| 1. |
- Malik, Amer, et al.
(författare)
-
Three dimensional elasto-plastic phase field simulation of martensitic transformation in polycrystal
- 2012
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 556, s. 221-232
-
Tidskriftsartikel (refereegranskat)abstract
- The Phase Field Microelasticity model proposed by Khachaturyan is used to perform 3D simulation of Martensitic Transformation in polycrystalline materials using finite element method. The effect of plastic accommodation is investigated by using a time dependent equation for evolution of plastic deformation. In this study, elasto-plastic phase field simulations are performed in 2D and 3D for different boundary conditions to simulate FCC -> BCT martensitic transformation in polycrystalline Fe-0.3%C alloy. The simulation results depict that the introduction of plastic accommodation reduces the stress intensity in the parent phase and hence causes an increase in volume fraction of the martensite. Simulation results also show that autocatalistic transformation initiates at the grain boundaries and grow into the parent phase. It has been concluded that stress distribution and the evolution of microstructure can be predicted with the current model in a polycrystal.
|
|
| 2. |
- Yeddu, Hemantha Kumar, et al.
(författare)
-
3D Phase Field Modeling of Martensitic Microstructure Evolution in Steels
- 2011
-
Ingår i: Solid State Phenomena. - 1012-0394 .- 1662-9779. ; 172-174, s. 1066-1071
-
Tidskriftsartikel (refereegranskat)abstract
- Complex martensitic microstructure evolution in steels generates enormous curiosity among the materials scientists and especially among the Phase Field (PF) modeling enthusiasts. In the present work PF Microelasticity theory proposed by A.G. Khachaturyan coupled with plasticity is applied for modeling the Martensitic Transformation (MT) by using Finite Element Method (FEM). PF simulations in 3D are performed by considering different cases of MT occurring in a clamped system, i.e. simulation domain with fixed boundaries, of (a) pure elastic material with dilatation (b) pure elastic material without dilatation (c) elastic perfectly plastic material with dilatation having (i) isotropic as well as (ii) anisotropic elastic properties. As input data for the simulations the thermodynamic parameters corresponding to Fe - 0.3% C alloy as well as the physical parameters corresponding to steels acquired from experimental results are considered. The results indicate that elastic strain energy, dilatation and plasticity affect MT whereas anisotropy affects the microstructure.
|
|
| 3. |
- Yeddu, Hemantha Kumar, 1980-, et al.
(författare)
-
A phase-field study of the physical concepts of martensitic transformations in steels
- 2012
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 538, s. 173-181
-
Tidskriftsartikel (refereegranskat)abstract
- A 3D elastoplastic phase-field model is employed to study various driving forces associated withmartensitic transformations, plastic deformation behavior as well as the habit plane concept. Usage ofthermodynamic parameters corresponding to Fe–0.3%C alloy in conjunction with anisotropic physicalparameters of steels as the simulation parameters have yielded the results in reasonable agreement withexperimental observations. From the simulation results, it is concluded that there exist three critical drivingforces that control the transformation and also that the plastic deformation behavior of the materialgreatly affects the transformation. The model predicts the initial habit plane of the first infinitesimalunit of martensite as (−1 1 1). The model also predicts that, as the transformation progresses, the abovementioned martensite domain rotates and finally orients along the new habit plane of (−2 1 1).
|
|
| 4. |
- Yeddu, Hemantha Kumar, 1980-, et al.
(författare)
-
Effect of martensite embryo potency on the martensitic transformations in steels-A 3D phase-field study
- 2013
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 577:Supplement: 1, s. S141-S146
-
Tidskriftsartikel (refereegranskat)abstract
- Nucleation during martensitic transformation (MT) has received considerable theoretical attention as it is a complex and rapid process that makes it difficult to study in situ. Earlier theoretical studies indicate that there exists a critical size of the embryo, dependent on the temperature, below which no nucleation would occur. Acquiring knowledge of the critical size and shape of the martensite embryo through simulated MT might yield a better understanding of some of the martensite nucleation aspects. In the present work phase-field method is employed to determine the critical size and shape parameters of the martensite embryo. 3D phase field simulations with pre-existing embryo of spherical as well as ellipsoidal shapes are performed by considering physical parameters corresponding to Fe-C alloys. The results indicate that the potency of martensite embryo affects the MT and also that an ellipsoidal embryo is the most favorable shape, which supports the earlier studies on martensite nucleation. Dislocation density also plays a major role in determining the embryo potency.
|
|
| 5. |
- Yeddu, Hemantha Kumar, et al.
(författare)
-
Martensite formation in stainless steels under transient loading
- 2014
-
Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 608, s. 101-105
-
Tidskriftsartikel (refereegranskat)abstract
- We present a 3D elastoplastic phase-field model to study the martensite formation in stainless steels under transient loading. Linear isotropic strain hardening is considered. Our results show that various combinations of martensite variants, which minimize the mechanical energy and maximize the net available driving force, are favored under different transient loading directions. The mechanical properties of steels under transient loading depend on the direction of loading. The areas where the load is applied, i.e. the grain boundaries, become favorable martensite nucleation sites.
|
|
| 6. |
- Yeddu, Hemantha Kumar, 1980-
(författare)
-
Martensitic Transformations in Steels : A 3D Phase-field Study
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Martensite is considered to be the backbone of the high strength of many commercial steels. Martensite is formed by a rapid diffusionless phase transformation, which has been the subject of extensive research studies for more than a century. Despite such extensive studies, martensitic transformation is still considered to be intriguing due to its complex nature. Phase-field method, a computational technique used to simulate phase transformations, could be an aid in understanding the transformation. Moreover, due to the growing interest in the field of “Integrated computational materials engineering (ICME)”, the possibilities to couple the phase-field method with other computational techniques need to be explored. In the present work a three dimensional elastoplastic phase-field model, based on the works of Khachaturyan et al. and Yamanaka et al., is developed to study the athermal and the stress-assisted martensitic transformations occurring in single crystal and polycrystalline steels. The material parameters corresponding to the carbon steels and stainless steels are considered as input data for the simulations. The input data for the simulations is acquired from computational as well as from experimental works. Thus an attempt is made to create a multi-length scale model by coupling the ab-initio method, phase-field method, CALPHAD method, as well as experimental works. The model is used to simulate the microstructure evolution as well as to study various physical concepts associated with the martensitic transformation. The simulation results depict several experimentally observed aspects associated with the martensitic transformation, such as twinned microstructure and autocatalysis. The results indicate that plastic deformation and autocatalysis play a significant role in the martensitic microstructure evolution. The results indicate that the phase-field simulations can be used as tools to study some of the physical concepts associated with martensitic transformation, e.g. embryo potency, driving forces, plastic deformation as well as some aspects of crystallography. The results obtained are in agreement with the experimental results. The effect of stress-states on the stress-assisted martensitic microstructure evolution is studied by performing different simulations under different loading conditions. The results indicate that the microstructure is significantly affected by the loading conditions. The simulations are also used to study several important aspects, such as TRIP effect and Magee effect. The model is also used to predict some of the practically important parameters such as Ms temperature as well as the volume fraction of martensite formed. The results also indicate that it is feasible to build physically based multi-length scale model to study the martensitic transformation. Finally, it is concluded that the phase-field method can be used as a qualitative aid in understanding the complex, yet intriguing, martensitic transformations.
|
|
| 7. |
- Yeddu, Hemantha Kumar, et al.
(författare)
-
Multi-length scale modeling of martensitic transformations in stainless steels
- 2012
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 60:19, s. 6508-6517
-
Tidskriftsartikel (refereegranskat)abstract
- In the present work a multi-length scale model is developed to study both the athermal and stress-assisted martensitic transformations in a single crystal of 301 type stainless steel. The microstructure evolution is simulated using elastoplastic phase-field simulations in three dimensions. The input data for the simulations is acquired from a combination of computational techniques and experimental works. The driving force for the transformation is calculated by using the CALPHAD technique and the elastic constants of the body-centered cubic phase are calculated by using ab initio method. The other input data is acquired from experimental works. The simulated microstructures resemble a lath-type martensitic microstructure, which is in good agreement with the experimental results obtained for a stainless steel of similar composition. The martensite habit plane predicted by the model is in accordance with experimental results. The Magee effect, i.e. formation of favorable martensite variants depending on the loading conditions, is observed in the simulations. The results also indicate that anisotropic loading conditions give rise to a significant anisotropy in the martensitic microstructure.
|
|
| 8. |
- Yeddu, Hemantha Kumar, et al.
(författare)
-
Stress-assisted martensitic transformations in steels : A 3-D phase-field study
- 2013
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 61:7, s. 2595--2606
-
Tidskriftsartikel (refereegranskat)abstract
- A 3D elastoplastic phase-field model is developed for modeling, using Finite Element Method (FEM), the stress-assisted martensitic transformation by considering plastic deformation as well as anisotropic elastic properties of steels. Phase-field simulations in 3D are performed by considering different loading conditions on a single crystal of austenite in order to observe the microstructure evolution. The thermodynamic parameters corresponding to an Fe – 0.3%C steel as well as the physical parameters corresponding to commercial steels, acquired from experimental results, are considered as the input data for the simulations. The simulation results clearly show the well-known Magee effect and Greenwood-Johnson effect. The results also show that even though the applied stresses are below the yield limit of the material, plastic deformation initiates due to the martensitic transformation,viz. the well known TRIP (transformation induced plasticity) phenomenon. Finally it is concluded that the loading conditions, TRIP phenomenon as well as the autocatalysis play a major role in the stress-assisted martensitic microstructure evolution.
|
|
| 9. |
- Yeddu, Hemantha Kumar, 1980-, et al.
(författare)
-
Three-dimensional phase-field modeling of martensitic microstructure evolution in steels
- 2012
-
Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 60:4, s. 1538-1547
-
Tidskriftsartikel (refereegranskat)abstract
- In the present work a 3-D elastoplastic phase-field (PF) model is developed, based on the PF microelasticity theory proposed by A.G.Khachaturyan and by including plastic deformation as well as anisotropic elastic properties, for modeling the martensitic transformation (MT) by using the finite-element method. PF simulations in 3D are performed by considering different cases of MT occurring in an elastic material, with and without dilatation, and in an elastic perfectly plastic material with dilatation having isotropic as well as anisotropic elastic properties. As input data for the simulations the thermodynamic parameters corresponding to anFe–0.3%C alloy as well as the physical parameters corresponding to steels acquired from experimental results are considered. The simulation results clearly show auto-catalysis and morphological mirror image formation, which are some of the typical characteristics of a martensitic microstructure. The results indicate that elastic strain energy, anisotropic elastic properties, plasticity and the external clamping conditions affect MT as well as the microstructure.
|
|
