Sharif Digital Repository

Finding the optimized set of manufacturing parameters to produce strong solder-copper connections requires investigating the main and interaction effects of processing variables on the joint strength and microstructure. In this study, solder joint specimens were prepared at different levels of cooling rate, time above liquidus (TAL), and soldering temperature. Mode I fracture experiments were designed and performed at a strain rate of 0.5 s−1. The fracture load remained constant from the cooling rate of 0.1 to 1.4 °C/s and then decreased by almost 34% with further increase in the cooling rate to 34 °C/s. Increasing TAL from 60 to 120 s reduced the fracture load by almost 27%, while it was... 

The nanocomposite Cu–Cr powder was consolidated by flash spark plasma sintering (FSPS), which involves applying an extremely rapid change in the electrical power passing through the bulk of the sample. It was demonstrated that an essentially fully dense material could be obtained in 15 s. Such short-term treatment typically preserves the nanostructured features of the material. However, investigation revealed a nonuniformity in the microstructure of the alloys obtained under such extreme conditions. To better understand the observed effects, the FSPS process was simulated. It was observed that a rapid change in the applied electrical power resulted in nonuniform distributions of current... 

Considering the microstructure-processing-properties relationship, the attempt was made to distinguish the main structural features of drip irrigation tape grades. In this regards, two different commercial polyethylene grades using for irrigation tape application (DB and MD samples) with various microstructural features were fully characterized by means of thermal, rheological and mechanical measurements and microscopic observations. A set of DSC techniques revealed that DB sample has faster crystallization kinetic probably due to its high crystallizable segments in chains and broad molecular weight distribution. It was found, the type of co-monomer used in DB sample is 1-hexene and in MD... 

The effects of zinc content (2 and 4 wt%), heat treatment (solution-Treated and T6), as well as hot deformation (extrusion and multi-directional forging (MDF)) on the microstructure, mechanical and degradation behavior of Mg-Zn alloys were studied. As the result of microstructure refinement, solid solution and precipitate strengthening (formation of MgZn second phases), the strength of pure Mg was increased after Zn addition. Solution treatment of the Mg-4Zn alloy resulted in 16% softening due to the dissolution of the MgZn second phases and also grain growth, while aging treatment increased the strength value by 8% in comparison to the as-cast material because of the formation of the fine... 

This paper deals with the effects of three low-carbon steel filler metals consisting of ferritic and austenitic phases on the weld joints of the tungsten inert gas (TIG) welding of Hardox 500 steel. The correlation between the microstructure and mechanical properties of the weld joints was investigated. For this purpose, macro and microstructure were examined, and then microhardness, tensile, impact, and fracture toughness tests were carried out to analyze the mechanical properties of joints. The results of optical microscopy (OM) images showed that the weld zones (WZ) of all three welds were composed of different ferritic morphologies, including allotriomorphic ferrite, Widmanstätten... 

In Mg–Si alloys, both primary and eutectic Mg2Si particles normally appear with sharp edges, which can lead to weak mechanical properties as the result of stress concentration at the sharp corners of these brittle particles. Thus, it would be of great importance to modify the morphology of these particles. In this study, microstructure modification mechanisms after 0.5 wt% Y addition and heat treatment (HT) at 420 °C for 24 h are comprehensively studied in hypo-eutectic Mg–1Si and hyper-eutectic Mg–2Si alloys. Microstructural observations were performed using optical and scanning electron microscopy equipped with electron disperse spectroscopy, while phase analysis was done by X-ray... 

This paper deals with an experimental investigation into the mechanical performance and microstructure characteristics of the cementitious mortars containing recycled waste materials subjected to acidic, neutral and alkaline environments. The recycled waste materials include glass, eggshell, iron and rubber powder in various amounts, namely 7, 14 and 21% by volume, as the replacement for ordinary Portland cement (OPC). In this respect, to examine the mechanical performance of the specimens, the compressive, tensile and bending strength tests as well as water absorption test were carried out at the ages of 7, 28 and 90 days. Moreover, to study the microstructure of the specimens, the scanning... 

Biodegradable magnesium (Mg) alloys exhibit great potential for use as temporary structures in tissue engineering applications. Such degradable implants require no secondary surgery for their removal. In addition, their comparable mechanical properties with the human bone, together with excellent biocompatibility, make them a suitable candidate for fracture treatments. Nevertheless, some challenges remain. Fast degradation of the Mg-based alloys in physiological environments leads to a loss of the mechanical support that is needed for complete tissue healing and also to the accumulation of hydrogen gas bubbles at the interface of the implant and tissue. Among different methods used to... 

In this research, the effect of applying severe strain before solid solution treatment (SST) for AA2024-O was studied. Providing concurrent insights into solutionizing behavior and microstructural evolution corresponding to hardness is important. Multi-directional forging (MDF) was used as a severe plastic deformation (SPD) method. After applying SST on MDFed (4 passes) and as-annealed samples, natural aging (NA) was used as the following treatment to examine the role of severe strain on the solutionizing behavior. In most previous attempts, SPD has been used after SST, but one of the innovations of the present work is the study of SPD before SST. Experimental results show that adding a... 

The effects of Sr additions, heat treatment (T4 and T6), and multi-directional forging on the microstructural evolution, mechanical properties and biodegradability of Mg-4Zn-xSr alloys were investigated. Corrosion behavior of the alloys was evaluated by the polarization and hydrogen evolution tests. Shear punch and hardness tests were employed to determine the mechanical properties. It was found that mechanical properties and corrosion resistance of the as-cast Mg-4Zn alloy increased by 0.3 wt% Sr addition. However, further increasing the Sr content not only did not improve the mechanical strength, but also had detrimental effects on the corrosion resistance, due to the increased size and... 

In this study, an attempt has been made to fabricate Cu-SiC nanocomposites by flake powder metallurgy and high-pressure torsion processing techniques at room temperature. Pure Cu and a mixture of Cu and nano-sized SiC powders were mechanically milled separately for 3 h and then green compacts were prepared by uniaxial pressing under 1 GPa pressure. The green compacts experienced 6-turn high-pressure torsion under a pressure of 6 GPa to prepare bulk Cu and Cu-SiC samples. The microstructures of the consolidated samples were characterized using an X-ray diffractometer and a high resolution scanning/transmission electron microscope, and the mechanical properties were evaluated by microhardness,... 

In this study, a pulsed Nd:YAG laser welding method is implemented to join Ti-G2 (1 mm thick) to AA3105-O (0.5 mm thick) via a ring of spots filled with AlScZr alloy (0.15 mm thick). The filler material improved the weld’s microstructure and mechanical properties by reducing the undesirable intermetallic compounds (IMCs) such as TiAl2 and TiAl3 in the aluminium re-solidified zone near the titanium/aluminium interface. The joints having AlScZr filler were mostly failed at Al heat affected zone (HAZ) during the tensile shear test. The addition of zirconium to binary Al–Sc system formed a substitutional solid-solution in which 50 wt% Zr+10 wt% Ti replaced Al3(Sc,Zr,Ti). Scandium had a... 

This study aims at investigating the effect of the substrate material on growth mechanism and also microstructure of Ta2O5 thin films. For this purpose, atomic force microscopy, scanning electron microscopy, and interferometry analyses were implemented to reveal the influence of silicon wafer and amorphous BK7 glass substrates on the nucleation and growth mechanisms of Ta2O5 thin films deposited via the radio frequency magnetron sputtering technique. Results indicated that those films with finer morphologies had relatively higher nucleation densities. Compared with BK7 glass substrate, crystals formed on the silicon wafer were shown to be finer and had lower mean areas in more nucleation... 

In this study, magnesium boro/carbothermal reduction of zirconium silicate (ZrSiO4) was employed to synthesize zirconium-based composite nanopowders of ZrB2–SiC, ZrB2–ZrC–SiC, ZrC–SiC, and ZrC. For this aim, three different temperatures of 1200 °C, 1300 °C, and 1450 °C were selected as the supposed temperatures for synthesis. Elemental Mg and NaCl were also selected to assist reduction process. In addition, effects of different C/Zr ratios as well as using elemental boron and B4C as two different boron sources were investigated on the final produced phases. Subsequently, XRD and SEM/EDS analyses were carried out to elaborate microstructure and phase studies. Finally, STA carried out up to... 

Abstract: Bead-on-plate submerged arc welding was conducted on St37 steel by manufactured Cr, Mo, and Cr–Mo active basic fluxes produced via the unfused bonded method. The base metal heat-affected zone and weld metal (WM) microstructures were identified and characterized by optical microscopy and scanning electron microscopy. Furthermore, each element’s recovery rate (η) and slag factor (α) determine the amount of element transferred from flux into WM. Then, the ferrite morphologies volume fraction of WMs was measured. Moreover, the chemical analysis of slag and inclusions was evaluated by point scan energy-dispersive X-ray spectroscopy and extensively discussed. The number density and... 

Surface integrity is one of the important parameters affecting the quality and functionality of mechanical components. This paper presents an investigation on effect of drilling parameter on the surface integrity of Inconel 718 through a combination of experimental and simulation works. The machining responses that are determined through the experimental work include microhardness, microstructure changes, and surface roughness. The average grain size of the microstructure of the workpiece is estimated by using a simulation model. The experimental and simulation results show that higher spindle speed facilitates the formation of white layer near the machined surface and decreases the average... 

There has been a growing demand for materials with superior absorption capabilities, such as strong absorbing capacity, thin thickness, and light weight, to solve challenges related to EM radiation pollution. While the majority of the research is focused on optimizing material compositions, component microstructure and absorber structure are also critical factors for improving microwave absorption performance. In this research, we show how the microstructure of components and absorber design may increase dissipation features. Solvothermal and hydrothermal methods were utilized for synthesizing mesoporous CuS micro-particles with a 3D hierarchical structure as a dielectric component and... 

Lightweight geopolymer concretes have gained attention because of their superior durability, lower environmental impact and sustainable characteristics. They are the product of natural or artificial aggregates with low specific gravities mixed with aluminosilicate binders, and an alkaline solution. In this study, different aspects of lightweight geopolymer concretes and mortars such as environmental and economic considerations, materials and mixture, durability-related properties like permeability, chloride attacks and performance at high temperatures, thermal conductivity, and the microstructure are reviewed. This study also discusses the effect of different geopolymer binders and various... 

Different heating rates of 200-1200 deg;C/s were utilized during ultra-rapid annealing (URA) up to the temperatures of 730 and 760 °C on the severely deformed low carbon steel. Higher hardness, strength and ductility achieved for the sample heated at 730 °C with 600 °C/s due to formation of bimodal grain size (BGS) microstructure than them for non-BGS samples. The BGS enhancement for the hardness, strength and ductility with respect to those of as received sample was 67%, 80% and 7%, respectively, and, with respect to those of severely deformed one was 16%, 44% and 24%, respectively. URA with the heating rate of 200 °C/s and 1000 °C/s leads to fully recrystallized and non-recrystallized... 

The effects of Sr additions (0.3, 0.6 and 0.9 wt%) on the microstructural evolution, thermal stability, and mechanical properties of a cast Mg–4Zn alloy were investigated. The extent of grain growth and stability of the intermetallic compounds were studied by optical and scanning electron microscopy (SEM), respectively. Mechanical properties of the studied alloys were evaluated by shear punch testing (SPT) method and also the hardness test. Hardness and shear strength of the base alloy were increased by Sr additions in the as-cast condition, due to the grain refinement effect of Sr and also presence of the Sr-containing Mg17Sr2 and Mg70Zn25Sr5 precipitates. However, the optimum amount of Sr...