مقاومت به اکسیداسیون پوشش آلومینایی روی زیرلایه مس

High temperature oxidation resistance and

microstructure change of aluminized coating on copper substrate

مقاومت اکسیداسیون دما بالا و تغییر ریزساختار پوشش آلومینایی روی زیرلایه مس

ABSTRACT

The outermost coating with single phase Ni2Al3 was obtained on copper surface by electrodepositing nickel followed by slurry pack aluminizing at 800 °C for 12 h. The oxidation resistance and microstructure of the coating oxidized in ambient air at 1000 °C for 25–250 h were investigated using SEM, X-ray diffraction and optical microscope methods. The results show that the copper with single phase Ni2Al3 coating possesses the best high temperature oxidation resistance, and the mass gain of the coating is 1/15 that of pure copper and 1/2 that of nickel coating, respectively. The specimen surface after being oxidized for 25 h still comprises Ni2Al3 phase. However, when the time of oxidizing treatment increases to 50 h, the NiAl phase is formed. It is also found that the Ni2Al3 phase completely turns into NiAl phase after oxidizing treatment for 100 h and above. The NiAl coating shows excellent high temperature oxidation resistance when oxidation time is 250 h.

 

آلیاژ پایه NiAl هیپویوتکتیک منجمد شده به صورت جهت دار که با Hf و Ho دوپ شده

Effect of withdrawal rate on microstructure and mechanical

properties of a directionally solidified NiAl-based hypoeutectic alloy doped with trace Hf and Ho

تأثیر سرعت بیرون کشی بر ریزساختار و خواص مکانیکی آلیاژ پایه NiAl هیپویوتکتیک

منجمد شده به صورت جهت دار و دوپ شده با مقادیر اندک Hf و Ho

ABSTRACT

The hypoeutectic alloy, with nominal composition NiAle31Cre2.9Moe0.1Hfe0.05Ho (at.%), was directionally solidified at three different withdrawal rates by liquid metal (Sn) cooling technique. Microstructural examination reveals that directional solidification gave rise to a shift in the coupled zone for the eutectic growth towards the Cr(Mo) phase. With the withdrawal rates increasing from 3 mm/min to 15 mm/min, the volume fraction of primary dendritic NiAl increases from 21.1% to 25.9%, while the size and the arm spacing of NiAl primary dendrite reduces simultaneously. The room temperature (RT) fracture toughness and the tensile strength at RT and elevated temperature (1373 K) present the valley value at intermediate rate (8 mm/min) among the withdrawal rate range which could be attributed to the decrease in volume fraction of eutectic NiAl/Cr(Mo) microstructure and the refinement of microstructure resulted from the increase of withdrawal rates. In terms of RT tensile elongation, the DS alloy grown at different withdrawal rates all break with no plastic flow.

 

رفتار اصطکاکی و سایشی کامپوزیت های سرامیک- آلیاژ آلومینیوم

Friction and Wear Behaviour of Brake Pads Dry Sliding Against

Semi-Interpenetrating Network Ceramics/Al-alloy Composites

رفتار اصطکاکی و سایشی ناشی از سایش خشک لنت های ترمز بر روی

شبکه نیمه نفوذی کامپوزیت های سرامیک/ آلیاژ آلومینیومی 

ABSTRACT

Semi-interpenetrating network composites containing 40 vol.% ceramics (5Al2O3·8SiO2) and 60 vol.% Al-alloy were fabricated in place of cast iron available for automotive brake rotors. The friction and wear performances of brake pads dry sliding against the composites were measured using a SRV testing machine. The test procedures include friction fade and recovery, load sensitivity at 100 and 250°C, and wear. The friction was found to increase first and then decrease with increasing temperature, followed by the inverse recovery upon cooling. Wear showed an incremental tendency over a wide temperature range. For loads from 40 to 160 N, the friction decreased at 100 and 250°C. At load below 128 N, the former friction was inferior to the latter while at load above 128 N the friction exhibited an inverse tendency. Wear mildly increased with load at 100 °C and decreased dramatically at 250 °C. SEM and EDS investigations revealed that the worn pad surfaces at 250 °C were covered by more tribofilms, including more coke and graphite with friction-reducing action as well as fewer compounds (corresponding to Si and Al) with friction-increasing action in comparison with those at 100 °C. The compression of the tribofilms contributed to a large decrease in the friction and wear with increasing load. However, at 100 °C E-glass fibers exposed at the worn surfaces inhibited the excessive wear of the pad despite lack of more tribofilms. Their glossy surfaces decreased the friction. The proposed friction models explain some friction and wear behaviour better.

 

مدل‎های چند مقیاسی از کامپوزیت‎های زمینه سرامیکی بافته شده

Multiscale model of woven ceramic matrix composites

considering manufacturing induced damage

مدل‎های چند مقیاسی از کامپوزیت‎های زمینه سرامیکی بافته شده

با توجه به آسیب‎های ایجاد شده‎ی تولید

ABSTRACT

Multiscale models play an important role in capturing the nonlinear response of woven carbon fiber reinforced ceramic matrix composites. In plain weave carbon fiber/silicon carbide (C/SiC) composites, for example, when microcracks form in the as-produced parts due to the mismatch in thermal properties between constituents, a multiscale thermoelastic framework can be used to capture the initial damage state of these composites. In this paper, a micromechanics-based multiscale model coupled with a thermoelastic progressive damage model is developed to simulate the elastic and damage behavior of a plain weave C/SiC composite system under thermal and mechanical loading conditions. The multiscale model is able to accurately predict composite behavior and serves as a valuable tool in investigating the physics of damage initiation and progression, in addition to the evolution of effective composite elastic moduli caused by temperature change and damage. The matrix damage initiation and progression is investigated at various length scales and the effects are demonstrated on the global composite behavior.

 

تفجوشی، شکل دهی، واکنش و رشد بلور توسط سیستم پلاسمای جرقه ای (SPS)

Sintering, consolidation, reaction and crystal growth by

(the spark plasma system (SPS

تفجوشی، شکل دهی، واکنش و رشد بلور توسط سیستم پلاسمای جرقه ای (SPS)

ABSTRACT

The graphite die set in spark plasma system (SPS) is heated by a pulse direct current. Weak plasma, discharge impact, electric field and electric current, which are based on this current, induce good effects on materials in the die. The surface films of aluminum and pure WC powders are ruptured by the spark plasma. Pure AlN powder is sintered without sintering additives in the electric field. The spark plasma leaves discharge patterns on insulators. Organic fibers are etched by the spark plasma. Thermosetting polyimide is consolidated by the spark plasma. Insoluble polymonomethylsilane is rearranged into the soluble one by the spark plasma. A single crystal of CoSb3 is grown from the compound powders in the electric field by slow heating. Coupled crystals of eutectic powder are connected with each other in the electric field.

 

اثر زیرلایه روی جوانه زنی و رشد نانو ورق های عمودی گرافن

Influence of substrate on nucleation and growth of

verticalgraphene nanosheets

اثر زیرلایه روی جوانه زنی و رشد نانو ورق های عمودی گرافن

ABSTRACT

The present study reports the role of substrate on nucleation and growth of vertical graphene nanosheets (VGNs) under electron cyclotron resonance chemical vapor deposition (ECR-CVD). The VGNs are grown on Pt, Ni, Au, Cu, Si(100), Si(111), SiO2 and quartz substrates simultaneously. The morphology of VGNs is found to vary significantly with substrate. VGNs on Pt have the highest aerial density of vertical sheets while quartz have the lowest. The structural defects in VGNs vary with substrate as evidenced from Raman spectroscopy. The observation of defect related Raman bands such as D'' and D* at 1150 and 1500 cm-1, respectively revealed the existence of pentagon-heptagon rings or carbon onions in VGNs. Formation of such defects at early stage of nucleation dictates the growth mechanism and hence the morphology. A phenomenological four stage model is discussed, to substantiate the nucleation and growth mechanism of VGNs on different substrates, by evoking substrate - plasma interaction during growth.

 

رشد نانولوله‌های کربنی روی فیبرهای کربنی توسط CVD حرارتی

Growth of Carbon Nanotubes on Carbon Fiber by

Thermal CVD Using Ni Nanoparticles as Catalysts

رشد نانولوله‌های کربنی روی فیبرهای کربنی توسط CVD حرارتی

با استفاده از نانوذرات نیکل به عنوان کاتالیزور

ABSTRACT

Nickel nanoparticles and thin film on carbon fiber have been prepared through electroless deposition. Moreover, carbon nanotubes were grown on carbon fiber covered by nickel nanoparticles using thermal chemical vapor deposition. The effects of changes in the thickness of the nickel catalyst layer and the growth temperature of carbon nanotubes were studied systemically, and the results are discussed in the present work.

 

بازیافت پلیمرهای تقویت شده با الیاف

Current status of recycling of fibre reinforced polymers:

Review of technologies, reuse and resulting properties

وضعیت فعلی بازیافت پلیمرهای تقویت شده با الیاف:

مروری بر روش‎ها، استفاده‎ی مجدد و خواص نهایی

ABSTRACT

A complete review of the different techniques that have been developed to recycle fibre reinforced polymers is presented. The review also focuses on the reuse of valuable products recovered by different techniques, in particular the way that fibres have been reincorporated into new materials or applications and the main technological issues encountered. Recycled glass fibres can replace small amounts of virgin fibres in products but not at high enough concentrations to make their recycling economically and environmentally viable, if for example, thermolysis or solvolysis is used. Reclaimed carbon fibres from high-technology applications cannot be reincorporated in the same applications from which they were recovered, so new appropriate applications have to be developed in order to reuse the fibres. Materials incorporating recycled fibres exhibit specific mechanical properties because of the particular characteristics imparted by the fibres. The development of specific standards is therefore necessary, as well as efforts in the development of solutions that enable reusers to benefit from their reinforcement potential. The recovery and reuse of valuable products from resins are also considered, but also the development of recyclable thermoset resins. Finally, the economic and environmental aspects of recycling composite materials, based on Life Cycle Assessment, are discussed.

 

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.

 

متالورژی منگنز -Manganese metallurgy

Manganese metallurgy review . Part I: Leaching of ores/secondary materials and

recovery of electrolytic/chemical manganese dioxide

مروری بر متالورژی منگنز. قسمت I: فروشویی سنگ‌های‌معدنی/مواد ثانویه

و بازیافت الکترولیتی/شیمیایی دی‌اکسید منگنز

ABSTRACT

The world rapidly growing demand for manganese hasmade it increasingly important to develop processes for economical recovery of manganese from low grade manganese ores and other secondary sources. Part I of this review outlines metallurgical processes for manganese production from various resources, particularly focusing on recent developments in direct hydrometallurgical leaching and recovery processes to identify potential sources of manganese and products which can be economically produced. 

High grade manganese ores (N40%) are typically processed into suitable metallic alloy forms by pyrometallurgical processes. Low grade manganese ores (b40%) are conventionally processed by pyrometallurgical reductive roasting or melting followed by hydrometallurgical processing for production of chemical manganese dioxide (CMD), electrolytic manganese (EM) or electrolytic manganese dioxide (EMD).