Effect of Nb2O5 Content on Microstructure and Dielectric Properties of Ba2-2xNa1-xNb5O15-5x/2 Ceramics

2003 ◽  
Vol 17 (08n09) ◽  
pp. 1273-1278 ◽  
Author(s):  
Peng Wang ◽  
Joon Hyung Lee ◽  
Jeong Joo Kim ◽  
Sang Hee Cho ◽  
Hee Young Lee
Keyword(s):  
Phase Transformation ◽  
Dielectric Properties ◽  
Transformation Temperature ◽  
Tungsten Bronze ◽  
Dielectric Behavior ◽  
Phase Transformation Temperature ◽  
Microstructure Development ◽  
Dielectric Characteristics ◽  
Optically Transparent ◽  
Second Phases

The effect of Nb 2 O 5 content on the microstructure development and the dielectric characteristics of tungsten-bronze-structured polycrystalline Ba 2 Na 1 Nb 5 O 15 (BNN) ceramics was studied. The compositions of stoichiometry, Nb 2 O 5–deficient and Nb 2 O 5–excess BNN were prepared and sintered at 1250 °C for 2 h in oxygen. We report the development of second phases, microstructure and dielectric behavior of polycrystalline BNN ceramics, which was not reported ever. The Nb 2 O 5 content affect lattice constant of the sintered body, which contributed to the change of phase transformation temperature. The stoichiometric BNN showed the lowest densification, while an optically transparent sample was obtained in Nb 2 O 5–excess highly dense sample.

Microstructure and Dielectric Properties of Tungsten Bronze Structured KLN and BNN Ceramics: TiO2 Effect

2003 ◽  
Vol 17 (08n09) ◽  
pp. 1267-1272 ◽  
Author(s):  
Peng Wang ◽  
Shu Lun Xu ◽  
Joon Hyung Lee ◽  
Jeong Joo Kim ◽  
Sang Hee Cho ◽  
...  
Keyword(s):  
Solid Solution ◽  
Phase Transformation ◽  
Dielectric Properties ◽  
Transformation Temperature ◽  
Tungsten Bronze ◽  
Phase Transformation Temperature ◽  
Dielectric Characteristics ◽  
Lattice Constants

The effect of TiO2 addition on microstructure and dielectric characteristics of tungsten bronze structured K 6 Li 4 Nb 10 O 30 (KLN) and Ba 2 Na 1 Nb 5 O 15 (BNN) was examined. Solid solution limits of TiO2 in KLN and BNN are thought to be around 0.5 and 0.4 mol, respectively. As the amount of TiO2 increased, lattice constants of KLN and BNN decreased. Microstructure of BNN was sensitively influenced by TiO2 addition, which was explained by the generation of vacancies. TiO2 addition was effective in decreasing the phase transformation temperature of KLN, while it was effective in suppressing the dielectric curve of BNN at the phase transformation temperature.

Crystallization and dielectric properties of SrO–BaO–Nb2O5–GeO2 tungsten–bronze glass–ceramics

2001 ◽  
Vol 16 (7) ◽  
pp. 2057-2063 ◽  
Author(s):  
Jiin-Jyh Shyu ◽  
Hsin-Wei Peng
Keyword(s):  
Heat Treatment ◽  
Dielectric Properties ◽  
Tungsten Bronze ◽  
Glass Ceramics ◽  
Dielectric Behavior ◽  
Dendritic Morphology ◽  
Dielectric Constants ◽  
Two Stage ◽  
Tetragonal Tungsten Bronze ◽  
Stage Heat Treatment

The crystallization and dielectric properties of SrO–BaO–Nb2O5–GeO2 glass–ceramics were investigated. One- and two-stage heat-treatment methods were used to convert the parent glass to glass–ceramics. Strontium barium niobate (SBN) with a tetragonal tungsten-bronze structure formed as the major crystalline phase. When the crystallizing temperature/time was increased, the secondary crystalline BaGe2O5 phase coexisted with SBN. BaGe2O5 formed as a surface layer grown from the surface into the interior of the sample. The dendritic morphology of SBN crystals was examined. The glass–ceramics crystallized by two-stage heat treatment have higher dielectric constants than those crystallized by one-stage heat treatment. The highest dielectric constant that was obtained in the present glass–ceramics was 320. The glass–ceramics showed relaxor-type dielectric behavior.

Capability of martensitic low transformation temperature welding consumables for increasing the fatigue strength of high strength steel joints

2020 ◽  
Vol 62 (9) ◽  
pp. 891-900
Author(s):  
Jonas Hensel ◽  
Arne Kromm ◽  
Thomas Nitschke-Pagel ◽  
Jonny Dixneit ◽  
Klaus Dilger
Keyword(s):  
Residual Stress ◽  
Phase Transformation ◽  
Fatigue Strength ◽  
High Strength Steel ◽  
Transformation Temperature ◽  
Fatigue Cracks ◽  
High Strength ◽  
Filler Material ◽  
Phase Transformation Temperature ◽  
Filler Materials

Abstract The use of low transformation temperature (LTT) filler materials represents a smart approach for increasing the fatigue strength of welded high strength steel structures apart from the usual procedures of post weld treatment. The main mechanism is based on the effect of the low start temperature of martensite formation on the stress already present during welding. Thus, compressive residual stress formed due to constrained volume expansion in connection with phase transformation become highly effective. Furthermore, the weld metal has a high hardness that can delay the formation of fatigue cracks but also leads to low toughness. Fundamental investigations on the weldability of an LTT filler material are presented in this work, including the characterization of the weld microstructure, its hardness, phase transformation temperature and mechanical properties. Special attention was applied to avoid imperfections in order to ensure a high weld quality for subsequent fatigue testing. Fatigue tests were conducted on the welded joints of the base materials S355J2 and S960QL using conventional filler materials as a comparison to the LTT filler. Butt joints were used with a variation in the weld type (DY-weld and V-weld). In addition, a component-like specimen (longitudinal stiffener) was investigated where the LTT filler material was applied as an additional layer. The joints were characterized with respect to residual stress, its stability during cyclic loading and microstructure. The results show that the application of LTT consumables leads to a significant increase in fatigue strength when basic design guidelines are followed. This enables a benefit from the lightweight design potential of high-strength steel grades.

Phase Transformation Temperature of NiTi Alloy Sheet Examined by Lamb Wave

2011 ◽  
Vol 320 ◽  
pp. 359-362
Author(s):  
Kai Sheng Wang ◽  
Ru Hui He ◽  
Zhi Min Zhao
Keyword(s):  
Phase Transformation ◽  
Lamb Wave ◽  
Transformation Temperature ◽  
Lamb Waves ◽  
Niti Alloy ◽  
Alloy Sheet ◽  
Phase Transformation Temperature ◽  
Wave Method

In this study, the ultrasonic PZT transducers were used for exciting and receiving Lamb waves on NiTi alloy sheet. Lamb waves were measured when the temperature of the NiTi alloy changed. Analysis on frequency spectrums of the Lamb waves was also done. Some marked changes were observed in the dependence of the waveforms and the frequency spectrums of the Lamb waves versus temperature during phase transformation of NiTi alloy. The results show that phase transformation temperature of NiTi alloy sheet may be examined by Lamb wave method.

scholarly journals Influence of Heat Treatment on the Workability of Modified 9Cr-2W Steel with Higher B Content

Metals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 904
Author(s):  
Hyeong Min Heo ◽  
Jun Hwan Kim ◽  
Sung Ho Kim ◽  
Jong Ryoul Kim ◽  
Won Jin Moon
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Phase Transformation ◽  
Transformation Temperature ◽  
Fracture Behavior ◽  
Rolling Process ◽  
Normal Direction ◽  
Phase Transformation Temperature ◽  
Treatment Conditions ◽  
Creep Characteristics

In this study, the effect of heat treatment on the fracture behavior of alloy B steel with boron (B) contents as high as 130 ppm was investigated. The Alloy B are derived from Gr.92 steel with outstanding creep characteristics. The amounts of minor alloying elements such as B, N, Nb, Ta, and C were optimized to achieve better mechanical properties at high temperatures. Hence, workability of the alloy B and Gr.92 were compared. An increase in the B content affected the phase transformation temperature and texture of the steel. The development of the {111}<uvw> components in γ-fibers depended on the austenite fraction of the steel after the phase transformation. An increase in the B content of the steel increased its α-to-γ phase transformation temperature, thus preventing the occurrence of sufficient transformation under the normalizing condition. Cracks occurred at the point of the elastic-to-plastic deformation transition in the normal direction during the rolling process, thereby resulting in failure. Therefore, it is necessary to avoid intermediate heat treatment conditions, in which γ-fibers do not fully develop, i.e., to avoid an imperfect normalization.

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