Li Qiulin

Effects of twin-dislocation and twin-twin interactions on the strain hardening behavior of TWIP steels

Tensile tests of Fe-30Mn-5Si-2Al steel were carried out for different strains of 0.05, 0.14, 0.26, and up to the strain-to-failure in order to observe the evolution of microstructure during deformation and investigating the strain hardening behavior. Three-stage strain hardening behavior was observed in this steel during tensile test. In stage I, planar dislocation structure was observed by TEM and regarded as main deformation mechanism, and low strain hardening rate exponent was exhibited. Primary deformation twinning occurred in stage II, and the strain hardening rate exponent increased due to the blockage of dislocations’ motion by twin boundaries. In stage III, the strain hardening rate exponent had increased to a value higher than 0.5. The obstacle effect of twin boundaries and twin-twin interaction had been observed by TEM, and the interactions between primary and secondary twins were found to cause the additional hardening in addition to the obstacle effect on dislocations’ motion, which led to the twinning induced plasticity effect in the later stage of deformation.

Fabrication and characterization of stir casting AA6061—31%B 4 C composite

Abstract A sophisticated stir casting route to fabricate large scale AA6061–31%B 4 C composite was developed. Key process parameters were studied, microstructure and mechanical properties of the composite were investigated. The results indicated that vacuum stirring/casting, B 4 C/Mg feeding and ingots cooling were essential to the successful fabrication of AA6061–31%B 4 C composite. Chemical erosion examination verified the designed B 4 C content; X-ray fluorescence spectrometer (XFS) showed the chemical composition of Mg and Si in the matrix conformed to industry standards; scanning electronic microscope (SEM) and X-ray diffraction (XRD) revealed that B 4 C particles were evenly distributed in the composites with well dispersed Mg 2 Si precipitates. Tensile testing results showed that the AA6061–31%B 4 C composite had a tensile strength of 340 MPa, improved by 112.5% compared with AA1100–31%B 4 C composite, which is attributed to the enhanced strength of the matrix alloy.

Magnetic Properties of Thermally Aged Fe-Cu Alloys with Pre-deformation

Magnetic properties of thermally aged Fe-Cu alloys with pre-deformation have been evaluated to improve the understanding of using magnetic technology for the nondestructive evaluation (NDE) of irradiation embrittlement in reactor pressure vessel (RPV) steels. Fe-Cu alloys with and without pre-deformation were thermally aged at 500 °C and the changes in microstructure, mechanical properties and magnetic properties were determined. It is found that the strain-induced dislocations recover and the Cu-rich particles precipitate during the aging process, and the magnetic properties variation depends on the combined influence of these two factors. From the point of view of NDE, a fully tempered or annealed microstructure is favorable before RPV is put into service. These results improve the understanding of magnetic property evolution in actual RPV steels and help to develop NDE theory for irradiation embrittlement.

Improving Al Wettability on B 4 C by Transition Metal Doping: a Combined DFT and Experiment Study

Abstract B4C/Al MMC is one of the most potential neutron-shielding materials. The poor wettability of B4C/Al interface damages the mechanical properties. To understand the alloying (or doping) effects in improving the wettability of B4C/Al interfaces, we investigated the Al(111)/AlB2(0001) and Al(111)/TiB2(0001) interfacial structures via a combined approach of experiment and DFT calculations. We find a larger work of adhesion (Wad) on the Al(111)/TiB2(0001) than the Al(111)/AlB2(0001) interfaces. The subsequently calculated partial density of states (PDOS) of doped-diborides show fewer anti-bonding states in Al(111)/TiB2(0001) than in Al(111)/AlB2(0001), which contribute to a stronger bonding between Ti-3d and B-2p states and lead to a higher Wad and better wetting. Furthermore, we predict improved wettability of Al/B4C by V-doping, because of the fewer anti-bonding states in vanadium-boron molecular orbitals. The same approach developed in this study may be applied for general design of alloy elements to improve the interfacial wetting of alloy-semiconductor systems.

Magnetization Reversal Process of Single Crystal α-Fe Containing a Nonmagnetic Particle

The magnetization reversal process and hysteresis loops in a single crystal α-iron with nonmagnetic particles are simulated in this work based on the Landau—Lifshitz—Gilbert equation. The evolutions of the magnetic domain morphology are studied, and our analyses show that the magnetization reversal process is affected by the interaction between the moving domain wall and the existing nonmagnetic particles. This interaction strongly depends on the size of the particles, and it is found that particles with a particular size contribute the most to magnetic hardening.