انواع خوردگی Corrosion

Corrosion

خوردگی 

ABSTRACT

Corrosion is often associated with welded structures, since the microstructure, properties, and composition of the weld metal and HAZ may be quite different than those of the base metal. Corrosion takes a number of forms, as described in the  following section, and may result in general (uniform), localized, or microstructurespecific attack.

Often, the corrosion rate associated with welds is much higher than the base metal. The reason for this is usually a combination of the effect of microstructure and residual stress. Highly stressed regions surrounding welds may result in accelerated corrosion relative to the base metal. For example, the spot welds in automotive steels are normally the first place where corrosion attack takes place in car bodies.

 

پیشرفت‌ها در فناوری پالایش فولاد و چشم‌انداز آینده

Advances in Steel Refining Technology and Future Prospects

پیشرفت‌ها در فناوری پالایش فولاد و چشم‌انداز آینده

ABSTRACT

By the 1980s, Nippon Steel Corporation established a separated refining process based on hot-metal pretreatment,2) whereby the contents of silicon, sulfur, and phosphorus in hot metal were decreased before the decarburization in converters, using torpedo ladle cars, hot-metal ladles, or converters as the reaction vessels. Thereafter, technical developments such as the following were achieved:
separation of desulfurization from the other hot-metal pretreatment; separate processing of hot-metal dephosphorization from decarburization; development of hot-metal dephosphorization using converters as the reaction vessels and not requiring fluorine; improvement in reaction efficiency of these processes; recycled use of slag; adjustment of silicon content in hot metal in case of excessively high Si; and increase in converter capacity for hot-metal dephosphorization in converters.

 

فرایند انجماد و ساختار ریختگی در ریخته گری شمش

Solidification and Processes and Cast Structures

فرایند انجماد و ساختار ریختگی

ABSTRACT

This swction deals with three tranitional solidificationprocesses: ingot casting, continous casting, and welding. however, the last to processe hold a key importance in todays technology. almost entire molten metal is cast into solid state by either the traditional ingot casting or reatively modern continuous casting. the development of the ingot and continuously cast structure as well as fusion welding structure and weld cracking are briefly described.

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چقرمگی شکست یک فولاد ضدزنگ سوپر داپلکس جوشکاری شده

Fracture toughness of a welded super duplex stainless steel

چقرمگی شکست یک فولاد ضدزنگ سوپر داپلکس جوشکاری شده

ABSTRACT

Fracture toughness testing was conducted on standard single-edge notched bend bar specimens of base and weld metal. The material was the SAF 2906 super duplex stainless steel. The aim was to evaluate the susceptibility for brittle failure at sub-zero temperatures for the base and weld metal. The base metal was tested between −103 and −60 °C and was evaluated according to the crack-tip opening displacement method. The fracture event at and below −80 °C can be described as ductile until critical cleavage initiation occurs, which caused unstable failure of the specimen. The welding method used was submerged arc welding with a 7 wt% nickel filler metal. The welded specimens were post-weld heat treated (PWHT) at 1100 °C for 20 min and then quenched. Energy-dispersive X-ray spectroscopy analysis showed that during PWHT substitutional element partitioning occurred which resulted in decreased nickel content in the ferrite. The PWHT weld metal specimens were tested at −72 °C. The fracture sequence was critical cleavage fracture initiation after minor crack-tip blunting and ductile fracture.

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رفتار زینترینگ و مقاومت هیدروژنی دولومیت واکنشی

Sintering, consolidation, reaction and crystal growth by

the spark plasma system (SPS)

رفتار زینترینگ و مقاومت هیدروژنی دولومیت واکنشی

ABSTRACT

Sintering of raw dolomite and hydroxides derived from dolomite was carried out in the temperature range 1350–1650 °C. The hydroxide derived from dolomite was developed through pre-calcination of dolomite followed by its hydration. For hydroxide development, after precalcination one sample was air-quenched and the other powder was furnace cooled before hydration. The air quenched samples showed better densification than that of the furnace cooling process at the same temperature. Fe2O3 addition enhances sintering by liquid formation at higher temperature. The grain size of doloma with Fe2O3 addition is bigger than that without additive. Hydration resistance was related to densification and grain size of sintered dolomite.

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شناسایی ساختار و انتقال بار لایه های گرافن

Structural and charge transport characteristics of graphene layers

obtained from CVD thin film and bulk graphite materials

شناسایی ساختار و انتقال بار لایه های گرافن حاصل از لایه نازک CVD و مواد گرافیتی

ABSTRACT

We report an experimental comparative study of graphene layers produced by micromechanical cleavage of bulk graphite materials of different origins and graphite films obtained by plasma enhanced chemical vapor deposition (PECVD). Structural characteristics of these materials were evaluated using Raman spectroscopy and electron microscopy. Field effect transistors (FETs) based on the PECVD graphene were produced using electron beam lithography. Conductivity, carrier mobility and other characteristics of the PECVD graphene obtained from Raman and FET tests were similar to the properties of graphene flakes obtained from bulk graphite materials. Taking into account the scalability of the CVD fabrication, these results confirm the possible industrial use of graphene films obtained by this method.

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آنالیز اشعه ایکس Ti-Nb-Ta-Zr در آلیاژهای تیتانیوم

In situ X-ray analysis of mechanism of nonlinear

super elastic behavior of Ti–Nb–Ta–Zr system beta-type titanium alloy

for biomedical applications

آنالیز اشعه X در جای مکانیسم‌ رفتار سوپرالاستیک غیر‌خطی سیستم Ti-Nb-Ta-Zr

در آلیاژهای تیتانیوم نوع بتا برای کاربردهای زیست‌پزشکی

ABSTRACT

Ti–XNb–10Ta–5Zr (mass %) alloys based on nominal compositions of Ti–35Nb–10Ta–5Zr, Ti–30Nb–10Ta–5Zr, and Ti–25Nb–10Ta–5Zr were fabricated through powder metallurgy and forging and swaging processes for biomedical applications. The tensile deformation mechanisms of the Ti–25Nb–10Ta–5Zr, Ti–30Nb–10Ta–5Zr, and Ti–35Nb–10Ta–5Zr alloys were investigated in situ by X-ray diffraction analysis under several loading conditions.

Under the loading conditions, the X-ray diffraction peaks of all the specimens shifted to higher angles than those obtained under the unloading conditions. For the Ti–30Nb–10Ta–5Zr alloy, the elastic deformation is considered to progress continuously in a different crystal direction although after the elastic strain reaches elastic limit in the crystal direction where the elastic limit is the smallest, slip deformation occurs in that crystal direction. The elastic modulus of this alloy appears to decrease in terms of strain over the proportional limit. Thus, the elastic deformation behavior of the Ti–30Nb–10Ta–5Zr alloy does not obey Hooke's law.

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پیوند نفوذی فاز مایع گذرا با استفاده از پوشش‎های نانوپراکنده‎ی Ni

Transient liquid phase diffusion bonding Al-6061 using

nano-dispersed Ni coatings

پیوند نفوذی فاز مایع گذرا با استفاده از پوشش‎های نانوپراکنده‎ی Ni

ABSTRACT

Transient liquid phase diffusion bonding (TLPDB) of Al-6061 containing 15 vol.% alumina particles was carried out at various bonding temperatures. A 5 μm thick electrodeposited Ni-coating containing 18 vol.% nano-size alumina particles was used at the interlayer. Joint formation was attributed to the solid-state diffusion of Ni into the Al-6061 alloy followed by eutectic formation and isothermal solidification at the joint interface. Examination of the joint region using scanning electron microscopy (SEM), wavelength dispersive spectroscopy (WDS) and X-ray diffraction (XRD) showed the formation of intermetallic phases such as Al3Ni, Al9FeNi and Ni3Si within the joint zone. The results indicate that the incorporation of nano-size Al2O3 dispersions into the interlayer can be used to improve joint strength.

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افزودن کاربید بور پراکنده شده به مواد ترموالکتریک برپایه تلوراید بیسموت

Spark Plasma Sintered bismuth telluride-based thermoelectric

materials incorporating dispersed boron carbide

افزودن کاربید بور پراکنده شده به مواد ترموالکتریک برپایه تلوراید بیسموت

سینتر شده به روش پلاسمای جرقه ای

ABSTRACT

The mechanical properties of bismuth telluride based thermoelectric materials have received much less attention in the literature than their thermoelectric properties. Polycrystalline p-type Bi0.5Sb1.5Te3 materials were produced from powder using spark plasma sintering (SPS). The effects of nano-B4C addition on the thermoelectric performance, Vickers hardness and fracture toughness were measured. Addition of 0.2 vol% B4C was found to have little effect on zT but increased hardness by approximately 27% when compared to polycrystalline material without B4C. The KIC fracture toughness of these compositions was measured as 0.80 MPa m1/2 by Single-Edge V-Notched Beam (SEVNB). The machinability of polycrystalline materials produced by SPS was significantly better than commercially available directionally solidified materials because the latter is limited by cleavage along the crystallographic plane parallel to the direction of solidification.

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چکیده

خواص مکانیکی مواد ترموالکتریک برپایه تلوراید بیسموت، خیلی کمتر از خواص ترموالکتریکی آنها مورد توجه قرار گرفته است. ماده Bi0.5Sb1.5Te3 نوع p پلی کریستال، به روش سینتر پلاسمای جرقه ای (SPS) از پودر تولید شد. اثر افزودن نانوذرات B4C روی عملکرد ترموالکتریکی، سختی ویکرز و چقرمگی شکست اندازه گیری گردید. مشخص شد که افزودن 2/0%  B4C اثر اندکی روی zT دارد، اما در مقایسه با ماده پلی کریستالی بدون B4C، تقریباً 27% افزایش سختی دارد. چقرمگی شکست KIC این ترکیبات به وسیله "آزمایش تیر با شیار V شکل لبه ای " (SEVNB) به صورت Mpa m1/2 80/0 اندازه گیری شد. قابلیت ماشین کاری مواد پلی کریستالی تولید شده به روش SPS، به طور قابل توجهی بهتر از مواد با انجماد جهت دار رایج تجاری است، چرا که ماشین کاری مواد با انجماد جهت دار، با کلیواژ در طول صفحه کریستالوگرافی موازی با جهت انجماد، محدود می گردد.

خواص سایش پوشش CrC–37WC–18M رسوب داده شده

Wear properties of CrC–37WC–18M coatings deposited by

HVOF and HVAF spraying processes

خواص سایش پوشش CrC–37WC–18M رسوب داده شده

توسط فرایندهای پاشش HVOF و HVAF

 

ABSTRACT

CrC–37WC–18M cermet coatings were deposited using new feedstock powders which seem to combine the properties of WC–CoCr and CrC–NiCr coatings. A conventional particle size CrC–37WC–18M powder was used as feedstock for the HVOF (high velocity oxygen fuel) thermal spraying process and a fine particle distribution was used as feedstock for the HVAF (high velocity air fuel) thermal spraying process. In order to characterize the morphology of the feedstock powders and deposited coatings SEM and X-ray diffraction were used. The microhardness of the coatings was also studied. The wear behavior of the coatings was evaluated by pin-on-disk and rubber wheel abrasion tests. The HVAF coating showed equal or even better wear resistance as compared to corresponding HVOF coatings

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