1,721,073 research outputs found
Pitting corrosion of the laser surface melted Alloy 600
No full textThe effect of laser surface melting (LSM) on the resistance to pitting corrosion of Ni-base Alloy 600 was investigated by a potentiodynamic polarization test in 1 M NaCl solutions at pH values of 4 and 10 at temperatures of 30, 60 and 90degreesC. The pitting potentials of Alloy 600 were markedly increased by the LSM process, when compared with those of the non-laser treated Alloy 600. From the microscopic examination after the corrosion test, it was found that the pitting was initiated at the junction between a TiN inclusion and the matrix, possibly at the site of a sulfide physically associated with the TiN inclusion. The homogeneous micro-structure associated with the reduction of the inclusion size during the LSM process could be attributed to the improvement of the pitting corrosion properties in the LSM alloy 600. (C) 2004 Elsevier B.V. All rights reserved.This work has been carried out as a part of the Nuclear
R&D Program by M.O.S.T. in Korea
Effects of sensitization treatment on the evolution of Cr carbides in rapidly solidified Ni-base alloy 600 by a CO2 laser beam
No full textThe effects of heat treatment on the precipitation of Cr carbides in Ni-base Alloy 600 laser surface melted by a CO2 laser beam were investigated with microscopic equipment. Aging treatment at 600 degrees C for 24 h induced precipitation of Cr-rich M23C6 and Cr7C3 carbides on some high angle grain boundaries, and the minimum Cr concentration along the grain boundary was measured to be about 12 wt%. In particular, the Cr-rich M23C6 was precipitated on TiN and MgS type particles surrounded by tangled dislocations along the cell boundaries in the laser melted zone. The precipitation behaviors of Cr carbides in the laser surface melted and subsequently sensitized Alloy 600 were analyzed and then compared with those of the conventionally processed, solution annealed and then identically sensitized Alloy 600 from the viewpoint of different microstructural features. (C) 2000 Elsevier Science S.A. All rights reserved
The strain relaxation in a lattice-mismatched heterostructure
No full textStrain relaxation phenomena of the heteroepitaxial lattice-mismatched semiconductors have been investigated. The relationship between the residual in-plane strain and the width of the misfit cell was obtained geometrically. The residual in-plane strain was calculated for various film thicknesses by using the energy minimization theory on the misfit cell in the InxGa1-xAs/GaAs(1 0 0) heterostructure system. A generalized strain relaxation model is presented on the basis of the energy minimization theory. (C) 1999 Elsevier Science B.V. All rights reserved
Particle formation in the rapidly solidified zone of alloy 600 surface melted by a CO2 laser beam
No full textCreating social value of interactive media installation: Case study of designing Wish Spark
No full textThe role and mechanism of a ZnTe buffer layer on the structural properties of the strained CdxZn1-xTe/ZnTe double quantum wells
No full textTransmission electron microscopy (TEM) measurements were performed to investigate the role and mechanism of a ZnTe buffer layer on the high-quality structural properties for strained CdxZn1-xTe/ZnTe double quantum wells. The bright-field TEM image near the ZnTe/GaAs interface showed the Moire patterns, indicative of initial island growth and of a difference in the growth directions between the islands. The high-resolution TEM image indicated that the difference in the growth directions originated from the formation of the plane defects, such as a sub-grain boundary. When a 1-mu m ZnTe buffer layer was grown on the GaAs substrate, the ZnTe buffer layer could be used as a defect-free substrate, as shown by the thickness fringes observed from the TEM image. The formation mechanism for the thickness fringes in the ZnTe buffer layer between the CdxZn1-xTe/ZnTe double quantum well and the GaAs substrate is discussed. The results indicate that the ZnTe buffer layer plays an important role for strained CdxZn1-xTe/ZnTe double quantum wells grown on GaAs substrates by eliminating the defects due to the lattice mismatch. (C) 1998 Elsevier Science Ltd. All rights reserved
A study on intergranular corrosion of laser treated alloy 600 by DL-EPR method and microscopic examination
No full textNi-base Alloy 600 has been widely used as a steam generator (SIG) tubing material in nuclear power plants because of its good mechanical and corrosion properties at high temperatures. However, degradations of SIG tubes due to intergranular attack (IGA) and intergranular stress corrosion cracking (IGSCC) during normal operation were frequently reported. in particular, Alloy 600 can be very susceptible to IGA/IGSCC in some sulfur-bearing environments by sensitization. In this paper, the beneficial effects of laser surface melting (LSM) to intergranular corrosion of the sensitized Alloy 600 is presented from the results of the double loop electrochemical potentiokinetic reactivation (DL-EPR) test. The DL-EPR test was performed in de-aerated 0.01 M H2SO4 + 20 ppm KSCN at a scan rate of 0.5 mV/sec at room temperature. The degree of sensitization (DOS) of the sensitized Alloy 600 measured from the DL-EPR test was considerably reduced by LSM. The sensitized Alloy 600 after LSM also exhibited a relatively low DOS, comparing with that of the sensitized but not laser treated Alloy 600. From the microscopic observation, it was found that the microstructural changes by the LSM process, especially changes in the precipitation behavior of grain boundary Cr-rich carbides, caused the improvement of resistance to intergranular corrosion of the laser treated Alloy 600. The resistance to IGSCC of the laser treated Alloy 600 in sulfur-bearing environments was also discussed from the results of measured DOS and microstructural examination
Double loop electrochemical potentiokinetic reactivation test of nickel-base alloy 600 surface-melted by a CO2 laser beam
No full textNi-base Alloy 600 has been widely used as a steam generator (S/G) tubing material in nuclear power plants because of its good mechanical and corrosion properties at high temperatures. However, degradations of S/G tubes due to intergranular attack (IGA) and intergranular stress corrosion cracking (IGSCC) during normal operation have been frequently reported. In particular, Alloy 600 can be very susceptible to IGA/IGSCC in some sulfur-bearing environments by sensitization. In this paper, the beneficial effects of laser surface melting (LSM) on intergranular corrosion of the sensitized Ahoy 600 is presented from the results of the double loop electrochemical potentiokinetic reactivation (DL-EPR) test. The DL-EPR test was performed in de-aerated 0.01 M H2SO4+20 ppm KSCN at a scan rate of 0.5 mV/sec at room temperature. The degree of sensitization (DOS) of the sensitized Alloy 600 measured from the DL-EPR test was considerably reduced by LSM. The sensitized Alloy 600 after LSM also exhibited a relatively low DOS, compared with that of the sensitized but not laser treated Alloy 600. From the microscopic observation, it was found that the microstructural changes brought about by the LSM process. especially changes in the precipitation behavior of grain boundary Cr-rich carbides, caused the improvement of resistance to intergranular corrosion of the laser treated Alloy 600. The resistance to IGSCC of the laser treated Alloy 600 in sulfur-bearing environments was also discussed from the results of measured DOS and microstructural examination
Strain-induced anisotropic Ge diffusion in SiGe/Si superlattices
No full textAnisotropic diffusion of Ge induced by nonuniform strain in SiGe/Si interfaces in the range of 700-850 degreesC is directly observed with medium-energy ion-scattering spectroscopy through its composition and strain profiles of atomic-layer depth resolution. For SiGe/Si interfaces with identical composition profiles but with different strain distributions, the anisotropic diffusion of Ge can be clearly correlated with the anisotropic relaxation of the nonuniform strain in the near-surface layer of several nm depth. The results suggest that atomic-scale strain control is critical to maintain abrupt SiGe/Si interfaces under thermal budget. (C) 2002 American Institute of Physics
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