Differential speed rolling (DSR) was applied to the AZ31 magnesium alloy, intended to modify the texture and thus to enhance the room temperature ductility. Especially, effect of DSR temperature on ...resulting room temperature tensile properties and texture was investigated at a fixed rolling speed ratio of 1.1. The strength was not affected by the rolling temperature: the yield strength and the ultimate tensile strength for all materials processed by DSR were approximately 240 and 290
MPa, respectively. On the other hand, elongation-to-failure increased from 13.6 to 18.5% with decreasing rolling temperature from 573 to 473
K. In addition, the material processed by DSR exhibited approximately 1.5 times larger ductility than that by conventional symmetric rolling at a rolling temperature of 473
K. The DSR at 523 and 473
K resulted in the basal plane orientation at the position inclined by ∼5 and 8° from the normal direction toward the rolling direction, respectively. It was suggested that the higher ductility of the material processed at lower temperatures is attributed to the slight change in the basal plane orientation and/or reduction in grain size.
Fine and coarse grained (5–20 μm) and ultra-fine-grained (down to 1 μm) samples of a binary Mg-Al alloy were fabricated by extrusion at various temperatures. When tested in compression, a slight ...stress drop was observed after yielding, followed by a plateau in flow stress. This behavior is typical of textured fine-grained samples. Examination of deformed structures within the ultra-fine-grained samples at various levels of deformation showed that the stress drop after yielding is due to an occurrence of long, thin twins across low angle boundaries and in unrecrystallized regions. In the plateau region, extensive twinning occurs inside individual grains. Then, in a rapid strain hardening region that follows the plateau region, stress concentrations were found to build up on boundaries. Such pile-ups could be responsible for a lowering of fracture strain.
•Compression deformation of an ultra fine grained Mg-Al alloy has been studied.•Yielding occurs by formation of long twins in unrecrystallized regions.•Limited number of twins in each grain gives rise to a plateau in the flow curve.•Refining grain size to ∼1 μm leads to activation of non-basal slips.•Intense activity of non-basal slip results in strain hardening beyond 6% strain.
Objective: This study aimed to determine the clinicopathological characteristics of cancer-associated venous thromboembolism (CAT-VTE).Methods: A total of 47 cases of lethal pulmonary thromboembolism ...(PTE) with active cancer were investigated by autopsy records.Results: We studied 22 men and 25 women who were deceased at a mean age of 66±11 years. Nine (19%) patients had recently undergone cancer resection, 14 (30%) were undergoing clinical treatment for cancer, and 24 (51%) were autopsy-proven CAT-VTE. The colon (eight cases), lungs (seven cases), and ovaries (six cases) were frequent sites of a tumor. There were 29 (62%) cases of acute PTE and 18 (38%) of recurrent PTE. The embolic source was detected in 36/39 (92%) cases. Among them, 33 cases were leg deep vein thrombosis (DVT) and 31 were calf-type DVT. Three cases were isolated vena cava thrombi that were present near the tumor. Twenty-three (64%) cases were recurrent DVT.Conclusion: Most of the lethal CAT-VTE cases were induced by the same mechanism as non-CAT-VTE that originated from calf-type DVT with proximal propagation. However, the finding that patients had tumor-related vena cava thrombi suggested that prevention of CAT-VTE requires individualized treatment of patients according to their pathological condition. (This is secondary publication from Jpn J Phlebol 2020; 31(3): 123–129.)
Ultrasonic vibration was introduced into the solidification of AZ91 alloy. Various microstructures were produced in this alloy using ultrasonic vibrations at different temperatures of the melt. The ...coarse dendrite microstructures were obtained with ultrasonic vibrations at temperatures below the liquidus temperature. The fine uniform grains were achieved under ultrasonic vibrations during the nucleation stage, which was mainly attributed to the cavitation and the acoustic flow induced by the ultrasonic vibration.
► Strain and ageing used to control β1′ precipitate size and distribution. ► Precipitate size and distribution are correlated with strength and ductility. ► Larger volume fraction of β1′ precipitates ...introduced by solute re-partitioning. ► 32% increase in yield strength achieved by 5% pre-ageing deformation.
The effect of pre-ageing deformation on the size and distribution of β1′ precipitates and subsequently on the resulting strength and ductility have been measured in a Mg-3.0at.%Zn-0.5at.%Y alloy. The alloy was extruded and then subjected to a T8 heat treatment comprised of a solution-treatment, cold-work and artificial ageing. Extrusion was used to introduce texture, ensuring that deformation occurred via slip rather than twinning. Samples were subjected to controlled uniaxial deformation and then isothermally aged to peak hardness. Precipitate length, diameter and number density were measured and evaluated in terms of the strength and ductility of the alloy. The nucleation of the β1′ precipitates in peak-aged condition without pre-ageing deformation (i.e. T6 treatment) was poor, with only 0.5% volume fraction, compared to approximately 3.5% in T6 treated binary Mg-3.0at.%Zn alloy. The microstructure of the Mg–Zn–Y alloy was less refined, with larger diameter precipitates and lower β1′ number densities than a binary Mg-3.0at.%Zn alloy. Deformation to 5% plastic strain increased the volume fraction of β1′ precipitates to approximately 2.3% and refined the β1′ precipitate length and diameter. The combination of these effects increased the yield strength after isothermal ageing from 217MPa (0% cold-work) to 287MPa (5% cold-work). The yield stress increased linearly with reciprocal interparticle spacing on the basal and prismatic planes and the alloy showed similar strengthening against basal slip to Mg–Zn. The elongation increased linearly with particle spacing. The ductility of Mg–Zn–Y alloys was similar to that of Mg-Zn for equivalently spaced particles.
Oxidative stress has been suggested to play a role in brain damage during carbon monoxide (CO) poisoning. Severe poisoning induced by CO at 3000 ppm, but not 1000 ppm, enhances hydroxyl radical (˙OH) ...production in the rat striatum, which might be mediated by NADPH oxidase (NOX) activation associated with Ras-related C3 botulinum toxin substrate (Rac) via cAMP signaling pathway activation. CO-induced ˙OH production was suppressed by antagonists of angiotensin II (AngII) type 1 receptor (AT1R) and type 2 receptor (AT2R) but not an antagonist of the Mas receptor. Suppression by an AT1R antagonist was unrelated to peroxisome proliferator-activated receptor γ. Angiotensin-converting enzyme inhibitors also suppressed CO-induced ˙OH production. Intrastriatal AngII at high concentrations enhanced ˙OH production. However, the enhancement of ˙OH production was resistant to inhibitors selective for NOX and Rac and to AT1R and AT2R antagonists. This indicates a different mechanism for ˙OH production induced by AngII than for that induced by CO poisoning. AT1R and AT2R antagonists had no significant effects on CO-induced cAMP production or ˙OH production induced by forskolin, which stimulates cAMP production. These findings suggest that the renin-angiotensin system might be involved in CO-induced ˙OH production in a manner independent of cAMP signaling pathways.
•Grain boundary migrations occurred due to the reduction in the internal energy.•The grain boundaries with high energies enhanced the grain boundary migration.•The origin of this behavior was {10−11} ...twinning induced grain boundary migration.•The addition of solute atoms (Al or Ag) suppressed the grain boundary migration.
The deformation behavior at the grain boundary was investigated by the molecular dynamics simulation using two models based on different kinds of 1−100 symmetric tilt boundaries (Σ25 with a tilt angle of θ=23° and Σ10 with θ=78°) in magnesium. Grain boundary migrations occurred in both models due to the reduction in the internal energy during deformation. The deformation mechanism at the grain boundary was shown to be the twinning induced grain boundary migration. The grain boundary migration was affected by the grain boundary structures, and it was enhanced in the grain boundaries with high energies. On the other hand, the grain boundary migration was suppressed by the addition of solute atoms, i.e., aluminum and silver. The silver atoms were found to be more effective for suppression than the aluminum atoms. These behaviors occurred in both the molecular dynamics simulation and the experiments.
The effect of solid-solution alloying on grain boundary sliding (GBS) was investigated using pure magnesium and six kinds of Mg-X (X = Ag, Al, Li, Pb, Y and Zn) dilute binary solid solutions with an ...average grain size of 10 µm. A sharp increase in damping capacity caused by GBS was observed above a certain temperature. The temperature at which a sharp increase in damping capacity occurred depended on the alloying element. The addition of Y and Ag markedly increased the onset temperature (more than 100 K) for a sharp increase in damping capacity, whereas the addition of Zn, Al and Li slightly increased the onset temperature (less than 50 K) as compared with that for pure magnesium. Tensile tests at a temperature of 423 K revealed that the higher the onset temperature, the lower the strain rate sensitivity of the flow stress. It is suggested that the former elements (Y and Ag) are more effective in suppressing GBS in magnesium alloys than the latter ones (Zn, Al and Li). The suppression of GBS was associated with low grain boundary energy, and the extent to which the energy is reduced depended on the alloying element. It was suggested that the change in the lattice parameter (the so-called c/a ratio) affects the grain boundary energy, and thus, the occurrence of GBS.
Background Operative clips used to ligate vessels in abdominal operation usually are made of titanium. They remain in the body permanently and form metallic artifacts in computed tomography images, ...which impair accurate diagnosis. Although biodegradable magnesium instruments have been developed in other fields, the physical properties necessary for operative clips differ from those of other instruments. We developed a biodegradable magnesium-zinc-calcium alloy clip with good biologic compatibility and enough clamping capability as an operative clip. In this study, we verified the safety and tolerability of this clip for use in canine cholecystectomy. Methods Nine female beagles were used. We performed cholecystectomy and ligated the cystic duct by magnesium alloy or titanium clips. The chronologic change of clips and artifact formation were compared at 1, 4, 12, 18, and 24 weeks postoperative by computed tomography. The animals were killed at the end of the observation period, and the clips were removed to evaluate their biodegradability. We also evaluated their effect on the living body by blood biochemistry data. Results The magnesium alloy clip formed much fewer artifacts than the titanium clip, and it was almost absorbed at 6 months postoperative. There were no postoperative complications and no elevation of constituent elements such as magnesium, calcium, and zinc during the observation period in both groups. Conclusion The novel magnesium alloy clip demonstrated sufficient sealing capability for the cystic duct and proper biodegradability in canine models. The magnesium alloy clip revealed much fewer metallic artifacts in CT than the conventional titanium clip.
Purpose
Non-absorbable clips are widely used in urologic surgery and they may come in contact with an open urinary tract intraoperatively. As a result, stray clips in the urinary tract and associated ...intractable infections have been reported. We developed a bioabsorbable metal and evaluated whether it would dissolve if it strayed into the urinary tract.
Methods
We prepared four types of alloys mainly comprising zinc (Zn) with small amounts of magnesium (Mg) and strontium (Sr), and the biological effects, degradability, strength, and ductility were investigated. Each alloy was implanted in the bladder of five rats for 4, 8, and 12 weeks. The alloys were removed and evaluated for degradability, stone adhesion, and tissue changes. The Zn–Mg–Sr alloy had degradability and no stone adhesion in the rat experiments, and it was implanted in the bladders of five pigs for 24 weeks. The Mg and Zn levels in the blood were measured, and staple changes were confirmed by cystoscopy.
Results
Zn–Mg–Sr alloys showed the best degradability of 6.51% at 12 weeks. In pig experiments, the degradation rate was 3.72% at 24 weeks. None of the pigs had changes in the Zn or Mg concentrations in the blood. Overall, the bladder incision was healed and the gross pathology showed wound healing.
Conclusions
The Zn–Mg–Sr alloys were safely used in animal experiments. Furthermore, the alloys are easy to process and can be formed into various shapes, such as staples, making them useful in robotic surgery.
PDF
