RESUMEN
In this study, two commercial Zr alloys (Zr702 and Zr-2.5Nb) were subjected to the same ß-quenching treatment (water cooling after annealing at 1000 °C for 10 min). Their microstructural characteristics and hardness before and after the heat treatment were well characterized and compared by electron channel contrast (ECC) imaging, electron backscatter diffraction (EBSD) techniques, and microhardness measurements. Results show that after the ß quenching, prior equiaxed grains in Zr702 are transformed into Widmanstätten plate structures (the average width ~0.8 µm) with many fine precipitates distributed along their boundaries, while the initial dual-phase (α + ß) microstructure in Zr-2.5Nb is fully replaced by fine twinned martensitic plates (the average width ~0.31 µm). Differences in alloying elements (especially Nb) between Zr702 and Zr-2.5Nb are demonstrated to play a key role in determining their phase transformation behaviors during the ß quenching. Analyses on crystallographic orientations show that the Burgers orientation relationship is well obeyed in both the alloys with misorientation angles between α plates essentially focused on ~60°. After ß quenching, the hardnesses of both alloys were increased by ~35%-40%. Quantitative analyses using the Hall-Petch equation suggest that such an increase was mainly attributable to phase transformation-induced grain refinements. Since Nb is able to effectively refine the ß-quenched structures, a higher hardness increment is produced in Zr-2.5Nb than in Zr702.
RESUMEN
A magnesium alloy containing Al2Y particles was successfully fabricated by changing the content of Al in the Mg-6Y alloy melt. Its microstructure and mechanical properties were subsequently characterized. The results show that two types of Al2Y particles were discovered in the Mg-6Y-xAl (x = 0.5â»5) alloys, which are namely the polygonal particles in the pre-precipitated phase and the discontinuous network of particles in the eutectic phase. With an increase in Al content, the amount of pre-precipitated Al2Y increases and the eutectic decreases gradually. When the Al content is 5 wt %, Al2Y particles are almost all in the pre-precipitated phase in the Mg-6Y alloy. After hot extrusion, the YA65 alloy could be regarded as the Mg master alloy that contains Al2Y particles with heterogeneous nucleation capability or Al2Y particle-reinforced magnesium matrix composites. The tensile strength of the as-extruded magnesium alloy is significantly improved at ambient temperatures.
RESUMEN
The tribological behaviors of graphene and graphene oxide (GO) as water-based lubricant additives were evaluated by use of a reciprocating ball-on-plate tribometer for magnesium alloy-steel contacts. Three sets of test conditions were examined to investigate the effect of concentration, the capacity of carrying load and the endurance of the lubrication film, respectively. The results showed that the tribological behaviors of water can be improved by adding the appropriate graphene or GO. Compared with pure deionized water, 0.5 wt.% graphene nanofluids can offer reduction of friction coefficient by 21.9% and reduction of wear rate by 13.5%. Meanwhile, 0.5 wt.% GO nanofluids were found to reduce the friction coefficient and wear rate up to 77.5% and 90%, respectively. Besides this, the positive effect of the GO nanofluids was also more pronounced in terms of the load-carrying capacity and the lubrication film endurance. The wear mechanisms have been tentatively proposed according to the observation of the worn surfaces by field emission scanning electron microscope-energy dispersive spectrometer (FESEM-EDS) and Raman spectrum as well as the wettability of the nanofluids on the magnesium alloy surface by goniometer.
RESUMEN
OBJECTIVE: To assess the expression and significance of vaccinia-related kinase 1 (VRK1) after rat heart transplantation. MATERIALS AND METHODS: Lewis and Wistar rats weighing 250 to 300 g were used as donors and recipients. Allografts were from Wistar transplanted into Lewis, and isografts were transplanted from Lewis into Lewis. Grafts were harvested at 1, 3, 5, and 7 days after transplantation. We performed Western Blot of heart tissues after cardiac transplantation. To analyze VRK1 express between the isografts and allografts for immunohistochemical staining. At 5th day after heart transplantation use related cytokines VRK1 for immunohistochemical. We used double immunofluorescent staining on transverse cryosections of graft tissues by co-labeling with different markers, including those for VRK1, activate caspase-3, α-actinin, VCAM-1, CD4. RESULTS: Compared with rare expression in syngeneic Lewis rat hearts, VRK1 protein level in allogeneic hearts were detected at various survival times after heterotopic heart transplantation, which observably expressed on day 5 postoperative. In addition, we examined the expression of activate caspase-3 in allogeneic hearts, which has a similar expression with VRK1. Immunohistochemical and immunofluorescent method displayed that VRK1 was widely expressed in cytoplasm of cardiac tissue and activate caspase-3 was also expressed in cardiomyocytes. However, the VRK1 wasn't express in inflammation. CONCLUSIONS: The VRK1 expression has increased after heart transplantation in allograft and isograft, and VRK1 may play a significant role in myocardial apoptosis after heterotopic heart transplantation in rats.