Wp Willem Pier Vellinga

Misfit dislocations : An atomistic and elastic continuum approach

This paper presents the results of an atomistic model in which the misfit and the bond strength between a metal and a substrate can be controlled. The model is applied to a simple case, i.e. an interface with misfit in one direction. Calculated energies are presented and the corresponding atomic structures for various misfits and interaction parameters are discussed. It turned out that the structure of the misfit dislocations depends both on misfit and bond strength. A trend from delocalized structures to localized structures that resemble bulk-like dislocations can be seen for decreasing misfit at constant interaction parameter, and increasing interaction parameter at constant misfit. This atomistic approach is compared with a description based on linear elasticity theory of interface dislocations. Although a fair correlation exists between these two different concepts, it is shown that the elastic continuum approach cannot account for the possible configurations at an interface, because it does not contain any information on the effects different bond strengths may have on the interface structure.

The microstructure of petroleum vacuum residue films for bituminous concrete: a microscopy approach

Selected carbon‐rich refinery residues (‘binders’) mixed with mineral particles can form composite materials (‘bituminous concrete’) with bulk mechanical properties comparable to those of cement concrete. The microstructural mechanism underlying the remarkable composite properties has been related to the appearance of a rigid percolating network consisting of asphaltenes and mineral particles [ Wilbrink M. et al. (2005) Rigidity percolation in dispersions with a structured visco‐elastic matrix. Phys. Rev. E71, 031402]. In this paper, we explore the microstructure of thin binder films of varying thickness with a number of microscopic characterization techniques, and attempt to relate the observed microstructure to the distinctive mechanical behaviour. Two binders, only one of which has been proven to be suitable for bituminous concrete were investigated, and their microstructure compared. Both binders show the formation of asphaltene aggregates. The binder suitable for bituminous concrete is distinguished by the fact that the asphaltenes show a stronger tendency towards such aggregation, due to a higher concentration and less stabilization in the maltene phase. They also show a clear affinity to other species (such as waxes) and may act as nucleation sites for crystals and aggregates of those species.

High-resolution transmission electron microscopy imaging of misfit-dislocation networks at Cu-MgO and Cu-MnO interfaces

Abstract Misfit dislocation networks at Cu-MgO and Cu-MnO {111}metal//{111}oxide interfaces were studied with high-resolution transmission electron microscopy. Experimental results were compared with image simulations of tentative atomic structures of the interface region derived from lattice statics calculations. The calculations take into account the two-dimensional misfit at the interface, which is necessary given the high misfit and short repeat distances at the interfaces. The lattice statics calculations use simplified potentials across the interface which capture essential characteristics that have emerged from recent experimental results and ab-initio calculations. Trigonal networks of edge misfit locations with Burgers vectors ⅙〈112〉 and line direction 〈110〉 follow from these calculations. These misfit-dislocation networks have associated strain fields in the metal, stretching out from the interface with approximately the repeat distance along the interface. These strain fields show up in image s...

Atomic structure and orientation relations of interfaces between Ag and ZnO

This paper presents the results of investigations of Ag-ZnO interfaces, produced by internal oxidation of an Ag-Zn alloy. ZnO precipitates with the wurtzite structure were found exhibiting mainly one orientation relation with the Ag matrix. However, closely related ORs were found, rotated by small angles from that orientation relation. The atomic structures of several interfaces surrounding these precipitates were studied and compared using HRTEM. The paper concentrates on interfaces between low index facets of ZnO and vicinal planes of Ag. These interfaces clearly show relaxations. An interpretation of these relaxations in terms of dissociation of partial dislocations at the interface is put forward.

Correlation between localized strain and damage in shear-loaded Pb-free solders

Abstract A digital image correlation (DIC) algorithm was employed to measure microscopic strain-field evolution in shear-loaded model solder interconnections made out of a number of Sn-based alloys. Four different solder alloys studied were Sn–36Pb–2Ag, Sn–3.8Ag–0.7Cu (SAC), Sn–3.3Ag–3.82Bi, and Sn–8Zn–3Bi. The measured strain fields were correlated with damage observed at the scale of the sample, and at microscopic length scales. Local strain differs significantly from applied global strain and has been shown to depend on the geometry of the samples as well as the microstructure (on a grain level) of the solder. Strain fields in all solder interconnections were found to localize near but not at the solder–substrate interface and along grain boundaries in the solders. The eventual failure path as observed on the scale of the sample (parallel to the two solder–substrate interfaces with a cross-over from one interface to the other somewhere in the connection) showed a good correlation with measured strain fields in all interconnections. In contrast to the similarity on a macroscopic scale, on a microscopic scale the failure mechanisms were observed to be material specific.

Correlation between thermal fatigue and thermal anisotropy in a Sn-rich solder alloy

Intrinsic thermal fatigue in a mechanically unconstrained Sn-rich Sn-3.8Ag-0.7Cu alloy has been investigated under cyclic thermal loading within the temperature range of 293 K to 353 K. Fatigue damage resulting from this cycling is shown to occur preferentially along some grain boundaries. From a combination of orientation imaging microscopy and finite element modelling it appears that fatigue damage and stresses resulting from the thermal anisotropy of Sn are highly correlated.

Microstructural stability and failure modes in eutectic Sn-Ag-Cu solder

Microstructural stability in eutectic Sn-3.8Ag-0.7Cu (SAC) solder has been investigated during isothermal annealing at 401 K or 454 K and cyclic annealing between 253 K to 401 K. Bulk Ag/sub 3/Sn and Cu/sub 6/Sn/sub 5/ intermetallics are found to be quite stable at these elevated temperatures. The distribution of local strain fields within SAC solder interconnections have been investigated under shear loading at ambient temperature by a digital image correlation (DIC) technique. DIC measurements show inhomogeneous distribution of strain fields in the solder interconnections, and localization of strains predominantly near the interface(s). Creep experiments have also been performed at 373 K and 423 K and are compared to the shear loading experiments. SAC solder interconnections show the largest plastic deformation and the highest creep-resistance and exhibit fracture in ductile mode.

Microscopic phenomenology of plastic deformation in polymer-metal laminates

Microscopic studies of the plastic deformation of a simple polymer-metal laminate (PET-steel) are outlined. Representative examples of deformation and failure modes are illustrated with qualitative results from birefringence microscopy. The relation between bulk PET mechanical behaviour and laminate properties is discussed.

FIB-Etching of Polymer/Metal Laminates and its Effect on Mechanical Performance

This paper investigates the adhesive interface in a polymer/metal (polyethylene terephthalate/steel) laminate that is subjected to uniaxial strain. Cross-sections perpendicular to such interfaces were created with a focused ion beam and imaged with scanning electron microscopy during straining in the electron microscope. During in situ straining, glide steps formed by the steel caused traction at the interface and initiated crazes in the polyethylene terephthalate (PET). These crazes readily propagated along the free surface of the PET layer. Similar crazing has not been previously encountered in laminates that were pre-strained or in numerical calculations. The impact of focused ion beam treatments on mechanical properties of the polymer/metal laminate system was therefore investigated. It was found that mechanical properties such as toughness of PET are dramatically influenced by focused ion beam etching. It was also found that this change in mechanical properties has a different effect on the pre-strained and in situ strained samples.

HREM investigation of Al-MgO interface

A metal-ceramic interface was produced by depositing Al on a (100) MgO substrate in a MBE system. The interface was studied with High Resolution Electron Microscopy. Results of some image simulations are shown, raising the question if effects of ionicity and charging should be taken into account.