پایداری ساختاری مواد نانوکریستالین – رشد دانه

Stability of structural nanocrystalline materials grain growth

پایداری ساختاری مواد نانوکریستالین – رشد دانه

ABSTRACT

Knowledge of the thermal stability of nanocrystalline materials is important for both tech­  nological and scientific reasons. From a technological point of view, the thermal stabil­ ity  is important for consolidation of nanocrystalline particulates without coarsening the  microstructure.That is, many methods, as described in Chapter 2, for synthesis ofnanocrys­ talline  materials result in particulate products which must be consolidated into bulk form. Since most  consolidation processes involve both heat and pressure, the thermal stability of the nanoscale  microstructure is always at risk. The goal of particulate consolidation is to attain essentially  100% theoretical density and good particulate bonding while preventing or minimizing grain growth  of the nanocrystalline grains. Understanding the scientific nature of stability, grain growth of nanocrystalline  microstructures is a criterion for allowing strategies for minimizing grain growth to be devel­  oped. A basic scientific question with regard to nanocrystalline materials is whether their  behavior involves ''new physics" or is simply the expected grain-size-dependent behavior  extrapolated to nanocrystalline grain sizes. Thermal stability is an important phenomenon to be  addressed in this regard. The thermal stability in a broader sense involves not only the  stability of the grain structure, that is the microstructure, but also the stability of the  structure of the grain boundaries in nanocrystalline materials. A number of investigations on the  thermal stability of nanocrystalline materials have been conducted. Grain growth in  nanocrystalline materials has been reviewed by Suryanarayana (1995), Weissmuller (1996), and  Malow and Koch (1996a,b). In this chapter we will discuss the thermal sta­ bility, grain growth  of nanocrystalline materials with reference to experimental methods for measuring grain growth,  grain-growth theories for conventional grain-size materials which may be applicable, grain growth  (secondary recrystallization) at ambient tempera­ tures in nanocrystalline metals, strategies for  inhibition of grain growth in nanocrystalline materials, and examples of experimental studies of  grain-growth kinetics in nanocrystalline materials.

اثر عملیات حرارتی در جوشکاری انفجاری فولاد زنگ نزن/مس

Effect of heat treatment on bonding interface in explosive welded
copper/stainless steel

اثر عملیات حرارتی روی فصل مشترک اتصال در جوشکاری انفجاری فولاد زنگ نزن/مس

ABSTRACT

In this investigation, explosive welding and heat treatment processes provided an effective method for manufacturing high-strength and high-ductility copper/ austenitic stainless steel couple. In order to improve diffusion in the interface of copper/stainless steel, first the tensile samples were provided from the welded part, then they were subjected to annealing at 300 C (below recrystallization temperature) for 8–32 h with 8 h intervals and then samples were cooled in the furnace. Optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were utilized to evaluate the possibility of diffusion in the joints. Moreover, in order to measure the hardness of the samples, microhardness test was performed. Microstructural evaluations showed that the stainless steel 304L had a wavy interface. Furthermore, the post heat treatment process resulted in great enhancement of diffusion. Microhardness measurements showed that the hardness of the sample near to the interface is greatly higher than other parts; this is due to plastic deformation and work hardening of copper and stainless steel 304L in these regions. The interface of samples with and without the post heat treatment was exhibited ductile and brittle fracture, respectively.

جوشکاری حالت جامد آلیاژ برنج Cu-Zn و فولاد

Solid-state bonding of alloy-designed Cu–Zn brass and steel

associated with phase transformation by spark plasma sintering

جوشکاری حالت جامد آلیاژ برنج Cu-Zn مخصوص و فولاد وابسته به استحاله فازی

به وسیله ی زینترینگ به کمک قوس پلاسما

ABSTRACT

Solid-state bonding between steel and a Cu alloy was studied to investigate fabrication of advanced bimetallic composites by using spark plasma sintering (SPS). In order to obtain proper bonding strength between the mating materials, Si and Al were alloyed to Cu–Zn brass to enhance interdiffusion with steel. The alloying elements diffused from the Cu alloy to steel, which transformed from the gamma to alpha phase during bonding. Owing to the phase stability of steel, the new columnar microstructure that evolved during the transformation across the joint interface showed high bonding strength between the mating alloys. The samples bonded without fracture, defects, or inhomogeneous deformation. Microstructural observations, elementary mapping, and mechanical testing demonstrated that the SPS technique and specific bonding parameters enhanced the interdiffusion between the metals. This novel method would be well suited to strengthen bonding between two dissimilar metals with different diffusion coefficients.

 

ارزیابی ساختار در اتصال نفوذی آلیاژ تیتانیوم/فولاد زنگ نزن

THE EVOLUTION CHARACTERISTICS AND NUMERICAL
ANALYSIS OF DIFFUSION BONDING INTERFACE
STRUCTURE OF TITANIUM ALLOY/Cu/STAINLESS STEEL

ارزیابی خصوصیات و آنالیز عددی ساختار در فصل مشترک اتصال نفوذی آلیاژ تیتانیوم/فولاد زنگ نزن

ABSTRACT

Carries on the investigation to the titanium alloy/Cu/stainless steel intermetallic compound of bonding interface in the meantime, to make a thermodynamic model of the interface element diffusion to have a numerical simulation of the diffusion distance and diffusion temperature, time. Using analysis methods of stretching test, microhardness test, SEM and EDS, to investigate and research the mechanical properties, the interface structure characteristic, the principal element atomic diffusion mechanism of joints thermal simulation and the vacuum diffusion bonding of Ti-6Al-4V/Cu/304, the reacting phases are produced and the distribution range . The results show that when bonding prssere is 5.0 MPa ، the joints tensile strength first increase and then decreases, with bonding temperature and time rising, When bonding temperature is 1223K, bonding time is 3.6 ks, there is a maximum tensile strength that is 162.73 MPa. However, it will is disadvantageous to performance of the joints, when bonding temperature and time extended overly. It formed multi-phase transition organizations by solid solution, intermetallic compounds in the bonding interface, such as Ti2Cu, TixCuy , Ti2Fe, TiFe2 and TiFe. Effect of TixFey on strength of the joints is slightly inferior the TixCuy compound. The fracture is mainly by the titanium alloy side region III for the source dehiscence, developing in the weak diffusion layer.

اتصال نفوذی آلیاژ مس به فولاد زنگ نزن تحت فشار ناگهانی

Impulse pressuring diffusion bonding of a copper alloy to a stainless

steel with/without a pure nickel interlayer

اتصال نفوذی آلیاژ مس به فولاد زنگ نزن تحت فشار ناگهانی همراه با یک لایه ی نیکل خالص بین آن ها و یا بدون آن

ABSTRACT

Impulse pressuring diffusion bonding of a copper alloy to a stainless steel was performed in vacuum. Using Ni interlayer of 12.5 lm, the joint produced at 825 C under 5–20 MPa for 20 min exhibited lower strength, which could result from the insufficient thermal excitation and plastic deformation. At 850 C under 5–20 MPa for 5–20 min, the strength of the joint improved with time. An optimized joint strength reached up to 217.2 MPa. Fracture occurred along the Cu–Ni reaction layer and the Ni layer and almost plastic fracture was confirmed by extensive dimples on the fracture surface. Using the interlayer of 50 lm, the fracture surface was similar. Without Ni assistance, under the same bonding condition, the joint strength was about 174.2 MPa. The lowered strength might be attributed to the appearance of some unbonded zones in the joint. Lots of brittle fracture areas appeared on the fracture surface.

مقدمه ای بر ریخته گری تحت فشار و عیوب رایج در آن

Introduction Of High Pressure Die-Casting

And Common Defects In Die-Casting

مقدمه ای بر ریخته گری تحت فشار و عیوب رایج در آن

ABSTRACT

Die casting is a manufacturing process that can produce geometrically complex metal parts through the use of reusable molds, called dies. The die casting process involves the use of a furnace, metal, die casting machine, and die. The metal, typically a non-ferrous alloy such as aluminum or zinc, is melted in the furnace and then injected into the dies in the die casting machine. There are two main types of die casting machines - hot chamber machines (used for alloys with low melting temperatures, such as zinc) and cold chamber machines (used for alloys with high melting temperatures, such as aluminum). The differences between these machines will be detailed in the sections on equipment and tooling. However, in both machines, after the molten metal is injected into the dies, it rapidly cools and solidifies into the final part, called the casting. The steps in this process are described in greater detail in the next section.

توسعه مواد کاربید تیتانیوم و هافنیوم فوق سخت

on Development of Ultrahard Hafnium and Titanium Carbide Materials 

توسعه مواد کاربید تیتانیوم  و هافنیوم فوق سخت

ترجمه فصل اول ودوم

ABSTRACT

A mixture of HfC and Itc powders and a (Hf,Ti)C powder have been hot pressed with 4wt% Ni , In the absence of Ni the hot pressed temperature was 2000 C and in the presence of Ni 1650 C . The pressure of 30 MPa was applied in both cases . The starting powders were substoichiometric as deduced from XRD spectra analyses , and the (Hf,Ti)C powders consisted of a range of composition , as indicated by the width of the XRD peaks. In the absence of Ni the powders sintered without the formation of a liquid phase.In the case of HfC and TiC mixture , high – energy dry milled HfC + TiC +C black powder sintering occurred with simultaneous formation of (Hf,Ti)C Solid solution . In the presence of Ni,sintering occurred with the formation of a liquid phase . the volume fraction of the liquid phase formed was sufficieng to yield a low porosity . grain growth was less than in the case of material sintered without Ni,Probably just on account of lower sintering temperature . In the case of high – energy dry milled the reduction in particle size was observed.

تأثیر مقدار HfC بر خواص مکانیکی کامپوزیت های HfC-W

The effect of HfC content on mechanical properties HfC–W composites

تأثیر مقدار HfC بر خواص مکانیکی کامپوزیت های HfC-W

ABSTRACT

For improving the mechanical properties of tungsten, HfC–W composites were fabricated by ball milling and spark plasma sintering process. Themicrostructure andmechanical properties of the compositeswere investigated. The interdiffusion of the Hf and Watoms during sintering produced a mixed carbide, identified as (Hf,W)C. This interfacial mixed carbide helped in developing a good interface joint with the adjacentW matrix. The increase in mechanical properties of the HfC–W composite at room temperature as well as high temperature was attributed to the reinforcement effect of the HfC particles. One of the strengthening mechanisms of the composite can be attributed to the formation of mixed carbide (Hf,W)C by interdiffusion at the interface, which assured the effective load transfer from the Wmatrix to the hard HfC particles.

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.