Free energy of crystal–liquid interface

It is demonstrated that a simple model, free of any adjustable parameter, can be developed to predict the free energy of a crystal–liquid interface σ_sl based on the Gibbs–Thomson equation and a model for the size-dependent melting temperature. This model has improved Turnbull's empirical equation. In the model, σ_sl depends on not only the melting enthalpy of crystals, but also the vibrational component of the overall melting entropy of the crystals. The predicted values of σ_sl for different types of crystals, such as true metals, meta metals, semiconductors, ionic crystals and organic crystals, are confirmed by available experimental results in the experimental error range.     

The effect of iron on liquid film migration and sintering of an Al–Cu–Mg alloy

Analytical transmission electron microscopy indicates that liquid film migration occurs during sintering of an Al–Cu–Mg alloy, that intragranular liquid pools develop from migrating films and that iron segregates to these pools. It is suggested that a high localised iron concentration retards the liquid film migration rate by reducing the coherency strain in the retreating grain, causing a region of the film to detach from the boundary, thus forming an intragranular pool in the advancing grain. Alloys with low iron levels develop few intragranular pools and have high sintered densities.     

The effect of trace elements on the sintering of Al–Cu alloys

Trace additions of Sn, In, Bi, Sb and Pb have been used to activate the liquid phase sintering of an Al–4Cu–0.15Mg alloy. Additions of as little as 0.05 wt% (∼0.01 at.%) increases the sintered density from 88 to 92% of the theoretical density. The elements which aid sintering have both high vacancy binding energies and high diffusivities in Al. It is suggested that the trace element diffuses into the Al, and forms trace element–vacancy clusters. This reduces the diffusivity of the Cu in the Al matrix, delaying Cu dissolution therefore causing the liquid to persist for longer times. This enhances sintering and therefore densification.     

The effect of Nd and Pr on the oxidation behavior of a Fe–13Cr alloy

The influence of neodymium (Nd) and praseodymium (Pr) on the oxidation behavior of a Fe–13Cr alloy has been studied in oxygen at 800 °C for 24 h. Additions (⩽0.03 wt.%) of either Nd or Pr reduce the oxidation rate of Fe–13Cr and change the morphology of the oxides formed on Fe–13Cr.     

Atomistic characterization of the chemically heterogeneous Al–Pb solid–liquid interface

The chemically heterogeneous interface between solid Al and liquid Pb at 625 K is examined by using molecular-dynamics simulation. For the interfacial orientations (1 0 0), (1 1 0) and (1 1 1), we characterize the interface by calculating the density, potential energy, stress and diffusion constant profiles as well as a two-dimensional Fourier analysis of the interfacial layers. Our results are consistent with experimental observations [Acta Mater 2001;49:4259], based on the equilibrium shape of liquid Pb inclusions in solid Al just above the melting temperature of Pb, that the (1 1 1) interface is faceted, while the (1 0 0) and (1 1 0) interfaces are rough. We found that Al and Pb form immiscible two-dimensional domains within the interfacial layers, rather than an intermixed interfacial alloy, as was observed in recent simulations of the Cu–Pb interface [Acta Mater 2011;59:3137]. In addition, in contrast to earlier observations on the (1 1 1) Cu–Pb interface at this temperature, no prefreezing layers are found in Al–Pb interfaces for any of the orientations studied.     

The effect of a counterion in a protective moisture-sensitive epoxy–polyelectrolyte/epoxy–carbon sandwich system

In this work, the effect of the ionic form of a KU 2-8 synthetic cation-exchange polyelectrolyte, which was used as a filler in the moisture-sensitive layer, on the behavior of two-layer anticorrosion systems with a low-resistivity damp-proof layer has been studied. The behavior of matrices with sodium (KU 2-8-Na⁺), magnesium (KU 2-8-Mg²⁺), nickel (KU 2-8-Ni²⁺), and zinc ions (KU 2-8-Zn²⁺) has been investigated. The remarkable effect of the nature of studied counterions on moisture-sensitive, protective properties, and behavior of coatings upon cathode polarization of surface has been demonstrated.     

The effect of trace elements on the sintering of an Al–Zn–Mg–Cu ALLOY

Trace elements can have a significant effect on the processing and properties of aluminium alloys, including sintered alloys. As little as 0.07 wt% (100 ppm) lead, tin or indium promotes sintering in an Al–Zn–Mg–Cu alloy produced from mixed elemental powders. This is a liquid phase sintering system and thin liquid films form uniformly throughout the alloy in the presence of the trace elements, but liquid pools develop in their absence. Analytical transmission electron microscopy indicates that the trace elements are confined to the interparticle and grain boundary regions. The sintering enhancement is attributed to the segregation of the microalloying addition to the liquid–vapour interface. Because the microalloying elements have a low surface tension, they lower the effective surface tension of the liquid. This reduces the wetting angle and extends the spreading of the liquid through the matrix. An improvement in sintering results.     

The effect of microstructure on the shape recovery of a Fe–Mn–Si–Cr–Ni stainless steel shape memory alloy

In this work the effect of varying the microstructure on the shape memory properties of a Fe-15Mn-7Si-9Cr-5Ni (wt.%) stainless steel shape memory alloy was evaluated using a simple bend test. The best shape recovery was obtained for a single-phase austenite microstructure and for a two-phase microstructure composed of an austenite matrix and Fe₅Ni₃Si₂ type intermetallic grain boundary phase. The maximum shape recovery was achieved at the reversion temperature of 600 °C and when the pre-stain was less than 2%.     

Investigation of the tarnish on the surface of a panda gold coin

In natural environment, tarnish was observed on the surface of historic and contemporary gold coins in several countries. Few years after the emergence of panda gold coins, several red spots were appeared on the surface. To identify the stains and to examine the spots, optical microscope （OM）, scanning electron microscope （SEM）, electron microprobe analysis （EMPA）, X-ray photoelectron spectroscopy （XPS）, and X-ray diffraction （XRD） were used. It was found by microscopic observation that the stain has a dark blue central area surrounded by a large area with a nuance of colors from brown to red. Red spots usually contain holes in the center, which are distributed along the forging stress zones formed in the struck process. From the surface analyses using EMPA, sulfur and silver are detected besides gold, and the contents of Ag and S at the tarnish part are higher than those at the other part. Furthermore, distributions of Ag and S are correlated with the morphology of stains. XPS shows that components of stains are Ag2S and Ag2SO4 and the former is much predominant. These results are confirmed using XRD analysis. Accelerated tarnish test of gold in an atmosphere containing sulfur compound proves that the similar phenomenon appears when a small amount of silver is present on the surface of gold. It can be concluded that the occurrence of tarnish stains is caused by the presence of Ag and S.     

The effect of scandium on the microstructure,mechanical properties and weldability of a cast Al–Mg alloy

The microstructure, mechanical properties and weld hot cracking behaviour of a cast Al–Mg–Sc alloy containing 0.17 wt.% Sc were compared with those of a Sc-free alloy of similar chemical composition. Although this level of Sc addition did not cause grain refinement, the dendritic substructure appeared to be finer. There was a significant increase in the yield and tensile strength and the microhardness of the Al–Mg–Sc alloy relative to its Sc-free counterpart. A discontinuous precipitation reaction was observed at the dendritic cell boundaries. Microchemical analysis revealed segregation of Mg and Sc at these interdendritic regions. No improvement was observed in the resistance of the alloy to weld solidification cracking or heat affected zone (HAZ) liquation cracking. This is explained in terms of the inability of this level of Sc addition to refine the solidification structure and to influence the liquation of solute-enriched dendritic cell boundaries of the cast material.     

The effect of annealing on the microstructure and tensile properties of a β/γ′ Ni–Al–Fe alloy

The evolution of the microstructure of a (β/γ ′) Ni–32 at.% Al–5 at.% Fe alloy during annealing has been studied by electron microscopy and X-ray diffraction. Annealing at 800°C and 1100°C causes a reverse martensitic transformation, L1₀→B2 (β), and a B2→L1₂ (γ ′) phase transformation. The lower annealing temperature leads to a higher volume fraction of the γ ′-phase but a smaller size of the γ ′-particles. The kinetic laws of the coarsening and of the increase in the volume fraction of the γ ′-phase are discussed. The orientation relationships between the β and γ ′ phases appeared to be mainly of Nishiyama–Wassermann and Bain types after 800°C annealing, while Kurdjumov–Sachs and Bain orientation relationships were predominant in the alloys annealed at 1100°C. A strong correlation between the volume fraction of the γ ′-phase and the tensile characteristics of the alloy has been established.     

The effect of heat treatment on the corrosion behavior of sputter-deposited aluminum–chromium alloys

The effect of heat treatment on the corrosion resistance of sputter-deposited aluminum–chromium alloys containing 16–51 at% chromium has been studied in 0.1 and 0.5 M HCl. Structural relaxation decreases the corrosion rate of Al–16Cr alloy on which the passive film cannot be formed, since the corrosion rate is controlled by the reactivity of the alloy surface. The corrosion rate of spontaneously passive Al–35Cr alloy increases by crystallization. The chromium enrichment of the matrix, as a result of precipitation of a nanocrystalline aluminum-rich phase, results in enhancement of the corrosion resistance. However, if the size of the less corrosion-resistant aluminum-rich grains exceeds a critical limit of ∼20 nm, the corrosion resistance decreases.     

The effect of niobium ion implantation on the oxidation behavior of aγ-TiAl-based intermetallic

The effect of niobium implantation (2×10¹⁶ and 10¹⁷ ions/cm²) on the oxidation behavior of a -TiAl-based intermetallic alloy Ti–48Al–2Cr in air at 800°C has been examined. Isothermal studies with exposure times up to 200 hr and cyclic-oxidation tests up to 800 hr revealed a negligible effect for the low implantation dose. However, a remarkable decrease in oxidation rates was observed for the material implanted with 10¹⁷ Nb ions/cm². The improvement in the oxidation resistance appeared to be similar to that obtained by alloying of the intermetallic with a few atomic percent niobium. Possible mechanisms for the effect of niobium on the oxidation resistance of TiAl-base intermetallics are discussed in view of the results obtained for the implanted material.     

The effect of Y-ion implantation on the oxidation of β-NiAl

The influence of Y-ion implantation on the oxidation of -NiAl single crystals has been investigated using SEM, TEM, and STEM. Y ions having an energy of 70 keV were implanted with a concentration of 5×10¹⁶ ions/cm². The oxidation experiments were performed in air at 1223 K. Y-ion implantation resulted in a 45-nm disordered layer. Oxidation of Y-implanted -NiAl leads to the formation of a fine-grain layer, consisting of -Al₂O₃ containing Y and a -Al₂O₃ layer. After further oxidation the metastable Al₂O₃ transformed into -Al₂O₃, which started at the metal-oxide interface. Y-Al-garnet (YAG) particles were observed and Y segregation to -Al₂O₃ grain boundaries has been detected.     

Role of the particle–matrix interface on the nucleation of acicular ferrite in a medium carbon microalloyed steel

The inclusions responsible for the nucleation of acicular ferrite in a medium carbon microalloyed steel have been studied using optical and transmission electron microscopy. The acicular ferrite microstructures for such studies were obtained by isothermal treatments following austenitization at 1250°C. The samples were maintained for different times at 450°C and then water quenched, permitting observation of the evolution of the microstructure. Intragranular nucleation is enhanced by the presence of MnS inclusions covered by a CuS layer leading to an improvement in the global energetic balance for the transformation. This better energetic balance is obtained by replacing a high-energy interface between inclusion and austenite with a lower energy interface between inclusion and ferrite. The result is a fully acicular microstructure.     

Influence of the surface etching on the corrosion behaviour of a three-dimensional printed Ti–6Al–4V alloy

Recently, there has been an extension of three-dimensional (3D) printing technology of metal materials in the medical field. Additive technology has made it possible to manufacture customized implants. However, 3D printing products often require surface treatment. The possible treatments include acid etching. This study investigated the effect of surface etching on the corrosion resistance of Ti–6Al–4V alloy concerning biological applications. The samples were etched in a mixture of hydrofluoric acid and nitric acid. The corrosion behaviour was described by measuring the time dependence of polarization resistance in a saline solution and surface analysis. The results showed that etching creates a fluoride-rich layer on the surface, which negatively affects the corrosion behaviour of the material for up to 24 hr. Cytocompatibility tests showed that the resulting layer does not affect the biocompatibility of the material.     

The effect of oxygen on the microstructural evolution in crystallized Cu–Zr–Al metallic glasses

Cu–45Zr–8Al and Cu–44.1Zr–7.8Al–2Y metallic glass ribbons were prepared by melt spinning and heat treated at two different temperatures followed by microstructural characterization by SEM and TEM. The compositions were selected to better understand the effect that oxygen has in the sequence and morphology of the phases formed during devitrification. A novel microstructure consisting of the Heusler Cu₂ZrAl phase precipitated inside a B2–CuZr matrix that has shape memory properties was produced. It is proposed that this novel microstructure may be used to prepare samples with improved shape memory responses. The known cube–cube relationship between the Heusler and B2 phases also provides direct evidence about the orientation relationship between the martensite and the parent B2 austenite and the results are in contrast to what is reported in the literature. The results also confirm that oxygen dissolved in these alloys leads to the formation of the B2–CuZr phase at lower temperatures than comparable low oxygen alloys.