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Aging Treatment (aging + treatment)
Selected AbstractsTensile-Compressive Creep Asymmetry of Recent Die Cast Magnesium Alloys,ADVANCED ENGINEERING MATERIALS, Issue 9 2007S. Xu The tensile-compressive creep asymmetry of die cast magnesium alloys is experimentally explored and the possible deformation mechanisms are discussed. Creep tests were performed under tension and compression at 125,°C and 150,°C on die cast Mg alloys AM50, AE44 and AJ62A. Higher tensile than compressive creep strengths were observed for all alloys except for low pressure die cast AM50 at a low creep stress of 35 MPa at 125,°C. An aging treatment of 250 hours at 180,°C was employed for AM50 samples to obtain an over-aged microstructure that would minimize the effects of dynamic precipitation of ,-Mg17Al12 on creep. The creep data for the aged samples showed significant scatter, and the trend in tensile-compressive creep asymmetry of the aged samples is not clear for the short-term creep tests under high creep stresses. [source] Synthesis and characterization of proton-conducting copolyimides bearing pendant sulfonic acid groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2005Yan Yin Abstract A series of sulfonated copolyimides (co-SPIs) bearing pendant sulfonic acid groups were synthesized from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), bis(3-sulfopropoxy) benzidines (BSPBs), and common nonsulfonated diamines via statistical or sequenced polycondensation reactions. Membranes were prepared by casting their m -cresol solutions. The co-SPI membrane had a microphase-separated structure composed of hydrophilic and hydrophobic domains, but the connecting behavior of hydrophilic domains was different from that of the homo-SPIs. The co-SPI membranes displayed clear anisotropic membrane swelling in water with negligibly small dimensional changes in the plane direction of the membrane. With water uptake values of 39,94 wt %, they showed dimensional changes in membrane thickness of about 0.11,0.58, which were much lower than those of homo-SPIs. The proton conductivity , values of co-SPI membranes with ion exchange capacity values ranging from 1.95,2.32 meq/g increased sigmoidally with increasing relative humidity. They displayed , values of 0.05,0.16 S/cm at 50 °C in liquid water. Increasing temperature up to 120 °C resulted in further increase in proton conductivity. The co-SPI membranes showed relatively good conductivity stability during the aging treatment in water at 100 °C for 300 h. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1545,1553, 2005 [source] Alkoxide Sol-Gel-Processed Cordierite FiberJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2002Mu-Tsun Tsai An alkoxide sol-gel route was developed to prepare stoichometric cordierite fibers. The influences of the aging treatment and heating rate on the sinterability of the gel fibers were also examined. X-ray diffraction analysis revealed that the unaged and aged fibrous gels all remained amorphous <800&, but began crystallization into ,-cordierite and ,-cordierite at ,900°C and 1050°C, respectively; single-phase ,-cordierite fibers were obtained at 1300°C. Heating the unaged fibers yielded denser microstructures, with fine grain sizes of ,0.2,0.4 ,m, whereas the aged fibers exhibited porous microstructures following heating at 1300°C. A higher heating rate and aging treatment resulted in a higher open porosity of the fired fiber. [source] Effects of Thermal Aging on the Mechanical Properties of a Porous-Matrix Ceramic CompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2002Eric A. V. Carelli The present article focuses on changes in the mechanical properties of an all-oxide fiber-reinforced composite following long-term exposure (1000 h) at temperatures of 1000,1200°C in air. The composite of interest derives its damage tolerance from a highly porous matrix, precluding the need for an interphase at the fiber,matrix boundary. The key issue involves the stability of the porosity against densification and the associated implications for long-term durability of the composite at elevated temperatures. For this purpose, comparisons are made in the tensile properties and fracture characteristics of a 2D woven fiber composite both along the fiber direction and at 45° to the fiber axes before and after the aging treatments. Additionally, changes in the state of the matrix are probed through measurements of matrix hardness by Vickers indentation and through the determination of the matrix Young's modulus, using the measured composite moduli coupled with classical laminate theory. The study reveals that, despite evidence of some strengthening of the matrix and the fiber,matrix interfaces during aging, the key tensile properties in the 0°/90° orientation, including strength and failure strain, are unchanged. This strengthening is manifested to a more significant extent in the composite properties in the ±45° orientation, wherein the modulus and the tensile strength each exhibit a twofold increase after the 1200°C aging treatment. It also results in a change in the failure mechanism, from one involving predominantly matrix damage and interply delamination to one which is dominated by fiber fracture. Additionally, salient changes in the mechanical response beyond the maximum load suggest the existence of an optimum matrix strength at which the fracture energy in the ±45° orientation attains a maximum. The implications for long-term durability of this class of composite are discussed. [source] | ||||||||||