Sharif Digital Repository

Microstructural characteristics and mechanical properties of a friction stir welded cast aluminum bronze (Cu-9Al-1Fe), produced by a sand casting method, have been investigated at tool rotation of 850-1500 rpm and traverse speed of 50-100 mm/min. Refinement of the primary coarse cast microstructure in the base metal was seen after friction stir welding. Microstructure of the stir zone was characterized in four distinct areas of non-isometric fine grains while a significant grain growth was noticed in some of the areas. Conditions of grain growth are defined with high heat input intensity and low heat transfer capability. The grain size was observed to decrease after FSW, resulting in a... 

Owing to the advantages of nanocomposites for structural applications, we present microstructural evolutions and texture development during dissimilar friction stir welding (DFSW) of an Al-matrix hybrid nanocomposite (Al-2 vol.-% Al2O3-2 vol.-% SiC) with AA1050. It is shown that DFSW can successfully be performed at a rotating speed of 1200 rev min−1 and a transverse speed of 50 mm min−1 while locating the nanocomposite at retreating side. Formation of macro-, micro-, and nano-mechanical interlocks between dissimilar base materials (BMs) as a result of FSW tool stirring action possessed an impact influence on the mechanical performance of dissimilar welds. Electron microscopy revealed... 

Manufacturing of complex-shaped bimetals utilizing two-color powder injection molding (2C-PIM) and three-dimensional printing (3DP) processes, which basically involve sintering of a powder/binder mixture, has been attracted a great interest. This article addresses sintering of biocompatible Co-Cr-Mo alloy for manufacturing stepwise porosity-graded composite structures. Such composite structures provide strength at the core and a porous layer for the tissue growth. To evaluate the process, two grades of gas atomized Co-Cr-Mo powder with an average particle size of 19 and 63 μm were used. Isothermal and nonisothermal sintering behavior of the loose powders under hydrogen and argon atmospheres... 

Mechanical properties and microstructural analysis of Expanded Perlite Aggregate (EPA) concretes are presented. Using 10% EPA, the effects of using various types of fibre were investigated. For all specimens, fibrous and non-fibrous, the compressive and the splitting tensile strengths were obtained. Complete stress–strain curves for fibre-reinforced specimens were obtained. A new index for representing the toughness of fibre-reinforced Perlite concretes is introduced. The addition of fibres substantially increased the splitting tensile strength. Steel fibres with “indentations” had the best performance in this regard. Regarding the toughness, specimens with “hooked” steel fibres performed... 

Owing to the advantages of nanocomposites for structural applications, we present microstructural evolutions and texture development during dissimilar friction stir welding (DFSW) of an Al-matrix hybrid nanocomposite (Al-2 vol.-% Al2O3-2 vol.-% SiC) with AA1050. It is shown that DFSW can successfully be performed at a rotating speed of 1200 rev min−1 and a transverse speed of 50 mm min−1 while locating the nanocomposite at retreating side. Formation of macro-, micro-, and nano-mechanical interlocks between dissimilar base materials (BMs) as a result of FSW tool stirring action possessed an impact influence on the mechanical performance of dissimilar welds. Electron microscopy revealed... 

Mechanical properties and microstructural analysis of Expanded Perlite Aggregate (EPA) concretes are presented. Using 10% EPA, the effects of using various types of fibre were investigated. For all specimens, fibrous and non-fibrous, the compressive and the splitting tensile strengths were obtained. Complete stress–strain curves for fibre-reinforced specimens were obtained. A new index for representing the toughness of fibre-reinforced Perlite concretes is introduced. The addition of fibres substantially increased the splitting tensile strength. Steel fibres with “indentations” had the best performance in this regard. Regarding the toughness, specimens with “hooked” steel fibres performed... 

Every year, about a thousand million tires reach the end of their service life, more than half of which are disposed of in landfills. The waste tire rubber has a great potential for application as aggregate phase in production of lightweight concrete/mortar. This study is aimed at evaluating the effects of using crumb rubber (CR) as fine aggregate at replacement ratios of 0–60% (by volume) in alkali-activated slag mortars. Furthermore, polypropylene fibre (PPF) was used at 0.5% and 1% of volume of the mix to enhance the properties of mortar mixes such as flexural strength and shrinkage behaviour. The compressive strength, flexural strength, water absorption, thermal conductivity, drying... 

This study was aimed at evaluating the effects of alkali activator solution and utilization of silica fume (SF) on durability and microstructural characteristics of alkali-activated ground granulated blast furnace slag (GGBFS) pastes. The pastes were activated with sodium silicate (SS) blended with NaOH (SH) solution with molar concentrations of 8 M, 12 M, and 16 M and SS:SH ratios of 1.0, 2.5, and 4.0. The same mixes were prepared with SF as partial replacement of GGBFS at a dosage of 10% by weight. The initial and final water absorption as well as the electrical resistivity of the specimens were measured. The optimal paste fabricated with 12 M NaOH solution and SS:SH ratio of 2.5 showed... 

An aluminum-magnesium alloy was friction-stir processed in the presence of TiO2 nanoparticles which were pre-placed in a groove on the surface to produce a composite. Field emission-scanning and transmission electron microscopy studies show that solid state chemical reactions occur between the Al-Mg matrix and the ceramic particles upon the severe plastic deformation process. The microstructure of the aluminum alloy consists of a coarse grain structure, large complex (Fe,Mn,Cr)3SiAl12 particles, and small Mg2Si precipitates. After friction stir processing, a deformed grain structure containing rod-like Al-Fe-Mn-Si precipitates is attained, along... 

Every year, about a thousand million tires reach the end of their service life, more than half of which are disposed of in landfills. The waste tire rubber has a great potential for application as aggregate phase in production of lightweight concrete/mortar. This study is aimed at evaluating the effects of using crumb rubber (CR) as fine aggregate at replacement ratios of 0–60% (by volume) in alkali-activated slag mortars. Furthermore, polypropylene fibre (PPF) was used at 0.5% and 1% of volume of the mix to enhance the properties of mortar mixes such as flexural strength and shrinkage behaviour. The compressive strength, flexural strength, water absorption, thermal conductivity, drying... 

This study was aimed at evaluating the effects of alkali activator solution and utilization of silica fume (SF) on durability and microstructural characteristics of alkali-activated ground granulated blast furnace slag (GGBFS) pastes. The pastes were activated with sodium silicate (SS) blended with NaOH (SH) solution with molar concentrations of 8 M, 12 M, and 16 M and SS:SH ratios of 1.0, 2.5, and 4.0. The same mixes were prepared with SF as partial replacement of GGBFS at a dosage of 10% by weight. The initial and final water absorption as well as the electrical resistivity of the specimens were measured. The optimal paste fabricated with 12 M NaOH solution and SS:SH ratio of 2.5 showed...