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 فولاد زنگ نزن 316 به روش تیگ TIG-welded 316 stainless steel

Acoustic emisson and ultrasonic wave characteristics

in TIG-welded 316 stainless steel

مشخصات انتشار آکوستیک و امواج مافوق صوت در

فولاد ضد زنگ 316 جوش داده شده به روش TIG

ABSTRACT

A TIG welded 316 stainless steel materials will have a large impact on the design and the maintenance of invessel components including pipes used in a nuclear power plant, and it is important to clear the dynamic behavior in the weld part of stainless steel. Therefore, nondestructive techniques of acoustic emission (AE) and ultrasonic wave were applied to investigate the damage behavior of welded stainless steel. The velocity and attenuation ratio of the ultrasonic wave at each zone were measured, and a 10 MHz sensor was used. We investigated the relationship between dynamic behavior and AE parameters analysis and derived the optimum parameters to evaluate the damage degree of the specimen. By measuring the velocity and the attenuation of an ultrasonic wave propagating each zone of the welded stainless steel, the relation of the ultrasonic wave and metal structure at the base metal, heat affected zone (HAZ) metal and weld metal is also discussed. The generating tendency of cumulated counts is similar to that of the load curve. The attenuation ratios from the ultrasonic test results were 0.2 dB/mm at the base zone, and 0.52 dB/mm and 0.61 dB/mm at the HAZ zone and weld zone, respectively.

 

محدوده دمایی برای تشکیل منطقه GP در آلیاژ آلومینیوم-منیزیم-روی

The Temperature Limit for GP Zone Formation

in an Al-Zn-Mg Alloy

محدوده دمایی برای تشکیل منطقه GP در آلیاژ آلومینیوم-منیزیم-روی  

ABSTRACT

The temperature limit for GP zone formation, Tlimit was determined for an Al-5 pct Zn-2 pct Mg alloy by examining the formation process of the intermediate phase. Studies of changes in hardness and electrical resistivity, together with electron metallography permitted a conclusion that the Tlimit for this alloy is 125 °C. The nucleation mechanism of the intermediate phase is also discussed. Two types of precipitation mode were found the partly coherent phase;i.e. heterogeneous nucleation on GP zones and homogeneous nucleation respectively. It is concluded that the dominant nucleation mode is determined by the quenching conditions.

 

مناطق GP در آلیاژهای Al-Zn-Mg و نقش آنها در پیرسازی مصنوعی

GP-zones in Al–Zn–Mg alloys and their role in artificial aging

مناطق GP در آلیاژهای Al-Zn-Mg و نقش آنها در پیرسازی مصنوعی

ABSTRACT

The structure of GP-zones in an industrial, 7xxx-series Al–Zn–Mg alloy has been investigated by transmission electron microscopy methods: selected area diffraction, conventional and high-resolution imaging. Two types of GP-zones, GP(I) and (II) are characterized by their electron diffraction patterns. GP(I)-zones are formed over a wide temperature range, from room temperature to 140–150°C, independently of quenching temperature. The GP(I)-zones are coherent with the aluminum matrix, with internal ordering of Zn and Al/Mg on the matrix lattice, suggested to be based on AuCu(I)-type sub-unit, and anti-phase boundaries. GP(II) are formed after quenching from temperatures above 450°C, by aging at temperatures above 70°C. The GP(II)-zones are described as zinc-rich layers on {111}-planes, with internal order in the form of elongated <110> domains. The structural relation to the η′-precipitate is discussed.

 

طیف مادون قرمز منیزیم و آلومینیم ‎جایگزین فریت‎های لیتیوم

Far-infrared spectral studies of magnesium and aluminum

co-substituted lithium ferrites

بررسی‎های طیف مادون قرمز دور منیزیم و آلومینیم جایگزین فریت‎های لیتیوم 

ABSTRACT

Polycrystalline MgxAl2xLi0.5(1−x)Fe2.5(1−x) O4 (x = 0.0, 0.2, 0.5, 0.6 and 0.7) ferrites were prepared by standard ceramic method, and characterized by X-ray diffraction and infrared absorption spectroscopy. The spectra show two significant absorption bands in the wave number range of 400–1000 cm−1 arising from interatomic vibrations in the tetrahedral and octahedral coordination compounds. The decrease in intensity and increase in broadness of bands with concentration (x) are explained on the basis of cation distribution. The force constants and bulk modulus are found to decrease with Mg-Al content (x) which suggested weakening of interatomic bonding. An alternate method for the determination of bulk modulus, longitudinal and transverse velocities is suggested. The magnetic and electrical properties of these compounds are explained in the light of structural and optical properties.

 

توزیع یونی و مغناطیسی کردن آلومینیوم جانشین فریت های لیتیمی

Ion distribution and saturation magnetization of

aluminum substituted lithium ferrites

توزیع یونی و مغناطیسی کردن آلومینیوم جانشین فریت های لیتیمی 

ABSTRACT

Ion distribution is determined in a series of aluminum substituted lithium ferrites by carefully analyzing the powder X-ray diffraction patterns. A new finding is that Al+3's substitute the Fe+3's in tetrahedral sites as well as in octahedral sites of the spinel structure. The proper formula, then, is (Fe1-a+3Ala+3)[Li0.5 +Fe1.5-(x-a)Alx-a+3]O 4, where a is approximately 0.23x2+0.22x. The saturation magnetizations are calculated and compared with the measured values.

 

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.

 

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.