Sharif Digital Repository

While it is well recognized that microstructure controls the physical and mechanical properties of a material, the complexity of the microstructure often makes it difficult to be simulated by analytical or numerical techniques. In this paper we present a suitable approach to compute microstructures within a casting using the finite element technique. This technique allows implementing microstructure data from experiments and equations that describe microstructure as function of local solidification parameters. The comparison of this model's predictions with the ones in the literature and also experimental measurements of secondary dendrite arm spacing, average length and diameter of silicon... 

Isothermal solidification is a key feature of transient liquid phase bonding which prevents the formation of deleterious intermetallic phases in the joint centerline and results in bonds with improved mechanical performance. This paper discusses the metallurgical characteristics and mechanical properties of an as-cast IN718 superalloy bonded by diffusion-induced isothermal solidification of Ni-7Cr-4.5Si-3.2B-3Fe (wt%) filler metal. After transient liquid phase bonding of as-cast IN718 at 1000 C for 60 min, a bond exhibiting a solid solution microstructure with joint efficiency of 72% in terms of shear strength was obtained. The joining process was effectively able to prevent the formation of... 

The microstructural evolutions and mechanical properties of vanadium microalloyed steel (30MSV6) during precipitation hardening were studied. The effects of aging temperature and cooling rate on mechanical strength (yield strength and ultimate tensile strength) were similar. Increasing aging temperature or cooling rate firstly increased the mechanical strength of specimens up to their maximum values, which then decreased with further increase in aging temperature or cooling rate. Microstructural evolutions revealed that cooling rate had significant effects on the pearlite interlamellar spacing and size of pre-eutectoid ferrite. Unlike the effect of austenitizing temperature, the pearlite... 

Activities conducted in this study can be divided into two general sections: synthesis and analysis and identifies the properties. A geopolymeric cement production process includes two steps of thermal activation and alkaline activation. Geopolymers are cementitious materials synthesized by a polycondensation reaction between an aluminate and silicate. The geopolymeric structures of the products were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). XRD results showed that there are no significant differences between the XRD patterns of geopolymers and metakaolin. The structure of the geopolymer is typically... 

The preparation of high aspect-ratio TiO2 nanotubes and their photocatalytic activity were demonstrated in this study. The high aspect-ratio TiO2 nanotube thin films were produced by electrochemical anodic oxidation of Ti in chloride-containing electrolytes. Nanotubes were doped with different concentrations of ZnO particles through anodization. The catalytic behavior was evaluated under batch reactor with photo-degradation test of Red Dye. The experimental results collectively demonstrate the successful ZnO doping of the resultant nanotube layers with significant abundant OH groups on their increased surfaces. The nanotubes doped with high content combined with an anatase as a two phase... 

In this study, microstructural aspects that control fracture and deformation resistance of P/M materials are evaluated. Several low-alloy steels were produced under both experimental and commercial conditions for achieving different matrix phases and porosity levels with varying shape factors. A 'porosity map' was constructed and used for a quantified study of the dominant mechanism controlling mechanical behaviors. The role of inclusion gathering and secondary pores, as well as sintering mechanism and alloying method is considered and discussed. The mechanism assessment was performed by using microstructure examination through optical and scanning electron microscopy. The results... 

In the present work, fcc-Al nanoparticle development in Al90−xNi10MMx (MM: Ce mischmetal; x=2, 4) amorphous alloys was studied via non-isothermal differential scanning calorimetry, X-ray diffraction, transmission electron microscopy, and nanoindentation test. Results showed that the crystallization of Al88Ni10MM2 alloy occurred by the precipitation of fcc-Al nanoparticles followed by the crystallization of Al11MM3 and Al3Ni phases. Transmission electron microscopy revealed that the aluminum precipitates had an average size of ~12 nm with a round morphology. Increasing the mischmetal content to 4 at% (Al86Ni10MM4 alloy) caused a three-stage crystallization process with a change in the size... 

Cu/SiC nanocomposite powders with homogeneously distributed nanosize SiC particles were produced by high energy mechanical milling (MM). Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and micro-hardness and density measurements were performed to understand the effects of microstructure and hardness on compaction behavior during MM. The effects of SiC nanoparticle content and mechanical milling time on apparent density (AD) and tap density (TD) of the nanocomposite powders were systematically investigated. The Hausner ratio (HR), defined as TD to AD, were estimated to evaluate friction between the particles. Increasing MM duration and SiC content resulted... 

The microstructural characteristic of HSLA welds containing different amounts of titanium were evaluated carefully. It was observed that the microstructure of welds consisted of ferrite with mixed morphologies, and small amounts of pearlite and martensite-austenite micro-constituents. Because of insufficient time for diffusion of carbon, formation of pearlite lamellae could not be completed in the weld region. Martensite was formed from carbon enrichment of austenite during nucleation and growth of acicular ferrite and bainitic ferrite. While coarse manganese sulfide particles had weak interface strength with matrix and formed some micro-fissures; increasing titanium amount of welds... 

Non-isothermal differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to study the nucleation and crystallization behavior of mica glass-ceramics with LiF as nucleating agent. The models enabled establishing the kinetic parameters for crystal growth of individual phases. The activation energies for crystal growth were found to be in the range of 161-301 KJ/mol, 416-424 KJ/mol, and 583-1011 KJ/mol for base glasses, samples with substitution of Li2O for K2O and samples with addition of LiF, respectively. Formation of transparent glass-ceramics from studied glass-samples has been investigated. Transparency is assumed to occur in the... 

Shot peening process is one of the severe plastic deformation methods which is well-recognized for the surface layer integrity of the components. This process, according to its energy level, can be categorized into three different cases of conventional, severe, and over shot peening. The aforementioned types of shot peening have positive and/or negative effects on their related performing conditions. In this study, the boundaries between these processes were determined for the first time by presenting novel approaches. The foundations of the presented approaches are microstructural investigations. The microstructures were characterized using optical microscopy, scanning electron microscopy,... 

B The combined influence of both melt filtration and cooling rate on the microstructure and mechanical properties of A356 cast alloy was studied. A step casting model with five different thicknesses was used to obtain different cooling rates. The effect of melt filtration was studied by using 10 and 20 pores per inch (PPI) ceramic foam filters in the runner. Results showed that secondary dendrite arm spacing decreased from 80 μm to 34 μm with increasing cooling rate. Use of ceramic foam filters in the runner led to the reduction of melt velocity and surface turbulence, which prevented the incorporation of oxide films and air in the melt and consequently had an overall beneficial effect on... 

The role of lubrication procedure on the consolidation behavior of metallic powders and subsequent microstructural development during sintering was investigated. Iron powder and iron-0.8 w/o graphite powder mixture were used as model materials. The effects of die wall lubrication procedure were compared to the traditional admixed powder lubrication method. The influences of manufacturing parameters such as the compacting pressure in the range of 150-800 MPa and the sintering temperature from 400 to 1300 °C were studied. It was found that the lubrication procedure has a great influence on the consolidation and microstructural features of the materials investigated. Admixed lubricant aids the... 

Dolomite base refractories have advantages such as high refractoriness, potential to produce pure steel molten, high alkaline corrosion resistance, and economical for consumers. However, application of these refractories has been limited due to their high potential to hydration with atmosphere humidity. In this research work, the impact of ZrSiO4 nanoparticles addition on the physical, thermo-mechanical, mechanical, and microstructure of the dolomite base refractories is investigated. Also, XRD and SEM/EDX analyses were used for determining generated ceramic phases and microstructure evaluation, respectively. Up to 3 wt% ZrSiO4 nanoparticles were added to the compositions. Compositions fired... 

Metallic or ceramic micro/nanoporous materials have attracted particular attention due to some interesting structural and functional properties. There exist a variety of methods for producing porous materials by which optimized features can be reached. Spark plasma sintering (SPS) is one of these new-emerging approaches. This technique is often combined with conventional technologies and produce a variety of porous structures with tailorable microstructure and physicomechanical properties. This review addresses SPS and obtainable porous materials with nanoscale and microscale microstructural features. The processing methods, microstructural phenomena, and physicomechanical properties of... 

In this work, cavitation during creep in AA7075-T76 was simulated employing a probabilistic cellular automata scheme. Two-dimensional cellular automata coupled with the governing equations for cavity growth were utilized to define the size and distribution of cavities during creep. Both diffusion and strain-controlled mechanisms were taken into account while the first and second neighboring cells were considered for determination of the cavity growth as well as to generate the initial microstructure. Moreover, uni-axial creep experiments on AA7075-T76 were carried out under different temperatures and applied stresses including 170 MPa at 150 °C and 150 MPa at 160 °C. The microstructural... 

Aluminum matrix nanocomposites were fabricated via friction stir processing of an Al–Mg alloy with pre-inserted TiO2 nanoparticles at different volume fractions of 3%, 5% and 6%. The nanocomposites were annealed at 300–500 °C for 1–5 h in air to study the effect of annealing on the microstructural changes and mechanical properties. Microstructural studies by scanning and transmission electron microscopy showed that new phases were formed during friction stir processing due to chemical reactions at the interface of TiO2 with the aluminum matrix alloy. Reactive annealing completed the solid-state reactions, which led to a significant improvement in the ductility of the nanocomposites (more... 

Aluminum matrix nanocomposites were fabricated by friction stir processing of Al–Mg alloy sheets with pre-placed TiO2 nanoparticles at a concentration of 2 to 6 vol%. Microstructural studies showed that solid state reactions between the metal matrix and TiO2 particles caused in situ formation of MgO and Al3Ti nanophases with an average size ~50 nm. These nanophases were homogenously distributed in an ultra-fine grain structure (0.2–2 µm) of the base metal. The results of pole figures evaluation obtained by electron back scattered diffraction studies revealed that the random orientation of initial annealed sheet was changed to components near to shear and silver texture in the friction stir... 

Nanostructured AA6063 (NS-Al) powder with an average grain size of ∼100 nm was synthesized by high-energy attrition milling of gas-atomized AA6063 powder followed by hot extrusion. The microstructural features of the consolidated specimen were studied by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques and compared with those of coarse-grained AA6063 (CG-Al) produced by hot powder extrusion of gas-atomized powder (without using mechanical milling). The consolidated NS-Al alloy consisted of elongated ultrafine grains (aspect ratio of ∼2.9) and equiaxed nanostructured grains. A high fraction (∼78%) of high-angle grain boundaries with average...