Response to thermal treatment of a powder metallurgy Fe-0.8 % B-1.3 % C-1.6 %Cr alloy

Argon atomized powders of the Fe-0.8%B-1.3%C-1.6%Cr alloy in the rapid solidification condition as well as the consolidated material were characterized. Consolidation was carried out by extrusion at 1050°C and by hot isostatic pressing at 700°C. The microstructure of powder particles in the rapid solidification condition is dendritic and remains unchanged after hot isostatic pressing. This microstructure is gradually lost after annealing at temperatures above 900°C. The extruded material presents a fine and homogeneous microstructure constituted by small grains of laminar pearlite and spherical M₂₃(B,C)₆ borocarbides of 1.8 μm in size. A martensite microstructure with a uniform dispersion of M₃(B,C) borocementite particles is obtained after annealing at 1095°C 10 min and water quenching. For long austenitization time at 1095°C, a coalescence of borocementite as well as decarburization is observed in the steel. Dilatometric studies, between 20 and 400°C, of samples quenched from 1095°C show the presence of two contraction volume points at 160 and 310°C. At 160°C, the high carbon martensite decomposes into a two phase mixture of metastable carbides and low carbon martensite. At 310°C simultaneous transformation of austenite to ferrite and metastable carbides into cementite occurs.     

Fracture of Al-4% Cu-0.1% Fe single crystals

The fracture behaviour of heat-treated Al-4% Cu-0.1% Fe single crystals was studied in tension at room temperature. Three heat-treatment conditions were examined: quenced, fully hardened and overaged. Slip lines, shear bands and fracture surfaces were studied to yield information on the plastic deformation processes occurring prior to fracture. The presence of stable Al₇Cu₂Fe particles was found to be an important factor in fracture formation. In the as-quenced condition two fracture planes of different topography were formed. Large shear zones together with scattered shallow dimples were observed in both planes due to stable particles. In the fully hardened condition fracture occurred without necking and usually by shearing along the conjugate slip system. The presence of shear zones and dimples of different sizes was observed. Finally, in the overaged condition fracture took place by void coalescence after strong necking, as in polycrystalline samples. No shear zones were observed on the fracture surface of these samples.     

Effect of emulsifier type on the copolymerization of styrene and acrylic acid

In this work we report the emulsion copolymerization of styrene and acrylic acid using a cationic (cetyltrimethylammonium bromide or CTAB) or an anionic (sodium dodecylsulfate or SDS) emulsifier. Latexes were stable and monodisperse with spherical particles of ～100 nm for the CTAB latex and of ～70 nm for the SDS latex. However, a random copolymer was produced with CTAB whereas a “blocky” copolymer was obtained with SDS. Here we propose a mechanism to explain these structural differences in terms of the relative reactivities of styrene and acrylic acid and of their initial location and distribution in the SDS and CTAB emulsions.     

On the structure of generalized toric codes

Toric codes are obtained by evaluating rational functions of a nonsingular toric variety at the algebraic torus. One can extend toric codes to the so-called generalized toric codes. This extension consists of evaluating elements of an arbitrary polynomial algebra at the algebraic torus instead of a linear combination of monomials whose exponents are rational points of a convex polytope. We study their multicyclic and metric structure, and we use them to express their dual and to estimate their minimum distance.     

The fabrication of bulk ultrafine-grained zirconium by accumulative roll bonding

This work demonstrates that bulk ultrafine-grained zirconium can be fabricated by accumulative roll bonding. Grain refinement takes place by geometrical thinning and grain subdivision through the formation of geometrically necessary boundaries. This is consistent with the stabilization of a typical rolling texture during processing and with the absence of any recrystallization texture components. The ultrafine-grained zirconium possesses high ultimate tensile strength, good ductility, and a remarkable strain hardening capacity.     

Role of particles on microstructure and mechanical properties of the severely processed 7075 aluminium alloy

The 7075-T6 Al alloy was processed by accumulative roll bonding (ARB) up to five passes by a 3:1 thickness reduction per pass at 300, 350 and 400 °C. Microscopical examinations revealed that the particle distribution varies with the processing parameters. As a consequence, the particle pinning effect decreases with increasing processing temperature and the number of ARB passes. For this reason, the evolution of grain structure with the number of passes is different for each processing temperature, and the superplastic properties are determined not only by the microstructural features before deformation, but also by the alloy thermal stability. The best superplastic properties are attained by the sample processed up to three passes at 300 °C, obtaining elongations to failure in excess of 200 %. Finally, ARB processing at high temperature leads to a decrease of hardness with respect to the peak-aged as-received alloy, especially with increasing number of passes and with decreasing processing temperature, due to the variation of the interparticle mean spacing and the amount of solute atoms.     

Filtration process cost in submerged anaerobic membrane bioreactors (AnMBRs) for urban wastewater treatment

The objective of this study was to evaluate the effect of the main factors affecting the cost of the filtration process in submerged anaerobic membrane bioreactors (AnMBRs) for urban wastewater (UWW) treatment. Experimental data for CAPEX/OPEX calculations was obtained in an AnMBR system featuring industrial-scale hollow-fiber (HF) membranes. Results showed that operating at J₂₀ slightly higher than the critical flux results in minimum CAPEX/OPEX. The minimum filtration process cost ranged from €0.03 to €0.12 per m³, mainly depending on SGD_m (from 0.05 to 0.3 m³·m^?2·h^?1) and MLSS (from 5 to 25 g·L^?1). The optimal SGD_m resulted in approx. 0.1 m³·m^?2·h^?1.     

Application of the Morris method for screening the influential parameters of fuzzy controllers applied to wastewater treatment plants

In this paper, we evaluate the application of a sensitivity analysis to help fine-tuning a fuzzy controller for a biological nitrogen and phosphorus removal (BNPR) plant. The Morris Screening method is proposed and evaluated as a prior step to obtain the parameter significance ranking. First, an iterative procedure has been performed in order to find out the proper repetition number of the elementary effects (r) of the method. The optimal repetition number found in this study (r = 60) is in direct contrast to previous applications of the Morris method, which usually use low repetition number, e.g. r = 10 - 20. Working with a non-proper repetition number (r) could lead to Type I error (identifying a not-important factor as significant (false positive)) as well as Type II error (identifying an important factor as not significant (false negative)), hence emphasizing the importance of finding the optimal repetition number for each study in question. With the proper r found, the Morris Screening helped identify the parameter significance ranking, thereby facilitating the calibration of fuzzy controllers, which contain many parameters that need to be adjusted for different wastewater treatment plant (WWTP) applications.     

Nonstationarity broadening reduction in pulsed Doppler spectrummeasurements using time-frequency estimators

The spectral width of Doppler signals is used as measure of lesion-induced flow disturbance. Its estimation accuracy is compromised using the conventional short-term Fourier transform (STFT) since this method implicitly assumes signal stationarity during the signal window while the Doppler signals from arteries are markedly nonstationary. The Wigner-Ville (WVD), Choi-Williams (CWD) and Bessel distributions (BD), specifically designed for nonstationary signals, have been optimized for spectral width estimation accuracy and compared to the STFT under different signal to noise ratios using simulated Doppler signals of known time-frequency characteristics. The optimum parameter values for each method were determined as a Hanning window duration of 10 ms for the STFT, 40 ms for the WVD and CWD and 20 ms for the BD and dimensionless time-frequency smoothing constant values of five in the CWD and two in the BD. Thresholding was used to reduce the effect of cross terms and side lobes in the WVD and BD. With no added noise the WVD gave the lowest estimation error followed by the CWD. At signal-to-noise ratios (SNRs) of 10 dB and 20 dB the CWD and BD had similar errors and were markedly better than the other estimators. Overall the CWD gave the best performance     

Analysis of Garofalo equation parameters for an ultrahigh carbon steel

Isothermal stress–strain curves data from torsion tests conducted at high temperature (950–1200 °C) and strain rates (2–26 s⁻¹) were analyzed in an ultrahigh carbon steel (UHCS) containing 1.3%C. The sine hyperbolic Garofalo equation was selected as an adequate constitutive equation for the entire range of the forming variables considered. The Garofalo parameters were assumed strain dependent allowing the prediction of stress–strain curves under transient and steady-state conditions. The average relative errors obtained were below 3% in stress. In addition, the creep deformation mechanisms in the UHCS were analyzed from the Garofalo equation parameters. For this aim, the stress exponent of the Garofalo equation was, for the first time, related to that of the power law equation. The results show that the controlled deformation mechanism at steady state is lattice diffusion-controlled slip creep.