperature (1100 \C) at various strains, strain rates and post-deformation holding times. Discontinuous dynamic recrystallization, with a clear nucleation of grains at grain boundaries, was observed to be the dominating recrystallization mechanism. For strains up to 0.8 the increase in recrystallized fractions stemmed from nucleation of new grains, whereas for larger strains continued increase in recrystallized fractions was caused by grain growth. Particle stimulated nucleation, where MC carbides acted as nucleation sites, was also observed. Carbides located at grain boundaries did not affect the recrystallization progression significantly. During deformation, the strain rate was seen as the governing factor on the final microstructure, while temperature, strain and holding times were the dominating parameters affecting the meta-dynamic recrystallization. Larger strains led to shorter times to reach a fully recrystallized microstructure during a post-deformation hold. The average grain size also decreased with higher strains applied prior to a static hold.
hot compression
EBSD
dynamic recrystallization
meta-dynamic recrystallization
Ni-base superalloys
PJ salen, Kemigården 1
Opponent: Prof. Soran Birosca, School of Mechanical & Design Engineering, University of Portsmouth, England
Author
Emil Eriksson
Chalmers, Physics, Microstructure Physics
Dynamic and Post-Dynamic Recrystallization of Haynes 282 below the Secondary Carbide Solvus
Metals,;Vol. 11(2021)p. 1-24
Journal article
The Effect of Grain Boundary Carbides on Dynamic Recrystallization During Hot Compression of Ni-Based Superalloy Haynes 282
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science,;Vol. 53(2022)p. 29-38
Journal article
Dynamic recrystallization during hot compression of Ni-based superalloy Haynes 282
Journal of Alloys and Compounds,;Vol. 960(2023)
Journal article
Meta-Dynamic Recrystallization in the Ni-Based Superalloy Haynes 282
Metals,;Vol. 13(2023)
Journal article
Forging is one of the oldest metal working techniques and still sees tons of applications today. But what once a blacksmith hammering a sword on an anvil is today a process to shape pieces of material weighing tons. It is also a science to understand how different forging procedures will affect the material.
During forging, the material is not only shaped, its entire microstructure changes. In a solid piece of a metallic material, atoms arrange themselves into specific lattices called crystal structures. For example, in the face centered cubic atoms occupy the corners and faces of a cube. A grain is a volume where all cubes can be perfectly stacked together. A metal usually consist of multiple grains, with grain boundaries in between. The size, shape and orientations of these grains is what is defined as the microstructure, and it determines the mechanical properties of the material.
During forging, the applied forces cause the atoms to move around and defects are introduced into the atomic planes. Eventually, the defects will be so numerous that in order to reduce the increase in energy they cause, new grains, with much fewer defects, will be created. This is called recrystallization. All parameters during forging, temperature, how fast and how much deformation is applied, will affect how the recrystallization.
With electron microscopy we can image the microstructure after forging procedures and determine the progression of recrystallization. We can also gather the mechanical data from the compression tests and correlate the mechanical behavior to the microstructural one.
During forging, the material is not only shaped, its entire microstructure changes. In a solid piece of a metallic material, atoms arrange themselves into specific lattices called crystal structures. For example, in the face centered cubic atoms occupy the corners and faces of a cube. A grain is a volume where all cubes can be perfectly stacked together. A metal usually consist of multiple grains, with grain boundaries in between. The size, shape and orientations of these grains is what is defined as the microstructure, and it determines the mechanical properties of the material.
During forging, the applied forces cause the atoms to move around and defects are introduced into the atomic planes. Eventually, the defects will be so numerous that in order to reduce the increase in energy they cause, new grains, with much fewer defects, will be created. This is called recrystallization. All parameters during forging, temperature, how fast and how much deformation is applied, will affect how the recrystallization.
With electron microscopy we can image the microstructure after forging procedures and determine the progression of recrystallization. We can also gather the mechanical data from the compression tests and correlate the mechanical behavior to the microstructural one.
Subject Categories
Other Physics Topics
Metallurgy and Metallic Materials
Areas of Advance
Materials Science
ISBN
978-91-7905-726-8
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5192
Publisher
Chalmers
PJ salen, Kemigården 1
Opponent: Prof. Soran Birosca, School of Mechanical & Design Engineering, University of Portsmouth, England