Effect Of Microstructure Heterogeneity Research Articles

Structural Aspects of the Behavior of Lead-Free Solder in the Corrosive Solution

In oxidizing environments, most tin-based lead (Pb)-free alloys form a tin oxide that is easily eroded or mechanically damaged, affecting corrosion resistance and thus reliability of the soldered joints. In this study, the effect of microstructure heterogeneity on corrosion behavior of Pb-free solder candidate systems has been investigated on the example of as-cast and heat-treated alloys. The research was focused on a comparison between the corrosion resistance of binary Sn-Zn and ternary Sn-Zn-Cu alloys. Accelerated corrosion tests were performed by means of electrochemical methods in the sodium sulfate solution (VI), Na2SO4, of about 0.5 M concentration, pH adjusted to 2 by means of concentrated H2SO4 acid. In these tests, the corrosion potentials as well as polarization curves were determined for the selected alloys in as-cast state and after their heat treatment using different combinations of processing parameters. The measurements of basic electrochemical characteristics were made, i.e., the corrosion current (i corr μA/cm2) and Tafel coefficients, both cathodic (b c V/dec) and anodic (b a V/dec) ones. Detailed structural characterization of as-cast and heat-treated alloys before and after accelerated corrosion tests has been made under a wide range of magnifications using light microscopy and scanning electron microscopy observations. The results showed that structural heterogeneity of the examined alloys, attributed to the presence of secondary phases, and affected by their size and distribution, significantly influences the behavior of the examined Pb-free Sn-Zn-based alloys in the corrosive environment.

Effect of microstructural heterogeneity on the mechanical behavior of nanocrystalline metal films

Abstract

Correlation Between Microstructure and Texture Development in a Cold-rolled TWIP Steel

X-ray diffraction and optical microscopy were used to characterize the crystallographic texture and the grain microstructure in cold-rolled Fe–23.2Mn–0.57C alloy. The development of texture and microstructure with increasing strain was systematically analyzed. From 10 to 85% rolling reduction the observed microstructure changes can be characterized by four distinctly different features: twin-matrix lamellae, alignment of twins with rolling plane, herring bone structure and macro shear bands. The effect of microstructural heterogeneity on texture was addressed. The observed change of the Cu texture component {112} with increasing strain was attributed to the competition of homogeneous dislocation slip and deformation twinning. The shift of the Brass component towards the Goss orientation at higher reduction levels (> 60%) corresponds to the appearance of a large amount of the shear bands and the formation of the // ND fiber texture – to the alignment of twin-matrix lamellae with rolling plane.

Analysis of welded tensile plates with a surface notch in the weld metal and heat affected zone

Abstract The behavior of the plates with a surface notch under tensile external loading is experimentally and numerically analyzed. The specimens were made of micro-alloyed steel NIOMOL 490 K, welded by MAG (CO2) welding method. Surface notches were machined by the spark erosion method in the weld metal and heat affected zone. A finite element analysis of the specimens subjected to the tensile external loading is performed, with a simplified treatment of the heat affected zone mechanical properties. Obtained results are compared with the results of the experimental investigation, and a satisfactory agreement for the specimens containing the weld metal notch is observed. However, results for the specimen containing a notch in the heat affected zone require further investigation, including the analysis of the effects of micro structural heterogeneity.

The Effect of Microstructure Heterogeneity on Fatigue Property of Powder Metallurgy Steels

Powder metallurgy is a new method for mass production of precision components with appropriate mechanical properties, but in this kind of materials (PM parts) with special microstructures (pores act as local stress risers), fracture due to fatigue is expected as an important destructive factor. Various microstructures in powder metallurgy steels, depending on alloying methods, have different response against cyclic loading. diffusion bonding is an effective method to obtain high fatigue performance in PM steels. The main characteristic of this materials consists of well-organized phases distribution due to incomplete diffusion of alloying elements. In this study fatigue behavior of diffusion-bonded, distaloy AE, steel with two carbon contents under different periodic loading are investigated. The effect of carbon content and various loading mode upon fatigue performance is analyzed. Metallugraphy and fractography examination on fatigue loaded samples revealed the positive effect of microstructure heterogeneity on fatigue crack behavior and this concept is a reason for increasing of diffusion-bonded powders application to manufacturing of components that are subjected to cyclic stresses.

Application of the Three-Dimensional Damage Percolation Model and X-Ray Tomography for Damage Evolution Prediction in Aluminium Alloys

A three-dimensional damage percolation model, which captures the effect of microstructural heterogeneity on damage evolution, has been developed to model damage initiation and propagation in materials containing second phase particles. It considers the three phenomena preceding ductile rupture of the material: void nucleation, growth, and coalescence. Threedimensional X-ray tomography is used to obtain measured three-dimensional second phase particle distributions in aluminum alloy sheet. Material damage evolution is studied within a tensile test simulation and compared to measured damage from an in situ tensile test utilizing X-ray tomography. Experimental and simulation results for material damage initiation and evolution are in good agreement.

Effects of microstructural heterogeneity on the mechanical properties of pressed soft magnetic composite bodies

The elastic and damping properties of two different soft magnetic composite (SMC) materials processed by a powder metallurgy route (Somaloy ™500 + 0.5 wt.% Kenolube and Somaloy ™500 + 0.6 wt.% LB1) have been characterised by means of non-destructive resonant vibration analysis, using the impulse excitation technique (IET). Microstructural characterisation by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) was carried out in order to understand the structural heterogeneity revealed with IET. A simple structural finite element model confirmed the link between microstructural heterogeneity of the SMC bodies and their vibration behaviour.

Micromechanical Simulation of Dynamic Fracture Using the Cohesive Finite Element Method

Dynamic fracture in two-phase Al2O3/TiB2 ceramic composite microstructures is analyzed explicitly using a cohesive finite element method (CFEM). This framework allows the effects of microstructural heterogeneity, phase morphology, phase distribution, and size scale to be quantified. The analyses consider arbitrary microstructural phase morphologies and entail explicit tracking of crack growth and arbitrary fracture patterns. The approach involves the use of CFEM models that integrate cohesive surfaces along all finite element boundaries as an intrinsic part of the material description. This approach obviates the need for any specific fracture criteria and assigns models the capability of predicting fracture paths and fracture patterns. Calculations are carried out using idealized phase morphologies as well as real phase morphologies in actual material microstructures. Issues analyzed include the influence of microstructural morphology on the fracture behavior, the influence of phase size on fracture resistance, the effect of interphase bonding strength on failure, and the effect of loading rate on fracture.

Effects of Inclusions and Porosity on the Indentation Response

ABSTRACTA combined numerical and experimental study was undertaken to investigate the effect of microstructural heterogeneity on indentation response. Finite element analyses were carried out to simulate the stress-strain behavior and the indentation response of two model heterogeneous systems: one with hard particles embedded within a soft matrix and the other with a pore-containing ductile material. For the particle-containing system, the indentation response consistently overestimates the overall strength of the composite. This is largely due to the localized increase in particle concentration directly underneath the indent. For the porous system, the indentation response consistently underestimates the overall strength due to the pore-crushing effect. Experiments on metal-ceramic composites confirmed the non-correspondence between the indentation and stress-strain responses, even when the indent size is much greater than the microstructural feature size. Implications of the present findings in utilizing indentation to quantify surface mechanical properties are discussed.

Crack-tip micro mechanical fields in layered elastic composites: crack parallel to the interfaces

Periodically layered bimaterial composites containing cracks parallel to the interfaces at the mid-plane of a layer are considered. The analytical solutions of the plane elastostatic problems under mode-I, mode-II and mixed-mode loading conditions are presented and equations for the crack-tip micro mechanical fields are developed using principles of asymptotic homogenization and the method of complex elastic potentials. An elastic stress singularity of the order r−1/2 is shown to exist. The dominating stress intensity factors are found to match with the corresponding values for the equivalent homogeneous orthotropic system. For all cases considered, the stress intensity factors dominating the micro stress field are also defined directly in terms of the stress functions. Comparisons of the analytical results with numerical solutions obtained via refined finite element analyses are presented. Numerical analyses have revealed that the stress field in the immediate vicinity of the crack-tip corresponds to the universal isotropic field dominated by the tip stress intensity factor which depends on the homogenized material properties and those of the layer containing the crack. The effects of micro structural heterogeneity and global anisotropy become predominant beyond the small isotropic region wherein the micro mechanical field is very nicely described by the analytical model. Crack location effects studies are also presented. Implications of the above near-tip fields on delamination fracture in layered systems are discussed.

Effect of Microstructure on Material‐Removal Mechanisms and Damage Tolerance in Abrasive Machining of Silicon Carbide

Effects of microstructural heterogeneity on material‐removal mechanisms and damage‐formation processes in the abrasive machining of silicon carbide are investigated. It is shown that the process of material removal in a conventional silicon carbide material with equiaxed‐grain micro‐structure and strong grain boundaries consists of the formation and propagation of transgranular cracks which results in macroscopic chipping. However, in a silicon carbide material, containing 20 vol% yttrium aluminum garnet (YAG) second phase, with elongated‐grain micro‐structure and weak grain boundaries, intergranular micro‐cracks are formed at the interphase boundaries, leading to dislodgment of individual grains. These different mechanisms of material‐removal affect the nature of machining‐induced damage. While in the conventional silicon carbide material the machining damage consists of transgranular median/radial cracks, in the heterogeneous silicon carbide material, abrasive machining produces interfacial micro‐cracks distributed within a thin surface layer. These two distinct types of machining damage result in a different strength response in the two forms of silicon carbide materials. In the case of the conventional silicon carbide, grinding damage results in a dramatic decrease in strength relative to the as‐polished specimens. In contrast, the ground heterogeneous silicon carbide specimens show no strength loss at all.

The effect of microstructural heterogeneities on the fracture behaviour of three-directional carbon-carbon composities

The effect of microstructural heterogeneities on the fracture behaviour of three-directional carbon-carbon composities

The effect of microstructure on the pitting tendency of a heat-resistant aluminium alloy (AAA 2618)

The effect of microstructural heterogeneity on the pitting tendency of aluminium alloy AAA2618 (2.5 Cu, 1.4 Fe, 1.8 Mg, 1.1 Ni was studied after solution treatment for 5 h at 530°C, followed by quenching in water at 80°C, and subsequent ageing for 20 h at 200°C. The microstructure was examined by optical microscopy, transmission electron microscopy, and electron-probe microanalysis. The pitting tendency was evaluated by measuring (a) the induction time for passivity breakdown in 0.1 N H 2SO 4 + 10 −3 N NaCl at − 500mV(SCE), and (b) the fraction of pitted area after 6 min exposure to treatment (a). Significant differences in pitting tendency between the two treatment versions are attributed to the weak passive film on Al 2CuMg, the strengthening phase in the aged alloy.