رشد سلولی و دندریتی Cellular and dendritic growth

Cellular and dendritic growth

رشد سلولی و دندریتی 

ABSTRACT

Many of the alloys used in practice, such as steel, aluminum-copper alloys, nickel-base and copper-base alloys, are single phase alloys, which means that the final product of solidification is a solid solution. Depending on the thermal and compositional field, cellular or, in most practical cases, dendritic morphology will occur. In other cases, even when the room temperature microstructure is mostly eutectic some primary phases solidify before the eutectic. They can be solid solutions, carbides, intermetallic phases, inclusions, etc. Their morphology affects mechanical properties, and thus, understanding how this morphology can be controlled is a mater of significant practical importance. A detailed discussion of primary phase growth, and in particular of dendrite growth, will be provided in the following sections.

 

طیف سنجی تبدیل فوریه فروسرخ ( FTIR )

FTIR - fourier transform infrared spectroscopy

طیف سنجی تبدیل فوریه فروسرخ ( FTIR )

ABSTRACT

The physical principles underlying infrared spectroscopy have been appreciated for more than a century. As one of the few techniques that can provide information about the chemical bonding in materials , it is particularly useful for the nondestructive analysis of solids and thin films, for which there are few alternative methods. Liquids and gases are also commonly studied , more often in conjuction with other techniques. Chemical bonds vary widely in their sensitivity to probing by infrared techniques.

 

خوردگی حفره‌ای در جوش فلزات فولاد ضد زنگ سوپر دوبلکس

Effects of Heat Input on Pitting Corrosion in

Super Duplex Stainless Steel Weld Metals

اثر حرارت ورودی بر خوردگی حفره‌ای در جوش فلزات فولاد ضد زنگ سوپر دوبلکس

ABSTRACT

Due to the difference in reheating effects depending on the heat input of subsequent weld passes, the microstructure of the weld metal varies between acicular type austenite and a mixture of polygonal type and grain boundary mixed austenite. These microstructural changes may affect the corrosion properties of duplex stainless steel welds. This result indicates that the pitting resistance of the weld can be strongly influenced by the morphology of the secondary austenite phase. In particular, the ferrite phase adjacent to the acicular type austenite phase shows a lower Pitting Resistance Equivalent (PRE) value of 25.3, due to its lower chromium and molybdenum contents, whereas the secondary austenite phase maintains a higher PRE value of more than 38. Therefore, it can be inferred that the pitting corrosion is mainly due to the formation of ferrite phase with a much lower PRE value.

 

فشار انفجاری لوله‎های فولاد زنگ‎نزن تحت کشش، فشار و دمای بالا

Burst pressure of super duplex stainless steel pipes subject to

combined axial tension, internal pressure and elevated temperature

فشار انفجاری لوله‎های فولاد زنگ‎نزن ابردوتایی در معرض سه مشخصه‎ی

کشش محوری ترکیبی، فشار داخلی و دمای بالا

ABSTRACT

The burst pressure of super duplex stainless steel pipe is measured under combined internal pressure, external axial tension and elevated temperature up to 160 °C. The experimental results are compared with existing burst pressure prediction models. Existing models are found to provide reasonable estimate of the burst pressure at room temperature but significantly over estimate the burst pressure at elevated temperature. Increasing externally applied axial stress and elevated temperature reduces the pressure capacity.

 

رفتار یک لوله‌ی فولاد زنگ نزن دوفازی با جوش‌کاری محیطی تحت فشار خارجی

Behavior of a girth-welded duplex stainless steel pipe underexternal pressure

رفتار یک لوله‌ی فولاد زنگ نزن دوفازی با جوش‌کاری محیطی تحت فشار خارجی

ABSTRACT

This study attempts to investigate the effects that external pressure has on the residual stress behavior in a girth-welded duplex stainless steel pipe. At first, FE simulation of the pipe girth welding is performed to identify the weld-induced residual stresses and depressions using sequentially coupled three-dimensional (3-D) thermo-mechanical FE formulation. Then, 3-D elastic–plastic FE analysis is carried out to evaluate the residual stress redistributions in the girth-welded pipe under external pressure. The residual stresses and plastic strains obtained from the thermo-mechanical FE simulation are employed as the initial condition for the analysis. The FE analysis results show that the hoop compressive stresses induced by the external pressure significantly alter the hoop residual stresses in the course of the mechanical loading, i.e. the hoop residual stress distributions on both surfaces of the pipe weld shift downward considerably, whilst the axial residual stresses are little affected by the superimposed external pressure.

 

تاثیر عناصر آلیاژی بر ریزساختار و خواص شکست غلتک‌های فولادی تندبر

Effects of alloying elements on microstructure and fracture properties of cast high speed steel rolls

Part I: Microstructural analysis

تاثیر عناصر آلیاژی بر ریزساختار و خواص شکست غلتک‌های فولادی تندبر

بخش اول: آنالیز ریزساختاری

ABSTRACT

A study was made of the effects of alloying elements on microstructural factors of six high speed steel (HSS) rolls manufactured by centrifugal casting method. Particular emphasis was placed on the role of hard carbides located along solidification cell boundary and the type of the martensite matrix. Microstructural observation, X-ray diffraction analysis, and hardness measurement were conducted on the rolls to identify carbides. Various types of carbides were formed depending on the contents of strong carbide forming elements. In the rolls containing the high Cr content, MC carbides inside cells and M7C3 carbides along cell boundaries were primarily formed, while in the rolls containing the high W and Mo contents, MC carbides inside the cells and fibrous M2C carbides in the intercellular regions were dominantly formed. The most important microstructural factor affecting overall roll hardness was the intercellular carbides and their distribution. The effects of alloying elements were analyzed on the basis of the liquidus surface diagram, suggesting that the proper contents of carbon, tungsten, molybdenum, chromium, and vanadium were 1.9–2.0, 3–4, 3–4, 5–7, and 5–6%, respectively.

 

سینتیک استحاله های مارتنزیتی در فولادها

Kinetics of martensite transformations in steels

سینتیک استحاله های مارتنزیتی در فولادها

ABSTRACT

Dislocation theory of the mechanism and kinetics of martensitic transformation has provided a foundation for the prediction of constitutive relations for transformation plasiticity. Application to the control of stress-state dependent shaping of stress–strain behavior has demonstrated substantial improvements in uniform ductility and ductile fracture toughness. The advance of such predictive science continues to play a central role in the new enterprise of science-based materials design.

 

تولید، خواص و قابلیت‌های گرافن Production, properties and potential of graphene

Production, properties and potential of graphene

تولید، خواص و قابلیت‌های گرافن

ABSTRACT

This review on graphene, a one-atom thick, two-dimensional sheet of carbon atoms, starts with a general description of the graphene electronic structure as well as a basic experimental toolkit for identifying and handling this material. Owing to the versatility of graphene properties and projected applications, several production techniques are summarized, ranging from the mechanical exfoliation of high-quality graphene to the direct growth on carbides or metal substrates and from the chemical routes using graphene oxide to the newly developed approach at the molecular level. The most promising and appealing properties of graphene are summarized from an exponentially growing literature, with a particular attention to matching production methods to characteristics and to applications. In particular, we report on the high carrier mobility value in suspended and annealed samples for electronic devices, on the thickness-dependent optical transparency and, in the mechanical section, on the high robustness and full integration of graphene in sensing device applications. Finally, we emphasize on the high potential of graphene not only as a post-silicon materials for CMOS device application but more ambitiously as a platform for post-CMOS molecular architecture in electronic information processing.

 

اتصالات بین فولاد زنگ نزن سوپر دو فازی و فولاد HSLA

Effect of heat input on microstructure and mechanical properties of

dissimilar joints between super duplex stainless steel and high strength low alloy steel

اثر حرارت ورودی بر ریزساختار و خواص مکانیکی اتصالات غیر مشابه بین

فولاد زنگ نزن سوپر دو فازی و فولاد کم آلیاژ با استحکام بالا

ABSTRACT

In the present study, microstructure and mechanical properties of UNS S32750 super duplex stainless steel (SDSS)/API X-65 high strength low alloy steel (HSLA) dissimilar joint were investigated. For this purpose, gas tungsten arc welding (GTAW) was used in two different heat inputs: 0.506 and 0.86 kJ/mm. The microstructures investigation with optical microscope, scanning electron microscope and X-ray diffraction showed that an increase in heat input led to a decrease in ferrite percentage, and that detrimental phases were not present. It also indicated that in heat affected zone of HSLA base metal in low heat input, bainite and ferrite phases were created; but in high heat input, perlite and ferrite phases were created. The results of impact tests revealed that the specimen with low heat input exhibited brittle fracture and that with high heat input had a higher strength than the base metals.

 

روش فیلترینگ غیرخطی برای حذف صدای ریزنگار HR(S)TEM

A nonlinear filtering algorithm for denoising HR(S)TEM micrographs

روش فیلترینگ غیرخطی برای حذف صدای ریزنگارهای HR(S)TEM

ABSTRACT

Noise reduction of micrographs is often an essential task in high resolution (scanning) transmission electron microscopy (HR(S)TEM) either for a higher visual quality or for a more accurate quantification. Since HR(S)TEM studies are often aimed at resolving periodic atomistic columns and their non-periodic deviation at defects, it is important to develop a noise reduction algorithm that can simultaneously handle both periodic and non-periodic features properly. In this work, a nonlinear filtering algorithm is developed based on widely used techniques of low-pass filter and Wiener filter, which can efficiently reduce noise without noticeable artifacts even in HR(S)TEM micrographs with contrast of variation of background and defects. The developed nonlinear filtering algorithm is particularly suitable for quantitative electron microscopy, and is also of great interest for beam sensitive samples, in situ analyses, and atomic resolution EFTEM.