تغییر فاز در فولادهای میکرو آلیاژ کم آلیاژ استحکام بالا (HSLA)

Phase transformations in microalloyed high strength low alloy (HSLA) steels

تغییر فاز در فولادهای میکرو آلیاژ کم آلیاژ استحکام بالا (HSLA)

ABSTRACT

The addition of small amounts of Nb, Ti or V singly or in combination has been the key to  producing high strength low alloy (HSLA) steels with greatly improved mechanical properties. Such  microalloyed HSLA steels are now commonplace in a huge variety of applications. The combinations of  strength, toughness and formability that are possible are directly related to the way in which the steel is processed from the as- cast slab (usually) to the final plate or strip dimensions. The effects of microalloying result principally from three main effects on the austenite to ferrite  transformation. Firstly, the microalloying additions form precipitates in both austenite and ferrite; this factor alone can be exploited in various ways to control the microstructure, hence  mechanical properties, of the steel. Secondly, although present in relatively small quantities,there are discernible effects on ferrite transformations in terms of the hardenability of the steel. Finally, there are interactions between the various deformation sequences used in  steel production and the presence of microalloying elements as solutes or precipitates which can be  exploited to control microstructure. The interactions between processing, microstructural  development and the effect of microalloying additions on the austenite­ ferrite transformations are  the topic of this chapter. A brief history of the use of microalloying is also given as is some  indication of the range of mechanical properties that result from the current understanding of the role of microalloying additions.

مواد عایق برق Electrical insulating materials

Electrical insulating materials

مواد عایق برق

ABSTRACT

Electrical insulating materials ensure the integrity of desired paths of electromagnetic power flow in electrical systems and equipment . They are materials at very high resistivity and can thus be used as isolators or separator between conductors having different potential (voltage) levels . In its use such as in isolators an insulating materials has the basic function of confining the current flow within the conductive circuit of a given device or part of equipment thus protecting the latter from short circuit current leakage and similar undesirable malfunctions . insulating materials may be solid liquid or gaseous substances , they may be monolithic ( discrete ) materials or may be constituted by physically cohesive composites structured with multiple constituents . Based on the primary functions electric insulation can be categorized as follows :

• Separation-type insulation
• Barrier insulation
• Creepege insulation

چقرمگی شکست اپوکسی اصلاح شده با لاستیک هیبریدی

Fracture Toughness of a Hybrid Rubber Modified
Epoxy. II. Effect of Loading Rate

چقرمگی شکست اپوکسی اصلاح شده با لاستیک هیبریدی.

II. اثر نرخ بارگذاری

ABSTRACT

Effect of loading rate on toughness characteristics of hybrid rubber-modified epoxy was investigated. Epoxy was modified by amine-terminated butadiene acrylonitrile (ATBN) and recycled tire. Samples were tested at various loading rates of 1–1000 mm/ min. Fracture toughness measurements revealed synergistic toughening in hybrid system at low loading rates (1–10 mm/min); hybrid system exhibited higher fracture toughness value in comparison with the ATBN-modified resin with same modifier content. However, synergistic toughening was eliminated by increasing the loading rate. At higher loading rates (10–1000), the fracture toughness of hybrid system decreased gradually to the level lower than that of ATBN-modified epoxy. Fractography of the damage zones showed the toughening mechanisms of ATBN-modified system was less affected by increasing the loading rate compared to that of hybrid system.

اثر ترکیب روی بافت کریستالوگرافی در آلیاژهای AL-Li-Cu

Effect of composition on crystallographic texture in hot-rolled Al-Li-Cu alloys

اثر ترکیب روی بافت کریستالوگرافی در آلیاژهای AL-Li-Cu نورد گرم شده

ABSTRACT

The hot-rolling textures of ternary Al-Li-Cu alloys have been characterized to determine their effects on the yield strength anisotropy. The alloys used in the study had (Li/Cu) ratios varying from 0 to co and were hot-rolled in the 520-400 “C temperature range. All the alloys showed well developed p-fibers, with a maximum intensity at Brass, and a weak background of a-fiber. The Brass components were very strong for the alloys with intermediate (Li/Cu) ratios that had relatively more T, precipitates in the microstructure compared with other alloys. In addition, all compositions showed a weak Cube or rotated Cube recrystallization texture components. The observed textures are attributed to the effects of constrained deformation during hot deformation. The texture results were used to predict the yield strength anisotropies in the alloys. The predictions were in agreemenwt ith the experimentalr esultsf or the high (Li/Cu) alloys. However, in the low (Li/Cu) alloys, the discrepancies between the predicted and the measured yield strength anisotropies can be attributed to a modifying effect of the directional platelet precipitates on deformation.

مواد دی­ الکتریک Dielectric Materials

Dielectric Materials

مواد دی­ الکتریک

ABSTRACT

Dielectric materials refer to those having the basic electric Property Of being Polarized in the Presence of an electric Field and having an electrostatic field within Them under the state of polarisation .(polarisation here refers to the molecular aligment along the direction of the applied electric field . ) Also synosymusly referred  to as an electrical insulation material the dielectric has the ability to prevent the leakage of electrical charges from the body on which it is deployed .In general electrical insulation materials which possess  dielectric properties offer a very hight resistance to the passage of electric current under the action of an applied direct - current voltage .Hence such materials differ distincty in basic electric properties from those classified as electric conductors such as metals .

خوردگی سرب و آلیاژهای سربی

Corrosion of Lead and Lead Alloys

خوردگی سرب و آلیاژهای سربی

ABSTRACT

LEAD has such a successful record of service in exposure to the atmosphere and to water that its resistance to corrosion by these media is often taken for granted. Underground, thousands of kilometers of lead-sheathed cable and lead pipe give reliable long-term performance all over the world. In the chemical industry, lead is used in the corrosion-resistant equipment necessary for handling many chemicals. Batteries account for the largest use of lead and are the source of most recycled lead. General information on compositions, properties, and applications can be found in the article “Lead and Lead Alloys” in Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, Volume 2 of ASM .The rate of corrosion is a function of the current flowing between the anodes and cathodes of the corrosion cell. Many factors and conditions can initiate or influence this flow of current. In the corrosion of a single metal, such as lead, local anodes and cathodes may be set up as a result of inclusions, inhomogeneities, stress variations, and differences in temperature. In galvanic corrosion, the anodic and cathodic sites are ondifferent metals, with the less noble metal (anode) corroding in preference to the more noble metal (cathode).

ممانعت کننده های خوردگی مس Copper Corrosion Inhibitors

Copper Corrosion Inhibitors

ممانعت کننده های خوردگی مس

ABSTRACT

Copper is metal that has a wide range of applications due to its good properties. It is used in electronics, for production of wires, sheets, tubes, and also to form alloys. Copper is resistant toward the influence of atmosphere and many chemicals, however, it is known that in aggressive media it is susceptible to corrosion. The use of copper corrosion inhibitors in such conditions is necessary since no protective passive layer can be expected. The possibility of the copper corrosion prevention has attracted many researchers so until now numerous possible inhibitors have been investigated. Amongst them there are inorganic inhibitors [1], but in much greater numbers there are organic compounds and their derivatives such as azoles [2-49], amines [50-56], amino acids [57, 58] and many others.

ممانعت از خوردگی مس در محلول H2SO4 اشباع از O2

Copper corrosion inhibition in O2-saturated H2SO4 solutions

ممانعت از خوردگی مس در محلول H₂SO₄ اشباع از O₂

ABSTRACT

Corrosion inhibition of copper in O2-saturated 0.50 M H2SO4 solutions by four selected amino acids, namely glycine (Gly), alanine (Ala), valine (Val), or tyrosine (Tyr), was studied using Tafel polarization, linear polarization, impedance, and electrochemical frequency modulation (EFM) at 30 C. Protection efficiencies of almost 98% and 91% were obtained with 50 mM Tyr and Gly, respectively. On the other hand, Ala and Val reached only about 75%. Corrosion rates determined by the Tafel extrapolation method were in good agreement with those obtained by EFM and an independent chemical (i.e., non-electrochemical) method. The chemical method of confirmation of the corrosion rates involved determination of the dissolved Cu2+, using ICP-AES (inductively coupled plasma atomic emission spectrometry) method of chemical analysis. Nyquist plots exhibited a high frequency depressed semicircle followed by a straight line portion (Warburg diffusion tail) in the low-frequency region. The impedance data were interpreted according to two suitable equivalent circuits. The kinetics of dissolved O2 reduction and hydrogen evolution reactions on copper surface were also studied in O2-saturated 0.50 M H2SO4 solutions using polarization measurements combined with the rotating disc electrode (RDE). The Koutecky–Levich plot indicated that the dissolved O2 reduction at the copper electrode was an apparent 4-electron process.

سیمان و بتن

Concrete and Cement

سیمان و بتن

ABSTRACT

Inorganic concretes are reviewed, emphasizing two major areas: construction concretes and high temperature (refractory) concretes. Although such materials are intended for completely different applications and markets, they have in common that they are made from inorganic ceramic oxides and both materials are used for structural purposes. Current applications and research topics representing new challenges are summarized.Concrete usually indicates a construction material made from Portland cement, aggregates (for instance, gravel and sand), water, and additives to improve mixing or specific properties of the final material. Refractory concretes (monolithic refractories) refer to high-temperature materials for the manufacture of shaped refractories. Most concrete refractories are based on calcium aluminates, although some applications require the use of other high-temperature ceramic materials, such as magnesium oxide. The distinguishable feature of these concretes is that the method of preparation does not involve forming or firing at the manufacturing plant as in the fabrication of refractory bricks. This compilation includes only concretes for construction and refractory applications.

مواد کامپوزیت دی الکتریک

Composite Dielectric Materials

مواد کامپوزیت دی الکتریک

ABSTRACT

Composite dielectrics represent, in general, a heterogeneous system of multiconstituent materials. Typically, a two-phase composite dielectric is constituted by a host material with an inclusion of another material. This host-inclusion system could be formed by a combination (or a mixture) of dielectric-dielectric, dielectric-conductor, and/or dielectric-semiconductor phases. The constituent phases may form structurally an embedment system consisting of multi-layer "layups" or random dispersion of the inclusions across the host medium; or there could be a structured matrix of specific type to yield certain desirable dielectric properties. Generically, a composite dielectric can be treated as as a mixture-medium, largely heterogeneous and could be anisotropic and nonlinear, as well.