رفتار سینترینگ، ریزساختار و خواص مکانیکی کاربیدهای بسیار دیرگداز

Sintering Behavior,Microstructure, and Mechanical Properties: A Comparison among

 Pressureless Sintered Ultra-Refractory Carbides

رفتار سینترینگ، ریز ساختار و خواص مکانیکی: مقایسه ای میان کاربیدهای بسیاردیرگداز سینترشده بدون اعمال فشار

ABSTRACT

Nearly fully dense carbides of zirconium, hafnium, and tantalum were obtained by pressureless sintering at 1950 ◦C with the addition of 5–20 vol% of MoSi2. Increasing the amount of sintering aid, the final density increased too, thanks to the formation of small amounts of liquid phase constituted by M-Mo-Si-O-C, where M is either Zr, Hf, or Ta. The matrices of the composites obtained with the standard procedure showed faceted squared grains; when an ultrasonication step was introduced in the powder treatment, the grains were more rounded and no exaggerated grains growth occurred. Other secondary phases observed in the microstructure were SiC and mixed silicides of the transition metals. Among the three carbides prepared by pressurless sintering, TaC-based composites had the highest mechanical properties at room temperature (strength 590 MPa, Young’s modulus 480 GPa, toughness 3.8MPa·m1/2). HfC-basedmaterials showed the highest sinterability (in terms of final density versus amount of sintering aid) and the highest high-temperature strength (300 MPa at 1500 ◦C).

رشد ترکیبات بین فلزی در ریخته گری مرکب دوفلزی مس و آلومینیوم

Formation of Intermetallic Phases in Al/Cu Compound Casting Process

بررسی رشد ترکیبات بین فلزی در ریخته گری مرکب دوفلزی مس و آلومینیوم

ABSTRACT

The purpose of this article is to study the growth rate of intermetallic compounds at the welded interface of Al/Cu bimetal were produced by compound casting process. The mechanism of the intermetallic compounds (IMCs) formations, the effects of aluminum pouring temperature and copper preheating temperature on the IMCs types and thickness were investigated and Al/Cu interface microstructure, were characterized by optical microscope (OM) and electron probe micro-analyzer (EPMA). Results show that the interface is consist of three main layers, the first Layer (I) is α-Al/Al2Cu eutectic structure, the second layer (II) is Al2Cu and the third layer (III) consists of the several intermetallic compounds such as AlCu, Al3Cu4, Al2Cu3, Al4Cu9. The first layer was formed by Al and Cu dissolving in liquid phase and rapid solidification, then the second layer II was formed by nucleation and growth mechanism at solid/liquid interface and finally the layer III was formed by solid-state phase diffusion. Raising the Al melt pouring temperature and preheating Cu leads to increase of the intermetallic compounds thickness at interface and consequently increases the specific electrical resistance and decreases the Al/Cu bond strength. From experiments, it is proposed that the bond strength is dominated by the thicknesses of layer II and III.

نفود ترکیب تک و چند جزئی در رقیق سازی بینهایت در فونیک ایزوبوتیل

Single and multi-component diffusion at infinite dilution in polyisobutylene  

نفود ترکیب تک و چند جزئی در رقیق سازی بینهایت در فونیک ایزوبوتیل

ABSTRACT

In this study, diffusion coef®cients of acetone, benzene, chloroform, cyclohexane and methyl ethyl ketone (MEK) in polyisobutylene (PIB) have been measured at temperatures in the range 40± 70°C using capillary column inverse gas chromatography (CCIGC). The measured diffusion coef®cients for the PIB/MEK system, considered to be at in®nite dilution of the solvent, agree very well with those determined previously from gravimetric and spectroscopic techniques when extrapolated to the limit of zero MEK concentration. The Vrentas±Duda free-volume theory for diffusion is used to correlate the diffusivity data at in®nite dilution as a function of temperature, and the effect of solvent size on the diffusion process in PIB is studied. In addition, diffusion coef®cients of MEK/toluene and MEK/ethanol mixtures in PIB have been measured at 50°C. The CCIGC model for binary systems is used to determine diffusion coef®cients for each solvent individually over a wide range of mixture compositions. The resulting values are identical to those determined from pure component data, con®rming the hypothesis that the diffusion coef®cient at in®nite dilution is independent of a second in®nitely-dilute component, with or without solvation between mixture components.

بررسی مشخصه AFM موانع نفوذی پایه Ta

AFM Characterization of Ta-based Diffusion Barriers for Use in Future Semiconductor Metallization

بررسی مشخصه AFM موانع نفوذی پایه Ta برای استفاده در متالورژیکی نیمه هادی­های آینده

ABSTRACT

In this paper the investigation of r.f.-sputter-deposited Ta, Ta-N and Ta-N-O thin Ðlms is presented. Using atomic force microscopy in combination with sheet resistance measurements, Auger electron spectroscopy and x-ray diffraction, the thin Ðlm properties and microstructure are examined. Two crystalline modiÐcations of Ta (tetragonal b-Ta and bcc a-Ta) are reported. By incorporation of nitrogen and/or oxygen into the Ta Ðlms, nanocrystalline and quasi-amorphous structures can be achieved. Finally, the usefulness of the Ðlms as di†usion barriers in Cu-based metallization systems is described. ( 1997 by John Wiley & Sons, Ltd.

استحکام انحلالی و قابلیت پیر سختی آلیاژهای Al-Mg-Mn

Solution strengthening and age hardening capability of

Al–Mg–Mn alloys with small additions of Cu

استحکام انحلالی و قابلیت پیر سختی آلیاژهای Al-Mg-Mn با مقدار کمی افزودنی مس

ABSTRACT

Nine Al–(1–3)Mg–(0–0.4)Cu–0.15Si–0.25Mn (in wt.%) alloys with potential applications in both packaging and automotive industries have been investigated. Tensile testing showed that solution strengthening is in good approximation linearly proportional to the Mg content. Mechanical testing and microstructural examinations of aged samples indicate that Mg2Si phase precipitates contribute to age hardening of Cu-free alloys, whilst both Mg2Si phase and S (Al2CuMg) phases contribute to that of Cu-containing alloys. The age hardening capability is critically influenced by solution treatment temperature: increasing the solution treatment temperature from 500 to 550 ◦C results in a marked increase in rate of hardening for Cu-containing alloys and solution treatment at about 550 ◦C or higher is needed to allow Mg2Si phase precipitation during ageing in Cu-free alloys with Mg content of about 2% or higher.

ساختار اتصالات جوشکاری شده فولادهای هاردوکس

Structure and hardness changes in welded joints of Hardox steels

ساختار و تغییرات سختی در اتصالات جوشکاری شده فولادهای هاردوکس (Hardox)

ABSTRACT

In the article, the structure and change in hardness of the welded Hardox 400 and Hardox 500 steels have been presented. It has been shown that structures of lower wear resistance are being created as a result of welding those materials in the “as delivered” state (i.e. with the tempered martensite structure) within the heat-affected zones. They are as much as up to 90 mm wide, and that causes their non-uniform and fast wear in the anticipated applications. Based on microscopic tests and hardness measurements a method of thermal joints treatment has been proposed, consisting in their hardening and low-temperature tempering (self-tempering) at the heat-affected zones. It leads to reproduction of that area structure, similar to the native material structure. In the laboratory conditions, a heat treatment differing from the usual practice (stress-relief annealing or normalizing) has not led to welding incompatibilities (cracks).

ارزیابی اثر نیتروژن روی خواص خزشی فولاد زنگ نزن 316LN

Evaluation of the effect of nitrogen on creep properties of 316LN stainless

steel from impression creep tests

ارزیابی اثر نیتروژن روی خواص خزشی فولاد زنگ نزن 316LN در نتیجه آزمون های خزش فشاری

ABSTRACT

Impression creep testing technique is an innovative tool to study creep deformation behavior of materials mainly because it requires relatively short test time and small volume of material for evaluating the creep properties when compared with conventional uniaxial creep testing which is both material and time consuming. The effect of nitrogen on creep deformation behavior of type 316LN stainless steel has been studied using impression creep testing technique. Impression creep tests have been carried out at 923 K up to 1000 h on 316LN stainless steel containing 0.07, 0.11, 0.14, and 0.22 wt.% nitrogen, in the punching stress range of 400–800 MPa. The impression creep curves were characterized by a loading strain, a primary creep stage, and a secondary creep stage similar to uniaxial creep curves. The tertiary stage observed in uniaxial creep tests was absent. The steady state impression velocity was found to increase with increasing punching stress. The calculated stress exponent values varied between 3.3 and 8.2 with increasing in nitrogen content. It was observed that impression velocity was sensitive to the variation in nitrogen content in the steel. The steady state impression velocity was found to decrease with increasing nitrogen content. Correlation between the impression creep parameters and conventional uniaxial creep parameters has been established based on the laws of mechanics for time dependent plasticity.

تأثیر واکنش پذیری ذرات MgSi بر خوردگی آلیاژهایAl-Mg-Si

The influence of MgSi particle reactivity and dissolution processes on

 corrosion in Al–Mg–Si alloys

 تأثیر واکنش پذیری ذرات MgSi و فرآیندهای انحلال بر خوردگی آلیاژهایAl-Mg-Si

ABSTRACT

In Al–Mg–Si alloys, MgSi and Si precipitates are reported to activate corrosion processes. However, their impact is not completely clear because only indirect studies on the influence of Mg and Si on corrosion processes within Al–Mg–Si alloys are available. For this reason, a detailed electrochemical and compositional characterization of MgSi precipitates in Al–Mg–Si during corrosion processes were performed in this study. It was found that in 1M NaCl solution, MgSi particles are selectively de-alloyed by Mg, the process starting within the first few seconds and ceasing after about 20 min. The open circuit potential of the whole surface is controlled by the active Mg dissolution within these 20 min. After de-alloying, the MgSi remnant (Si-rich) is cathodic-active. The cathodic current density is raised by a factor of 3 due to the presence of 0.6% surface fraction MgSi remnants. With regard to the anodic activity, it is seen that MgSi remnants (hole with Si enrichment) do not change the pitting potential in electrochemical micro- and macro-cell experiments. Fe-containing intermetallics can be inactive for the first minutes of immersion and then become active within about 40 min of exposure even though the mixed carbon, Al oxide layer has not completely dissolved.

اثر میکروساختار ماده بر فرسایش ابزار هنگام ماشینکاری آلیاژهای Ti

 Experimental investigation on the effect of the material microstructure on tool wear when machining hard titanium alloys: Ti–6Al–4V and Ti-555

بررسی اثر میکروساختار ماده بر فرسایش ابزار هنگام ماشینکاری آلیاژهای سخت تیتانیوم :  Ti-555; Ti – 6Al – 4V

ABSTRACT

An experimental investigation was conducted in this work to analyze the effect of the workpiece microstructure on tool wear behavior and stability of the cutting process during marching difficult to cut titanium alloys: Ti–6Al–4V and Ti-555. The analysis of tool–chip interface parameters such as friction, temperature rise, tool wear and workpiece microstructure evolution under different cutting conditions have been investigated. As the cutting speed increases, mean cutting forces and temperature show different progressions depending on the considered microstructure. Results show that wear modes of cutting tools used for machining the Ti-555 alloy exhibit contrast from those obtained for machining the Ti–6Al–4V alloy. Because of the fine-sized microstructure of the near-β titanium Ti-555, abrasion mode was often found to be the dominate wear mode for cemented cutting tools. However, adhesion and diffusion modes followed by coating delamination process were found as the main wear modes when machining the usual Ti–6Al–4V alloy by the same cutting tools. Moreover, a deformed layer was detected using SEM–EDS analysis from the sub-surface of the chip with β-grains orientation along the chip flow direction. The analysis of the microstructure confirms the intense deformation of the machined surface and shows a texture modification. 

 

ماشین کاری تیتانیوم و آلیاژهای آن

MACHINING TITANIUM AND ITS ALLOYS

ماشین کاری تیتانیوم و آلیاژهای آن 

ABSTRACT

Titanium and its alloys are attractive materials due to their unique high strength-weight ratio that is maintained at elevated temperatures and their exceptional corrosion resistance. The major application of titanium has been in the aerospace industry. However, the focus shift of market trends from military to commercial and aerospace to industry has also been reported. On the other hand, titanium and its alloys are notorious for their poor thermal properties and are classified as difficult-to-machine materials. These properties limit the use of these materials especially in the commercial markets where cost is much more of a factor than in aerospace. Machining is an important manufacturing process because it is almost always involved if precision is required and is the most cost effective process for small volume production. This paper reviews the machining of titanium and its alloys and proposes potential research issue .