Tailoring heterogeneities in high-entropy alloys to promote strength–ductility synergy

Conventional alloys are usually based on a single host metal. Recent high-entropy alloys (HEAs), in contrast, employ multiple principal elements. The strength of HEAs is considerably higher than traditional solid solutions, as the many constituents lead to a rugged energy landscape that increases the resistance to dislocation motion, which can also be retarded by other heterogeneities. The wide variety of nanostructured heterogeneities in HEAs, including those generated on the fly during tensile straining, also offer elevated strain-hardening capability that promotes uniform tensile ductility. Citing recent examples, this review explores the multiple levels of heterogeneities in multi-principal-element alloys that contribute to lattice friction and back stress hardening, as a general strategy towards strength–ductility synergy beyond current benchmark ranges.

Temperature Dependence of the Yield Stress in α-Titanium Investigated with Crystal Plasticity Analysis

The effect of the activated slip systems on the temperature dependence of yield stress was investigated in α-Ti by using crystal plasticity finite element method. A model for finite element analysis (FEA) was constructed based on experimental results. The displacement in FEA was applied up to the nominal strain of 4% which is the same strain as the experimental one. Stress-strain curves were obtained, which corresponds to experimental data taken every 50 K between 73 K and 673 K. The used material constants which are temperature dependent were elastic constants, and lattice friction stresses. The lattice friction stresses of basal slip systems were set to be higher than that of pyramidal slip systems at 73 K. Then, the lattice friction stresses were set to be closer as the temperature increases. It was found that the activation of slip systems is strong temperature dependent, and that the yield stress depends on the number of active slip systems.

Modelling of Needle Domains in Barium Titanate Single Crystals Using Dislocation Theory

A model is established to study needle domains in barium titanate single crystals using the theory of dislocations. Considering the mechanical and electrical compatibility in ferroelectrics, the fields produced by a needle domain are represented using the equivalent fields due to an effective edge dislocation coupled with a line charge. Accordingly, the dislocation fields derived by Barnett and Lothe for anisotropic piezoelectric media are used to analyze the stress and electric fields around needle domains. The interaction of the pairs of needle domains in an infinite piezoelectric body is studied by computing the interactive force and the total energy. It is found that the needle tip interactions tend to be dominated by the electrostatic terms. Additionally, comb-like arrays of needle domains are investigated. Stable configurations of needle domains in a herringbone pattern are identified, consistent with experimental evidence. However, comb-like arrays of needles are found to be unstable if perfectly insulating conditions without lattice friction are assumed.