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21.
We have previously shown that small additions of the rare-earth (RE) element La to Sn-Ag-Cu alloys significantly increases
their ductility, without significant loss in the overall strength. However, due to the high reactivity of La with oxygen,
oxidation of the La-containing phases can affect the mechanical performance of the solder. In this work, we have investigated
the effect of the addition of 2 wt.% Ce, La and Y on the oxidation behavior of Sn-3.9Ag-0.7Cu. Oxidation kinetics were established
by heating samples in ambient air to 60°C, 95°C or 130°C for up to 250 h. Microstructural characterization of the samples,
before and after oxidation, was conducted in order to determine the influence of RE-containing phases on the oxidation kinetics.
The oxidation mechanism, including the phenomenon of Sn whiskering during oxidation, is also discussed. 相似文献
22.
In this article, we report on the microstructure and mechanical properties of Ce- and Y-containing Sn-3.9Ag-0.7Cu solders.
The microstructures of both as-processed solder and solder joints containing rare-earth (RE) elements (up to 0.5 wt pct) are
more refined compared to conventional Sn-3.9Ag-0.7Cu, with decreases in secondary Sn dendrite size and spacing and a thinner
Cu6Sn5 intermetallic layer at the Cu/solder interface. These results agree well with similar observations seen in La-containing
solders reported previously. The monotonic shear behavior of reflowed Sn-3.9Ag-0.7Cu-X(Ce, Y)/Cu lap shear joints was studied as well as the creep behavior at 368 K (95 °C). The data were compared with results
obtained for Sn-3.9Ag-0.7Cu and Sn-3.9Ag-0.7Cu-XLa alloys. All RE-containing alloys exhibited creep behavior similar to Sn-3.9Ag-0.7Cu. Alloys with Ce additions exhibited
a small decrease in ultimate shear strength but higher elongations compared with Sn-Ag-Cu. Similar observations were seen
in La-containing solders. The influence of the RE-containing intermetallics (CeSn3 and YSn3) that form in these alloys on the microstructural refinement, solidification behavior, and mechanical performance of these
novel materials is discussed. 相似文献
23.
24.
25.
The HBr-initiated solid-state polymerization of hexamethylcyclotrisiloxane has been investigated. Up to about 70% conversion, the rate of polymerization is found to be constant but the molecular weight of the polymer formed was observed to increase with conversion. Temperature did not have a marked effect on the polymerization rate as an activation energy of only 2.8 kcal/mole was observed, whereas the rate was found to be exponentially related to the HBr vapor pressure. The HBr and the radiation-initiated solid-state polymerization are compared. 相似文献
26.
27.
The efficacy of γ-irradiation for the formation of Maillard reaction products (MRPs) from glucose and lysine/glycine and the antioxidant potential of MRPs thus formed were examined. Formation of MRPs was observed by monitoring absorbance at 284 nm and 420 nm. Upon irradiation, there was a dose-dependent increase in absorbance (r2 = 0.99) at both the wavelengths. Irradiation of glucose/lysine solution resulted in higher absorbance at 284 nm than did that of glucose/glycine solution. Similarly, increase in absorbance at 420 nm was observed upon irradiation in both the systems. No significant absorbance was observed with unirradiated solution of glucose and lysine/glycine. These findings thus clearly revealed the formation of intermediate products and brown complexes (of Maillard reaction) upon irradiation of glucose/amino acid solution. A fluorescence was also observed in irradiated glucose/amino acid solution, whereas, none was seen in non-irradiated solution. These observations further confirmed the formation of MRPs, as fluorescent compounds are known to be precursors of brown pigments formed during the Maillard reaction. These MRPs exhibited excellent antioxidant activity, as measured by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and β-carotene bleaching assays. MRPs, formed at a 40 kGy dose, scavenged up to 62% of DPPH radical and 82% of β-carotene was protected from bleaching. Reducing power of MRPs, estimated using the ferricyanide, method was also increased as compared to non-irradiated solutions. Further, these MRPs were able to scavenge hydroxyl radical and superoxide anion radical to the extents of 33% and 58%, respectively. These MRPs could chelate iron to an extent of 32% under in vitro conditions. Thus, these studies clearly demonstrated that radiation technology could be employed for obtaining novel antioxidants from sugar and amino acid combinations. 相似文献
28.
G. Tang Y. -L. Shen D. R. P. Singh N. Chawla 《International Journal of Mechanics and Materials in Design》2008,4(4):391-398
A numerical study was undertaken to study the elastic property of metal-ceramic multilayered composites derived from indentation
testing. The model system features alternating thin films of aluminum (Al) and silicon carbide (SiC), free from any effect
due to the underlying substrate. The anisotropic composite elastic response was obtained by simulating overall loading of
the multilayer structure. Finite element modeling of instrumented indentation was then employed to calculate the indentation-derived
modulus using the unloading portion of the load–displacement curve. The results from indenting the homogenized composite (with
the built-in multilayer property) and from indenting the real multilayers (with Al and SiC layers explicitly accounted for)
were compared. It was found that an indentation depth beyond approximately 8–10 initial layer thicknesses is sufficient to
yield a valid composite elastic response. The effective modulus thus obtained is representative of the out-of-plane modulus
of the multilayer composite. 相似文献
29.
Linepipe steels are susceptible to hydrogen-induced cracking (HIC) in wet, sour gas environments. Two commercially produced
linepipe steels were investigated with regard to HIC on cathodic charging. Both steels, B and C, showed a high banded microstructure
consisting of alternative layers of polygonal ferrite and a mixture of non-ferritic constituents (pearlite, bainite, and martensite-austenite).
The degree of banding was higher in Steel B than in Steel C. Also present were elongated inclusions in Steel B, while in Steel
C they were more or less equiaxed. On cathodically hydrogen-charging in the absence of external stress, microvoids formed
at low current densities at or around inclusions. On prolonged charging, these voids grew and propagated parallel to the bands,
running along the interface between ferrite/non-ferrite constituents, along inclusions lodged in the non-ferritic consitituents,
and at places through the non-ferritic constituents. Steel B, not unexpectedly, showed more severe permanent microstructural
damage than Steel C, leading to the conclusion that a high banded structure and/or the presence of elongated inclusions is
deleterious to resistance against HIC. 相似文献
30.
The role of tin dioxide (SnO2) interphase for the alumina/glass composite system was investigated using fractography. Alumina (Al2O3) and glass form a strong chemical bond which is undesirable for toughness in a ceramic matrix composite. SnO2 interphase was incorporated to prevent this strong bond between alumina and glass. SnO2 was deposited on Al2O3 substrates via chemical vapour deposition and bonded with glass. The role of the interphase was then studied by characterizing
the fracture surfaces of the bend test and special composite disc samples loaded in diametral compression. Bend tests results
showed that the SnO2 interphase and/or the SnO2/Al2O3 interface acted as a plane of weakness. Secondary cracking at 90° to the major crack direction was observed along this plane
of weakness, which appears to be in accord with the Cook and Gordon model. Crack deflection and secondary cracking were also
observed in the SnO2 region of the compression samples. These results indicate the suitability of SnO2 interphase for the alumina/glass composite system. 相似文献