K-S Relationship Identification Technique by EBSD

2011 ◽  
Vol 465 ◽  
pp. 415-418 ◽  
Author(s):  
M.C. Marinelli ◽  
M.G. Moscato ◽  
Javier Signorelli ◽  
A. El Bartali ◽  
I. Alvarez-Armas
Keyword(s):  
Slip System ◽  
Grain Boundaries ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Electron Backscattered Diffraction ◽  
Identification Technique ◽  
Cold Rolled ◽  
Ebsd Technique ◽  
Relationship Identification

This paper focuses on the identification of activated slip system in flat specimens of hot- and cold-rolled UNS S32750 DSS plates subjected to low-cycle fatigue, paying particular attention on the existence of the K-S relationship. Electron Backscattered Diffraction (EBSD) technique was used to determine the local crystallographic properties of both phases. Although 27182 couples of α/γ grains were analyzed, the crystallographic K-S relationships were rarely observed between them. As a conclusion, it was observed that microcracks were mostly nucleated at grain boundaries and rarely at the extrusions.

Crystal Visco-Plastic Model for Directionally Solidified Ni-Base Superalloys Under Monotonic and Low Cycle Fatigue

2021 ◽  
Author(s):  
Navindra Wijeyeratne ◽  
Firat Irmak ◽  
Ali P. Gordon
Keyword(s):  
Grain Boundaries ◽  
Gas Turbines ◽  
Thermal Stresses ◽  
Low Cycle Fatigue ◽  
Turbine Blades ◽  
Material Behavior ◽  
Flow Rule ◽  
Cycle Fatigue ◽  
Directionally Solidified ◽  
Crystallographic Slip

Abstract Nickel-base superalloys (NBSAs) are extensively utilized as the design materials to develop turbine blades in gas turbines due to their excellent high-temperature properties. Gas turbine blades are exposed to extreme loading histories that combine high mechanical and thermal stresses. Both directionally solidified (DS) and single crystal NBSAs are used throughout the industry because of their superior tensile and creep strength, excellent low cycle fatigue (LCF), high cycle fatigue (HCF), and thermomechanical fatigue (TMF) capabilities. Directional solidification techniques facilitated the solidification structure of the materials to be composed of columnar grains in parallel to the <001> direction. Due to grains being the sites of failure initiation the elimination of grain boundaries compared to polycrystals and the alignment of grain boundaries in the normal to stress axis increases the strength of the material at high temperatures. To develop components with superior service capabilities while reducing the development cost, simulating the material’s performance at various loading conditions is extremely advantageous. To support the mechanical design process, a framework consisting of theoretical mechanics, numerical simulations, and experimental analysis is required. The absence of grain boundaries transverse to the loading direction and crystallographic special orientation cause the material to exhibit anisotropic behavior. A framework that can simulate the physical attributes of the material microstructure is crucial in developing an accurate constitutive model. The plastic flow acting on the crystallographic slip planes essentially controls the plastic deformation of the material. Crystal Visco-Plasticity (CVP) theory integrates this phenomenon to describe the effects of plasticity more accurately. CVP constitutive models can capture the orientation, temperature, and rate dependence of these materials under a variety of conditions. The CVP model is initially developed for SX material and then extended to DS material to account for the columnar grain structure. The formulation consists of a flow rule combined with an internal state variable to describe the shearing rate for each slip system. The model presented includes the inelastic mechanisms of kinematic and isotropic hardening, orientation, and temperature dependence. The crystallographic slip is accounted for by including the required octahedral, cubic, and cross slip systems. The CVP model is implemented through a general-purpose finite element analysis software (i.e., ANSYS) as a User-Defined Material (USERMAT). Uniaxial experiments were conducted in key orientations to evaluate the degree of elastic and inelastic anisotropy. The temperature-dependent modeling parameter is developed to perform non-isothermal simulations. A numerical optimization scheme is utilized to develop the modeling constant to improve the calibration of the model. The CVP model can simulate material behavior for DS and SX NBSAs for monotonic and cyclic loading for a range of material orientations and temperatures.

Cold-Rolled Micro-Texture in Polycrystalline 3%Si-Fe

2007 ◽  
Vol 558-559 ◽  
pp. 885-890
Author(s):  
Takeshi Imamura ◽  
Yasuyuki Hayakawa ◽  
Mineo Muraki
Keyword(s):  
High Resolution ◽  
Slip System ◽  
Grain Boundaries ◽  
Orientation Relationship ◽  
Applied Stress ◽  
Slip Plane ◽  
Deformation Bands ◽  
Maximum Value ◽  
Resolution Electron ◽  
Cold Rolled

Cold-rolled micro-texture of polycrystalline 3%Si-Fe was investigated using high-resolution Electron BackScattering Patterns (EBSP) method. There were deformation bands near grain boundaries. The orientation relationship between the deformation bands and the surrounding deformed grains is explained by the orientation rotation around a <211> axis. The activated slip to generate these deformation bands is estimated from the <211> rotation. The S-value, which is a geometrical index of slip operation against applied stress, of this slip system was not maximum value of all, but it had a common slip plane with an adjacent grain. A hypothesis that the slip system having a common slip plane with an adjacent grain is activated was proposed from the present results.

Fatigue Deformation Behavior of FGH96 Superalloy under Low Cycle Fatigue Loading

2013 ◽  
Vol 641-642 ◽  
pp. 418-422
Author(s):  
Yu Li Gu ◽  
Yu Huai He ◽  
Chang Kui Liu ◽  
Chun Hu Tao
Keyword(s):  
Grain Boundaries ◽  
Fatigue Failure ◽  
Small Angle ◽  
Electron Backscatter Diffraction ◽  
Low Cycle Fatigue ◽  
Fatigue Loading ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Cycle Fatigue ◽  
Nickel Based Superalloy

Low cycle fatigue failure tests of the powder metallurgical nickel based superalloy FGH96 at 550°C and 720°C were carried out under total strain-controlled mode (R=-1). The fatigue failure behaviors were investigated by analyzing cyclic stress response and observing microstructure after fatigue through scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The results show that FGH96 superalloy exhibits cyclic stability at 550°C, and cyclic softening afterwards at 720°C with Δε/2=0.4% , and of cyclic softening at 720°C with Δε/2=0.7%. After high temperature low cycle fatigue, the γ′ precipitates are cuboidal for all samples. No coarsening of γ′ precipitates was detected at 550°C and at 720°C with Δε/2=0.4%, but small γ′ precipitates get together to be larger precipitates at 720°C with Δε/2=0.7%. EBSD shows that the continuous small angle grain boundaries are produced during the fatigue. The small angle grain boundaries have a significant increase at 720°C, especially that case at Δε/2=0.7%.

Effect of Pre-Recovery on Recrystallization Texture in Nickel Substrates for Coated Conductors

2013 ◽  
Vol 537 ◽  
pp. 274-278
Author(s):  
Xing Pin Chen ◽  
Xue Chen ◽  
Jing Peng Zhang
Keyword(s):  
Grain Boundaries ◽  
Recrystallization Texture ◽  
Cube Texture ◽  
Pure Nickel ◽  
Coated Conductors ◽  
Recrystallization Annealing ◽  
Electron Backscattered Diffraction ◽  
Recovery Treatment ◽  
Nickel Substrates ◽  
Cold Rolled

Electron backscattered diffraction (EBSD) technology was applied to study the effect of pre-recovery on the recrystallization texture in nickel substrates for coated conductors. Pure nickel (99.999%) was cold rolled by a 95% total reduction, and then samples were annealed at 200 °C for 1 hour and quenched for fully recovery, and finally annealed at 600 °C for 1 hour and quenched in water. The results show that pre-recovery had a strong influence on the formation of cube recrystallization texture. Compared with samples without pre-recovery treatment at 200 °C, samples through pre-recovery treatment can achieve stronger cube texture after recrystallization annealing, and develop more low-angle grain boundaries but less sigma 3 (Σ3) grain boundaries.

scholarly journals Microstructural Evolution along the NiCrMoV Steel Welded Joints Induced by Low-Cycle Fatigue Damage

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 811
Author(s):  
Shuo Weng ◽  
Yuhui Huang ◽  
Mingliang Zhu ◽  
Fuzhen Xuan
Keyword(s):  
Dislocation Density ◽  
Grain Boundaries ◽  
Strain Amplitude ◽  
Microstructural Evolution ◽  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Tensile Tests ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Nicrmov Steel

The degradation of mechanical properties of materials is essentially related to microstructural changes under service loadings, while the inhomogeneous degradation behaviors along welded joints are not well understood. In the present work, microstructural evolution under low-cycle fatigue in base metal (BM) and weld metal (WM) of NiCrMoV steel welded joints were investigated by miniature tensile tests and microstructural observations. Results showed that both the yield strength and ultimate tensile strength of the BM and WM decreased after low-cycle fatigue tests, which were attributed to the reduction of dislocation density and formation of low-energy structures. However, the microstructural evolution mechanisms in BM and WM under the same cyclic loadings were different, i.e., the decrease of dislocation density in BM was attributed to the dislocation pile-ups along the grain boundaries, dislocation tangles around the carbides at the lower strain amplitudes (±0.3% or ±0.5%). Additionally, when the strain amplitude was ±8%, the dislocation density was further decreased by the formation of subgrains in BM. For WM, the dislocation density decreased with the increase of strain amplitude, which was mainly caused by the dislocation pile-ups along the grain boundaries and the formation of subgrains.

Effects of Grain Boundaries in Columnar Grained Electrical Steels during Deformation and Recrystallization

2013 ◽  
Vol 753 ◽  
pp. 173-176
Author(s):  
Ping Yang ◽  
Yuan Yuan Shao ◽  
Ning Zhang ◽  
Ling Cheng ◽  
Wei Min Mao
Keyword(s):  
Grain Boundaries ◽  
Grain Orientation ◽  
Rolling Direction ◽  
Single Type ◽  
Electrical Steels ◽  
Grain Orientations ◽  
Columnar Grains ◽  
Cold Rolled ◽  
Ebsd Technique ◽  
Hot Rolled

The crystallographic and topographic anisotropies of columnar grains can exert strong influence on the subsequently hot rolled, cold rolled and annealed microstructures, textures and properties. The single type tilting grain boundaries among columnar grains will behave differently depending on grain orientations, rolling direction and stress state due to hot rolling and thus affect in return the microstructure and texture to some extents. This work aims to reveal the effects of grain boundaries and their neighboring grain orientation gradients in three types of Fe-3Si in differently processed samples using EBSD technique.

Microstructural Analysis of Low-Cycle Fatigue Damage Process of Sn-Ag-Cu Solder Joint

2013 ◽  
Author(s):  
Hiroyuki Kontani ◽  
Yoshiharu Kariya ◽  
Tomoya Fumikura
Keyword(s):  
Stress Concentration ◽  
Solder Joint ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
High Angle ◽  
Concentration Region ◽  
Joint Area ◽  
Stress Concentration Region

In this study, the relationship between microstructural change and fracture in the process of low-cycle fatigue of Sn-Ag-Cu solder joint was investigated using the solder ball of 630μm and 100μm in diameter by analysis of crystallographic orientation by means of EBSD. The 630μm specimen has subgrain boundaries formed by dynamic recovery in the stress concentration region, and the subgrain boundaries become high-angle random grain boundaries by additional cycles. The fatigue crack stably propagates along the random grain boundary in the stress concentration region. In contrast, the 100μm specimen has subgrain boundaries and high-angle random grain boundaries formed across the entire joint area. Since the occurrence of grain boundary fracture across the entire joint area by the connection of high energy grain boundaries, the crack propagation life of the 100μm specimen shortens without the stable crack growth compared to the 630μm specimen.

Effect of Crystallographic Properties on Low Cycle Fatigue Strength at Elevated Temperature for Ni-Based Directionally Solidified Superalloy

2014 ◽  
Author(s):  
Takashi Yokoyama ◽  
Masaru Sekihara
Keyword(s):  
Elevated Temperature ◽  
Crack Initiation ◽  
Grain Boundaries ◽  
Low Cycle Fatigue ◽  
Equivalent Plastic Strain ◽  
Cycle Fatigue ◽  
Directionally Solidified ◽  
Crack Location ◽  
Loading Direction ◽  
Secondary Axis

Low cycle fatigue tests at elevated temperature were conducted on a Ni-based directionally solidified superalloy subjected to transverse loading. To investigate the effect of the arrangement and crystal orientation of grains on the crack initiation, the electron back-scatter diffraction (EBSD) method was applied on the surface of the tested specimens. In addition, finite element analysis that considered the plastic behavior of crystal grains was performed to evaluate the relationship between the crack initiation and the local stress or strain that develops near the grain boundaries. The results are summarized below. As for the effect of crystallographic properties in the specimen surface, cracks generally initiated near the grain boundaries that neighbored the grain whose secondary axis inclined to loading direction by more than 20 degrees and Schmid factor to uniaxial loading was more than 0.48. The crack location was not confirmed to correlate with the grain boundary misorientation of the neighboring grains on the surface. However, most cracks initiated near the grain boundaries that neighbored the grain whose secondary axis met the loading direction at a larger angle than the grain located in the opposite surface. The results of FEM analysis revealed that the location where high cumulative equivalent plastic strain developed generally corresponded to the crack location and that the cumulative equivalent plastic strain correlated with the number of crack initiation cycles.

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