Sharif Digital Repository

The effect of the nucleating agent masterbatch carrier resin on the nonisothermal crystallization of a pipe-grade polypropylene block copolymer was investigated at three different cooling rates using differential scanning calorimetry (DSC). Bis(3,4-dimethylibenzylidene) sorbitol (DMDBS), a well-known, third-generation sorbitol derivative, was used as a nucleating agent in this study. Crystallization kinetic parameters obtained from DSC cooling curves showed that incorporation of a nucleating agent by means of a masterbatch increased the crystallization rate by approximately two times compared to that of the sample with the same concentration of nucleating agent without the use of a... 

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... 

Three steels were designed based on HSLA-100 with additional levels of Mn, Ni, Cr and Cu. The steels were prepared by controlled rolling and tempered at temperatures in range of 550-700°C. The continuous cooling time curves were shifted to longer times and lower temperatures with the increased tendency for the formation of martensite at lower cooling rates. The microstructures revealed that controlled rolling results in austenite with uniform fine grain structure. The steel with the highest amount of Mn showed the greatest strength after tempering at 750 °C. The top strength was attributed to the formation of Cu-rich particles. The steel with 1.03 wt.% Mn, tempered at 650 °C exhibited the... 

Nucleic acid amplification using polymerase chain reaction (PCR) method has been widely used in different fields such as agricultural science, medicine, pathogen identification, and forensics to name a few. Today, it seems inevitable to have a robust, simple PCR system for diagnostics at the point-of-care (POC) level. Many photonic PCR systems have been proposed in the literature that benefit from plasmonic photothermal heating to achieve the common PCR thermal cycling. However, non-homogeneous temperature distribution is a challenge in some of them. In the present work, to achieve more efficient gene amplification, the effect of adding TiO2 nanoparticles has been investigated in a photonic... 

The concept of critical ambient pressure is introduced in this paper. The particle escapes from its trap when the ambient pressure becomes comparable with or smaller than a critical value, even if the particle motion is cooled by one of the feedback cooling (or cavity cooling) schemes realized so far. The critical ambient pressure may be so small that it is not a limiting factor in ground-state cooling, but critical feedback cooling rates, which are also introduced in this paper, are limiting factors. The particle escapes from its trap if any of the feedback cooling rates (corresponding to the components of the particle motion) becomes comparable with or larger than its critical value. The... 

Nucleic acid amplification using polymerase chain reaction (PCR) method has been widely used in different fields such as agricultural science, medicine, pathogen identification, and forensics to name a few. Today, it seems inevitable to have a robust, simple PCR system for diagnostics at the point-of-care (POC) level. Many photonic PCR systems have been proposed in the literature that benefit from plasmonic photothermal heating to achieve the common PCR thermal cycling. However, non-homogeneous temperature distribution is a challenge in some of them. In the present work, to achieve more efficient gene amplification, the effect of adding TiO2 nanoparticles has been investigated in a photonic... 

The existence of universal semi-log linear relation between potential energy and cooling rate during the molecular dynamics simulations of metallic glasses for Cu-Zr system was formerly reported. For this purpose, different classes of metallic glasses are considered and the validity of this correlation is studied. It is shown that it holds for other thermodynamics potentials and some physical quantities like density and Wendt and Abraham parameter, too. This observation enables us to economically construct atomic scale metallic glass structures equivalent to very low cooling rates, more consistent to experimental works, not accessible using classic molecular simulations. © 2020 Elsevier B.V  

In the present study, the structural features, corrosion behavior, and in vitro bioactivity of TiO 2 nanotubular arrays coated on Ti–6Al–4V (Ti64) alloy were investigated. For this reason, Ti64 plates were anodized in an ammonium fluoride electrolyte dissolved in a 90:10 ethylene glycol and water solvent mixture at room temperature under a constant potential of 60 V for 1 h. Subsequently, the anodized specimens were annealed in an argon gas furnace at 500 and 700 °C for 1.5 h with a heating and cooling rate of 5 °C min −1 . From XRD analysis and Raman spectroscopy, a highly crystalline anatase phase with tetragonal symmetry was formed from the thermally induced crystallization at 500 °C.... 

Molecular dynamics (MD) simulations have been widely used to study the structure of metallic glasses (MGs) at atomic scale. However, ultrafast cooling rates in MD simulations create structures that are substantially under-relaxed. In this study, we introduce long-term pressurized annealing up to 1 μs slightly below the glass-transition temperature, Tg, in MD simulation, which effectively relaxes the structure of Cu64Zr36 MG toward experimental conditions. It is found that applying hydrostatic pressure up to 2 GPa relaxes the MG to low-energy states whereas higher pressures retard relaxation events. In the sample annealed at 2 GPa pressure, equivalent cooling rate reaches to 3.7 × 107 K/s,... 

In this study, graphene sheets and carbon nanotubes (CNTs) were selectively grown on Fe foil at a relatively low growth temperature and varying cooling rates using a hot filament chemical vapor deposition (HFCVD) apparatus with C2H2 as the precursor. The results of the scanning electron microscopy and Raman spectroscopy revealed that the increase of the cooling rate from 7 to 10 or 20 °C/min provoked a structure transition from CNT to graphene. The optimum crystal quality of the graphene sheets (Iq/Id ∼1.1) was achieved at the cooling rate of 20 °C/min. According to the AFM analysis, the thickness of the stacked graphene sheets was found to be ∼2.9-3.8 nm containing ∼8-11 monolayers. The XRD... 

Weldability is one of the key requirements for automotive materials. This two-part paper aims at understanding the metallurgical phenomena during resistance spot welding of stainless steels, as interesting candidates for automotive body in white. Part I addresses the phase transformations in the fusion zone of three types of stainless steels including austenitic, ferritic and duplex types. The solidification and solid state phenomena including columnar to equiaxed transition, ferrite– austenite post-solidification transformation, martensitic transformation and carbide precipitation are discussed. Particular attention is given to the effect of high cooling rate of resistance spot welding... 

Data are presented on the solidification of aluminum alloys and their macro segregation behavior. Three alloys with different solidification ranges were prepared in two temperatures. Two types of molds were also prepared by sand and metallic materials. The solidification of Al alloys were studied and the effects of four parameters were determined, including cooling rate, casting temperature, degassing and nucleation effects on solidification and a comparison was conducted to Scheil model performance. Three types of aluminum alloys (Al-12.1%Si, Al-6.9%Si and Al-4.4% Cu) with short, medium and wide solidification ranges were studied and the results showed that degassing, nucleation, increasing... 

An investigation was performed on the static strain aging behavior of warm-rolled low carbon steel during a nearly 1-year aging period, from the view point concerning with influence of changing the deformation speed and cooling media. Mechanical response of the examined material during aging period was evaluated through variations occurred in strength and hardness of the warm-deformed steel. It was shown that changing the rolling speed as well as cooling rate, may result in the occurrence of different metallurgical phenomena, consequently altering the aging kinetics of the material. It was also found that by increasing rolling speed, an increase in the value of hardness and UTS takes place,... 

In the present work, a mathematical model was developed based on finite difference method to predict the microporosity distribution in A356 aluminum alloy casting. Heat, mass, and gas conservation equations were solved in this model. Moreover, Darcy's equation was considered in the mushy zone. Results show that the distribution and concentration of microporosities in cast parts vary with both cooling rate and initial gas content. Simulation results were compared with experimental data where proportionally good agreement with experimental results was found. Finally, a complex cast part was simulated presenting the ability of the model to predict the porosities in industrial cast parts  

In this paper, effects of strain rate and mean strain on the cyclic behavior and the lifetime of aluminum-silicon alloys are investigated under thermo-mechanical and isothermal fatigue loadings. To achieve these goals, low cycle fatigue tests are accomplished at evaluated temperatures under various strain rates (by changing the loading frequency) and different strain ratios (minimum to maximum strain). Thermo-mechanical fatigue experiments are performed in an out-of-phase condition where the temperature varies between 50 and 250 °C. Various heating/cooling rates are taken into account to assess the strain rate effect and different starting temperatures are considered to study the mean strain... 

A molecular dynamics simulation study has been performed to investigate the solidification and remelting of aluminum using Sutton-Chen many body potential. Different numbers of atoms from 108 to 2048 atoms were considered to find an adequate size for the system. Three different cooling and heating rates, i.e. 10 12 K/s, 10 13 K/s and 10 14 K/s, were used. The structure of the system was examined using radial distribution function. The melting and crystallization temperatures of aluminum were evaluated by calculating the variation of heat capacity during the phase transformation. Additionally, Wendt-Abraham parameters were calculated to determine the glass transition temperature. It is shown... 

To predict the amount of different phases in gray cast iron by a finite difference model (FDM) on the basis of cooling rate (R), the volume fractions of total γphase, graphite, and cementite were calculated. The results of phase composition were evaluated to find a proper correlation with cooling rate. More trials were carried out to find a good correlation between the hardness and phase composition. New proposed formulas show that the hardness of gray cast iron decreases as the amount of graphite phase increases, and increases as the amount of cementite increases. These formulas are developed to correlate the phase volume fraction to hardness. The results are compared with experimental data... 

In this research, an algorithm based on the Q-state Potts model is presented for modeling the austenite to ferrite transformation. In the algorithm, it is possible to exactly track boundary migration of the phase formed during transformation. In the algorithm, effects of changes in chemical free energy, strain free energy and interfacial energies of austenite-austenite, ferrite-ferrite and austenite-ferrite during transformation are considered. From the algorithm, the kinetics of transformation and mean ferrite grain size for different cooling rates are calculated. It is found that there is a good agreement between the calculated and experimental results  

IN738LC is one of the superior nickel base superalloys utilized at high temperatures in aggressive environments. However, experiencing high temperatures and stresses during service causes microstructure deterioration and degradation of mechanical properties in this alloy. To restore the microstructure and mechanical properties of the degraded alloy, rejuvenation heat treatments can be considered. In this study, the evolution of microstructural features in a creep damaged IN738LC superalloy during different stages of rejuvenation heat treatment cycles was investigated. During solution treatment stage, dissolution of coarsened γ′ precipitates, grain boundary films and transition zone around... 

The present study investigates the evolution of γ′ precipitate microstructure in a creep damaged IN738LC superalloy during different stages of rejuvenation heat treatment cycles. Dissolution of coarsened γ′ precipitates in the creep damaged alloy occurred during different solution treatments. The precipitates that did not dissolve completely during solution treatment and those formed during subsequent cooling were considered to be as remnant and cooling precipitates respectively. It was found that higher solution treatment temperatures result in lower volume fraction of remnant precipitates and further formation of cooling precipitates. Slower cooling rates after solution treatment gave the...