Yanchun ZHOU(Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang
,
110015
,
China)M.N.Rahaman (Ceramic Engineering Department
,
University of Missouri-Rolla
,
Rolla
,
MO 65401
,
USA)
材料科学技术（英文）
Nanocrystalline CeO2 powders (particle size ≈10-15 nm), doped with up to 20 at.-% of Mg,Ca or Y were prepared by chemical precipitation under hydrothermal conditions. The particle size and shape of the powders change slightly with the dopant concentrations. The the of the dopants on the sintering of the compacted powders was investigated during heating at a constant rate of 10℃/min. The elemental composition and the concentration of the dopant has significant efFect on the densification and grain growth. Compared to undoped CeO2, the dopants produce a shift in the densification curve to higher temperatures. For the same dopant concentration and under identical sintering conditions, the Ca doped samples reach nearly full density with the smallest grain size (≈50 nm), however, the Mg doped sample has the lowest density (≈95% of the theoretical) with the largest grain size (≈1 μm)
关键词:
QIAO Lijie LIU Rui XIAO Jimei University of Science and Technology Beijing
,
Beijing
,
China
金属学报(英文版)
The effects of stress components on nucleation sites and propagation directions of stress cor- rosion cracks in brass were investigated with specimens under mode Ⅱ and mode Ⅲ loadings. The results indicated that under mode Ⅱ loading,stress corrosion cracks nucleated on the site with maximum normal stress component and propagated along the plane perpendieular to the maximum normal stress,under mode Ⅲ loading,the stress corrosion crack was not evident on the 45°plane due to the general corrosion in aqueous solution with high NH_4OH concentra- tion,while stress corroded in aqueous solution with low NH_4OH concentration, numerous cracks with spacings of 10—150μm were found on the 45°plane with maximum normal stress and no stress corrosion cracks was observed on the plane with maximum shear stress.
关键词:
stress corrosion cracking
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null
,
null
,
null
Wear
Reciprocating ball-on-flat dry sliding friction and wear experiments have been conducted on single-phase gamma-Y(2)SO(7) ceramic flats in contact with AISI 52100 bearing steel and Si(3)N(4) ceramic balls at 5-15 N normal loads in an ambient environment. The kinetic friction coefficients of gamma-Y(2)Si(2)O(7) varied in the range over 0.53-0.63 against AISI 52100 steel and between 0.51-0.56 against Si(3)N(4) ceramic. We found that wear occurred predominantly during the running-in period and it almost ceased at the steady friction stage. The wear rates Of gamma-Y(2)Si(2)O(7) were in the order of 10(-4) mm(3)/(N m). Besides, wear debris strongly influenced the friction and wear processes. The strong chemical affinity between gamma-Y(2)Si(2)O(7) and AISI 52100 balls led to a thick transfer layer formed on both contact surfaces of the flat and counterpart ball, which changed the direct sliding between the ball and the flat into a shearing within the transfer layer. For the gamma-Y(2)Si(2)O(7)/Si(3)N(4) pair, a thin silica hydrate lubricant tribofilm presented above the compressed debris entrapped in the worn track and contact ball surface. This transfer layer and the tribofilm separated the sliding couple from direct contact and contributed to the low friction coefficient and wear rate. (C) 2009 Elsevier B.V. All rights reserved.
关键词:
Y(2)Si(2)O(7);Friction and wear;Wear mechanism;Wear debris;hot corrosion;molten-salt;si3n4-sio2-y2o3;tribofilm;mechanism;friction;system;wear
ZENON OPIEKUN
金属学报(英文版)
The manuscript presents changes of macrostructure and microstructure of plate and shaft castings made of cobalt alloy MAR-M509. They have different values of geometric module M within the range of 0.91-5.56 mm that have been created with multilayer ceramic shell moulds (MSC) of different initial temperatures of 200-1000℃ at the moment of pouring. It has been stated that decrease of initial temperature of MSC and value M causes increase in casting fine-granularity, distance reduction between dendrite branches λ2 and refinement of initial carbides in irregular ternary eutectic γ+$M23C6+MC.
关键词:
Multilayer ceramic shell mould (MSC)
Materials Science and Engineering B-Solid State Materials for Advanced Technology
The wettability of Si-Al-O-N ceramic by ternary alloys of Sn-Ti and copper, nickel, silver, indium or aluminum was investigated by sessile drop method in vacuum at 800-1100 K. The results show that a small addition of Ni (1-3 at.%) or Cu (5-10 at.%) is beneficial to the wettability of the solder on the ceramic at 1000 K, but Ag or In has little effect, and Al is harmful. In discussion, it was suggested that it is important to the chemical wetting of metal on ceramic, i.e. an interaction between the third element and the active metal or the matrix metal, and a fresh liquid surface: as a result, three criteria of how to select the third element to improve wetting of an active solder on ceramics were also proposed.
关键词:
brazing filler metal;silicon-nitride;alumina;systems;joints;behavior;titanium;solids;alloys;steel
材料科学技术（英文）
Changes of surface morphology following XeCl excimer laser irradiation were investigated for three engineering ceramic materials (Al2O3, Al2O3-SiC nanocomposite and Si3N4) Al2O3 and Al2O3-SiC nanocomposite samples exhibit a smooth rapid melt layer on the surface, and the formation of the metastable gamma-Al2O3 was observed. A silicon-rich layer on the surface was formed after laser irradiation of Si3N4. The toughness K-1c of the materials was measured by the indentation fracture method. After laser irradiation, the toughness of Al2O3, Al2O3-SiC nanocomposite and Si3N4 was improved to various degrees: Al2O3-SiC nanocomposite, 60% (max.); Al2O3, 40% (max.); Si3N4, 12% (max.).
关键词:
alumina
Y.B. Hou
金属学报(英文版)
In this paper, the PMMA films doped with N,N'-diphenyl-N,N'-di(m-tolyl)-benzidineand rubrene were fabricated by spin coating, and the effect of photooxidation onthe photoluminescence of the doped PMMA thin films was investigated. The resultsshowed that under the irradiation of 350nm UV light, N,N'-diphenyl-N,N'-di(m-tolyl)-benzidine can sensitized rubrene and results in the enhancement in the photooxrationof rubrene. The effect of photooxidation on the photoluminescence from rubrene w asmore obvious. Both lifetime measurement and in situ measurement of photolumines-cence showed that rubrene molecules exist in two chemical surroundings.
关键词:
photoluminescence
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null
