انتقال بین مرزدانه با زاویه کم و زیاد

Transition between low and high angle grain boundaries 

انتقال بین مرزدانه با زاویه کم و زیاد 

ABSTRACT

The migration of planar, symmetric tilt grain boundaries with different tilt axes was investigated. The driving force for the grain boundary migration was due to an external mechanical stress field. Low as well as high angle grain boundaries can move under this driving force and the activation parameters for the stress induced grain boundary motion are different for low and high angle grain boundaries. The experiments showed a sharp transition from low angle grain boundary to high angle grain boundary behavior. The transition is marked by a clear change in the activation enthalpy for the grain boundary motion without any extended range. We present an overview of the existing experimental results and theoretical considerations of the structure of grain boundaries at the transition. The observation that the transition depends on the rotation axis of the grain boundary and on the grain boundary plane is particularly important, because this will influence the Brandon criterion which is often used in experiments and simulations of grain growth and recrystallization processes. 

 

ساختار مرزدانه‌های زاویه - باز The structure of high-angle grain boundaries

The structure of high-angle grain boundaries

ساختار مرزدانه‌های زاویه - باز

ABSTRACT

A coincidence model of high-angle grain boundaries can be extended to include deviations from coincidence. The generalised boundary has a terraced structure, corresponding to the densely packed planes in the coincidence lattice, and a superimposed dislocation network, corresponding to a sub-boundary in the coincidence lattice. This model is a natural extension of previous dislocation models and models based on coincidence relationships. The model explains many of the observed properties of grain boundaries and should have wide validity for the cubic system.

 

مرزدانه هایی با زاویه بالا high angle grain boundaries

Disclination model of high angle grain boundaries

مدل disclination در مرزدانه هایی با زاویه بالا

ABSTRACT

Since the grain boundary is a rotational defect and so is a disclination, it is proposed here that a grain boundary may be made of disclinations instead of dislocations which are translational defects. The excess elastic energy for a symmetric tilt boundary whose orientation is between two low energy orientations is calculated by using this model. Such calculation cannot be easily performed using dislocations.

 

مقایسه ذرات ریز τ-MnAl تولید شده از طریق راه های مختلف

A comparison of τ-MnAl particulates produced via different routes

مقایسه ذرات ریز τ-MnAl تولید شده از طریق راه های مختلف

ABSTRACT

MnAl alloys are very promising rare-earth-free permanent magnets. Nanocrystalline microstructures can have beneficial effects on the properties of magnetic MnAl alloys. In the present work we examined multiple routes to process MnAl alloys and studied the effects of milling on Mn-46 at.% Al powders. Mn54Al46 was produced via gas atomization, melt spinning, and rapid solidification rate processing. It was then mechanically milled using a water-cooled Union Process attritor for times up to 20 h. X-ray diffraction patterns showed the presence of mostly the high-temperature ε-phase with significant amounts of the equilibrium γ2 and β phases in both the cast and milled particulates. The powders were annealed for various temperatures and times in order to obtain the ferromagnetic τ-phase. Magnetic measurements of the optimally annealed powders showed a coercivity of 3.62 kOe and saturation magnetization of 59.8 emu g(-1) for mechanically milled gas-atomized powder annealed at 500 °C for 30 min.

 

مرزدانه های با زاویه زیاد در فلزات و اکسیدهای سرامیکی

Structure of High-Angle Grain Boundaries in Metals and

Ceramic Oxides

ساختار مرزدانه های با زاویه زیاد در فلزات و اکسیدهای سرامیکی 

ABSTRACT

The current knowledge of the structure of high-angle grain boundaries in metals and ceramic oxides is critically reviewed. Particular attention is given to effects due to differences in the bonding and crystal structure in these solid types. The results of recent experimental work and efforts to model grain-boundary structure using computer simulation methods are described. Important characteristic features of boundaries in these materials are discussed. Difficulties which are presently being encountered in efforts to determine their structure are pointed out.

 

آلیاژهای هیپویوتکتیک آلومینیوم-سیلیسیوم

Nucleation mechanism of the eutectic phases in

aluminum–silicon hypoeutectic alloys

سازوکار جوانه‌زنی فازهای یوتکتیک در آلیاژهای هیپویوتکتیک آلومینیوم-سیلیسیوم

ABSTRACT

A theory is presented to explain the mechanism of formation of the eutectic phases in Al–Si hypoeutectic alloys. Results include optical, scanning and transmission electron microscopy, as well as selected area electron diffraction analysis and elemental X-ray mapping performed on Al–Si hypoeutectic alloy samples. The alloy samples had precisely controlled chemistry and were solidified at various cooling rates. The data presented support the proposed theory with microstructural and crystallographic evidence.

 

مقدمه ای بر نیمه هادی ها Introduction to semiconductor

Introduction to semiconductor  

مقدمه ای بر نیمه هادی ها 

ABSTRACT

A semiconductor material is one whose electrical properties lie in between those of  insulators and good conductors. Examples are: germanium and silicon.  In terms of energy bands, semiconductors can be defined as those materials which  have almost an empty conduction band and almost filled valence band with a very  narrow energy gap (of the order of 1 eV) separating the two. 

 

پایلوت پلنت های آزمایشی HIsarna Pilot Plant Project

HIsarna Pilot Plant Project

پروژه ماشین آلات آزمایشی به روش HIsarna

ABSTRACT

HIsarnaTM represents a new phase in the  global direct smelting development cycle.  It is,  in essence, a merger between Tata Steel- developed smelt cyclone technology and HIsmelt TM (Rio Tinto)-developed bath smelting  technology.  A pilot plant at IJmuiden,  Netherlands with a nominal capacity of 60,000  t/a is nearing completion and is due to start shortly. 

The catalyst that brought these technologies  together and made the pilot plant project  possible is ULCOS.  The key driver from this  perspective is efficient, cost-effective carbon  dioxide collection for potential geological  storage. HIsarna’s inherently simple, once- through gas flow path provides an easy carbon  dioxide collection option without the need for a carbon dioxide scrubber. 

 

بررسی عیوب دوقلویی شکل τ-MnAl-C منظم شده با L10 به وسیله ی EBSD

Twin-like defects in L1 ordered s-MnAl-C studied by EBSD

بررسی عیوب دوقلویی شکل τ-MnAl-C منظم شده با L10  به وسیله ی EBSD

ABSTRACT

Twin-like defects in τ-MnAl-C, which has the L10 structure, have been studied using electron backscattered diffraction (EBSD) in as-transformed and in subsequently hot extruded samples. In both states, three distinct twin-like defects were found, whose misorientations were described by rotations of 62°, 118° and 180° about the normal to {111}. These are denoted as pseudo twins, order twins and true twins, respectively. The true twins are often observed in this type of material. The order twins formed the boundaries between regions where the c-axes were almost perpendicular to each other and these were thought to form due to the accumulation of strains during the transformation to τ from the hexagonal parent phase, ε. Due to symmetry, pseudo twins necessarily appeared at points where order twins interacted with true twins. The frequency of the different defects was very sensitive to the sample state. As the parent phase ε is not involved in the dynamic recrystallization which occurred during hot extrusion, there was a greatly reduced fraction of order twins and pseudo twins in the hot extruded state. The misorientation angle of the magnetically easy ⟨001⟩ axis across the three twin-like defects was 48°, 86° and 75° for pseudo, order and true twins, respectively. The interaction of the three twin-like defects with 180° magnetic domain walls and the resulting effect on the magnetic properties of the material may therefore be different.

 

اثر میدان مغناطیسی عرضی بر رشد دانه های هم محور حین انجماد جهت دار

Effect of a transverse magnetic field on the growth

of equiaxed grains during directional solidification

اثر میدان مغناطیسی عرضی بر رشد دانه های هم محور حین انجماد جهت دار

ABSTRACT

The effect of a transverse magnetic field on the growth of equiaxed grains during directional solidification of Al-10wt% Cu alloys was investigated experimentally and numerically. The experimental results show that the magnetic field has a great influence on the size and distribution of equiaxed grains. Indeed, the magnetic field causes refined and coarsen equiaxed grains to distribute on the both sides of the sample, respectively. In-situ synchrotron X-ray imaging shows that a transverse magnetic field induced some force which can act on equiaxed grains and cause the movement of equiaxed grains during directional solidification. Numerical results reveal that the modification of the structure may be attributed to the thermoelectric (TE) magnetic effects produced by the magnetic field. Furthermore, a new method of removing inclusions in molten metal is developed by means of the TE magnetic force.