3D atomistic simulation of fatigue behaviour of cracked single crystal of bcc iron loaded in mode III

We present new results of 3D molecular dynamic (MD) simulations of a mechanical behaviour of an edge crack $(\overline{1}10)$ [1 1 0] (crack plane/crack front) in a single crystal of bcc iron cyclically loaded in mode III at room temperature. Our previous 3D molecular dynamic simulations showed that this crack under monotonic uniaxial tension loading in mode I emitted blunting dislocations in the inclined $〈1\overline{1}1〉\{\overline{1}12\}$ slip systems and it was stable up to very high loads, in qualitative agreement with experiments and continuum predictions. Our question is how the cyclic loading in mode III changes the crack behaviour and its stability. The paper also brings information on how the distribution of external forces in mode III influences the fatigue crack behaviour and how the defects generated by the crack can produce experimentally observed advances of the crack front in local modes I, II, I + II and II + III.     

Effect of strain rate on microstructure evolution of a nickel-based superalloy during hot deformation

The hot deformation behavior of a nickel-based superalloy was investigated by means of isothermal compression tests in the strain rate range of 0.001–10 s⁻¹ at 1110 °C. Transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) technique were used to study the effect of strain rate on the microstructure evolution of the alloy during hot deformation. The results revealed that the dynamic recrystallization (DRX) process was stimulated at high strain rates ($\dot{\epsilon }⩾5{\text{s}}^{-1}$) due to the high dislocation density and adiabatic temperature rise. Meanwhile, high nucleation of DRX and low grain growth led to the fine DRX grains. In the strain rate rage of 0.001–1 s⁻¹, the volume fraction of DRX grains increased with the decreasing strain rate, and the grain growth gradually governed the DRX process. Moreover, the strain rate has an important effect on DDRX and CDRX during hot deformation. On the other hand, particular attention was also paid to the evolution of twin boundaries during hot deformation. It was found that there was a lower fraction of Σ3 boundaries at the intermediate strain rate of 1 s⁻¹, while the fractions of Σ3 boundaries were much higher at both the lower strain rates ($\dot{\epsilon }⩽0.1{\text{s}}^{-1}$) and higher strain rates ($\dot{\epsilon }⩾5{\text{s}}^{-1}$).     

Formation of face-centered cubic titanium in laser surface re-melted commercially pure titanium plate

Micron-scale face-centered cubic titanium phase(named as δ phase) were noticed in the re-melted zone of laser surface re-melted commercially pure titanium plate.The morphology,sub-structure,orientation and distribution of δ phase were investigated by scanning electron microscopy,electron back-scattered diffraction and transmission electron microscopy.Three kind formation processes of δ phase were put forward based on the investigation.The first one is α'→δ transformation which takes place in single α'grains and leads to the orientation relationship {001}δ//{0001}α' 110 δ// 1120 α'.The second one is β→α'+ δ transformation which takes place at α'/α'interfaces and leads to the orientation relationship{001}δ//110β110 δ//111β.The third one is another kind of β→α'+ δ transformation that takes place at α'/α'interfaces and leads to the orientation relationship111δ//110β 110 δ// 111 β.It is believed that the transformations of δ phase are stress assistant ones and in the present investigation,the phase transformation stress of β→α'transformation acts as the assistant driving force for the formation of δ phase.     

Effect of crystal orientation on corrosion behavior of directionally solidified Mg-4 wt% Zn alloy

Microstructure and crystallographic orientation of directionally solidified Mg-4 wt% Zn alloy were characterized by X-ray computed tomography (XCT) and electron backscatter diffraction (EBSD) in this study. Results reveal that Mg-4 wt% Zn alloy with dendritic microstructure exhibits typical $\left\{0002\right\}$ basal texture along growth direction. Based on this, the effect of grain orientation on corrosion behavior of directionally solidified Mg-4 wt% Zn alloy in 0.9 wt% NaCl solution was investigated. Result shows that $\left\{0002\right\}$ oriented planes have better corrosion resistance than $\left\{11{\displaystyle \overline{2}}0\right\}$ and $\left\{10{\displaystyle \overline{1}}0\right\}$ ones, which is attributed to a synergistic effect of surface energy, atomic packing density and the stability of oxidation film.