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In this work, the surface of a fully recrystallized Zr702 is treated by pulsed laser following which microstructural changes are investigated by use of electron backscatter diffraction and electron channeling contrast imaging techniques. The pulsed laser treatment results in three distinctly different microstructural features from the surface to the substrate: fine α plates with a few hundred nanometers in width (zone I), irregular-shaped grains with varied sizes (zone II), and essentially unchanged equiaxed grains (zone III). The α plates result from rapid phase transformation due to easy heat extraction of the pulsed laser with dense nanoscale twins inside those plates closer to the surface. The origin of the irregular-shaped grains is found to be related to insufficient recrystallization of antecedently formed α plates near the substrate. Hardness tests reveal highest value (∼356.7 HV) near the surface in zone I and the lowest value (∼165.2 HV) in zone II. Reasons accounting for the difference are discussed in terms of various microstructural characteristics induced by the pulsed laser surface treatment. [ABSTRACT FROM AUTHOR]

A commercially pure Zr sheet was treated by pulsed laser at two different powers (25 and 400 W) and microstructural features in various laser-modified zones were characterized by electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECC) techniques. Results show that in the 400 W specimen, there are three laser-modified zones with distinct microstructural characteristics: melting zone (MZ), solid state phase transformation zone (SSPTZ), and recrystallized zone (RXZ). Both the MZ and the SSPTZ are mainly composed of Widmanstätten structures with fine precipitates decorating coarse α plate boundaries. Based on measured mean widths of α plates, cooling rates experienced by both zones are calculated to be a few hundred degrees per second. For the RXZ, second phase particles (SPPs) are found to distribute linearly inside bulk grains, suggesting the occurrence of recrystallization from earlier formed plate structures. Orientation examination by EBSD on plate structures in the MZ reveals presence of all 12 α variants transformed from the same β parent grain according to the Burgers orientation relationship, which may shed some light on suppressing α-variant selection in Zr alloys. For the 25 W specimen, the decreased laser power cannot melt the substrate and only solid state phase transformation occurs at very high cooling rates (> 6000 °C/s). The laser-modified zones could be distinguished as SSPTZ-1 or SSPTZ-2 for cooling from β or α + β domains accordingly. Plate structures in both zones are produced by diffusionless martensitic transformation, as suggested by dense inner-plate nanotwins and absence of SPPs. For those untransformed α grains in the SSPTZ-2, although their initial bulk morphologies are maintained, slight subdivision by many subgrains in their interiors is noticed. In addition, aggregates of three α plates with the “indentation mark” morphology are often observed for the martensitic plate structures in the 25 W specimen and boundary misorientations between the α plates are found to be 60 ° / < 11 2 ̅ 0 > (the second Burgers misorientation). [ABSTRACT FROM AUTHOR]

A 10 1 ¯ 1 twin relationship between α plates was repeatedly reported in β-quenched Zr alloys in literature. In this paper, however, we demonstrate that the special twin relationship between α plates should be correctly identified as one of five common Burgers misorientations. The shared plane between two α plates with such a Burgers misorientation is determined to be 10 1 ¯ 1.06 . Such a clarification helps to reach more accurate understanding of boundary characteristics of β-quenched microstructure in Zr alloys. [ABSTRACT FROM AUTHOR]

Abstract: The relationship between Agricultural risks and rural poverty is always a central issue for anti-poverty policies designing. Natural disasters risk is a common form of agricultural risks in china. The paper estimates the extent that the natural disaster has impacted on household vulnerability in the stricken areas. To discover the different characteristics associated with vulnerability between pre-disaster and post-disaster, we regressed vulnerability against a set of geographical and household characteristics. The paper shows that although a relatively small number of household have average revenue below the poverty line after attaining the government post-disaster subsidy, a much larger number of households have a greater probability of being poor in the future. There are some different characteristics associated with vulnerability between pre-disaster and post-disaster. This research will explore the implications for the design of effective poverty reduction policy for post-disaster reconstruction in the case of Wenchuan earthquake. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel self-lubricating layer was fabricated on M50NiL steel through a plasma-assisted thermochemical treatment. • The DLC structure is anchored in the pre-nitrided layer by carbide/nitride. • That layer shows excellent adhesion strength, wear resistance, and low friction coefficient. • The relation between Fe 5 C 2 crystal facet and growth of DLC is investigated by first-principle calculation. • The thermodynamic calculation reveals the formation mechanism of the graded layer. Diamond-like carbon (DLC) with excellent mechanical properties has aroused great interest. However, the weak adhesion between the DLC film and steel substrate restricts its application. Considering that the addition of interlayers needs cumbersome steps, fabricating a functionally graded self-lubricating layer through one-step remains a challenge. We reported a novel integrated self-lubricating layer, inspired by the gradient structure formed during the traditional thermochemical treatment. That integrated layer from DLC structure gradual transition to nitrided diffusion layer is in-situ fabricated on the M50NiL steel through a plasma-assisted thermochemical treatment. The gradient structure possesses excellent wear resistance due to the self-lubricating of the DLC structure and provides sufficient adhesion strength. A deep insight into the relation between Fe 5 C 2 crystal facet and growth of DLC is conducted by first-principle calculation and find low Miller Index of Fe 5 C 2 facets are favorable for the growth of DLC. The thermodynamic calculation reveals that gradient structure formation is the collaboration effect of non-equilibrium and equilibrium processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fabricate self-lubricating gradient composite layer by a straightforward method. • The composite layer from DLC gradually transforming to nitrided layer is spontaneously formed during carburizing without adjusting parameters. • The gradient structure introduces functionally graded mechanical properties. • The layer owns excellent wear resistance and a lower friction coefficient than the nitridied. • The nature of self-lubricating effect is graphitization of the tribo-film. Diamond-like carbon (DLC) has excellent performance but cannot be directly applied in gears and bearings due to poor adhesion. A novel gradient composite layer that includes a hardened nitrided layer and a self-lubricating DLC structure at the outermost surface was fabricated on M50 steel via plasma-assisted thermochemical treatment. The structure evolution of the modified layer was comprehensively characterized by optical microscopy, scanning electron microscope (SEM), atomic force microscopy (AFM), transmission electron microscope (TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results show that the nanoparticles embedded in the DLC structure gradually increase until the nitrided diffusion layer. The DLC structure is like being anchored in the nitrided layer by nanoparticles carbide/nitride. The inner of the pre-nitrided layer is hardly affected during the plasma carburizing process. The gradient structure is verified to endow the treated samples with functionally graded hardness profile and super wear resistance by Vickers hardness tester, Nano-indentation tester, and pin-on-disk tribometer. The composite layer's tribological behavior was discussed through wear scar morphology observation by SEM and chemical structure in tracks with Raman spectroscopy. This method proposes a promising way for self-lubricating layer application in the steel matrix without complex operation and high economic cost. [ABSTRACT FROM AUTHOR]