Quenching and partitioning (Q&P) and a novel combined process of hot straining (HS) and Q&P (HSQ&P) treatments have been applied to a TRIP-assisted steel in a Gleeble®3S50 thermomechanical simulator. The heat treatments involved intercritical annealing at 800 °C and a two-step Q&P heat treatment with a partitioning time of 100 seconds at 400 °C. The “optimum” quench temperature of 318 °C was selected according to the constrained carbon equilibrium (CCE) criterion. The effects of high-temperature deformation (isothermal and non-isothermal) on the carbon enrichment of austenite, carbide formation, and the strain-induced transformation to ferrite (SIT) mechanism were investigated. Carbon partitioning from supersaturated martensite into austenite and carbide precipitation were confirmed by means of atom probe tomography (APT) and scanning transmission electron microscopy (STEM). Austenite carbon enrichment was clearly observed in all specimens, and in the HSQ&P samples, it was significantly greater than in Q&P, suggesting an additional carbon partitioning to austenite from ferrite formed by the deformation-induced austenite-to-ferrite transformation (DIFT) phenomenon. By APT, the carbon accumulation at austenite/martensite interfaces was observed, with higher values for HSQ&P deformed isothermally (≈ 11 at. pct), when compared with non-isothermal HSQ&P (≈ 9.45 at. pct) and Q&P (≈ 7.6 at. pct). Moreover, a local Mn enrichment was observed in a ferrite/austenite interface, indicating ferrite growth under local equilibrium with negligible partitioning (LENP).
We address the problem of code generation for embedded DSP systems. Such systems devote a limited quantity of silicon to program
memory, so the embedded software must be sufficiently dense. Additionally, this software must be written so as to meet various
high-performance constraints. Unfortunately, current compiler technology is unable to generate dense, high-performance code
for DSPs, due to the fact that it does not provide adequate support for the specialized architectural features of DSPs via
machine-dependent code optimizations. Thus, designers often program the embedded software in assembly, a very time-consuming
task. In order to increase productivity, compilers must be developed that are capable of generating high-quality code for
DSPs. The compilation process must also be made retargetable, so that a variety of DSPs may be efficiently evaluated for potential
use in an embedded system. We present a retargetable compilation methodology that enables high-quality code to be generated
for a wide range of DSPs. Previous work in retargetable DSP compilation has focused on complete automation, and this desire
for automation has limited the number of machine-dependent optimizations that can be supported. In our efforts, we have given
code quality higher priority over complete automation. We demonstrate how by using a library of machine-dependent optimization
routines accessible via a programming interface, it is possible to support a wide range of machine-dependent optimizations,
albeit at some cost to automation. Experimental results demonstrate the effectiveness of our methodology, which has been used
to build good-quality compilers for three fixed-point DSPs.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
Magnetic pulse welding is a solid state impact welding process, similar to explosive welding, which produces metallurgical
bond by oblique high-speed impact between two metal bodies. This violent impact removes the metal surface oxide layers and
then joins the two atomic level clean metal surfaces together by the incidental compression pressure. The impact velocity
is at 200–400 m/s and the being welded metal surface undergoes severe plastic deformation with strain rate in the order of
106–107 s−1. The ultrafine-grained structure was observed on the welded interface. This article studied two types of similar material
lap joint interfaces and the base metals were aluminum alloy 6061 and copper alloy 110. Nano-indentation testing shows that
the welded interfaces have significantly greater hardness than the base metals. The interface microstructure was studied by
optical microscopy, electron backscatter diffraction microscopy, and transmission electron microscopy. The welded aluminum
alloy 6061 interface exhibits extremely fine grains and an extremely high dislocation density. The impact welded copper alloy
110 interface presents nano-scale lamellar band structure and deformation twins. The interface hardness increasing was attributed
to this impact-induced microstructural refinement. 相似文献
A new Fe-Cr-Al (FCA) alloy system has been developed with good oxidation resistance and creep strength at high temperature. The alloy system is a candidate for use in future fossil-fueled power plants. The creep strength of these alloys at 973 K (700 °C) was found to be comparable with traditional 9 pct Cr ferritic–martensitic steels. A few FCA alloys with general composition of Fe-30Cr-3Al-.2Si-xNb (x = 0, 1, or 2) with a ferrite matrix and Fe2Nb-type Laves precipitates were prepared. The detailed microstructural characterization of samples, before and after creep rupture testing, indicated precipitation of the Laves phase within the matrix, Laves phase at the grain boundaries, and a 0.5 to 1.5 μm wide precipitate-free zone (PFZ) parallel to all the grain boundaries. In these alloys, the areal fraction of grain boundary Laves phase and the width of the PFZ controlled the cavitation nucleation and eventual grain boundary ductile failure. A phenomenological model was used to compare the creep strain rates controlled by the effects of the particles on the dislocations within the grain and at grain boundaries. (The research sponsored by US-DOE, Office of Fossil Energy, the Crosscutting Research Program). 相似文献
Electron microscopy, X-ray diffraction, and atom probe tomography have been used to identify the changes which occur during the tempering of a carbide-free bainitic steel transformed at 473 K (200 °C). Partitioning of solute between ferrite and thin-films of retained austenite was observed on tempering at 673 K (400 °C) for 30 minutes. After tempering at 673 K (400 °C) and 773 K (500 °C) for 30 minutes, cementite was observed in the form of nanometre scale precipitates. Proximity histograms showed that the partitioning of solutes other than silicon from the cementite was slight at 673 K (400 °C) and more obvious at 773 K (500 °C). In both cases, the nanometre scale carbides are greatly depleted in silicon.
The present study was undertaken to develop a novel and easy practical approach for synthesis of cyclopentanone, a versatile industrial ingredient. Accordingly, ceria–zirconia based nano-oxide catalysts, namely, CexZr1?xO2 and CexZr1?xO2/M (M = SiO2 and Al2O3) were prepared and evaluated for the title reaction. The physicochemical characterization has been achieved using different techniques, namely, XRD, BET surface area, XPS, Raman, OSC, and HREM. The catalytic results revealed that CexZr1?xO2 based nano-oxides are promising heterogeneous catalysts for synthesis of cyclopentanone. Amongst, the CexZr1?xO2/Al2O3 catalyst exhibited ~100% conversion with 75% desired cyclopentanone product selectivity owing to its favorable physicochemical characteristics. 相似文献
The feasibility of acetylation of glycerol with acetic acid was investigated employing CeO2–ZrO2, CeO2–Al2O3, SO42?/CeO2–ZrO2, and SO42?/CeO2–Al2O3 solid acid catalysts to synthesize monoacetin, diacetin and triacetin having interesting applications as bioadditives for petroleum fuels. Intensive physicochemical and surface characterization of the prepared catalysts were performed using XRD, BET surface area, ammonia-TPD and Raman spectroscopy techniques. Characterization results revealed that impregnated sulfate ions strongly influence the physicochemical characteristics of the investigated mixed oxide catalysts. Among various catalysts investigated, the SO42?/CeO2–ZrO2 combination catalyst exhibited superior catalytic activity under mild conditions. The effect of various parameters such as reaction temperature, molar ratio of acetic acid to glycerol, catalyst wt% and time-on-stream were studied over the SO42?/CeO2–ZrO2 catalyst to optimize the reaction conditions. Catalyst reusability was also carried out to understand its stability. 相似文献