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In the present paper, the following topics are reviewed in detail: (a) the available adhesives, as well as their recent advances, (b) thermodynamic factors affecting the surface pretreatments including adhesion theories, wettability, surface energy, (c) bonding mechanisms in the adhesive joints, (d) surface pretreatment methods for the adhesively bonded joints, and as well as their recent advances, and (e) combined effects of surface pretreatments and environmental conditions on the joint durability and performance. Surface pretreatment is, perhaps, the most important process step governing the quality of an adhesively bonded joint. An adhesive is defined as a polymeric substance with viscoelastic behavior, capable of holding adherends together by surface attachment to produce a joint with a high shear strength. Adhesive bonding is the most suitable method of joining both for metallic and non-metallic structures where strength, stiffness and fatigue life must be maximized at a minimum weight. Polymeric adhesives may be used to join a large variety of materials combinations including metal-metal, metal-plastic, metal-composite, composite-composite, plastic-plastic, metal-ceramic systems. Wetting and adhesion are also studied in some detail in the present paper since the successful surface pretreatments of the adherends for the short- and long-term durability and performance of the adhesive joints mostly depend on these factors. Wetting of the adherends by the adhesive is critical to the formation of secondary bonds in the adsorption theory. It has been theoretically verified that for complete wetting (i.e., for a contact angle θ equal to zero), the surface energy of the adhesive must be lower than the surface energy of the adherend. Therefore, the primary objective of a surface pretreatment is to increase the surface energy of the adherend as much as possible. The influence of surface pretreatment and aging conditions on the short- and long-term strength of adhesive bonds should be taken into account for durability design. Some form of substrate pretreatment is always necessary to achieve a satisfactory level of long-term bond strength. In order to improve the performance of adhesive bonds, the adherends surfaces (i.e., metallic or non-metallic) are generally pretretead using the (a) physical, (b) mechanical, (c) chemical, (d) photochemical, (e) thermal, or (e) plasma method. Almost all pretreatment methods do bring some degree of change in surface roughness but mechanical surface pretreatment such as grit-blasting is usually considered as one of the most effective methods to control the desired level of surface roughness and joint strength. Moreover, the overall effect of mechanical surface treatment is not limited to the removal of contamination or to an increase in surface area. This also relates to changes in the surface chemistry of adherends and to inherent drawbacks of surface roughness, such as void formations and reduced wetting. Suitable surface pretreatment increases the bond strength by altering the substrate surface in a number of ways including (a) increasing surface tension by producing a surface free from contaminants (i.e., surface contamination may cause insufficient wetting by the adhesive in the liquid state for the creating of a durable bond) or removal of the weak cohesion layer or of the pollution present at the surface, (b) increasing surface roughness on changing surface chemistry and producing of a macro/microscopically rough surface, (c) production of a fresh stable oxide layer, and (d) introducing suitable chemical composition of the oxide, and (e) introduction of new or an increased number of chemical functions. All these parameters can contribute to an improvement of the wettability and/or of the adhesive properties of the surface. [ABSTRACT FROM AUTHOR]

Phase equilibria in Ti-Al-Mo ternary system are of fundamental importance to better acquire the phase-forming regulation of TiAl-based alloys. In this paper, phase relations in this system have been investigated with Ti-TiAl-Mo diffusion triples combined with key equilibrated alloys. Five isothermal sections of the Ti-Al-Mo ternary system at 1473, 1373, 1273, 1173, and 1073 K were experimentally determined by means of electron probe microanalysis, scanning electron microscope, and X-ray diffraction. The TiAl and TiAl phases show wide ternary composition ranges, while the solubility of Mo in the TiAl and αTi phases is relatively limited. The solubility of Al in the β(Ti, Mo) phase decreases from 49.0 at.% at 1473 K to 39.9 at.% at 1073 K while that of Ti in the AlMo phase decreases from 25.4 at.% at 1473 K to 20.8 at.% at 1073 K. Moreover, the ternary compound σ forms at a temperature between 1423 and 1373 K through a peritectoid reaction β(Ti, Mo) + AlMo → σ. A peri-eutectoid invariant reaction β(Ti, Mo) + AlMo → σ + TiAl at 1373-1273 K was further deduced and the existence of another invariant reaction β(Ti, Mo) + TiAl → σ + TiAl at a temperature between 1273 and 1173 K was also confirmed. The established phase equilibria of the Ti-Al-Mo ternary system may provide essential data required for the construction of reliable thermodynamic assessment of the Ti-Al-Mo system. [ABSTRACT FROM AUTHOR]

The properties and the structures of liquid melt above the liquidus play an important role in determining the resultant properties of the alloy and the composite. In this paper, the melt structures of SiCp/Al composites with two different reinforcement volume fractions were investigated using liquid metal X-ray diffraction and differential scanning calorimetry. The experimental results showed that the melt structures of SiCp/Al composite are different from that of liquid matrix alloy, a Si–Si hump in the pair radial distribution function in SiCp/Al composite melt and the DSC trace indicated that Si is not well distributed above the liquidus, the size change of short-range-order (SRO) in SiCp/Al composite melt indicated the diffusion of Si from chemical reaction between SiC and molten Al is possible only after a given temperature or after some extent concentration fluctuation of Si. The mechanisms for the observed phenomenon are also discussed in this paper. [ABSTRACT FROM AUTHOR]

This paper describes some technical limitations encountered in joining ceramics–ceramics or ceramics–metals, and how, to some extent, they have been practically overcome. The effect of the residual stresses on the strength of joints fabricated between alumina–alumina or alumina and the nickel base alloy HAYNES® 214™ using a solid-state bonding technique with Ni interlayer was studied. Finite element analyses (FEA) for the elastic–plastic and elastic–plastic–creep behavior have also been used to better design the joints and to predict their performance. It was found that the residual stresses caused by the thermal expansion mismatch between alumina (Al2O3) and the Ni-based superalloy (HAYNES® 214™) have severely deteriorated the joints compared to Al2O3–Al2O3 joint fabricated with the same solid-state bonding parameters. The high residual stresses zones obtained through the FEA simulation fitted well with the fractographic observations of the Al2O3/Ni/HAYNES® 214™ joints. Also, in order to use the joint material as a structural material, the study about the effect of geometrical parameters has been performed. Optimal geometries have been determined. [ABSTRACT FROM AUTHOR]

The characterization of lead-free solders, especially after isothermal aging, is very important in order to accurately predict the reliability of solder joints. However, due to lack of experimental testing standards and the high homologous temperature of solder alloys ( Th > 0.5 Tm even at room temperature), there are very large discrepancies in both the tensile and creep properties provided in current databases for both lead-free and Sn–Pb solder alloys. Some recent researches show that the room temperature aging has significant effects on mechanical properties of solders. This paper is intended to review all available data in the field and give rise to the possible factors including room temperature effects which causes the large discrepancies of data. This review of the research literatures has documented the dramatic changes that occur in the constitutive and failure behavior of solder materials and solder joint interfaces during isothermal aging. However, these effects have been largely ignored in most previous studies involving solder material characterization or finite element predictions of solder joint reliability during thermal cycling. It is widely acknowledged that the large discrepancies in measured solder mechanical properties from one study to another arise due to differences in the microstructures of the tested samples. This problem is exacerbated by the aging issue, as it is clear that the microstructure and material behavior of the samples used in even a single investigation are moving targets that change rapidly even at room temperature. Furthermore, the effects of aging on solder behavior must be better understood so that more accurate viscoplastic constitutive equations can be developed for SnPb and SAC solders. Without such well-defined relationship, it is doubtful that finite element reliability predictions can ever reach their full potential. [ABSTRACT FROM AUTHOR]

In this paper, the plastic deformation behavior and strain homogeneity of the ZK60 Mg alloy during the multi-pass cyclic extrusion and compression (CEC) was simulated using the finite-element method (FEM) with a view to provide an insight into the mechanics of the process. Physical modeling (PM) experiment with same alloy was carried out to verify the results of the numerical simulations. The results show that two vortex flow regions with opposite flow direction are formed inside the cylindrical workpiece during CEC deformation. Although the deformation is inhomogeneous in both end regions of workpiece, a uniform region of equivalent strain exists, and the extent of uniform deformation increased with the increase in workpiece length. [ABSTRACT FROM AUTHOR]

Knowledge of the fracture and fatigue behaviour of metallic alloys at extreme environmental temperature conditions is required to assess the safety of structural components operating in particular fields: aero-spatial, off-shore structures, power plants superconductors, polar Antarctic facilities, etc. Among the structural metallic alloys for civil, mechanical engineering and plant applications, steel S275 J2 is widely used, whereas aluminium alloys such as Al7075 T6 are significant especially for aero-spatial and polar Antarctic applications. In this paper, the main experimental mechanical characteristics of such metallic materials at room temperature as well as at low temperatures are examined. Three temperatures are considered: 293 K (+20 °C, room temperature RT), 243 K (−30 °C) and 193 K (−80 °C). The corresponding values of fracture toughness and endurance limit available in the literature are reported herein. Further, experimental tests have been performed to determine the unavailable mechanical properties. Then, the values of such fracture and fatigue parameters at various temperatures are critically discussed. [ABSTRACT FROM AUTHOR]

The oxidation of the bulk amorphous alloy Zr65Cu17.5Ni10Al7.5 in air in its amorphous and the supercooled liquid states was studied in the temperature range 573–663 K using X-ray photoelectron spectroscopy (XPS). The oxide film mainly consisted of the oxides of Zr (as ZrO2) and Al (as Al2O3). No Cu or Ni was found in the oxide film formed on the amorphous state of the alloy while significant Cu (as CuO) was present in the oxide film formed on the alloy in its supercooled liquid state. The role of the various alloying elements during oxidation at high temperatures in air is discussed in the paper. The XPS data from oxide film support the previously suggested mechanism for oxidation of this alloy, i.e. the rate controlling process during oxidation of the alloy at low temperatures (in the amorphous state) is the back-diffusion of Ni and Cu, while the oxidation at high temperatures (in the supercooled liquid state) is dominated by the inward diffusion of oxygen. [ABSTRACT FROM AUTHOR]

The microstructures, machinability and surface characteristics of Al–7Si and Al–7Si–2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. Results indicate that combined grain refined and modified Al–7Si–2.5Cu cast alloys have microstructures consisting of uniformly distributed α-Al grains, eutectic Al–silicon and fine CuAl2 particles in the interdendritic region. These alloys exhibited better machinability and surface characteristics in the cast condition compared with the same alloy subjected to only grain refinement or modification. Performances of the turning inserts (Un-coated, PVD and Polished CVD diamond coated) were evaluated in machining Al–7Si and Al–7Si–2.5Cu cast alloys under dry environment using a lathe. The Polished CVD diamond coated insert outperformed the Un-coated or PVD-coated cutting inserts which suffered from sizeable edge buildup leading to higher cutting force and poor surface finish. The Polished CVD diamond coated insert shows a very small steady wear without flaking of the diamond film during cutting. This paper attempts to investigate the influence of grain refinement, modification and combined action of both on the microstrutural changes in the Al–7Si and Al–7Si–2.5Cu cast alloys and their machinability and surface finish when different turning inserts used. [ABSTRACT FROM AUTHOR]

The microstructures and dry sliding wear behavior of Al–7Si and Al–7Si–2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. Results indicate that combined grain refined and modified Al–7Si–2.5Cu cast alloys have microstructures consisting of uniformly distributed α-Al grains, eutectic Al– silicon and fine CuAl2 particles in the interdendritic region. These alloys exhibited better wear resistance in the cast condition compared with the same alloy subjected to only grain refinement or modification. The improved wear resistances of Al–7Si–2.5Cu cast alloys are related to the refinement of the aluminum grain size, uniform distribution of eutectic Al-silicon and fine CuAl2 particles in the interdendritic region resulting from combined refinement and modification. This paper attempts to investigate the influence of the microstructural changes in the Al–7Si and Al–7Si–2.5Cu cast alloys by grain refinement, modification and combined action of both on the sliding wear behavior. [ABSTRACT FROM AUTHOR]

Consolidated nano/sub-micron AZ31 Mg alloy is a new structural material that combines nano-scale grains with a size of up to 100 nm and sub-micron grains with a size of up to 300 nm. Inherently, this new material should have significantly improved strength, making it a potential candidate for special applications requiring increased specific strength. The present paper evaluates the properties of nano/sub-micron AZ31 Mg alloy in terms of mechanical properties and corrosion resistance. The obtained properties are explained and associated with the micro-structure of the alloy. In addition, the nano/sub-micron structural alloy was compared to conventional extruded alloy with the same composition in order to distinguish the main differences between the two alloys. [ABSTRACT FROM AUTHOR]

The Gibbs energies of liquid Zr–Al–Ni and Zr–Al–Ni–Cu alloys with multi-clusters are calculated based on the statistical mechanism in this paper. The results show that the quantity of clusters depends mainly on the temperature and the concentration of the melt. It increases gradually with the decrease of temperature or with the increase of x Ni in liquid (Zr80Al20)1− x Ni x alloys; the quantity of Zr2Ni clusters reaches its maximum of 0.061 mole at x Ni = 0.336. In (Zr80Al20)1− x Ni x liquid alloy the existence of clusters causes the falling of the Gibbs energy. The Gibbs energy drops about 4000 J/mol at x Ni = 0.35 if the effect of cluster of Zr2Ni is considered or about 8000 J/mol at x Ni = 0.40 if both of clusters of Zr2Ni and ZrNi are taken into account. [ABSTRACT FROM AUTHOR]

The processing, structure and properties of deformed metals and alloys with a structural scale from the micrometer to the nanometer dimensions has been the subject of a recent viewpoint set []. The present paper will focus on deformed metals and alloys with a structural scale from 5 nm to 100 nm, concentrating on materials processed by high pressure torsion (HPT), surface mechanical attrition treatment (SMAT) and sliding. A detailed microstructural characterization has been followed by an analysis of the relationship between structural features and processing parameters. In this analysis, some general approaches have been applied for example scaling of the evolution of the boundary spacing. This analysis is the basis for a brief discussion of the relationship between the microstructural parameters and the strength. [ABSTRACT FROM AUTHOR]

The effect of Friction Stir Processing (FSP) on the mechanical properties of a Sc, Zr modified 2024 aluminium alloy was investigated in the present paper. The room temperature tensile properties of the material were obtained in longitudinal direction respect to the processing one and compared with those of the unstirred material and unmodified alloy. Tensile tests were also performed at higher temperatures and different strain rates in the nugget zone. The superplastic properties of the recrystallized material were evaluated and the differences with the parent material as a function of the strong grain refinement due to the Friction Stir Process were put in evidence. The high temperature behavior of the material was studied, in longitudinal direction, by means of tensile tests in the temperature and strain rate ranges of 450–525°C and 10−1–10−3 s−1 respectively. [ABSTRACT FROM AUTHOR]

A new semisolid metal processing technology, rheo-diecasting (RDC) has been developed for production of Mg-alloy components with high integrity. The RDC process innovatively combines the dispersive mixing power of the twin-screw mechanism for creation of high quality semisolid slurry and the high efficiency, low cost nature of the high pressure die casting (HPDC) process for component shaping. AZ91D Mg-alloy was used to optimise the RDC process and to establish its advantages over both the HPDC process and other existing semisolid processing techniques. In this paper we present the RDC process for processing Mg-alloys and the resulting microstructure and mechanical properties of RDC AZ91D alloy. The solidification behaviour of the Mg-alloys in the RDC process and the co-relationships between microstructure and mechanical properties of the RDC AZ91D alloy are discussed. It was found that the RDC process is capable of producing Mg-alloy samples with close-to-zero porosity and a fine, uniform microstructure throughout the entire sample irrespective of the section thickness. Compared with those obtained by other existing processing techniques, the RDC samples have substantially improved or equivalent mechanical properties, with the tensile elongation showing more than 100% improvement. [ABSTRACT FROM AUTHOR]

Tin-rich organ pipes are often affected by localised deterioration in the form of grey pustules, pinholes, cracks and exfoliations at the surface. Two main types of decay of tin-base materials that might have a similar appearance, i.e. the surface of the object covered with dark grey pustules, are known. The first is the allotropic transformation of white metallic tin into grey tin, the so-called “tin-pest”. The second form of decay is due to corrosion in the form of localised oxidation of tin. The identification of the causes of deterioration is of main concern because, whereas oxidised material can be treated, an object that suffers “tin pest” cannot be reconstituted. In the present paper the results of investigations on ancient tin-rich organ pipes affected by localised degradation are presented. The study of the composition and the microstructure of the pipes has been coupled with the results of analyses on the corrosion products. It was shown that oxidation clearly has a significant role in the deterioration of tin pipes, but it was not possible to establish if the allotropic transformation took place or not, because of the low probability of detecting the residual grey tin. [ABSTRACT FROM AUTHOR]

This research is part of a project whose scope was to develop high strength ternary alloys based on Cu-Ti system with the primary aim of substituting them for toxic and expensive Cu-Be alloys. In this pursuit, age hardening behaviour of Cu-4Ti-1Cd alloy has already been investigated and the present paper reports the investigations on the influence of prior cold work by rolling of 50, 75 and 90% on the age hardening of a Cu-4Ti-1Cd alloy using hardness and tensile tests and optical as well as transmission electron microscopy. As a result of cold work followed by aging, hardness of the alloy increased from 237 Hv in solution treated condition to 425 Hv on 90% cold work and peak aging. Similarly, yield and tensile strengths of the alloy reached maxima of 1037 and 1252 MPa respectively on 90% deformation and peak aging. The microstructure of the deformed alloy exhibited elongated grains and deformation bands. The maximum strength on peak aging was obtained due to precipitation of ordered, metastable and coherent βl, Cu4Ti phase in addition to high dislocation density and deformation twins. Both hardness and strength of the alloy decreased on overaging due to the formation of incoherent and equilibrium β, Cu3Ti phase. However, the morphology of the discontinuous precipitation was changed to globular shape due to large deformations and overaging. [ABSTRACT FROM AUTHOR]

We are studying reactions of Ti, V, Zr, and Hf with ceramics as part of a program to understand fundamental reaction and bonding mechanisms in active metal brazing of ceramics. In this paper we present results of experiments with model systems comprising Ag alloys that contain different amounts of Hf or Zr that were reacted with sapphire or 99.6% alumina for different times and temperatures in a controlled atmosphere furnace. In these alloys the Ag functions as an inert solvent, which allowed us systematically to determine the effects of changes in concentration of the active element. We observed qualitative wetting and spreading tendencies of the alloys during heating and examined cross sections after cooling using electron analytical techniques. For all reaction times studied, the Hf/Ag alloys formed a discontinuous reaction layer, which was consistent with earlier high-resolution electron microscopy that showed sub-micrometer HfO2 particles embedded in the surfaces of the Al2O3 grains. By contrast, initial reaction of the Zr/Ag alloys with Al2O3 produced a continuous interface layer. With longer reaction times, the ZrO2 reaction product became much thicker and exhibited three distinct zones at the interface. The results suggest that the rate limiting step in the Zr/Ag reaction is the chemical reaction at the interface, whereas with Hf/Ag reaction diffusion of products away from the interface is rate limiting. [ABSTRACT FROM AUTHOR]

This paper reports an experimental investigation on the effect of multiple twinning on the interface population in two low stacking-fault alloys. This is an important topic for grain boundary engineering because annealing twinning is the indirect cause of improved intergranular corrosion resistance in this class of materials. Proportions of S 3n (n= 1-5) boundaries were analysed in both a brass specimen and a superalloy specimen where the boundaries had been processed so as to be very mobile and less mobile respectively. When S 3 twin boundaries (as distinct from S 3 grain boundaries) are discounted, the S 3n distribution for both specimens had a peak at S 9, because S 3 + S 9 ? S 3 occurs more frequently than S 3+S 9 ? S 27. The distributions and reactions between various S 3n values are described and discussed in detail. A novel trace analysis procedure is used to extract information from S 3 boundaries to decide whether or not they are annealing twins, and so provide a convenient means to assess proportions of twin and non-twin S 3s. The data show unambiguously that a significant proportion of S 3s are not on 111, and these boundaries have on average higher angular deviations from the exact S 3 reference misorientation than do other S 3s. A population of S 3s which were vicinal to annealing twins were also recorded. These data support the contention that profuse annealing twinning produces concurrently many not-twin S 3s, which are pivotal in grain boundary engineering. [ABSTRACT FROM AUTHOR]

The principle and advantages of multi-pass friction stir processing (FSP) for the production of a highly formable Mg alloy, and some convincing experimental results are reported in this paper. FSP is a solid state processing technique which involves plunging and traversing a cylindrical rotating FSP tool through the material. FSP achieved grain refinement and homogenization of the as-cast microstructure in Mg alloy AZ91D. Multi-pass FSP produced a fine homogeneous microstructure having a grain size of 2.7 µm throughout the plate. The plate containing this FSPed microstructure exhibited fracture limit major strains six times larger than the diecast plate in the fracture limit diagram (FLD). The present study shows that multi-pass FSP is an efficient production method for a large-scale plate of a highly formable Mg alloy. [ABSTRACT FROM AUTHOR]

This paper presents the results of micro-tensile testing of the individual struts that were extracted from open cell aluminum foams in the as-fabricated (F), annealed (O) and T6-strengthened (T6) conditions. The results reveal that foam struts are generally stronger and more dutile than the corresponding solid alloys under the same heat treatment conditions. The distinguished strut properties are attributed to the unique grain structures of the struts typically consisting of one grain or having bamboo-like grain structure. The measured strut strengths are also incorporated into mechanics models to estimate foam strengths. A comparison of the predicted and measured foam strengths shows that direct measurement of strut properties is critical to make precise estimation of foam strengths. [ABSTRACT FROM AUTHOR]

Heat capacity is a critical input parameter in mathematical models of solidification and casting. It appears in its own right, and is required for the extraction of thermal conductivity from thermal diffusivity data. It also provides a measure of the latent heat associated with changes of phase, and the precipitation or dissolution of precipitates. Calorimetry is a well-established technique and is used to solve a wide range of materials problems such as studying precipitation or phase changes in alloy systems, and the kinetics of these phase transformations. The quality and range of data that can be obtained will be demonstrated by applying it to nickel base superalloys. This paper discusses important aspects of the measurement including control of the atmosphere, suitable reference materials for temperature and enthalpy calibration, size of the sample and the rate of heating and cooling. The optimised DSC technique was used to investigate the properties of two nickel based superalloys (CMSX4 and IN738LC), comparing the results with previous values and determining sources of error in the method. [ABSTRACT FROM AUTHOR]

The material properties of maraging steels are greatly affected by the alloy and inclusion content and hence by the production route. This paper describes various past and current production routes at Böhler Edelstahl GmbH and the effect of these routes on the specified element (alloy) and non-specified element (inclusion) contents. Non-metallic inclusions were investigated by EDX analysis. The effects of various alloying and tramp elements on the material properties are presented as a statistical evaluation of previous melts. Nitrogen solubility was calculated with Thermo–Calc for maraging steel Mat.-No. 1.6354 and the precipitation of nitrides is discussed. A proposal is made for the production of melts with improved properties. [ABSTRACT FROM AUTHOR]

The thermal stability of two-phase (α + γ) lamellar microstructure in Ti-Al-Mo PST (polysynthetically twinned that has single colony) crystals, containing C or Si, was investigated. In addition, the variation of α-phase volume fraction in Ti-Al-Mo-(C,Si) systems was investigated at several temperatures. Ti-46Al-1.5Mo-0.2C and Ti-46Al-1.5Mo-1.0Si alloys did not recrystallized (‘stable’ in this paper) during heat treatments at various heating rates and temperatures. Moreover, the α-phase volume fractions of Ti-46Al-1.5Mo-0.2C and Ti-46Al-1.5Mo-1.0Si alloys which were stable compositions, changed less than those of Ti-47Al and Ti-46Al-1.5Mo alloys which were unstable compositions. The instability of the latter alloys was caused by their relatively higher variation of α-phase volume fraction during heating. Therefore, it is suggested that the variation of α-phase volume fraction is an important factor in controlling the thermal stability of lamellar microstructure. [ABSTRACT FROM AUTHOR]

The factors affecting the mechanical and environmental durability (or stability), and performance of the adhesively bonded joints in various adherends including metallic alloys, polymers and composite materials are studied in detail. The primary function of a joint is to transfer load from one structural member to another. In most bonded joints the load transfer takes place through interfacial shear. At present the use of adhesive bonded joints are largely applied to secondary non-critical structures. Whereas the use of adhesive bonding in primary structural applications has been somewhat limited because of the difficulty in defining and predicting joint strength, and designing the joint geometry to optimize strength and reliability. The determination of adhesive joint strength is complicated primarily by the nature of the polymeric material itself. Since these problems are mainly mechanical in nature, stress analysis is required to understand how the force loads are distributed along the adherends and adhesive layer. Most structural engineers consider the durability or stability of a joint to be fatigue related. This is only partly true for adhesive bonds as most durability issues are driven by environmental resistance rather than fatigue loads. The environmental resistance of an adhesive bond is determined by the chemical bonds formed during cure of the adhesive and the resistance of the chemical bonds to environmental degradation. Environmental resistance is fundamental to the durability of a bonded joint or repair. Most in-service failures are caused by environmental degradation of the interface between the bonding surface and the adhesive. Although the use of adhesive bonding is increasing rapidly, there are still important issues which need to be addressed in joint analysis, design, durability, and performance considerations. Therefore, the study of joints usually involves consideration of (a) joint geometries, (b) materials (i.e., adhesives and adherends), (c) loading conditions (i.e., static and dynamic loadings), (d) failure modes (i.e., cohesive, adhesive or mixed failure modes), and (e) temperature and moisture or environmental effects (humidity, solvents, corrosion, temperature extremes, thermal cyling etc.). Therefore, in the present paper the adhesive joints are critically assessed in terms of these factors which affect the durability and performance of them. There are two basic mathematical approaches for the analysis of adhesively bonded joints: (a) closed-form or analytical model and (b) numerical solutions (i.e., finite element analysis, FEA). In the closed-form approach, a set of differential equations and boundary conditions is formulated. The solutions of these equations are analytical expressions which give values of stresses at any point of joint. The analytical approach for the solution of complex stress distributions in the joints has been progressively refined until recent times. In the second approach, solutions of differential equations are obtained by numerical methods or the continuum is represented by a discrete model at the outset. The solution of these equations gives displacements at the determined points from which strains and stresses can be obtained for any point within the model. Among the numerical methods, finite element analysis (FEA) has been extensively used with success. The two- and three-dimensional finite element analyses approaches have been extensively applied by many workers to analyse the adhesive joints considering the linear and geometric nonlinearities. [ABSTRACT FROM AUTHOR]

The diffusion-multiple approach can be used to map phase diagrams at an efficiency orders of magnitude faster than the conventional equilibrated alloy method. This paper addresses a concern about the reliability of the results, especially whether the data obtained from diffusion multiples can produce reliable equilibrium phase diagrams. The following topics will be discussed: (a) establishment of local equilibrium at the phase interfaces, (b) X-ray interaction volume vs. thickness of the phases (microprobe related issues), (c) reliability of phase diagrams from equilibrated alloys, (d) usefulness of electron backscatter diffraction, (e) impurity-induced stabilization of metastable phases, and, (f) missing phase situations. A direct comparison of several ternary systems obtained from both diffusion multiples and equilibrated alloys was made. The good agreement between them clearly demonstrates the reliability of phase diagrams determined from diffusion multiples. [ABSTRACT FROM AUTHOR]

Minor alloying addition or microalloying technology has already shown dramatic effects on glass formation and thermal stability of bulk metallic glasses (BMGs). This paper intends to provide a comprehensive review of recent developments of this technology in the field of BMGs. The beneficial effects of minor alloying additions on the glass formation and the thermal stability of BMGs will be summarized and analyzed. In addition, principles and guidelines for future application of this technology will also be proposed. [ABSTRACT FROM AUTHOR]

The development of cast TiAl-based components for the automotive industry and the possibility of wrought components for applications in gas turbines are clear indications that these alloys are maturing as materials for engineering components. There are however problems in the cost of manufacture and in the properties of these alloys. In this paper it is argued that recent developments, which have resulted in a totally new microstructure, taken together with improved casting technology, open the way for wider application of these alloys. The new microstructure has been obtained by tempering massively transformed TiAl alloys so that a highly convoluted fine scale microstructure is obtained by simply heat treating cast samples. This fine microstructure can thus be obtained in cast components, without the need to add boron and problems associated with the extreme plastic anisotropy of fully lamellar samples are also eliminated. [ABSTRACT FROM AUTHOR]

Alloys based on intermetallics have been considered for high temperature structural applications. However, many of these alloys suffer from intrinsic brittleness and low fracture toughness at ambient temperature. Therefore, ductile-phase-toughened intermetallic composites are being investigated as a means to improve the fracture toughness. A subset of this class of materials is in-situ composites produced by directional solidification of intermetallic eutectics. In this paper, we review recent developments related to the processing and properties of these composites. [ABSTRACT FROM AUTHOR]

This paper reports on the density of cubic primitives made by Direct Metal Laser Re-Melting, a process variant of selective laser sintering (SLS). Here, stainless steel 316L powder fractions are scanned and fused by a 90 W Nd:YAG laser in consecutive 100 μm layers in order to build a 3-Dimensional object. The effects of Q-Switch pulsing frequency, scanning speed and scan spacing on sample density are described. The samples are measured by two methods: a weight/volume analysis and a xylene impregnation technique. The results are supported by microscopy analysis for qualitative arguments. The results show the significant influence of pulsing the beam on the density of the fabricated material. Also reported is the relationship of material density with energy density (as a function of the process parameters; power, scan speed and scan spacing). Optical analysis of material cross sections shows a periodic occurrence of porosity across the whole range of samples. Causes for this are discussed. [ABSTRACT FROM AUTHOR]

Rapidly solidified Al-Fe-Mo-Si powders were produced by centrifugal atomization and then consolidated by hot extrusion. Five compositions were chosen in order to obtain a theoretical constant volume fraction of (silicide + Al12Mo) of 20%, with different relative fractions of [silicide]/[α-matrix] and different ratios of [Fe]/[Mo] within the silicide. This paper presents the microstructures observed in both as-atomized and consolidated states. The only phase detected by X-Ray Diffraction, the non equilibrium ternary Al12-13(Fe,Mo)3Si, exhibits different sizes and morphologies and is inhomogeneously distributed within the matrix. Accurate electron microscopy observations indicate that this silicide may grow from a quasicrystalline precursor. Grains within the polycrystalline silicide often exhibit orientation relationships (micro twinning) giving rise to quasicrystalline-like patterns. [ABSTRACT FROM AUTHOR]

Recent advances in manufacturing technology have led to the development of a new breed of advanced materials. These new materials are process dependent and would be difficult, if not impossible, to produce using conventional methods. Laser direct manufacturing (LDM) is a solid freeform fabrication process that enables the production of these advanced materials. LDM utilizes a high energy density heat source, powdered metal feedstock, and computer driven machine controls to produce bulk materials in near-net shape form. The combination of powdered metallurgy (P/M) and rapid solidification processing (RSP) allow bulk structures to be made with novel compositions and unique properties. In addition, near-net shape production eliminates the need for thermomechanical post-processing that can nullify some of the metallurgical advantages gained through RSP and P/M. These advantages have led to the development of alloys specifically tailored to the LDM process. This paper describes a dispersion hardened erbium-bearing titanium alloy developed to couple with the processing advantages found in the laser direct manufacturing process. [ABSTRACT FROM AUTHOR]

The present paper describes a surface-microstructural modification due to cold work and the fatigue behaviour of the surface-modified specimens in beta Ti-22V-4A1 alloy. As-solution treated specimens were shot peened and then aged to achieve the modification. The obtained microstructure was first characterized and rotating bending fatigue tests were then performed using the surface-modified smooth specimens. The fatigue behaviour was evaluated and compared with the results of the conventional solution treated and aged specimens without modification. Surface-microstructural modification was successfully achieved within the region of 350 µm underneath the surface where hardness increased significantly compared with the core of the specimen, although there were some inhomogeneous precipitation areas in the modified region. The specimens without modification showed a step-wise S-N curve with the transition stress of approximately 600 MPa below which subsurface fracture occurred, while the surface- modified specimens did not exhibit step-wise S-N curve, but both surface-related and subsurface fractures took place up to a higher stress level of 720 MPa, leading to improved fatigue strength. In the surface-modified specimens, several facets were seen at the subsurface crack origin. The initiation sites were deeper than the specimens without modification, which corresponded to the in homogeneous precipitation areas. The subsurface fracture process is further discussed on the basis of some mechanical approaches. [ABSTRACT FROM AUTHOR]

The microstructural evolution of Al72Ni12Co16 alloy at various undercoolings was investigated in this paper. A single-phase decagonal quasicrystal (D-phase) was obtained in the undercooled Al72Ni12Co16 alloy melts. Different microstructure morphologies of the D-phase were formed with increasing undercoolings. Based on Toner's model of the step growth of quasicrystals, the growth mechanisms of the D-phase under various undercoolings were discussed. The D-phases formed at various undercoolings in the undercooled melts show different microstructures owing to the change of preferential growth direction from the quasiperiodic to periodic direction. [ABSTRACT FROM AUTHOR]

To understand the nature of Sb2 Se3 semiconductor as a bulk sample, the X-ray diffraction study was carried out to identify the sample structure. Dc and ac electrical properties measured in the temperature range 290-370 K, and frequency range 10²-105 Hz were the subject of the present work. Properties such as dielectric constant ζ, loss function tanδ, and electrical conductivities σac as a function of both frequency and temperature are reported. Different models of electrical conduction in semiconductor materials have been used to explain the observed results. A trail has been made to correlate the results of this paper with the average heat of atomization Hs and the average coordination number M. The experimental and theoretical investigation is in accordance with Liang criterion. [ABSTRACT FROM AUTHOR]

Besides altering the kinetics of precipitation, the reinforcements with alumina particles appear to alter the relative proportions of the various phases formed in the matrix alloy during ageing. Alumina also seems to reduce the volume fractions of hardening phase in these materials, especially at higher contents. One reason for this effect could be the dislocation relief of the matrix strain associated with the early precipitates. Additionally, the diffusion of Mg and its subsequent incorporation into the reinforcement at the Al2O3/Al interface could also result in Mg depletion from the matrix, accounting for the reduction of the β (Mg2Si) particle sizes. Magnesium incorporation into interfacial alumina to form MgAl2O4 has been observed in these materials. This paper shows that the nature and morphology of the second phases depend the heat treatment conditions on. [ABSTRACT FROM AUTHOR]

Thixoforming requires semi-solid slurries, which contain a high volume fraction of non-dendritic solid phase with special grain morphology. Volume fraction, geometry and connectivity of the solid α-phase has to be kept within narrow limits. The paper illustrates the development of a new aluminium based wrought alloy AIMgSi1 alloy, adapted with barium, characterised by a microstructure which exhibits a low sensitivity towards fluctuations in process parameters resulting in improved mechanical properties of the alloy. The rheological behaviour of the new alloy by means of backward extrusion experiments is described, and an overview of the static and dynamic strength properties is given that can be achieved when the alloy is processed by means of the New Rheocasting process. [ABSTRACT FROM AUTHOR]

This research is part of a project whose scope was to investigate the engineering properties of new non-commercial alloy formulations based on the Cu rich corner of the Cu-Fe-Cr ternary system with the primary aim of exploring the development of a new cost-effective high-strength, high-conductivity copper alloy. Promising properties have been measured for the following alloys: Cu-0.7wt%Cr-0.3wt%Fe and Cu-0.7wt%Cr-2.0wt%Fe. This paper reports on the microstructural characterisation of these alloys and discusses the mechanical and electrical properties of these alloys in terms of their microstructure, particularly the formation of precipitates. These alloys have evinced properties that warrant further investigation. Cost modelling has shown that Cu-0.7wt%Cr-0.3wt%Fe is approximately 25% cheaper to produce than commercial Cu-1%Cr. It has also been shown to be more cost efficient on a yield stress and % IACS per dollar basis. The reason for the cost saving is that the Cu-0.7%Cr-0.3%Fe alloy can be made with low carbon ferro-chrome additions as the source of chromium rather than the more expensive Cu-Cr master-alloy. For applications in which cost is one of the primary materials selection criteria, it is envisaged that there would be numerous applications in both cast and wrought form, where the Cu-0.7%Cr-0.3%Fe alloy would be more suitable than Cu-1%Cr. [ABSTRACT FROM AUTHOR]

The Hunt and Lu [ Metall. Mater. Trans. A 27A (1996) 611] model for the selection of primary spacing, λ, during cellular and dendritic growth predicts a range of spacings falling between minimum and maximum values of λmin and λmax respectively. Within the model λmax/λmin will be at least 2 and may, under certain circumstances, be significantly greater. In this paper we use a free boundary model of solidification within an array to demonstrate that interaction between the tips of the cells or dendrites leads to a transverse adjustment mechanism that will tend to equalise the spacing as growth proceeds. This transverse adjustment mechanism is shown to be rapid for the spacings characteristic of cellular growth but much more gradual for the spacings characteristic of dendritic growth. These findings are consistent with observations of the primary spacing of dendrites grown in alloys of the transparent casting analogue, succinonitrile. [ABSTRACT FROM AUTHOR]

This paper describes the spray forming of SiC particle reinforced Al metal matrix composites (MMCs) with particular emphasis on microstructure characterization of SiC particle distribution. A 5182 Al-Mg alloy was used as matrix material, and SiC particles with a mean diameter of 1.2 μm and 2.0 μm as reinforcement. The reinforcing particle distribution and microstructural characteristics of MMCs were analyzed in the current study using TEM, SEM and optical microscopy. The distribution of SiC particles in the as-spray deposited and hot-extruded conditions was characterized. SEM results indicate that the SiC particles are homogeneously distributed although some clustering was evident in the matrix. TEM and OM examinations show that most of SiC particles are present intergranularly in the Al matrix. EDS analysis indicated that Mg tends to segregate and form oxide phases in the vicinity of SiC particles and that there is no compositional variation of Mg across grain boundaries in the Al matrix. [ABSTRACT FROM AUTHOR]

The present paper reports kinematic studies of the glass transition in glassy Se80-xTe20Sbx alloys using the differential scanning calorimetric technique. The glass transition temperature (Tg) is found to increase monotonically with the heating rate. Tg also increases with the increase of Sb concentration in ternary Se80-xTe20Sbx system. From the heating rate dependence of glass transition temperature, the activation energy (Δ Et) for the relaxation time controlling the structural enthalpy, is calculated. The composition dependence of Tg and Δ Et is discussed in terms of the structure of the Se-Te-Sb glassy system. [ABSTRACT FROM AUTHOR]

NiTi alloy is considered to have great application potential in the fabrication of metal implant materials. However, the NiTi alloy still suffers from some disadvantages, such as poor corrosion resistance and health hazards caused by the release of nickel ions. In order to improve the corrosion resistance of NiTi alloy, a healing composite coating was prepared on NiTi alloys by micro-arc oxidation doped with ZnO nanoparticles and sol–gel sealing with polyacrylamide. The surface morphology, composition, roughness, thickness, and electrochemical performance of the prepared coating were investigated by SEM, EDS, Eddy current thickness gauge, electrochemical workstation, and so on. The adhesion of the prepared coating was also tested using the pull-off method. The results show that compared with NiTi alloy substrate, composite coating of MAO–ZnO@PAM has a dense microstructure, a flatter surface, the largest inner and interfacial charge transfer resistances, outstanding corrosion resistance, and possesses the self-healing ability under the humid condition. [ABSTRACT FROM AUTHOR]

The present study conducted a detailed investigation to determine the effects of adding Sc and applying low-frequency electromagnetic casting (LFEC) on the bendability and ductility of hot-rolled 7A36 alloy using optical microscopy, electron backscatter diffraction, and scanning electron microscopy by two different solid solution heating rate treatments. Results showed that the rapidly solid-solution-heated rates specimen (R specimen) exhibited several micro-cracks, while the slow solid-solution-heated rates specimen (S specimen) displayed visible cracks and even fractures. Additionally, increasing the solid solution heating rate resulted in a decreased diameter of the second phase but larger average grain size. The coarse second-phase grains of the alloys most likely lead to the formation of microcracks; however, the coarse recrystallized grains prevent the further propagation of bending cracks. The strap-like and finer recrystallized grains of the R specimen lead to an improved bendability of the 7A36 alloy by coordinating plastic deformation and accommodating more dislocations. Further, adding Sc improves the bendability and tensile properties by refining grain size and improves the texture strength, while applying LFEC slightly increases the average grain size and the recrystallizing degree, which result in a high Schmid factor value and lower texture strength, and dislocation density benefits the bendability and ductility of the 7A36 alloy with a little strength reduction. [ABSTRACT FROM AUTHOR]

The microstructure, compressive properties and in vitro degradation behavior of as-cast Mg alloys with high Zn or Ca content were investigated. The results showed that the addition of Ca (1 wt%) to Mg–5Zn or Zn (1 wt%) to Mg–5Ca changed the shape, distribution, volume fraction and the type of second phase. When 1 wt% Ca was added to Mg–5Zn alloy, the second phase changed from Mg7Zn3 to Ca2Mg6Zn3 phase and it was distributed from granular formation to a continuous network structure. While the second phase was changed from Mg2Ca in Mg–5Ca alloy to the coexistence of Mg2Ca(Zn) and slight Ca2Mg6Zn3 phase in Mg–5Ca–1Zn alloy. The second phase exhibited a continuous network distribution in both of Mg–5Ca and Mg–5Ca–1Zn alloys, but the width of Mg2Ca(Zn) phase was reduced obviously after adding 1 wt% Zn to Mg–5Ca alloy. The compressive test revealed that Zn element was contributed to the promotion of ultimate compressive strength and fracture elongation, while Ca element was beneficial for improving the yield strength of Mg alloys. The immersion test proved that the weight loss of Mg–5Zn–1Ca was the highest, followed by Mg–5Zn, Mg–5Ca and Mg–5Ca–1Zn alloy. The Mg–5Zn-based alloys suffered severe pitting, while Mg–5Ca-based alloy exhibited a relatively uniform corrosion. The Ca addition accelerated the corrosion of Mg–5Zn alloy due to the expansion of potential difference between second phase and Mg matrix, while Zn addition reduced the micro-galvanic corrosion of Mg–5Ca alloy due to the lowest potential difference between Mg2Ca(Zn) phase and Mg matrix. [ABSTRACT FROM AUTHOR]

To conquer the trade-off between strength and ductility, a new strategy for preparing heterostructured (HS) 2024Al alloys with various heterogeneity levels through introducing submicro-Al3Ti particles and adjusting partial remelting duration of powder thixoforming was proposed. The results indicate that the difference in volume fraction between soft and hard domains of the resultant HS alloys gradually decreases from 0.27 to 0.02, while that of microhardness also decreases from 1.58 to 1.17 GPa, i.e., the heterogeneity level gradually decreases with prolonging the remelting time. The excellent strength–ductility synergy is simultaneously achieved by a moderate heterogeneity level (the differences in microhardness of 1.23 GPa and volume fraction of 0.02) in the HS alloy thixoformed at the partial remelting time of 80 min. This is primarily ascribed to the largest strain gradient caused by the accumulation of the highest density dislocations at the boundary during deformation, which produces the highest heterodeformation-induced (HDI) strengthening and hardening. In addition, the dislocations emitted from the submicro-Al3Tip during the later deformation stage also improve the strain strengthening and hardening, further leading to the improvement in strength–ductility synergy. [ABSTRACT FROM AUTHOR]

Introducing of thermodynamically stable strengthening phases is an important means enhancing the properties of magnesium alloys. To introduce a stable Al2Nd strengthening phase, the Mg-Al-Nd alloys were prepared with a fixed atomic ratio of 2:1 for Al and Nd. The total content of Al and Nd was varied at 1%, 3%, 5%, and 7%, respectively. The effects of Al2Nd phase on the microstructure and mechanical properties of the Mg-Al-Nd alloys were systematically studied in this work. The experimental results indicated that the as-cast alloy primarily consisted of the acicular Al11Nd3 phase as a secondary phase. After undergoing a homogenization treatment at 500 °C for 12 h, the secondary phase underwent a transformation, resulting in the formation of short rod shape Al2Nd structures. Simultaneously, layered Al2Nd precipitated within the α-Mg matrix. The formation of twinning was inhibited, while the Al2Nd phase promoted recrystallization and refined the microstructure through the mechanism of particles stimulated nucleation (PSN), as the Al and Nd contents increased during thermal deformation. At the same time, the increases of Al2Nd phase can enhance the strength and the plasticity of the alloy. The mechanical properties of extruded Mg-1.36Al-3.64Nd (AE5) alloy were excellent with yield strength of 175 MPa, ultimate tensile strength of 249 MPa, and the elongation of 15.4%. The enhanced performance can be primarily attributed to the refined microstructure and the presence of Al2Nd precipitates with small size, which contributed to effective fine grain strengthening and secondary phase strengthening. [ABSTRACT FROM AUTHOR]

Data-driven methodology has become a key tool in computationally predicting material properties. Currently, these techniques are priced high due to computational requirements for generating sufficient training data for high-precision machine learning models. In this study, we present a support vector regression (SVR)-based machine learning model to predict the stability of silicon (Si)–alkaline metal alloys, with a strong emphasis on the transferability of the model to new silicon alloys with different electronic configurations and structures. We elaborate on the role of the structural descriptor in imparting transferability to the model that is trained on limited data (~ 750 Si alloys) derived from the Material Project database. Three popular descriptors, namely X-ray diffraction (XRD), sine coulomb matrix (SCM), and orbital field matrix (OFM), are evaluated for representing Si alloys. The material structures are represented by descriptors in the SVR model, coupled with hyperparameter tuning techniques like Grid Search CV and Bayesian optimization, to find the best performing model for predicting total energy, formation energy and packing fraction of the Si alloy systems. The models are trained on Si alloys with lithium (Li), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), and aluminum (Al) metals, where Si–Na and Si–Al systems are used as test structures. Our results show that XRD, an experimentally derived characterization of structures, performs most reliably as a descriptor for total energy prediction of new Si alloys. The study demonstrates that by qualitatively selection of training data, using hyperparameter tuning methods, and employing appropriate structural descriptors, the data requirements for robust and accurate ML models can be reduced. [ABSTRACT FROM AUTHOR]

The effect of grain size and second-phase distribution on the corrosion performance of metal inert gas-welded Al–MgSi–Mn–Cr alloy in different regions was investigated. Due to the welding heat, the transformation of the strengthening phase β″ (Mg5Si6) to B′ phase (Al3Mg9Si7) in heat-affected zone I leads to the reduction in strengthening ability of the joint. In comparison with the equiaxed grain of weld zone, base metal exhibits high grain boundary density of the fibrous grain and a large amount of second phases on the grain boundary, which increases the anodic dissolution site, leading to the highest pitting corrosion susceptibility. Additionally, the continuous distribution of β (Mg2Si) precipitate and Al(MnFe)Si dispersoid at grain boundary forms a corrosion channel, which promotes the corrosion propagation along grain boundary. [ABSTRACT FROM AUTHOR]

The formation of a Ni3Al(γ′)+Ni7Hf2 unidirectionally solidified lamellar eutectic composite has been investigated in this paper. The results show that Ni-5.8Al-32Hf alloy, which has the Ni3Al+Ni7Hf2 eutectic structure, is a suitable composition of D.S eutectic material. The melting range of this composition is 41 °C as determined by DTA. The critical ratio of G/R for Ni3Al+Ni7Hf2 eutectic is found to be 5× 105 °C · s · cm−2, and the lamellar Ni3Al+Ni7Hf2 eutectic aligned parallel to the direction of solidification was made with R = 5 μm/s and G = 250 °C/cm. The investigation shows that the lamellar eutectic has a preferred crystallographic orientation between the Ni3 Al and Ni7Hf2 lamellae, i.e., (111)NiAl//(100)NiHf and [110]NiAl//[010]NiHf. The lamellar Ni7Hf2 did not degrade or coarsen obviously, and no harmful phase formed in the interface of Ni3Al/Ni7Hf2 after long time soaking of 1100 °C/110 h. This demonstrates that the Ni3Al+Ni7Hf2 lamellar eutectic has high interface thermal stability. [ABSTRACT FROM AUTHOR]

omistic simulation of transformation toughening due to martensitic transformation in Ti-V phase particles dispersed in a γ-TiAl matrix containing cracks requires knowledge of the continuum elastic stress and displacement fields for the problem of a crack touching the γ-β interface. Because of the anisotropic characters of the two phases, analytical solutions for these fields are not available and they must be determined numerically. In the present paper a finite element method-based eigenanalysis is developed and subsequently applied to the γ-β system to determine the order of the stress singularity and the angular dependences of the stress and displacement fields. These fields are subsequently used to enrich the finite elements surrounding the crack tip and, through the use of the general finite element code ABAQUS, to determine the generalized stress intensity factors and thus the total singular crack-tip stress and displacement fields. It is found that there are two coupled singular terms in the singular stress and displacement fields, and consequently pure (uniaxial) mode I loading gives rise to mixed modes I-II near-crack-tip behaviour. [ABSTRACT FROM AUTHOR]