Materials Science Forum Vols. 638-642

Abstract: A novel Sn-2.5Ag-2.0Ni alloy has been developed for soldering of SiCp/Al composites substrate with various types of Ni coatings. An investigation about electroplated Ni layer, electroless Ni-5 wt.% P, Ni-10wt.% P and Ni-B layers has been carried out. It is found that the solder joints possess a single intermetallic compound (IMC) Ni3Sn4, which coarsens with an increase in aging time. The formation of Ni2SnP has been observed to significantly affect the reliability of the solder joints. But the formation of Ni2SnP can be suppressed by lowering the P contents in as-deposited Ni coatings. It has been also found that the thermal stresses generated in solder joint increases with the decrease of P contents in Ni-P layer. Furthermore, the concentration of thermal stresses in the electroplated Ni solder joint is found to be higher than that in other three electroless Ni layers. Out of four as-deposited Ni coatings, the Ni-B layer exhibits good wettability with solder and low IMC growth rate during aging. Also, the shear strength of solder joint decreases with an increase in aging time and Ni-B solder joint demonstrates the highest shear strength after long term aging.

Abstract: The limit load is an essential input parameter of flaw assessment procedures. The present paper deals with an effect of plastic anisotropy on its value. An upper bound solution for three-dimensional deformation of a highly under-matched welded specimen subject to tension is proposed. The base material is assumed to be rigid, and the weld material obeys Hill’s quadratic yield criterion for orthotropic materials. It is demonstrated that it is crucial to account for both plastic anisotropy and three dimensionality of deformation in limit load calculations for flaw assessment procedures.

Abstract: ray diffraction method is used to determine the stress field in polycrystalline materials. The measurement of peak shifts enables the determination of the macrostresses and the plastic incompatibility stresses (intergranular stresses). In the interpretation of the experimental results self-consistent model of elatoplastic deformation is used. In the present work, the plastic incompatibility stresses and the elastic energy stored in cold rolled brass and ferritic steel were determinate. The results are discussed and presented in Euler space.

Abstract: Oxide Dispersion Strengthened (ODS) Fe-based alloys often contain 0.5wt% of fine, uniformly dispersed, yttrium oxide particles in a Fe-Cr-Al matrix. They are ideal candidates for high temperature applications such as high temperature heat exchangers or nuclear power plants due to their good combination of creep and oxidation resistance. Numerous studies of annealing phenomena have shown that nucleation and growth of recrystallized grains, as well as the recrystallization texture, strongly depend on the deformed state of a previously cold worked alloy. In the present work, we examined the effect of strain heterogeneity on the development of recrystallized grain structures using bend samples. A bend test introduces a stress gradient and both compressive and tensile deformation. After a further heat treatment at 1380°C for 1 hour in air, the recrystallization behavior was characterized on both the tension and compression sides of the samples at varied levels of strain. Electron backscattering diffraction (EBSD) was used to analyze recrystallization behavior and texture. The results demonstrated that: recrystallized grains only formed in areas of sample subject to plastic compression; maximum grain size increased with increasing severity of bending deformation; there was heterogeneity in the recrystallized grain size, which varied with distance from the bending neutral axis. This indicates that the strain heterogeneity conducive to recrystallization was introduced by the non-uniform plastic strains in the compression region. However, the regions of tensile bending in all samples remained unrecrystallized and strong shear banding was evident.

Abstract: The influence of production conditions and Nb microalloy on the very high cycle fatigue (VHCF) behaviors of different Carbide-free bainite/martensite (CFB/M) steels was studied, which include steels produced in laboratory and steelworks. Results show the Nb-microalloy can strengthen the microstructure including the soft bainite plate and improve the VHCF property evidently. In addition, the high purity of steels can avoid inclusion induced crack initiation, but can not improve the VHCF property unless the microstructure possesses favorable uniformity. The critical inclusion size is suggested to be 10-15μm and the CFB/M complex microstructure may be less sensitive to inclusions than other high strength steels.

Abstract: In a high-purity 8Y-CSZ, the doping of 0.15 - 5 mass% pure silica introduces a glass phase dispersing uniformly along grain-boundary facets and at multiple junctions. For materials with grain sizes of 0.75 - 2.4 m, the dispersion of the glass phase decreases the elastic modulus, the Vickers hardness and the elastic modulus-to-hardness ratio, whereas it affects little in the fracture toughness measured by a Vickers-indentation method and a single-crack-precracked-beam method. Inspection of crack propagation paths shows that the glass phase with sizes smaller than those of the matrix grains is not a site for easy crack-propagation, but provides a site for a crack-deflection mechanism.

Abstract: There have been two different CTOD calculations, geometric CTOD calculation in BS7448 and J-based conversion in ASTM E1290 since the ASTM International revised E1290 in 2002, and it is useful to transform one CTOD into the other CTOD. In this study, analytical and experimental investigations into the ratio of ASTM E1290-CTOD to BS7448-CTOD were carried out, and two ratios of ASTM-CTOD to BS-CTOD, R1 and R2, were characterised in terms of cleavage cracking. These two characteristic CTOD ratios are helpful in simply transforming one critical CTOD to the other.

Abstract: Recent experimental results on phase stability and deformation behavior in a multifunctional Ti-36Nb-2Ta-3Zr-0.3O alloy, Gum Metal, are summarized and its deformation mechanisms are discussed. The crystal structure of the alloy is essentially unstable to tensile loading in <110> direction, but the microstructure of the cold worked state stabilizes the crystal structure. Work hardening in Gum Metal was far smaller than the other materials even when huge amount of strain is accumulated by severe plastic deformation. By comparing actual applied stress during plastic deformation with ideal shear strength, the alloy is likely to deform at near ideal strength with stress concentrations along with the highly inhomogeneous deformation behavior.

Abstract: For designing the fatigue life of shaft with a circumferential notch exactly, the influencing factors have been analyzed completely. The modified mechanics model to estimate the fatigue life of shaft with a circumferential notch is set up. The assessment method of fatigue life for shaft with a circumferential notch is put forward. The effects of notch on stress concentration factor and fatigue life of shaft with a circumferential notch are discussed and the influencing parameters are obtained. The results show that the tip radius of notch has a great effect on fatigue life of shaft; on the other hand, the open angle of notch has a little effect on it. The results will establish the base of anti-fatigue design of shaft.

Abstract: The fatigue life of notched torus under random scan vibration is discussed in this paper. The stress function and stress field intensity of the materials under composted cyclic stress are analyzed. The experiments of vibration of the notched torus under random load are made in the digital vibration equipment. The fatigue life of notched torus is predicted by use the local stress-strain field method and three parameters formula. The elasto-plastic properties of the material are described by Von Mises yield criterion and stress-strain of uniaxial cyclic loading. The field of local fatigue damage of notched torus under random vibration is determined by using the method of local stress-strain field intensity, and the cycle stress-strain response near the tip of notch is obtained. The revised factor of fatigue life of LY12-CZ material is determined, the relationship between high-frequency cycle of stress and fatigue life is set up by use three parameters formula, and the fatigue life of the notched torus is obtained.