Magnetization-Enhanced Dislocation Motion and Decreased Yield Strength of 60Fe40Ni Alloy

Using a special constant deflection device, the changes in dislocation configuration ahead of a loaded crack tip for 60Fe40Ni alloy. before and after magnetization in a magnetic field, have been studied in TEM. The results showed that the magnetization for 60Fe40Ni alloy could enhance dislocation emission, multiplication and motion. Also, the mechanical properties of 60Fe40Ni alloy, in air and in the magnetic field respectively have been investigated using the slow strain rate tension. And the results indicated that magnetization could make the yield strength corresponding to decrease by 26 percent, but did not influence the ultimate tensile strength and the fracture strain, which showed that magnetization could enhance plastic deformation.

Effects of minor Sc and Zr additions on mechanical properties and microstructure evolution of Al−Zn−Mg−Cu alloys

The effects of minor Sc and Zr additions on the mechanical properties and microstructure evolution of Al Zn Mg Cu alloys were studied using tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ultimate tensile strength of the peak-aged Al Zn Mg Cu alloy is improved by about 105 MPa with the addition of 0.10% Zr. An increase of about 133 MPa is observed with the joint addition of 0.07% Sc and 0.07% Zr. For the alloys modified with the minor addition of Sc and Zr (0.14%), the main strengthening mechanisms of minor addition of Sc and Zr are fine-grain strengthening, sub-structure strengthening and the Orowan strengthening mechanism produced by the Al3(Sc,Zr) and Al3Zr dispersoids. The volume of Al3Zr particles is less than that of Al3(Sc,Zr) particles, but the distribution of Al3(Sc,Zr) particles is more dispersed throughout the matrix leading to pinning the dislocations motion and restraining the recrystallization more effectively.

An investigation of corrosion-induced stress during SCC

TEM (Transmission Electron Microscope) observations show that corrosion process during stress corrosion cracking (SCC) enhances dislocation emission and motion; and microcrack of SCC initiates when the corrosion-enhanced dislocation emission and motion reaches a certain condition. The passive film or dealloyed layer formed during corrosion or SCC can induce a large tensile stress, which can assist the applied stress to enhance dislocation emission and motion, and then SCC occurs. Experiments show that the variation of SCC susceptibility of brass,α-Ti and stainless steel with the applied potential and pH value of the solution is consistent with that of the corrosion-induced additive stress. Molecular dynamics simulations show that a dealloyed layer can generate a tensile stress; and the corrosion (dealloyed layer)-induced tensile stress can assist the applied stress to enhance dislocation emission and crack propagation.

High-temperature mechanical behavior of ultra-coarse cemented carbide with grain strengthening

Ultra-coarse grained cemented carbides are often used under conditions of concurrently applied stress and high temperature.Improvement of high-temperature mechanical performance of ultra-coarse grained cemented carbides is highly desirable but still a big challenge.In this study,it is proposed that the hightemperature compression strength of ultra-coarse cemented carbides can be enhanced by modulating hard matrix grains by activated Ta C nanoparticles,through solid solution strengthening of Ta atoms.Based on the designed experiments and microstructural characterizations combined with finite element simulations,the grain morphology,stress distribution and dislocation configuration were studied in detail for ultra-coarse grained cemented carbides.The mechanisms of Ta dissolving in WC crystal and strengthening ultra-coarse grains through interaction with dislocations were disclosed from the atomic scale.This study opens a new perspective to modulate hard phases of cemented carbides for improving their hightemperature performance,which will be applicable to a variety of cermet and ceramic-based composite materials.

Fragility under shocking: molecular dynamics insights into defect evolutions in tungsten lattice

Tungsten has promising applications in high-radiation,high-erosion and high-impact environments.Laser peening is an effective method to enhance the surface mechanical properties of tungsten materials.However,the ultrafast dynamic mechanism of defect evolutions induced by laser shockwave in tungsten lattice is unclear.Here,we investigated the evolutions and interactions of various defects under ultrafast compressive process in tungsten lattice using molecular dynamic method.The results confirm the brittleness of tungsten and reveal that void can reduce the yield strain and strength of the tungsten lattice by accelerating defect mesh extension and promoting the dislocation nucleation around itself.Dislocation density is increased with compressive strain rate.Meanwhile,dislocation multiplication and motion reduce the elastic stage and play a dominant role during the plastic deformation of tungsten lattice.Additionally,void can disrupt the dislocation displacement and promote the pinning effect on dislocations by defect mesh extension.