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The purpose of this study is to demonstrate that isothermal intermetallic growth data for gold ball bonds can be non-parabolic with explanations of why deviation from parabolic kinetics may occur.

Intermetallic thickness measurements were made at the centre of cross-sectioned ball bonds that were isothermally annealed at 175°C. Intermetallic growth kinetics were modelled with a power law expression(x(t) − x₀)² = α₁t^α₂. The parameters of the power law model were obtained by transformation of the response and explanatory variables followed by data fitting using simple linear regression (SLR).

Ball bonds made with 4 N (99.99%Au) and 3 N (99.9%Au) gold wires exhibited two consecutive time regimes of intermetallic growth denoted Regime I and Regime II. Regime I was characterised by reactive diffusion between the gold wire and the aluminium alloy bond pad, during which Al was completely consumed in the formation of Au–Al intermetallics with non-parabolic kinetics. In Regime II, the absence of a free supply of Al to sustain intermetallic growth led to the conclusion that thickening of intermetallics was caused by phase transformation of Au₈Al₃ to Au₄Al. Ball bonds made with 2 N (99%Au) wire also exhibited non-parabolic kinetics in Regime I and negligible intermetallic thickening in Regime II.

The analysis of intermetallic growth is limited to total intermetallic growth at a single temperature (175°C).

The value of this study lies in showing that the assumption that only parabolic intermetallic growth is observed in isothermally aged gold ball bonds is incorrect. Furthermore there is no need to assume parabolic growth kinetics because with an appropriate data transformation, followed by fitting the data to a power law model using SLR and with the use of statistical diagnostics, both the suitability of the kinetic model and the nature of the growth kinetics (parabolic or non-parabolic) can be determined.

Proper selection of the stability parameter determines the accuracy of dendrite tip kinetics at a single crystal scale. Recently developed sophisticated phase field modelling of a single grain evolution provides evidence that this parameter is not constant during the process. Nevertheless, in the commonly used micro-macroscopic simulations of alloy solidification, it is a common practice to use a constant value of the stability parameter, resulting from the marginal stability theory. This paper aims to address the issue of how this inaccuracy in modelling crystal growth kinetics can influence numerically predicted zones of columnar and equiaxed dendrites and the macro-segregation formation.

Using the original authors’ micro-macroscopic computer simulation model of binary alloy solidification, the calculations have been performed for the Kurz-Giovanola-Trivedi (KGT) crystal growth kinetics with two different values of the stability parameter, and for two different compositions of Al-Cu alloys. The computational model is based on single domain-based formulation of transport equations, which are discretized on control-volume mesh. To identify zones of different grain structures, developing within the two-phase liquid-solid region, an envelope of columnar dendrite tips is tracked on a fixed non-orthogonal, triangular control volume grid. The models of porous and slurry media are used, along with the concept of the switching function, to account for diverse flow resistances in the columnar and equiaxed crystal zones. The numerical predictions are carefully studied to address the question of how the chosen stability parameter influences macroscopic structures of a cast, the most important issue from the engineering point of view.

The carried-out comprehensive numerical analysis shows that the value of the stability parameter of the KGT-constrained dendrite growth model does not have a direct significant impact on the macrosegregation formation. It, however, visibly influences the undercooling along the front, separating different dendritic structures and the size of the undercooled melt region where the equiaxed grains can develop. It also affects the amount of eutectic phase created.

To the best of the authors’ knowledge, this is the first attempt at estimating the influence of some inaccuracies, caused by possible ambiguities in choosing the stability constant of the KGT law, on numerically predicted macroscopic fields of solute concentration, the developing zones of columnar and equiaxed crystals and the macrosegregation patterns.

The purpose of this paper is to endorse the idea of using a special post-calculating front tracking (FT) procedure, along with the enthalpy-porosity front tracking (EP-FT) single continuum model, in order to identify zones of different dendritic microstructures developing in the mushy zone during cooling and solidification of a binary alloy.

The 2D and 3D algorithms of the FT approach along with different crystal growth laws were implemented in macroscopic calculations of binary alloy solidification with the identification of different dendrite zones developing during the process.

Direct comparison of results predicted by the FT model with that based on the concept of the critical value of the solid volume fraction shows the sensitivity of the latter on an arbitrary assumed value of the dendrite coherency point (DCP). Moreover, for a carefully chosen DCP value the second model provides results that are close to those given by the FT-based approach. It is also observed that the macro-segregation pattern obtained by the proposed method is hardly influenced by chosen dendrite tip kinetics.

To the best authors’ knowledge, for the first time the 3D FT model has been used along with the enthalpy porosity approach to simulate the development of zones of different dendrite morphology during binary alloy solidification. And, a weak influence of assumed different dendrite tip kinetics on the macro-segregation pattern has been proved, what justifies this underlying assumption of the EP-FT method.

Interfacial roughness in heterostructures critically degrade the optical and electrical properties of the devices fabricated with III‐V semiconductor compounds. Experimental work on the surface roughening processes during MBE growth by monitoring the reflection high energy electron diffraction (RHEED) intensity concluded that the surface roughening is a result of competition between surface roughening processes such as adsorption and evaporation and the surface smoothening process such as surface migration to stable sites. In this work, the stochastic model of MBE growth is employed to study the surface roughening kinetics in GaAs (100). The growth condition was chosen similar to that of experiments: temperature range of study: 773 – 873°K; cation to anion flux ratio in the range: 1 : 10 to 1 : 20. Diatomic arsenic molecular specie is employed for the study was As2. The time averaged RHEED intensity was obtained from the growth data and with the experimental results. The agreement between the results was excellent. A transition temperature at which the time averaged RHEED intensity is a maximum was observed for flux ratios 1 : 10 and 1 : 20. The RHEED intensity increases with temperature till the transition temperature due to surface smoothening resulting from the surface migration of Ga and As to energetically favorable sites. The RHEED intensity decreases beyond the transition temperature due to the evaporation of As from the surface. The transition temperature is observed to be a function of the flux ratio and can be explained by the difference in time for the formation of energetically stable surface adatom clusters resulting from the difference in the effective surface migration rates for various flux ratios.

A methodology was developed to establish baseline metrics for assessing the isothermal aging of 63Sn‐37Pb (or 60Sn‐40Pb) solder joints in circuit board assemblies. Those metrics were the intermetallic compound layer thickness at the Sn‐Pb solder/Cu interface and the Pb‐rich phase particle size distribution in the solder. The baseline, or as‐fabricated, values for these metrics were 0.71±0.27 μm and 3.2±6.5×10⁻⁶ mm², respectively. The rate kinetics were determined for growth of the intermetallic compound layer and coarsening of the Pb‐rich phase particles by isothermal aging experiments. The/were: (1) intermetallic compound layer thickness (μm)=0.714+ 3.265×10³ t^0.58 exp(−52200/RT); and (2) Pb‐rich phase particle size (mm²)=3.2×10⁻⁶+1.47× 10⁻³ t^0.32 exp(−31000/RT).

The purpose of this paper is to investigate the microstructural development of SnAgCu solder joints under different loading conditions (isothermal storage, thermal cycling and vibration).

The observed microstructural changes have been studied with respect to grain growth and grain refinement, crack formation and crack growth. The growth kinetics of the intermetallic phases encountered as particles in the bulk as well as a reaction layer on the copper pad, were studied in the temperature range of 125‐175°C.

Dynamic recrystallisation of the tin matrix leads to a change in the diffusion controlled growth mechanism, which causes an increase of the particle growth rate compared to isothermal storage. Thus, these grain boundaries are separated forcibly by crack growth during thermal cycling. This stress causes intergranular cracks while vibration stress induces transgranular cracks.

The paper adds insight into microstructural changes of lead‐free solder joints during long‐term ageing, thermal cycling and vibration fatigue.

Carotenoids have been extensively used in many industries owing to their colorant and strong antioxidant properties. Because of their useful properties, the purpose of this paper is to investigate the effect of penicillin‐adding time on stimulation of carotenoid production by Neurospora intermedia, and the effect of drying methods on stability of synthesized carotenoids.

In the first stage, curve of growth kinetic of cultures incubated at 31°C and different times (24, 48, 72, 80, 96, 104, 112, 120, 128, 136 and 144 h) to determine log and stationary phases was depicted. Then penicillin (1 mg/l) at initial and middle of log phase and initial of stationary phase was applied and its effect on carotenoid production was evaluated. In the second stage, mycelia containing carotenoid were dried by microwave oven, vacuum microwave, vacuum oven and freeze drier. Thereafter, effect of drying methods applied on stability of synthesized carotenoid was determined.

The results showed that penicillin could stimulate carotenoid biosynthesis in N. intermedia. Furthermore, this study indicated that the best time of penicillin adding is middle of log phase or after this time. Also the study indicated that there was a significant difference among applied methods as microwave‐dried mycelium had the highest carotenoid contents in comparison to the other drying methods.

This paper is believed to be the only one which investigates the effect of different factors on stimulate and stability of synthesized carotenoid by N. intermedia. Also mycelia containing carotenoid were dried by using new drying methods.

Additive manufacturing (AM) is revolutionizing the manufacturing industry due to several advantages and capabilities, including use of rapid prototyping, fabrication of complex geometries, reduction of product development cycles and minimization of material waste. As metal AM becomes increasingly popular for aerospace and defense original equipment manufacturers (OEMs), a major barrier that remains is rapid qualification of components. Several potential defects (such as porosity, residual stress and microstructural inhomogeneity) occur during layer-by-layer processing. Current methods to qualify AM parts heavily rely on experimental testing, which is economically inefficient and technically insufficient to comprehensively evaluate components. Approaches for high fidelity qualification of AM parts are necessary.

This review summarizes the existing powder-based fusion computational models and their feasibility in AM processes through discrete aspects, including process and microstructure modeling.

Current progresses and challenges in high fidelity modeling of AM processes are presented.

Potential opportunities are discussed toward high-level assurance of AM component quality through a comprehensive computational tool.

Although the first part of this article (published in the November issue) is highly relevant to grid corrosion, certain other considerations are also very important, namely, stresses within the grid and grid growth.

The purpose of this study is to reveal the effect of nano-Al₂O₃ particle addition on the nucleation/growth kinetics, microhardness, wear resistance and corrosion resistance of Co–P–xAl₂O₃ nanocomposite plating.

The kinetics and properties of Co–P–xAl₂O₃ nanocomposite plating prepared by electroplating were investigated by electrochemical measurements, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Vickers microhardness measurement, SRV5 friction and wear tester and atomic force microscopy.

A 12 g/L nano-Al₂O₃ addition in the plating solution can transform the nucleation/growth kinetics of the plating from the 3D progressive model to the 3D instantaneous model. The microhardness of the plating increased with the increase of nano-Al₂O₃ content in plating. The wear resistance of the plating did not adhere strictly to Archard’s law. An even and denser corrosion product film was generated due to the finer grains, with a high corrosion resistance.

The effect of different nano-Al₂O₃ addition on the nucleation/growth kinetics and properties of Co–P–xAl₂O₃ nanocomposite plating was investigated, and an anticorrosion mechanism of Co–P–xAl₂O₃ nanocomposite plating was proposed.