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The effects of stress-aging processing on corrosion resistance of an Al–Zn–Mg–Cu alloy were investigated. It is found that the one-stage stress-aged alloy is strongly sensitive to the electrochemical corrosion. The poor corrosion resistance of the one-stage stress-aged alloy can be attributed to fine intragranular aging precipitates and continuous distribution of grain boundary precipitates. Meanwhile, the incomplete precipitation of solute atoms results in high electrochemical activity of aluminum matrix. However, when the alloy is two-stage stress-aged, the corrosion resistance is greatly improved. Furthermore, the corrosion resistance decreases firstly and then increases with increasing the first stage stress-aging temperature. Increasing external stress can enhance the corrosion resistance of the two-stage stress-aged alloy. These phenomena are mainly related to aging precipitates within grains and along grain boundaries. The coarse and relatively low-density intragranular aging precipitates, as well as the discontinuously distributed grain boundary precipitates can enhance the corrosion resistance of the stress-aged alloy. [ABSTRACT FROM PUBLISHER]

Generally, the obvious work hardening, dynamic recrystallization (DRX), and dynamic recovery behaviors can be found during hot deformation of Ni-based superalloys. In the present study, the classical dislocation density theory is improved by introducing a new dislocation annihilation item to represent the influences of DRX on dislocation density evolution for a Ni-based superalloy. Based on the improved dislocation density theory, the peak strain corresponding to peak stress and the critical strain for initiating DRX can be determined, and the improved DRX kinetics equations and grain size evolution models are developed. The physical framework and algorithmic idea of the improved dislocation density theory are clarified. Moreover, the deformed microstructures are characterized and quantitatively correlated to validate the improved dislocation density theory. It is found that the improved dislocation density-based models can precisely characterize hot deformation and DRX behaviors for the studied superalloy under the tested conditions. [ABSTRACT FROM PUBLISHER]

The effects of pre-treatments on the precipitate microstructures of an Al–Zn–Mg–Cu alloy are investigated. Meanwhile, the creep-rupture behavior of the under-aged and peak-aged alloys are comparatively analyzed. Additionally, the effects of pre-treatment on the fracture mechanisms are discussed. It is found that the precipitate microstructures are sensitive to pre-treatments. The intragranular precipitates of the peak-aged alloy are larger than those of the under-aged. The precipitate free zone of the peak-aged alloy is wider than that of the under-aged. Some large intergranular precipitates appear on the grain boundaries of the under-aged alloy, and induce the nucleation of microvoids. Eventually, the creep fracture of the under-aged alloy is accelerated. Therefore, the differences in microstructures lead to the shorter creep-rupture life of the under-aged alloy, compared to the peak-aged alloy. [ABSTRACT FROM PUBLISHER]

The strain hardening effect and dynamic recovery behavior of a Ni-based superalloy are studied by isothermal compressive tests. A new unified dislocation-density based constitutive model is developed to characterize the strain hardening effect and dynamic recovery behavior of the studied superalloy. In the developed constitutive model, some material parameters (yield stress, strain hardening coefficient, and dynamic recovery coefficient) are assumed as functions of initial grain size, deformation temperature, and strain rate. An iterative algorithm is designed to predict the high-temperature deformation behaviors under time-variant hot working conditions. The hot deformation parameters and material parameters can be updated in each strain increment. Comparisons between the experimental and calculated flow stresses indicate that the developed constitutive model can accurately describe the high-temperature deformation behavior of the studied superalloy. Furthermore, the developed constitutive model is also successfully used for analyzing time-variant hot working processes. [ABSTRACT FROM PUBLISHER]

In this study, the microstructural evolution of Sn-3Ag-0.5Cu/Au/Pd(P)/Ni(P) microbumps during isothermal aging was examined by electron probe microanalysis and scanning electron microscopy equipped with electron backscatter diffraction. The Au/Pd(P)/Ni(P) trilayer was deposited on 85- μm (opening diameter) Cu pads with a thickness combination of 0.15 μm/0.2 μm/8 μm. The reaction of the Au/Pd(P) dual layer with the molten solder yielded plenty of AuSn and PdSn grains in the solder matrix after reflow, which has never been observed previously in the literature. At the interface, discontinuous, facet-type CuSn [or (Cu,Ni)Sn] nucleated. Interestingly, the CuSn transformed into layered NiSn after subsequent aging for 250 h at 180°C. Moreover, the AuSn and PdSn agglomerated with each other and resettled to the region neighboring the interface. This configuration changed significantly when a pronounced corrosion occurred in the as-plated Ni(P) metallization pad. In the corroded Ni(P) case, CuSn rarely appeared at the interface immediately after reflow, but a large quantity of PdSn formed in the solder region near the corroded Ni(P) layer. AuSn in this case distributed uniformly throughout the entire solder joint. Isothermal aging treatment drove the PdSn and AuSn to deposit onto the corroded Ni(P) surface, where they merged with each other as a dense layer of (AuPdNi)Sn (250 h). The formation of the (Au,Pd,Ni)Sn layer over the corroded Ni(P) substrate provided a crack initiation site, deteriorating the mechanical reliability of the solder joint. The results of this study show that appropriate deposition of Au/Pd(P)/Ni(P) is very important for the thermal/mechanical reliability of microbumps. [ABSTRACT FROM AUTHOR]

Mechanical properties of thin films on substrates can be evaluated directly through nanoindentation. For a comprehensive study, thin films should be characterized via Young’s modulus, yield stress and strain-hardening exponent at constant temperature. In this paper, we evaluate these effects of thin films on silicon substrate through finite element analysis. Thin films, from soft to hard relative to the silicon substrate, are investigated in three categories: soft films on hard substrates, soft to hard films on no elastic mismatch substrates, and hard films on soft substrates. In addition to examining the load-displacement curve, the normalized hardness versus normalized indentation depth is checked as well to characterize its substrate effect. We found that the intrinsic film hardness can be acquired with indentation depths of less than 12% and 20% of their film thickness for soft films on hard substrates and for soft to hard films on no elastic mismatch substrates, respectively. Nevertheless, nanoindentation of hard films on soft substrates cannot determine the intrinsic film hardness due to the fact that a soft substrate cannot support a hard film. By examining the von Mises stresses, we discovered a significant bending phenomenon in the hard film on the soft substrate. [ABSTRACT FROM AUTHOR]

This work investigates the surface polishing of silicon carbide SiC using the tribochemical reaction mechanism. Different metal discs - cast iron, AISI 304 stainless steel, S45C medium carbon steel plated chromium, brass and copper - are used to polish SiC in water and kerosene, respectively. The experimental results show that ferrous metal discs can effectively polish SiC in water. Also, no surface damage or scratches on the polished surface of SiC are observed by this method. The polishing debris was analyzed by electron spectroscopy for chemical analysis. The analyzed results indicate that the polishing surface of SiC is removed tribochemically with the aid of catalytic effect of iron oxide. Moreover, in this process the maximum material removal rate is about 0.06 µm/h. [ABSTRACT FROM AUTHOR]

NZB mice develop an age-related malignant expansion of a subset of B cells, B-1 cells, with autocrine production of IL-10. IL-10, a pleiotropic cytokine with anti-inflammatory properties, is a potent growth and survival factor for malignant B cells. To further examine the in vivo requirement for IL-10 in the development and expansion of malignant B-1 clones in NZB mice, we developed a strain of homozygous IL-10 knockout (KO) mice on an NZB background. The NZB IL-10 KO mice develop peritoneal B-1 cells with approximately the same frequency as heterozygous and wild-type littermates. In contrast, the development of malignant B-1 cells in the peripheral blood and spleen, observed in wild-type NZB, rarely occurred in the NZB IL-10 KO. Phenotypic analysis of surface marker expression in splenic B cells indicated that, in contrast to the NZB with malignant B-1 splenic lymphoma, the surface marker expression of NZB IL-10 KO splenic B cells indicated that the majority of the B cells were typical B-2 cells. In the absence of IL-10, spontaneously activated B cells and antiapoptotic gene expression were reduced and lymphoma incidence was decreased. These results indicate that IL-10 is a critical factor for the progression of this B-cell malignant disease.Leukemia (2004) 18, 597-606. doi:10.1038/sj.leu.2403244 Published online 8 January 2004 [ABSTRACT FROM AUTHOR]

A chitinase was separated from the culture broth of Vibrio sp. 11211 isolated from sediment from the South China Sea. The chitinase was purified 18.3-fold with 33% recovery by ammonium sulphate precipitation and chromatography. The subunit molecular weight of the enzyme was estimated by SDS-PAGE to be about 30 kDa. The enzyme showed optimum pH at 6.5 and optimum temperature at 50 °C, and was stable in the pH range of 4 to 9 and at the temperature below 40 °C. [ABSTRACT FROM AUTHOR]