طیف سنجی نشر اتمی با پلاسمای جفت شدۀ القایی

Inductively coupled plasma atomic emission spectroscopy

طیف سنجی نشر اتمی با پلاسمای جفت شدۀ القایی

ABSTRACT

Inductively coupled plasma atomic emission spectroscopy (ICP-AES) is an analytical technique for elemental determinations in the concentration range of major to trace based on the principles of atomic spectroscopy. In theory, the technique applies to all elements except argon, and samples may be introduced as liquids, gases, or solids. In practice, favorable analytical results are obtained for approximately 70 elements, with detection limits usually attainable at the parts per billion level, and most samples are introduced in liquid form as aqueous solutions. The technique has found widespread application in the metallurgical, geological, environmental, agricultural, industrial, and biological fields and is an important technique in the modem analytical laboratory.

 

تولید کامپوزیت‌های B4C-TiB2 با پرس گرم

Microstructure and mechanical properties of B4C–TiB2

composites prepared by reaction hot pressing using Ti3SiC2

ریزساختار و خواص مکانیکی کامپوزیت‌های B4C-TiB2 تولیدشده توسط پرس گرم

با استفاده از Ti3SiC2 به عنوان افزودنی

ABSTRACT

B4C–TiB2 composites were fabricated via reaction hot pressing at 2100 °C under a pressure of 25 MPa, using B4C and Ti3SiC2 powders as raw materials. The phase transformations, microstructure and mechanical properties were investigated by XRD, TG–DTA, SEM, TEM and EDS. It is found that the SiC and TiB2 particles are homogenously dispersed in the B4C–TiB2 composites, where nano-sized TiB2 particles are mainly located within the B4C matrix grains, while the large-sized TiB2 particles at the matrix grains boundaries. Due to the pinning effect of SiC and TiB2 particles on B4C grain growth, the grain size of the composite is significantly reduced, leading to a great improvement of the mechanical properties. B4C–TiB2 composite prepared from B4C-10 wt% Ti3SiC2 starting powder shows high flexural strength, fracture toughness and micro-hardness of 592 MPa, 7.01 MPa m1/2 and 3163 kg/mm2, respectively. Crack deflection and crack bridging are most likely the potential toughening mechanisms in the composites. Furthermore, according to the XRD and TG–DTA analysis, the possible reaction mechanisms leading to the in-situ formation of TiB2 were proposed.

پوشش‎های سخت با روانسازی تطبیقی دما بالا و مدیریت حرارتی محل تماس

Hard coatings with high temperature adaptive lubrication

and contact thermal management

پوشش‎های سخت با روانسازی تطبیقی دما بالا و مدیریت حرارتی محل تماس

ABSTRACT

Progress in the design and exploration of hard coatings with high temperature adaptive behavior in tribological contacts is reviewed. When coupled with most recent surface engineering strategies for high temperature contact thermal management, this progress opens a huge opportunity for adaptive coating applications on machine parts, where oils and coolants are commonly used. The adaptive mechanisms discussed here include metal diffusion and formation of lubricant phases at worn surfaces, thermally- and mechanically-induced phase transitions in hexagonal solids, contact surface tribo-chemical evolutions to form phases with low melting point, formation of easy to shear solid oxides, and others. All of these adaptive mechanisms are combined in nanocomposite coatings with synergistic self-adaptation of surface structure and chemistry to lubricate from ambient temperatures to 1000 °C and provide surface chemical and structural reversibility during temperature cycling to maintain low friction coefficients. The review also highlights emerging surface adaptive concepts, where advances with ab initio modeling of intrinsically layered solids point to new compositions for thermally stable, easy to shear ceramic coatings, load- and temperature-adaptive surfaces with arrays of compliant carbon and boron nitride nanotubes as well as low friction two-dimensional structures. Approaches for self-regulation of coating thermal conductivity, heat flow, and thermal spike mitigations are discussed in the context of surface structure evolution and phase transitions. Future progress is linked to the development of in situ exploration techniques, capable of identifying adaptive surface chemistry and structural evolutions in broad temperature regimes. When combined with predictive modeling, such approaches drastically accelerate adaptive coating developments. The review identifies opportunities, strategies, and challenges for designs and applications of hard coatings with high temperature adaptive lubrication and contact thermal management.

 

رفتار قالب پرکنندگی مذاب های تیتانیوم Mold-filling behavior of titanium melts in vertically rotating molds

Effect of centrifugal and Coriolis forces on

the mold-filling behavior of titanium melts in vertically rotating molds

اثرات نیروهای گریز از مرکز و نیروهای کوریولیس بر رفتار قالب پرکنندگی مذاب های تیتانیوم

در قالب هایی که به صورت عمودی می چرخند

ABSTRACT

The vertical centrifugal-casting technique is widely used in the manufacture of various irregularly-shaped castings of advanced structural alloys with thin walls, complex shapes and/or large sizes. These castings are used in the increasing applications in aero-space/aviation industries, human teeth/bone repairs with near-net shaped components, etc. In a vertically rotating casting system, the mold-filling processes of alloy melts, coupled with solidification-heat transfer, may be much more complicated, because they are driven simultaneously by gravity, centrifugal and Coriolis forces. In the present work, an N-S/VOF-equations-based model, solved using a SOLA-VOF algorithm, under a rotating coordinate system was applied to numerically investigate the impacts of centrifugal and Coriolis forces on metallic melt mold-filling processes in different vertical centrifugal-casting configurations with different mold-rotation rates using an authors' computer-codes system. The computational results show that the Coriolis force may cause remarkable variations in the flow patterns in the casting-part-cavities of a large horizontal-section area and directly connected to the sprue via a short ingate in a vertical centrifugal-casting process. A "turn-back" mold-filling technique, which only takes advantage of the centrifugal force in a transient rotating melt system, has been confirmed to be a rational centrifugal-casting process in order to achieve smooth and layer-by-layer casting-cavities-filling control. The simulated mold-filling processes of Ti-6AI-4V alloy melt, in a vertical centrifugal-casting system with horizontally-connected plate-casting cavities, show reasonable agreement with experimental results from the literature.

 

روش های حرارتی برای بازیافت ضایعات کامپوزیتی

Thermal methods for recycling waste composites

روش های حرارتی برای بازیافت ضایعات کامپوزیتی

ABSTRACT

This chapter describes a thermal process based on a fluidised  bed for the recycling of glass and carbon fi bre from thermoset  composites. The process is particularly suitable for producing high  quality fi bre from contaminated or mixed materials. The chapter will  describe the fl uidised bed process, and detail the quality of the fi  bres  that are recovered. Applications for the reuse of the fi bre that have  been investigated will then be explained and the prospects for  commercial scale operation considered. Current and future research  directions will be outlined; other relevant research activities will also be mentioned.

 

شکست خستگی در اتصال جوش داده شده آلیاژ آلومینیوم

Features of AcousticEmission Signals during the Initiation 

of a Fatigue Failure in a Welded Joint of an Aluminum Alloy

of the Al–Cu–Mn System

ویژگی های سیگنال انتشار آکوستیک در طول شروع یک شکست خستگی

در یک اتصال جوش داده شده آلیاژ آلومینیوم سیستم Al-Cu-Mn

ABSTRACT

The features of the generation of acoustic emissions (AEs) during the initiation of a fatigue failure in various zones of a welded joint of thermally hardened 2219T6grade aluminum alloy, which is produced using electronbeam welding, are  considered. Metallographic studies showed that a welded joint of the alloy is structurally and mechanically inhomogeneous. This predominantly influ ences the initiation and development kinetics of fatigue cracks in the joint and the AE kinetics. It is shown that the area of a formed flaw is proportional to the sum of the amplitude of detected signals, and the transition from the initiation to the stable propagation of a failure is accompanied by an abrupt increase in AE activity.

 

جوشکاری تیگ آلومینیوم و منیزیم

اتصال آلومینیوم و منیزیم از طریق جوشکاریA-TIG

 با پیش نورد کمکی همراه با لایه میانی روی 

ABSTRACT

AZ31B Mg and 6061 Al alloys were successfully welded via a novel pre-roll-assisted A-TIG welding technique with Zn interlayer at an overlap configuration. The rolling operation increased the contact area and control tightly between Zn interlayer and plates at an interlayer-assisted overlap configuration to avoid the adverse effect of gaps. B2O3 activating flux was coated on the upper Al plates to provide contraction of the arc column to increase the arc energy density; welding penetration was increased without improving heat input, which reduced the formation and grain coarsening of Al–Mg IMCs. Therefore, the tensile–shear strength of the joints was improved obviously. The average of tensile–shear strength joined was 71.2 MPa with a maximum of 74 MPa compared to 41.1 MPa with a maximum of 45.2 MPa by conventional TIG with Zn interlayer.

 

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.

 

مکانیزم تشکیل رنگ در نانورنگدانه های سرامیکی

Colour performance of ceramic nano-pigments

مکانیزم تشکیل رنگ در نانورنگدانه های سرامیکی

ABSTRACT

Ceramic nano-pigments have been recently developed for ink-jet decoration of ceramic tiles using quadrichromic technology (cyan, magenta, yellow, and black colours). The colouring mechanisms and performance of CoAl2O4, Au, (Ti,Cr,Sb)O2 and CoFe2O4 nano-pigments were investigated by DRS, XRD and colorimetry. The nano-pigments were dispersed in several ceramic glazes and glassy coatings and their colour performance was compared with that of conventional micro-pigments. Each nano-pigment was characterized in terms of its colour mechanism and chemico-physical stability. Although the micro-pigments provided more saturated hues, intense colours were achievable in nano-pigments despite their very small particle size (<50 nm). Limitations to the use of nano-pigments arose for very high firing temperatures (>1200 °C) due to particle growth (e.g. Au) or dissolution in the glassy phase (e.g. titania).

 

جوشکاری اینکونل 625 و فولاد زنگ‎نزن L 304 با پرتوی الکترونی

Microstructure and hardness studies of electron beam

welded Inconel 625 and stainless steel 304L

مطالعه ریزساختار و سختی اینکونل 625 و فولاد زنگ‎نزن L 304

جوشکاری شده با پرتوی الکترون

ABSTRACT

In this study, electron beam welding of dissimilar Inconel 625 and SS 304L alloys was successfully performed by employing optimized electron beam welding parameters. The welded joint was characterized using SEM/EDS, XRD and micro-hardness tester. The welded joint was found homogeneous, well bonded and defect free. Two types of microstructure i.e. columnar dendritic and cellular dendritic were observed in the fusion zone. The development of different microstructures in the fusion zone was attributed to the localized cooling effects during solidification. Few micro-cracks along with dendrites splitting were observed in the vicinity of end crater that was mainly due to the segregation of S element. A significant variation of Ni and Fe was observed across Inconel/FZ and FZ/SS interfaces due to their fast diffusion in the melt pool. Micro-hardness measurements across Inconel/FZ and FZ/SS interfaces showed an increasing trend in the FZ from SS 304L towards Inconel base alloy.