اثر سرعت جوشکاری اصطکاکی اغتشاشی در زیر آب روی آلیاژ آلومینیوم

Effect of welding speed on microstructures and mechanical properties

of underwater friction stir welded 2219 aluminum alloy

اثر سرعت جوشکاری بر ریز ساختارها و خواص مکانیکی آلیاژ آلومینیوم 2219

جوشکاری اصطکاکی اغتشاشی شده در زیر آب 

ABSTRACT

Underwater friction stir welding (underwater FSW) has been demonstrated to be available for the strength improvement of normal FSW joints. In the present study, a 2219 aluminum alloy was underwater friction stir welded at a fixed rotation speed of 800 rpm and various welding speeds ranging from 50 to 200 mm/min in order to clarify the effect of welding speed on the performance of underwater friction stir welded joint. The results revealed that the precipitate deterioration in the thermal mechanically affected zone and the heat affected zone is weakened with the increase of welding speed, leading to a narrowing of softening region and an increase in lowest hardness value. Tensile strength firstly increases with the welding speed but dramatically decreases at the welding speed of 200 mm/min owing to the occurrence of groove defect. During tensile test, the joint welded at a lower welding speed is fractured in the heat affected zone on the retreating side. While at higher welding speed, the defect-free joint is fractured in the thermal mechanically affected zone on the advancing side.

 

نیتروژن دهی و آلیاژسازی سطح فولادها با اتم های Ti و Nb توسط عملیات تراکمی جریان های پلاسمایی

Surface nitriding and alloying of steels with Ti and Nb atoms

by compression plasma flows treatment

نیتروژن دهی و آلیاژسازی سطح فولادها با اتم های Ti و Nb توسط عملیات تراکمی جریان های پلاسمایی

ABSTRACT

Phase and element composition, microhardness of Ti/steel and Nb/steel systems treated by compression plasma flows have been investigated in this work. Auger electron spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersion X-ray microanalysis and Vickers microhardness measurements were used for sample characterization. The findings showed that treatment of a “coating/steel” system by compression plasma flows generated in nitrogen atmosphere allowed alloying of the surface layer of steel by the coating element and nitriding it simultaneously. The variation of the pulses number (1–6) resulted in change of the alloying element concentration and formation of a number of phases in the alloyed layer: Fe2Ti, a supersaturated solid solution α-Fe(Ti,C) in the Ti alloyed layer and a supersaturated solid solution α-Fe(Nb,C) in the Nb alloyed layer. The formation of Ti(C,N) and Nb(C,N) carbonitrides with fcc crystal structure at the surface was also found. The change of phase composition and quenching effects resulted in substantial increase of microhardness.

 

فرآیند شکل دهی ادغام شده با لحیم کاری القایی Induction Brazing

Forming Process Integrated Induction Brazing 

فرآیند شکل دهی ادغام شده با لحیم کاری القایی

ABSTRACT

Processing steps additional to forming operations, such as joining, usually require a vast effort for transport and storage. Due to integration of currently external production steps, processes could be synchronized. Brazing represents an additional operation, which is likely to gain of importance in the light of an increasing relevance of light weight construction. Servo presses enable an adjustment of the ram motion to process requirements. Hence, the ram motion can be adjusted to create a time slot for the execution of additional processes inside the press. In this paper, the possibility to integrate brazing into forming process chains is investigated.  For a demonstration part, a tool that allows brazing inside a servo press is developed. Achievable part qualities and cycle times are  evaluated. 

 

اهمیت بیو‌فیلم‌های میکروبی در صنایع غذایی: باز‌نگری

Significance of microbial biofilms in food industry: a review

اهمیت بیو‌فیلم‌های میکروبی در صنایع غذایی: باز‌نگری

ABSTRACT

In nature and food systems, microorganisms get attracted to solid surfaces conditioned with nutrients, that are sufficient for their viability and growth. These microorganisms initially are deposited on the surfaces and later get attached, grow and actively multiply to form a colony of cells. In this regard, the formation of organic polymers are essential which helps in the proper colonization of microorganisms (Allison and Sutherland, 1987). These mass of cells further become large enough to entrap organic and inorganic debris, nutrients and other microorganisms leading to the formation of a microbial biofilm. The term biofilm refers to the biologically active matrix of cells and extracellular substances in association with a solid surface (Bakke et al., 1984). However, according to Costerton et al. (1987) a biofilm is a functional consortium of microorganisms attached to a surface and is embedded in the extracellular polymeric substances (EPS) produced by the micro- organisms.

 

مناطق GP در آلیاژهای Al-Zn-Mg و نقش آنها در پیرسازی مصنوعی

GP-zones in Al–Zn–Mg alloys and their role in artificial aging

مناطق GP در آلیاژهای Al-Zn-Mg و نقش آنها در پیرسازی مصنوعی

ABSTRACT

The structure of GP-zones in an industrial, 7xxx-series Al–Zn–Mg alloy has been investigated by transmission electron microscopy methods: selected area diffraction, conventional and high-resolution imaging. Two types of GP-zones, GP(I) and (II) are characterized by their electron diffraction patterns. GP(I)-zones are formed over a wide temperature range, from room temperature to 140–150°C, independently of quenching temperature. The GP(I)-zones are coherent with the aluminum matrix, with internal ordering of Zn and Al/Mg on the matrix lattice, suggested to be based on AuCu(I)-type sub-unit, and anti-phase boundaries. GP(II) are formed after quenching from temperatures above 450°C, by aging at temperatures above 70°C. The GP(II)-zones are described as zinc-rich layers on {111}-planes, with internal order in the form of elongated <110> domains. The structural relation to the η′-precipitate is discussed.

 

نیتروژن دهی پلاسمایی فولاد ضدزنگ سوپرمارتنزیت

Plasma nitriding of HP13Cr supermartensitic stainless steel

نیتروژن دهی پلاسمایی فولاد ضدزنگ سوپرمارتنزیت HP13Cr

ABSTRACT

Supermartensitic stainless steels (SMSS) are commonly employed in the oil exploitation industry and present a good balance between the necessary physical and chemical properties and financial costs. Certain applications, such as in extreme corrosive and abrasive environments, demand improvements in the surface properties of these steels. In the present work, HP13Cr SMSS with a fully martensitic microstructure were plasma nitrided in the 350–450 °C range. The high diffusivity and low solubility of nitrogen in the martensitic structure allowed the production of thick layers (16–61 μm) containing ɛ-Fe2–3N, γ′-Fe4N and expanded phase (αN) in all the temperatures. In addition, anisotropic sputtering rate and N-diffusion were observed for different grain orientations. Mechanical properties were measured by instrumented indentation, appropriately corrected from roughness effects on the results. Hardness profiles increased from 3.8 GPa (bulk) to ∼14 GPa (near surface region) in all the working temperatures, whereas the elastic modulus was 230 GPa, presenting no statistically significant differences with respect to the bulk value. Nanoscratch tests revealed a hardened-ductile like behavior of these nitride layers. The surface tribo-mechanical behavior was correlated with elastic–plastic responses of the precipitate-containing texturized layers. Results are interpreted in light of the effectiveness of plasma nitriding to modify the surface properties of SMSS.

 

حرکت دانه های هم محور در حین انجماد جهت دار تحت میدان مغناطیسی استاتیک

Motion of equiaxed grains during directional solidification

under static magnetic field

حرکت دانه های هم محور در حین انجماد جهت دار تحت میدان مغناطیسی استاتیک

ABSTRACT

The in situ and real time observations of the equiaxed grain motion during directional solidification of Al–10 wt% Cu under static magnetic field has been carried out by means of synchrotron X-ray radiography. It was observed that equiaxed grains moved approximately along the direction perpendicular to both the imposed magnetic field and the temperature gradient. Based on the radiographs, the motion of the solid grains was analyzed for various temperature gradients, and it was shown that the trajectories were imposed by the combination of the Thermo-Electric Magnetic forces, induced by the coupling of thermo-electric currents with the permanent magnetic field and the gravity force. The variations of the velocities and sizes of grains during the equiaxed growth under static magnetic field were measured and compared to a simple analytical model for the Thermo-Electric Magnetic forces and the Stokes law. A good agreement was achieved for the deviation angle as a function of the grain diameter, while a large discrepancy was observed for the velocity intensity when the dimensions of the equiaxed grains increased. In the latter case, it was shown that the corrections for both sample confinement and grain morphology were mandatory to explain the very low values of grain velocities.

 

فرآیند نیتروژن دهی پلاسمایی در فولاد قالب تزریق پلاستیک

A Study on Formation and Growth Mechanism of

Nitride Layers During Plasma Nitriding Process of

Plastic Injection Mold Steel

تحقیق روی مکانیزم رشد و تشکیل لایه های نیتریدی

حین فرآیند نیتروژن دهی پلاسمایی در فولاد قالب تزریق پلاستیک

ABSTRACT

Ion nitriding modifies composition of surface layer in steel used in plastic mold application and this consequently improves their lifecycle. In this study, pulsed plasma nitriding technique was used to produce a protecting hard layer on AISI P20 steel at three process temperatures of 450°C, 500°C, and 550°C for durations of 2.5, 5, 7.5, and 10 h at a constant gas mixture of 75% N2–25% H2. Surface morphology was studied by optical and scanning electron microscope and the phases formed on the surface layer were determined by X-ray diffraction (XRD). Elemental depth profile was measured by techniques including energy dispersive spectroscopy, wavelength dispersive spectrometer, and glow discharge spectroscopy and for identifying hardness profile, microhardness variations from surface to core of samples were recorded. Results showed that, thickness of compound layer of plastic mold steel AISI P20 was negligible. Moreover in ion nitriding of AISI P20, nitride were formed and grown in some preferred directions and upward diffusion of carbon and downward diffusion of nitrogen occurred during ion nitriding of AISI P20. XRD results showed that, ϵ-nitride is the dominant phase after plasma nitriding in all strategies. Furthermore, ion nitriding improved hardness of AISI P20 up to three times and as time and temperature increased, hardness and hardness depth of diffusion zone increased considerably.

 

نانوسرامیک های هیدروکسی آپاتیت

Hydroxyapatite nanoceramics: Basic physical

properties and biointerface modification

نانوسرامیک های هیدروکسی آپاتیت : خواص فیزکی اصلی و  اصلاحbiointerface 

ABSTRACT

A new method of surface energy modification and engineering of the hydroxyapatite (HAp) nanoceramics coatings is presented. It is performed by electron-induced surface energy modification resulting in deep and tunable variation of its wettability state. It is found from electronic traps state spectroscopy studies of the HAp ceramics implemented by various methods such as photoluminescence and surface photovoltage spectroscopy, that the HAp nanoceramics is a wide band gap p-type semiconductor with complex structure of electron/hole bulk and surface localized states. It is shown that a low-energy electron irradiation leads to surface potential modulation and provides tailoring any wettability state in a wide range of contact angles by variation of injected and trapped electron charge. The diverse wettability states engineered on the HAp surface enable selective adhesion of basic biological cells such as proteins, DNA and various bacteria.

 

سنتز شیمیایی لایه های نازک نانوکریستال کادمیوم تلوریم

Structural and optical properties of CdTe-nanocrystals

thin films grown by chemical synthesis

خواص نوری و ساختار لایه های نازک نانوکریستال CdTe رشد کرده به روش سنتز شیمیایی

ABSTRACT

By mans of a chemical synthesis technique stoichiometric CdTe-nanocrystals thin films were prepared on glass substrates at 70 °C. First, Cd(OH)2 films were deposited on glass substrates, then these films were immersed in a growing solution prepared by dissolution of Te in hydroxymethane sulfinic acid to obtain CdTe. The structural analysis indicates that CdTe thin films have a zinc-blende structure. The average nanocrystal size was 19.4 nm and the thickness of the films 170 nm. The Raman characterization shows the presence of the longitudinal optical mode and their second order mode, which indicates a good crystalline quality. The optical transmittance was less than 5% in the visible region (400–700 nm). The compositional characterization indicates that CdTe films grew with Te excess.