Martensite decomposition under thermal-mechanical coupling conditions to fabricate an ultrafine-grained Ti6Al4Mo4Zr1W0.2Si alloy

The fabrication of ultrafine-grained microstructures(grain size below 1μm)in titanium alloys is beneficial for improving their mechanical properties at room temperature and medium tempera-tures(400-550°C).However,a long-standing challenge involves the low-cost manufacturing of bulk ultrafine-grained titanium alloys.In this work,we developed a facile strategy through martensite de-composition at thermal-mechanical coupling conditions,to fabricate an equiaxed microstructure in a Ti6Al4Mo4Zr1W0.2Si model alloy with an averageαgrain size of 315±62 nm.The formation of the ultrafine-grained microstructure was because the lattice strain stored in the martensitic initial mi-crostructure enhanced the nucleation rate of dynamic recrystallization,meanwhile,the pinning role of martensite decomposition productsβand(Ti,Zr)_(5)Si_(3)phases suppressed grain coarsening at high tem-peratures.Compared to conventional(α+β)alloys,the tensile strength of this alloy improved by 20%-30%at both room temperature and 550°C,without decreasing its ductility.In situ SEM observations revealed that the ultrafine-grained microstructure would not only suppress dislocation motions but also contribute to the homogenous deformation in the matrix of the material,therefore,it resulted in higher mechanical performance.The research results may be of great significance to the development of next-generation aviation titanium alloys.

A Model of High-Speed Endovascular Sonothrombolysis with Vortex Ultrasound-Induced Shear Stress to Treat Cerebral Venous Sinus Thrombosis

This research aims to demonstrate a novel vortex ultrasound enabled endovascular thrombolysis method designed for treating cerebral venous sinus thrombosis(CVST).This is a topic of substantial importance since current treatment modalities for CVST still fail in as many as 20%to 40%of the cases,and the incidence of CvST has increased since the outbreak of the coronavirus disease 2019 pandemic.Compared with conventional anticoagulant or thrombolytic drugs,sonothrombolysis has the potential to remarkably shorten the required treatment time owing to the direct clot targeting with acoustic waves.However,previously reported strategies for sonothrombolysis have not demonstrated clinically meaningful outcomes(e.g.,recanalization within 30 min)in treating large,completely occluded veins or arteries.Here,we demonstrated a new vortex ultrasound technique for endovascular sonothrombolysis utilizing wavematter interaction-induced shear stress to enhance the lytic rate substantially.Our in vitro experiment showed that the lytic rate was increased by at least 64.3%compared with the nonvortex endovascular ultrasound treatment.A 3.1-g,7.5-cm-long,completely occluded in vitro 3-dimensional model of acute CVST was fully recanalized within 8 min with a record-high lytic rate of 237.5 mg/min for acute bovine clot invitro.Furthermore,we confirmed that the vortex ultrasound causes no vessel wall damage over ex vivo canine veins.This vortex ultrasound thrombolysis technique potentially presents a new life-saving tool for severe CVST cases that cannot be efficaciously treated using existing therapies.

{332}<113> Twinning transfer behavior and its effect on the twin shape in a beta-type Ti-23.1Nb-2.0Zr-1.0O alloy

The interaction between twins and grain boundaries(GB) has an important influence on the deformation and fracture behavior of materials. In the present work, {332}<113> twinning transfer(TT) behavior and its effect on the twin shape in a deformed β-type Ti-23.1 Nb-2.0 Zr-1.0 O Ti alloy were investigated experimentally and with molecular dynamics simulation. The crystallographic alignment factor of the two twinning systems in the neighboring grains and the misorientation angle of the grain pairs were found to influence the occurrence of TT. This further determines the twin shape: twins present a ruler shape when TT occurs but are in a lenticular shape otherwise. Such different twin shapes are attributed to the local stress states related to TT occurring or not. Both ruler-shaped paired twinning and lenticular twinning would provide effective mechanisms to release or reduce the stress concentration in front of the twin tips in different grain pairs.

Nanodroplet-mediated catheter-directed sonothrombolysis of retracted blood clots

One major challenge in current microbubble(MB)and tissue plasminogen activator(tPA)-mediated sonothrombolysis techniques is effectively treating retracted blood clots,owing to the high density and low porosity of retracted clots.Nanodroplets(NDs)have the potential to enhance retracted clot lysis owing to their small size and ability to penetrate into retracted clots to enhance drug delivery.For the first time,we demonstrate that a sub-megahertz,forwardviewing intravascular(FVI)transducer can be used for ND-mediated sonothrombolysis,in vitro.In this study,we determined the minimum peak negative pressure to induce cavitation with low-boiling point phase change nanodroplets and clot lysis.We then compared nanodroplet mediated sonothrombolysis to MB and tPA mediate techniques.The clot lysis as a percent mass decrease in retracted clots was 9±8%,9±5%,16±5%,14±9%,17±9%,30±8%,and 40±9%for the control group,tPA alone,tPA+US,MB+US,MB+tPA+US,ND+US,and ND+tPA+US groups,respectively.In retracted blood clots,combined ND-and tPA-mediated sonothrombolysis was able to significantly enhance retracted clot lysis compared with traditional MB and tPA-mediated sonothrombolysis techniques.Combined nanodroplet with tPA-mediated sonothrombolysis may provide a feasible strategy for safely treating retracted clots.