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In situ aluminum matrix composites were fabricated by the addition of a gelated BS290 silicone polymer precursor to molten aluminum where the polymer gel was pyrolyzed in the melt and produced ceramic phases with chemical composition close to that of SiOC. The results indicated successful incorporation of in situ formed micro-sized particles in the melt, which acted as reinforcement and nucleation sites in the aluminum matrix. Homogeneous dispersion of the in situ formed particles in the matrix was attributed to rapid release of a large amount of gas during pyrolysis, which would disintegrate the particles’ agglomerates. The fabricated composites had mostly equiaxed and much finer grains than their corresponding monolithic cast sample. To improve SiOC particles’ distribution and to remove the structural porosity, both composite and monolithic samples were hot extruded at 400 °C. Hardness, yield strength and compressive strength of the extruded composite sample were found to be about 23, 53 and 18% higher than those of the extruded monolithic sample, respectively. Fractography of the fracture surface of the tensile test samples indicated a ductile fracture mode for both extruded samples. Elastic modulus mismatch was recognized as the main strengthening mechanism for the composite sample.

Dissimilar transient liquid phase (TLP) bonding between stainless steel 310 and Inconel 617 was carried out using a BNi-2 interface layer. TLP joints were fabricated at 1040, 1070 and 1100 °C for a bonding time of 60 min. In addition to microstructural evaluations, the mechanical properties of different TLP joints were also studied. The results indicated that increasing the bonding temperature resulted in decreasing the solidification zones and accelerating the formation of the intermetallic compounds. Among different TLP joints, the joint fabricated at 1040 °C exhibited the highest shear strength of 611 MPa. SEM investigations of the fractured surfaces revealed that the formation of higher amount of intermetallic compounds at higher temperatures deteriorated the shear strength of the Inconel 617/Stainless Steel 310 TLP joint.

In the present study, AA2024-SiO2np nanocomposites were prepared by the vortex method and effects of SiO2 content on resulting microstructural and mechanical properties were investigated. The results indicate that the addition of 0.5vol% of nanoparticles decreased the size of the dendrite cell intervals by about 16%. The observed mechanical properties exhibited an improvement of about 17, 28, 10, 157, 8 and 13%, in hardness, ultimate tensile strength, yield strength, tensile elongation, flexural and shear strengths, respectively. With more considerable additions of nanoparticles, scanning electron microscopy investigations confirm that there were more significant amounts of nanoparticle agglomerates in the microstructure, which reduced the mechanical properties of 1vol% SiO2np reinforced nanocomposite. The primary strengthening mechanisms evaluated appeared to be the effect of grain refinement (Hall–Petch), Orowan strengthening and the mismatch in coefficient of thermal expansion of the reinforcements and the matrix alloy. Evidence of some agglomerations of nanoparticles was recognized on the tensile fractured surfaces of the nanocomposites.

In this research the microstructure evolution and mechanical behavior of dissimilar weld between AISI 321 stainless steel (SS) and INCOLOY 825 using ERNiCrMo-3 (Inconel 625) filler wire were investigated. Electron back scattered diffraction (EBSD) analysis was used to characterize the weld substructure. The microstructural examination exhibited an austenitic matrix in either of the two base materials in which formation of Ti-bearing precipitates, more often with cubic morphology, were unveiled. An incomplete transformation of ferrite to austenite led to a significant accumulation of δ-ferrite at the heat affected zone (HAZ) of AISI 321 SS. An entirely austenitic structure accompanied by evidences of secondary phases, rich in Mo and Nb, at the inter-dendritic spaces in the weld metal were observed. Some columnar grains showed the direction parallel to the normal direction relationship. The grain orientation spread map indicated that misorientation variations within the weld metal grains were significantly higher than those of the base metals and HAZs. Texture intensities of HAZs were relatively low. The abnormal grain growth observed in INCOLOY 825 HAZ had a significant effect on orientations of the austenite grains. However, it did not weaken the tensile strength of the weldment. Tensile specimen failure from SS side indicated that this material was more feeble comparing to the INCOLOY one and the weld area. Presence of brittle phases at the inter-dendritic spaces led to a fall in the weld impact toughness in comparison with the parent materials.

Given the nonuse of TiO2 nanoparticles as the reinforcement of AA2024 alloy in fabricating composites by ex-situ casting methods, it was decided to process the AA2024−xTiO2(np) (x=0, 0.5 and 1 vol.%) nanocomposites by employing the stir casting method. The structural properties of the produced samples were then investigated by optical microscopy and scanning electron microscopy; their mechanical properties were also addressed by hardness and tensile tests. The results showed that adding 1 vol.% TiO2 nanoparticles reduced the grain size and dendrite arm spacing by about 66% and 31%, respectively. Also, hardness, ultimate tensile strength, yield strength, and elongation of AA2024− 1vol.%TiO2(np) composite were increased by about 25%, 28%, 4% and 163%, respectively, as compared to those of the monolithic component. The agglomerations of nanoparticles in the structure of nanocomposites were found to be a factor weakening the strength against the strengthening mechanisms. Some agglomerations of nanoparticles in the matrix were detected on the fractured surfaces of the tension test specimens.

Light-weight high-strength composites (particularly with aluminum and magnesium base alloys) have principal applications in a wide variety of fields ranging from automotive and aerospace structures to medical and energy applications wherein the materials undergo both static and dynamic (fatigue) loading conditions. Conventional metal matrix composites (MMCs), i.e. those filled by micro-sized reinforcements, have usually poor ductility and insufficient mechanical performance made them, therefore, unreliable to be used in some critical applications. Instead, those composites strengthened by nano-sized reinforcing agents, namely metal matrix nano-composites (MMNCs), have newly been developed in order to boost the mechanical properties. The current paper aims to study the fatigue behavior of the MMCs with a particular attention on recent investigations made on MMNCs. It is believed that the materials selection, microstructural features, manufacturing and processing parameters, etc. have a dominant influence on the fatigue response of MMNCs.

Effect of melt degassing on the hot tearing susceptibility of A206 alloy was examined using the ICTC apparatus. The results of thermal and load analyses, as well as macroscopic examinations, were then used to evaluate predictions of Davies’s criterion, Load Rate criterion and NNC. Load Rate criterion and NNC predicted that degassing increased the hot tearing susceptibility due to increasing the contraction load of the alloy which was consistent with the results of macroscopic investigation of the castings. Davies’s criterion predicted that degassing decreased the hot tearing susceptibility which was in contrast to the other two criteria and the actual observations.

Tribological behaviors of monolithic A356 aluminum alloy castings and A356−CNT nanocomposite castings, fabricated by fully liquid and semisolid routes were examined. Samples were prepared by melt agitation, rheocasting, stir casting, and compocasting techniques. Effects of addition of carbon nanotubes (CNTs), casting process and the applied load on wear properties and mechanisms were investigated. It was found that wear loss, wear rate and friction coefficient of nanocomposite samples remarkably declined by the addition of CNTs. Moreover, changing the casting process from fully liquid to semisolid routes, plus increasing fractions of the primary phase were the two factors that improved the wear properties of the investigated samples, especially nanocomposite ones. In addition, it was revealed that adhesion and delamination were the dominant wear mechanism of the monolithic samples produced by fully liquid and semisolid routes, respectively. However, regardless of fabrication techniques, the abrasion was the main wear mechanism of nanocomposite samples.

A facile and innovative method to improve bonding between the two parts of compound squeeze cast Al/Al−4.5wt.%Cu macrocomposite bimetals was developed and its effects on microstructure and mechanical properties of the bimetal were investigated. A special concentric groove pattern was machined on the top surface of the insert (squeeze cast Al−4.5wt.%Cu) and its effects on heat transfer, solidification and distribution of generated stresses along the interface region of the bimetal components were simulated using ProCAST and ANSYS softwares and experimentally verified. Simulation results indicated complete melting of the tips of the surface grooves and local generation of large stress gradient fields along the interface. These are believed to result in rupture of the insert interfacial aluminum oxide layer facilitating diffusion bonding of the bimetal components. Microstructural evaluations confirmed formation of an evident transition zone along the interface region of the bimetal. Average thickness of the transition zone and tensile strength of the bimetal were significantly increased to about 375 μm and 54 MPa, respectively, by applying the surface pattern. The proposed method is an affordable and promising approach for compound squeeze casting of Al−Al macrocomposite bimetals without resort to any prior cost and time intensive chemical or coating treatments of the solid insert.

The objective of this work was to investigate the thermal and mechanical interactions between the two components of a compound squeeze cast macrocomposite bimetal. First, an Al/Al–4.5wt.%Cu macrocomposite bimetal was fabricated by compound squeeze casting process. Then, heat transfer, solidification and distribution of the generated stresses along the interface region of the bimetal were analyzed using Thermo-Calc, ProCAST and ANSYS softwares, and structure, copper distribution and microhardness changes across the interface of the bimetal were studied. The results showed no noticeable change in the structure of the Al–4.5wt.%Cu insert and no obvious micromixing and diffusion of copper across the interface. Simulation results were in good agreement with the experimental ones only when an equivalent oxide layer at the interface was defined and its effect on heat transfer was considered. This layer caused up to 50% decrease in local liquid fraction formed on the surface of the insert. Simulation of the generated stresses showed a uniformly distributed stress along the interface which was significantly lower than the compressive strength of the oxide layer, resulting in its good stability during the fabrication process. It was postulated that this continuous oxide layer not only acted as a thermal barrier but prevented the direct metal–metal contact along the interface as well.

In this study, AA2024-(X vol.% SiO2np + Y vol.% TiO2np) (X, Y = 0.5, 1.0) hybrid nanocomposites were fabricated the via stir casting process and their structural and mechanical properties were examined. The results indicated that the grain sizes of the hybrid nanocomposites were reduced by the addition of nanoparticles into the matrix alloy. The analysis of mechanical properties also showed an increase of about 30, 36 and 7% in the hardness, tensile strength, and tensile yield strength, respectively. In the larger amounts of nanoparticles, scanning electron microscopy studies showed that there were more quantities of nanoparticles agglomerates in the structure, reducing the mechanical properties of the nanocomposite with 1 vol.% of SiO2 nanoparticles, as compared to the nanocomposite with 0.5 vol.% of SiO2 nanoparticles. The main strengthening mechanisms were estimated to be Hall-Petch strengthening, Orowan strengthening, and the coefficient of thermal expansion mismatch and elastic modulus mismatch between the reinforcements and the metal matrix. There was also some evidence showing some of the singular and agglomerated nanoparticles in the matrix on the fractured surfaces of the nanocomposites.

Metal matrix composites (MMCs) have been developed in response to the enormous demand for special industrial materials and structures for automotive and aerospace applications, wherein both high-strength and light weight are simultaneously required. The most common, inexpensive route to fabricate MMCs or metal matrix nanocomposites (MMNCs) is based on casting, wherein reinforcements like nanoceramics, -carbides, -nitrides, elements or carbon allotropes are added to molten metal matrices; however, most of the mentioned reinforcements, especially those with nanosized reinforcing particles, have usually poor wettability with serious drawbacks like particle agglomerations and therefore diminished mechanical strength is almost always expected. Many research efforts have been made to enhance the affinity between the mating surfaces. The aim in this paper is to critically review and comprehensively discuss those approaches/routes commonly employed to boost wetting conditions at reinforcement-matrix interfaces. Particular attention is paid to aluminum matrix composites owing to the interest in lightweight materials and the need to enhance the mechanical properties like strength, wear, or creep resistance. It is believed that effective treatment(s) may enormously affect the wetting and interfacial strength.

Effects of SIMA processing on size and shape of primary solid particles of Cu34wt.%Zn2wt.%Pb brass alloy was investigated. The optimal temperature for semisolid processing of the alloy was found to be around 890 °C using Thermo-calc simulation software. Liquid fraction sensitivity of the alloy around this temperature is 0.012. The results indicated the formation of non-dendritic microstructure even after 1 min holding of 10% cold worked sample at 890 °C. Sphericity of the primary solid particles increased by increasing the cold working ratio and holding time. The smallest size (103 μm) and highest shape factor (0.84) of the primary solid particles were achieved at 30% cold working ratio and 5 min holding time.

Semisolid casting and non-dendritic solidification of commercially pure tin (about 1 °C freezing range) and Zamak 3 alloy (about 10 °C freezing range) by a modified serpentine channel method were studied. It was shown that semisolid casting of very small freezing range metals with a non-dendritic structure was possible using this method. The results showed that the wall of the copper serpentine channel mold acted as a substrate for heterogeneous copious nucleation of primary solid particles and the channel provided sufficient self-steering action to disperse the nuclei in the melt. The average diameter and shape factor of the primary particles in the semisolid cast CP-Sn sample was measured to be about 107 μm and 0.75, respectively. The average diameter and shape factor of the primary particles in the semisolid cast Zamak 3 alloy was measured to be about 16 μm and 0.8, respectively. Hardness of semisolid samples was slightly higher than those of conventional gravity cast samples.

Composition effect of Inconel 625, Incoloy 65 and ER347 fillers on microstructural evolution and solidification crack (SC) sensitivity of gas tungsten arc welded Incoloy 825 to AISI 321 SS was investigated. The structure of welds had been mostly austenitic, and solute segregation caused formation of eutectic-nature secondary phases in inter-dendritic/cellular spaces of three weld alloys. The dilution effect led to a transition from FA to AF mode of solidification in ER347 weld and decreased its ferrite content. Inconel 625 and ER347 welds had the highest and lowest resistance to SC during Longitudinal Varestraint Test, respectively. Fine dendritic structure of Inconel 625 weld resulted in easier strain accommodation and better weldability properties of this alloy. Severe cracking and high sensitivity of ER347 weld to SC were characterized because of low ferrite content and easier wettability of solidification grain boundaries due to formation of low-melting Nb and Ti-rich phases. Inconel 625 filler could play an effective role in establishing an appropriate bridge in terms of thermal expansion coefficient between dissimilar parent metals.

This article presents the results of a comparative investigation on microstructure, mechanical properties and magnetic characteristics of aluminum matrix nanocomposites reinforced with nickel ferrite nanoparticles. Magnetic nickel ferrite (NiFe2O4) nanoparticles with average size of 35 nm were synthesized via citrate-nitrate route and were used as the reinforcement phase in commercially pure aluminum matrix. Aluminum matrix samples with 0, 1, 2.5, 5 and 10 wt% ceramic reinforcement were fabricated using the powder metallurgy process. The sintered samples were then extruded at 400 °C to improve the density and homogeneity of the composite. Optical microscopy, SEM, FESEM, densitometry, XRD, DSC and VSM analyses were all used to evaluate the microstructure, porosity distribution, density, existing phases, possible reactions between the matrix and the reinforcements and magnetic properties of the samples. The results showed that the relative density of the composites decreased as the reinforcement weight percent was increased. The samples yield stress and ultimate tensile strength increased by increasing the weight percent of the reinforcement up to 5 wt%, however, they dropped at 10 wt% reinforcement content. The compressive yield stress, magnetization and coercivity of the composites were all observed to increase as the reinforcement content increased. However, the elongation of composite samples decreased considerably as the reinforcement content increased.

Thermal and mechanical activation methods for crystallization of amorphous nano silica particles were investigated. Thermal crystallization of amorphous SiO2(np) was studied by differential scanning calorimetry as well as heating the amorphous particles under argon atmosphere. The results showed that crystallization of amorphous SiO2(np) started at temperatures above 700 °C and the synthesized crystalline silica had an average size of about 200 nm. Furthermore, 50 wt%Al-50 wt% amorphous SiO2(np) mixtures were mechanically activated at ambient conditions. The results showed that crystallization of amorphous SiO2(np) started after about 7.5 h of ball milling and reached its peak at 60 h. Longer milling times resulted in re-amorphization of part of the crystallized silica. The average size of crystalline SiO2(np) synthesized by mechanical activation was about 30 nm. A diffusion induced mechanism for crystallization of the amorphous nano silica, based on diffusion of aluminum atoms assisted by mechanical activation, was also proposed and discussed.

In the present study, variation in surface wetting behavior of a hypoeutectic cast iron with its microstructural features and surface roughness was investigated. Samples with an identical composition, i.e. Fe-3.2 wt%C.E., and different microstructures (a gray cast iron with A-type flake graphite and a white cast iron) were fabricated by gravity casting of molten cast iron in a chill mold at different cooling rates. A variation of surface roughness was also developed by polishing, a four-stage electroetching and a four-stage mechanical abrading on the samples. Roughness and water contact angles of all surfaces were then measured. The surface roughness factor and the solid fraction in contact with water by the Wenzel and Cassie-Baxter contact models were also calculated and compared with the corresponding measured contact angles to find out which regime was active. Results indicated that the surface microstructure and the type of constituents present at the surface influenced the cast iron surface wettability and that it was possible to change the surface contact angle by modification of the surface microstructure. The mechanically abraded gray cast iron followed the Wenzel-type regime while the electroetched surfaces of gray cast iron exhibited a transition from Wenzel to Cassie-Baxter type regime. In white cast iron, the results indicated Wenzel type behavior in the electroetched samples while for the mechanically abraded samples, none of these two models could predict the wetting behavior. Furthermore, the wetting angles of both gray and white cast irons were measured after 1, 2, 3 and 4 weeks of air exposure. The results showed that the wetting angles of both samples increased to above 90° after one week of air exposure which was likely due to adsorption of low surface energy hydrocarbons on the surfaces.

Metal matrix composites (MMCs) acquire their improved physical and mechanical properties through the careful reinforcement of their matrices by a variety of light but strong and stable reinforcemen...

Squeeze casting is a process in which a high external pressure is applied and maintained on the molten metal during the whole solidification process resulting in the lower porosity, higher solidification rate and improved mechanical properties. In this research, the effects of applied pressure on the morphology of graphite flakes in a squeeze cast hyper-eutectic grey cast iron were investigated. The molten grey cast irons were solidified under atmospheric pressure as well as 25, 50 and 75 MPa externally applied pressures. The results indicated that the pressure increase during solidification decreased the amount of free graphite flakes, reduced the size of pro-eutectic Kish graphite flakes and increased the density of the castings. D-type graphite enclosing austenite dendrites, resembling that expected in hypo-eutectic grey cast iron, was observed near the surfaces of the castings solidified under externally applied pressures. Moreover, some compacted and spheroidal graphite particles were observed in the castings solidified under 50 and 75 MPa pressures. Furthermore, by increasing the squeeze casting pressure from atmospheric pressure to 75 MPa, the hardness, ultimate tensile strength and elongation increased by about 13, 68 and 128%, respectively. The results have been discussed in terms of increased cooling rate, expected change in the phase diagram of the alloy, different atomic structure of the interfaces of graphite and austenite as well as some proposed theories for formation of eutectic cells and spheroidal graphite.

Aluminothermic reaction between aluminum and a metallic oxide is worth noting, because it is applicable in some applications such as in-situ aluminum/alumina composites synthesis, welding, etc. All the metallic oxides with Gibbs free energy of formation higher than Al2O3 can be used as the reactant oxide. Among them, the aluminothermic reaction between Al and ZnO is thermodynamically possible, because its free energy change is negative, even at room temperature. Depending on the processing method, part of the reduced Zn can be vaporized during the procedure, while the rest remains in the Al matrix. This paper attempts to review the published research works on Al/ZnO aluminothermic reaction by different processing routes giving an overview of the reactions in the liquid and solid state processes. Highlighting the technical barriers against the aluminothermic reaction propagation in Al/ZnO system, discussing the effects of different approaches on the ignition temperature as well as demonstrating how the reaction is kinetically possible even at ambient temperature are the main aspects of the present review paper. Moreover, the mechanism of the reaction and microstructural properties of the products are discussed in details. It was shown that aluminothermic reaction in the liquid state processes might be hindered kinetically due to poor wettability between aluminum and zinc oxide particles. Moreover, the results revealed that the combined mechanical and thermal treatments and mechanochemical methods facilitate the aluminothermic reaction compared to exothermic dispersion (XD). Changing the diffusion mode from bulk diffusion to grain boundary diffusion was considered as the main reason.

The growing need to develop cost-effective and efficient alloys requires enhancing the flexibility of the current production methods. Additive manufacturing (AM), as an emerging technology, has re-shaped the manufacturing strategies and largely influenced the industrial production lines. The feedstock, the main concern with regard to the powder-based AM methods, are mostly in the form of pre-alloyed powders. Pre-alloyed powders have a narrow composition range, suffer from limited availability and are expensive, making additive manufacturing of new alloys inflexible and costly. A growing number of works in the literature are dedicated to AM in-situ alloying, i.e. employing pure elemental blends as opposed to pre-alloyed ones for producing samples using additive manufacturing. This strategy gives added flexibility to the AM methods by benefiting from the laser local energy and paves the way towards an on-demand alloy design framework that is proportionate to the growing needs of the industry. This review is intended to shed light on the key components of AM in-situ alloying process, from initial blend preparation to requirements for the final composition homogeneity.

In this study, a facile method was employed for synthesis of amorphous ceramic nanoparticles from the commercially available BS290 polymer. The polymer precursor was found to be a silane compound using gas chromatography technique. The polymer was processed by sol-gel and pyrolysis methods and the product was characterized by FESEM, BET, FTIR, XRD and TG techniques. The synthesized particles were found to be amorphous silicon oxycarbide (SiOC). Particles of the ammonia derived powder were nano-size and the surface area of the powder was 191 m2/g. It was found that the synthesized powders in the base medium were finer (nano-size) as compared to that produced in the ethanol medium.

In this study, the effects of pouring temperature (solid fraction of primary particles) on the structure and liquid segregation behaviour of a cup-shaped semi-solid rheocast processed casting made from the A356 aluminium alloy were investigated. Results showed that the solid fraction of primary particles at the bottom of the castings was greater than in other parts of the castings, and the highest liquid segregation occurred in the mid-height (wall) of the castings. Liquid segregation was increased with an increase in the initial solid fraction of primary particles. The critical solid fraction at pouring for minimum liquid segregation was found to be approximately 25%.This paper is part of a thematic issue on Light Alloys.

In this paper, the optimization of the surface composite of Mg AZ31B-carbon nanotub(CNT) via friction stir processing was investigated. Then, the most effective process parameters such as transverse speed, rotational speed, CNT weight percent and welding passes were studied by Response Surface Methodology (RSM) design of experiment. The specimens were also characterized by micro-hardness, tensile, shear punch and pin on disk dry sliding wear tests. The optimization results of hardness and weight reduction responses showed that the best conditions would be achievable with a transverse speed of 24 mm/min, rotational speed of 660 rpm, 4wt.% CNT and 3 welding passes. Moreover, fracture analysis of the surfaces proved auniform distribution of CNTs in the matrix resulted in higher tensile and shear strength. &nbsp

A nanocomposite obtained by introduction of carbon nanotubes into the surface layer of magnesium alloy AZ31B by the method of friction stir processing is studied. Dependences of the hardness and wear resistance on the speed of motion of the friction tool, the speed of rotation of the friction head, the number of passes of the tool and the relative content of carbon nanotubes in the layer are determined. The method of design of experiment is used to find the optimum modes for production of a nanocomposite with high hardness and wear resistance.

A413 aluminum matrix composites reinforced with short carbon fibers (CSFs) were produced using a combination of vortex and squeeze casting processes and the effects of reinforcement volume fraction and reinforcement coating on density, porosity, reinforcement distribution and mechanical properties of the produced composites were studied. The results showed that increasing the volume fraction of CSFs led to decreased density and increased porosity of the cast composites. Distribution of uncoated CSFs in the matrix of the reinforced samples was poor and most of the fibers were in agglomerated bundle form. Utilization of coated CSFs resulted in a rather uniform distribution of the reinforcement in the matrix. Mechanical properties of squeeze cast composites fabricated using uncoated CSFs improved by increasing the reinforcement volume fraction up to 2% and decreased beyond it. Mechanical properties of the squeeze cast composites fabricated using coated CSFs improved steadily by increasing the reinforcement volume fraction up to 3%. Ultimate tensile strength and hardness values of the composites reinforced with 3 vol% coated CSFs increased by more than 100% and 60%, respectively, in comparison with those of the monolithic cast sample.

In this study, in situ aluminum matrix composites were synthesized through pyrolysis of high temperature vulcanization silicone in commercially pure aluminum melt. For this purpose, 1 to 4 wt% of high temperature vulcanization silicone was added to a vortex of molten aluminum at 750℃ and the resulting slurries were cast in steel dies. Microstructure, hardness, and tensile properties of the as-cast samples were examined at ambient and high temperatures. The results revealed the in situ formation and distribution of reinforcement particles in the matrix. Energy-dispersive X-ray analysis indicated that the formed reinforcement particles consisted of O and Si elements. This confirms the in situ reinforcement formation by pyrolysis of high temperature vulcanization silicone in the melt. The size of the in situ formed particles was mostly in the range of 200–2000 nm. It was shown that the composites synthesized by the addition of 4 wt% high temperature vulcanization had the highest mechanical properties both at ambient and high temperatures. Room temperature hardness, tensile strength, and yield strength of this sample were increased by about 50%, 23%, and 19% compared to the monolithic sample, respectively.

Sn-0.7Cu is among the least expensive types of lead-free solders available. However, its poor mechanical properties have limited its application. In this study, Sn-Cu lead-free solder reinforced with amorphous silica (SiO2) nanoparticles was synthesized through powder metallurgy route. Desired mixtures of raw materials was mechanically milled, compressed, sintered and extruded to prepare bulk solder samples. The samples were characterized by optical and electron microscopy as well as mechanical tests. The results showed that mechanical properties were increased by addition of SiO2 nanoparticles to the solder matrix. Addition of 1.5 wt% ceramic reinforcement to the composite increased tensile, yield and compressive strengths up to 27%, 23% and 41%, respectively, compared to those of the monolithic sample. In addition, the ceramic nanoparticles caused an up to 50% decrease in the wetting angle between the substrate and the nanocomposite solder.

Additive manufacturing has emerged as a promising method for developing new Ti-based alloys. However, very few works have been dedicated to the in-situ synthesis of Ti-Cu alloys using Laser powder bed fusion (LPBF) method. The current work investigates the correlations between the volumetric energy density (VED) and some structural features of the in-situ Ti-5 wt.% Cu alloys produced by LPBF of the elemental powders. The results highlighted the importance of selecting the size of constituents in accordance with their thermophysical properties. It was also shown that crystallite size and lattice distortion of the α phase increased with increasing the VED. These were attributed to the higher temperature and lower cooling rate of the melt pools as well as improved particles melting and copper dissolution in the titanium lattice at higher VEDs. Isotropy of the microstructure was also improved at higher VEDs.

In the original version of the online article Beitallah Eghbali’s family name was misspelled. The original article has been corrected.

The present research investigates the ability of the Lipton–Glicksman–Kurz (LGK) model in predicting dendritic growth velocity under an applied electric field. In order to solve the LGK model, the stability criterion, σ*, was first calculated. It was found that σ* was not constant and was reduced by applying the electric field and decreasing the growth velocity. The decrease in the σ* means the increase in the possibility of formation of side branches in the dendrites as well as the hills in the interface. The growth velocities predicted by the model were less than those obtained experimentally. This could be due to the failure of the LGK model to consider convection. The results showed that, by changing the distribution coefficient, the accuracy of the model could increase. Despite some differences in the point-to-point comparison between the model results, the predicted general trend was correct.

Internal defects are among the problems in gravity casting of aluminum parts. The main internal volumetric defects are gas and shrinkage defects which form during solidification of the melt and drastically reduce the quality of the produced parts. These defects adversely affect the mechanical properties of thin walled castings parts. In this study, ceramic nanoparticles coatings were applied on the sand mold and the effect of mold coatings on the reduction of defects were investigated. X-ray radiography was used to detect defects in sand molds with ceramic nanoparticles coatings. For comparison, this test was performed on molds with micro-ceramic and graffiti coatings and uncoated sand mold. The results showed that the maximum amount of gas and shrinkage defects was observed in casting parts from AL4-1 alloy in uncoated molds. On the other hand, the minimum defects were found in molds coated with ceramic nanoparticles. It seems that the reduced defects in casting parts in molds coated with ceramic nanoparticles may be due to high thermal and chemical stability and higher heat transfer rate of the coating. These results can facilitate the production of high quality aluminum alloys parts using nanotechnology.

In the present research, the possibility of single stage semi-solid casting of a hypereutectic gray cast iron in a sand mold was investigated. For this purpose, a specially designed chilled sprue sand mold rigged to a vertical centrifugal casting machine was used. The molten cast iron was poured in the chilled sprue sand mold at 1275 oC at a rotation speed of 400 rpm. Two control samples were also poured at 1275 oC under gravity and centrifugal casting conditions in the same mold without sprue chilling. Microstructures and mechanical properties of the specimens were then characterized. The results showed that the average length and thickness of the primary solid phase, i.e. the Kish graphite, and those of the eutectic flake graphite were smaller in semi-solid centrifuged castings and their hardness were higher than those of the control samples. The results are discussed in terms of the shearing and chilling effects of the designed sprue during the initial stages of pouring.

In this study for the first time, the effects of decrease in heat inflow to the weld metal in friction stir process by utilising semisolid processing and decreasing the pin rotational speed as well as increasing the pin transverse speed were examined. As a result, the characteristic loss of hardness and strength in the weld zone were eliminated. The results showed that by approaching the ultrafine microstructure in the weld zone through the hybrid FSW/SSW process, the hardness and elongation values reached to 90 Hv and 8.88%, respectively. These are only slightly different from those of the base metal of the welded samples. Furthermore, the ultimate tensile strength of the samples welded by the hybrid technique was found to be about 167 MPa that was higher than those of the samples welded by friction stir welding (151 MPa) and semisolid welding (114 MPa) techniques.