S2E5

Ab initio modeling of the role of local chemical short-range order on the energy landscape of screw dislocations in body-centered cubic high-entropy alloys

Transcranial focused ultrasound generates skull-conducted shear waves: computational model and implications for neuromodulation

Abstract:

In traditional body-centered cubic (bcc) metals, the core properties of screw dislocations play a critical role in plastic deformation at low temperatures. Recently, much attention has been focused on refractory high-entropy alloys (RHEAs), which also possess bcc crystal structures. However, unlike face-centered cubic high-entropy alloys (HEAs), there have been far fewer investigations on bcc HEAs, specifically on the possible effects of chemical short-range order (SRO) in these multiple principal element alloys on dislocation mobility. Here, using density functional theory, we investigate the distribution of dislocation core properties in MoNbTaW RHEAs alloys, and how they are influenced by SRO. The average values of the core energies in the RHEA are found to be larger than those in the corresponding pure constituent bcc metals, and are relatively insensitive to the degree of SRO. However, the presence of SRO is shown to have a large effect on narrowing the distribution of dislocation core energies and decreasing the spatial heterogeneity of dislocation core energies in the RHEA. It is argued that the consequences for the mechanical behavior of HEAs is a change in the energy landscape of the dislocations which would likely heterogeneously inhibit their motion.

Abstract:

Low intensity modality of focused ultrasound (fUS) have recently attracted a lot of attention primarily for neuromodulation applications. While longitudinal waves induced by fUS have been extensively studied, the transverse waves are often overlooked, due to the low shear resistance of soft tissues for the most part. Yet, if fUS is imposed in the vicinity of a bone, shear waves with magnitudes comparable to pressure waves will propagate through the bone. We investigate wave propagations in human head through a realistic computational model with a region in the frontal lobe subjected to fUS. We demonstrate that the skull guides the shear waves towards cochlea. This, in turn, explains the off-target auditory responses observed in neuromodulation experiments [1, 2]. We further validate the idea of bone as a waveguide for shear waves by looking into a mouse model. We subject the mouse tail to fUS and demonstrate that the spine serves as a waveguide and carries the transverse waves to the mouse skull.