1,721,037 research outputs found
Effects of tungsten on corrosion and kinetics of sigma phase formation of 25% chromium duplex stainless steels
No full textDuplex stainless steels (DSS) of 25% Cr-7% Ni-x% Mo-y% W-0.25% N (x = 1.5 to 3, and y = 0 to 3) were designed with the same pitting resistance equivalent (PRE) value of 42 by varying the contents of Mo and W. Effects of W on pitting and stress corrosion of the solution-annealed or aged alloys in chlorides were examined using anodic polarization testing, critical pitting temperature measurements, and slow strain rate testing. Influences of W on degradation of mechanical properties of the alloys caused by precipitation of secondary phases during aging at 850 degrees C were investigated using the Charpy impact and tensile tests, x-ray diffraction, and backscattered scanning electron microscopy. Resistance to pitting and stress corrosion increased with the ratio of W to Mo content. During aging, the alloys were embrittled rapidly by precipitation of the sigma (sigma) phase, with the rate of embrittlement delayed significantly by increases in W content. Thus, the alloy containing 3% W-1.5% Mo exhibited the highest resistance to pitting and stress corrosion in the solution-annealed rendition and the highest resistance to embrittlement induced by aging. The degree of degradation in corrosion and mechanical properties of the alloys during aging was associated closely with the amount of sigma precipitates. Addition of W to 25% Cr DSS retarded nucleation and growth of the sigma phase during aging, thereby delaying degradation of the corrosion and mechanical properties of the alloys. Retardation of precipitation of the sigma phase by W during aging resulted from its inherently slower diffusion rate compared to that of Mo. W in the alloys caused preferential precipitation of the chi (chi) phase along the grain boundaries and, hence, inhibited nucleation and growth of the sigma phase by depleting W and Mo around the chi precipitates, This beneficial effect of W on retardation of sigma phase precipitation was most dominant in the alloy containing 3% W and 1.5% Mo
Moving frame technique for planar acoustic holography
No full textAcoustic holography is one of the best methods to visualize sound fields. The quality of the visualized sound is primarily determined by the size of the hologram, its microphone spacing, and the number of microphones. This paper describes a way to virtually increase the hologram size and the spatial resolution of the holograph. For a stationary sound field, the method continuously sweeps the sound field by a line array of microphones. For moving sound sources, radiating sound is measured by using a line array of microphones fixed in space. In both cases, the measured signals have Doppler effects. The theoretical formulation has been systematically addressed by employing a moving coordinate which has relative motion between the measurement coordinate and the hologram coordinate. Simulations and experiments support the proposed theory. The drawback is that the method is only applicable to discrete frequencies. (C) 1998 Acoustical Society of America
MINIMIZATION OF BIAS ERROR DUE TO WINDOWS IN PLANAR ACOUSTIC HOLOGRAPHY USING A MINIMUM ERROR WINDOW
No full textBias errors in the prediction of a sound field using planar acoustic holography are due to aliasing and window effects. It is noteworthy that aliasing is negligible in the forward predictions if the sampling space is less than a quarter wavelength. However, bias error induced by a window is the major concern for accurate holographic prediction because of the small number of measurement points in the planar acoustic holography. For the reduction of this error, a new class of window, the MEW, is proposed and compared with Ham, Gaussian, and Kaiser-Bessel windows. It is built by modifying the method that Papoulis proposed by minimizing the second-order moment of the window spectrum. The characteristics of the MEW vary with the number of weighting values and the number of higher-order moment terms to be eliminated. The applicability of the MEW on planar acoustic holography is demonstrated. (C) 1995 Acoustical Society of America
Repassivation Kinetics of Fe-20Cr-xNi Alloys (x = 0∼80 wt%) and Its Relation to Stress Corrosion Susceptibility
No full textEffects of Nickel on the Repassivation Kinetics of Fe-20Cr-xNi (x = 0~80) Alloys in a Chloride Solution
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BONDING STRUCTURE AND OPTICAL BANDGAP OF RF-SPUTTERED HYDROGENATED AMORPHOUS-SILICON CARBIDE ALLOY-FILMS
No full textHydrogenated amorphous silicon carbide (a-Si1-xCx:H) alloy films were deposited by radio frequency (rf) magnetron sputtering at room temperature with variable rf powers. Effects of deposition parameters on the bonding structure and optical properties of the films were measured. Infrared (IR) absorption and optical transmittance measurements of films deposited under methane gas flow rates of 2 and 3 sccm showed that they differed. In the case of 2 sccm flow rate, the optical bandgaps gradually decreased with increasing rf power and slopes, B, of the Tauc plot increased up to a power of 5 W/cm2. In the case of 3 sccm flow rate, optical bandgaps increased and the slopes were invariant with power. This difference is attributed to the differences in the bond structure of the films. Under the condition of flow methane gas flow rate as in the former case, the Si-C bonding concentration is saturated and those of Si-H(n) bonds still increase while those of C-H(n) bonds decrease with power. However in the latter, both concentrations of Si-C and Si-H(n) bonds increase and those of C-H(n) bonds decrease. As a result, optical bandgaps of rf sputtered films which have a high fraction of carbon, greater than 0.65, are more influenced by the Si-C bonds than by the hydrogen-related bonds
RELATION BETWEEN POISSONS RATIO AND IONICITY IN SIMPLE BINARY CUBIC COMPOUNDS
No full textThe nature of the atomic forces in solids may be obtained from a knowledge of the elastic constants. Covalent compounds have a tetrahedral structure, whereas ionic compounds have a rock salt or caesium chloride structure, and it is necessary that appropriate models should be applied to explain the elastic properties of covalent and ionic crystals because of the difference in the crystal symmetry and bonding character. Elastic properties of covalent and ionic compounds have been explained using a valence-force-field model and deformation dipole model respectively. A more qualitative interpretation concerning the relation between Poisson's ratio and ionicity in simple binary cubic compounds is given in this study
Effects of Alloying Elements (Cr, Mo, Ni) on Repassivation Kinetics of Ferritic Stainless Steels
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