Dislocation‐free zone model of fracture: The effect of transgranular microcrack nucleated from a grain‐boundary ledge

1994 ◽  
Vol 76 (4) ◽  
pp. 2115-2121 ◽  
Author(s):  
Sham‐Tsong Shiue
Keyword(s):  
Grain Boundary ◽  
Zone Model ◽  
Free Zone ◽  
Boundary Ledge

How to Measure a Dislocation’s Breakthrough Stress to Estimate the Grain Boundary Resistance against Slip Transfer Based on the DFZ-Model of Fracture

2016 ◽  
Vol 258 ◽  
pp. 93-96 ◽  
Author(s):  
Florian Schaefer ◽  
Matthias Thielen ◽  
Michael Marx ◽  
Christian Motz
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Plastic Zone ◽  
Density Distribution ◽  
Fatigue Cracks ◽  
Local Stress ◽  
Boundary Resistance ◽  
Zone Model ◽  
Free Zone ◽  
Slip Transfer

Stage-I-fatigue-cracks are used as highly localized dislocation sources with well-known Burger’s vectors to study the interaction between dislocations and grain boundaries. This interaction in the plastic zone is of particular interest to understand the fluctuating crack growth in the very short crack regime. In the case of a blocked slip band the dislocations pile up at the grain boundary causing a local stress concentration. The resulting local stress distribution is calculated based on measurements of the dislocation density distribution in the plastic zone. For this purpose the slip line profiles were measured by AFM, the dislocation density distribution was determined and the dislocation-free zone model of fracture (DFZ) was validated. With this it is possible to quantify the grain boundary resistance and to combine geometric and stress approach for grain boundary resistance against slip transfer.

Processing of high strength Mg–9Gd–3Nd–1Sn–1Zn–0.6Zr alloy by hot rolling and subsequent aging

2020 ◽  
Vol 10 (7) ◽  
pp. 1020-1031
Author(s):  
Zehua Yan ◽  
Yandong Yu ◽  
Yanchao Sang ◽  
Yiming Yao ◽  
Jiahao Qian
Keyword(s):  
Grain Boundary ◽  
Aging Time ◽  
Hot Rolling ◽  
Aging Treatment ◽  
High Strength ◽  
Subsequent Aging ◽  
Free Zone ◽  
Treatment Conditions ◽  
Peak Aging ◽  
Equilibrium Phases

Magnesium alloy plates can be strengthened by rolling, however, it is easy to crack or even break when the reduction of Mg–RE alloys is too large. Herein, the strengthening mechanical of the Mg–9Gd–3Nd–1Sn–1Zn– 0.6Zr alloy under different treatment conditions were investigated after hot-rolling to 80% reduction in thickness (0.8 mm) by multi-step methods. Furthermore, the rolled alloy by aging strengthening are explored. The results show that the hot-rolled alloy with 80% reduction are basically composed of dynamically recrystallized grains with the size of about 60 m, improving the mechanical properties significantly. The precipitates within grains undergo SSSS→ β″ → β′ phase transformation with the aging treatment up to 200 °C. Fine β″ precipitates were found in the grains of the rolled alloy under aged time (2 h), while β″ precipitates changed into β′ phase when the aging time was extended to 32 h. The base phase which is perpendicular to phase was precipitated in the alloy in longer aging time (96 h). In addition, the thickness of precipitates and precipitation-free zone (PFZ) at the grain boundary gradually increased as the time went on. Meanwhile, the discontinuous equilibrium phases at the grain boundary are gradually become continuous. The ultimate tensile strength and hardness were reached to 431.14 MPa, 105.9 HV at peak-aging, in addition, the elongation is reached to 3.11%, respectively. The formation of crack sources is due to the stress concentration between the brittle PFZ and the magnesium matrix, which leads to the decrease of ductility.

The origin of the grain boundary precipitate free zone

1969 ◽  
Vol 17 (11) ◽  
pp. 1363-1377 ◽  
Author(s):  
P.N.T Unwin ◽  
G.W Lorimer ◽  
R.B Nicholson
Keyword(s):  
Grain Boundary ◽  
Precipitate Free Zone ◽  
Boundary Precipitate ◽  
Free Zone

Dislocation emission criterion: Grain boundary effect

1993 ◽  
Vol 8 (8) ◽  
pp. 1853-1857 ◽  
Author(s):  
Sham-Tsong Shiue ◽  
Tong-Yi Zhang ◽  
Sanboh Lee
Keyword(s):  
Grain Size ◽  
Stress Intensity ◽  
Grain Boundary ◽  
Plastic Zone ◽  
Critical Stress ◽  
Boundary Effect ◽  
Critical Stress Intensity Factor ◽  
Dislocation Emission ◽  
Brittle Behavior ◽  
Free Zone

Based on the results of Shiue and Lee [J. Appl. Phys. 70, 2947 (1991)], the effect of plastic zone and grain boundary on the dislocation emission criterion was investigated. The emission criterion is based on the concept of spontaneous emission. The critical stress intensity factor for dislocation emission increases with the increasing size of dislocation-free zone and the number of piled-up dislocations in the plastic zone, but decreases with increasing grain size. The ductile versus brittle behavior of material was determined by the competition of critical stress intensity factors for dislocation emission and crack propagation. A material with larger grain size is easier to emit dislocation and allows more dislocations to be piled up, so that it behaves more ductile.

Modeling of Segregation and Microstructural Evolution near Grain Boundary in FE-CR-NI Alloy Under Irradiation

1998 ◽  
Vol 538 ◽  
Author(s):  
N. Sakaguchi ◽  
S. Watanabe ◽  
H. Takahashi
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Point Defects ◽  
Solute Segregation ◽  
Extended Defects ◽  
Diffusional Process ◽  
Free Zone ◽  
Ni Alloy ◽  
Radiation Induced ◽  
Simultaneous Evolution

AbstractWe have investigated the solute segregation and simultaneous evolution of extended defects in an Fe-Cr-Ni alloy during irradiation by computer simulation. It sheds a light on the accomplishment of performing “the combined total calculation” or “the muliscale modeling” which deals with both radiation-induced segregation and various kinds of internal sink evolution. The formation of dislocation-free zone (DLFZ) was predicted in the vicinity of a grain boundary. It indicated that DLFZ formation is controlled by solute diffusional process via point defects diffusion near the grain boundary and the activation energy obtained by the width of DLFZ corresponds to the half of the value of the radiation-enhanced solute diffusivity.

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