مجله مهندسی متالورژی
پیاپی 53 (بهار 1393)

در این مقاله یک تحقیق بنیادی بر روی استخراج پالادیوم بوسیلهحلال آلی کروزن-تری­بوتیل فسفات انجام شده­است. براساس اطلاعات ترمودینامیکی در سیستم پالادیوم-کلر، کمپلکسهای کلریدی در غلظت­های ناچیز یون کلرو کمپلکسهایدر غلظتهای بالای یون کلر تشکیل می­شوند. استخراج پالادیوم با افزایش غلظت اسید کلریدریک و نمک کلریدی (کلرید سدیم) کاهش می­یابد. به نظر می­رسد علت اصلی این کاهش تمایل کمتر تری­بوتیل فسفات برای استخراج نسبت است. چناچه 25/0 مول بر لیتر تری­بوتیل فسفات در غلظتهای پایین اسید 58% و در غلظتهای بالای اسید 8% را استخراج می­نمایند. براساس روش آنالیز شیب ماکرومولکول استخراجی (حاوی پالادیوم و تری­بوتیل فسفات) برای و کمپلکس مطرح­شده به صورت می باشد. در حالیکه براساس بررسی­های انجام شده، تری­بوتیل فسفات نمی­تواند کمپلکس از محلول کلریدی استخراج ­نماید.

In this study, Influence of formation of Cr-rich precipitates on microstructure and mechanical properties of Fe-23­Cr-2.4­Mo ferritic stainless steel has been investigated. In this regard, samples of this steel were homogenized at 1100°C for 48 hours and then were cooled in furnace. Microstructure, phase composition, and hardness of the samples were investigated using optical and scanning electron microscopes, X-ray diffraction and micro-hardness measurements. Results of microstructural observations and thermodynamic evaluations showed that Cr-rich precipitates are formed in the steel microstructure due to slow cooling after homogenizing treatment. In order to dissolve the Cr-rich precipitates; formed during slow cooling, a number of samples were subjected to solution treatments at 1100°C, 1150°C for 5 hours and then were quenched in water. Results showed that at temperature of 1100°C precipitates are not dissolved entirely but at 1150°C they are dissolved completely. After solution treatment at 1150°C followed by water quenching no longer precipitation is took place due to the fast cooling rate. Results of phase analysis and microhardness measurements showed that solution treatment at 1150°C lead to increase of ferrite lattice parameter from 2.880 Åto 2.893Å and also enhancement hardness from 211 to 317 Vickers despite an increase in ferrite grain size. These results confirm dissolution of Cr-rich precipitates in the ferrite matrix.

In this research properties of Single-Step High temperature-High activity Si-modified Nickel Aluminide coating on superalloy Inconel 100 at 1000 and 1100˚C have been investigated. Si-modified NiAl coating were prepared using 5 and 10 percent mass of Al and Si powders as well as Al2O3 and NH4Cl activators. Microstructure, phase distribution and coating composition of as-coated specimens were analyzed by using OM, SEM equipped with EDS/WDS and XRD. The results showed that co-precipitation of Al and Si using Single-Step High Temperature-High Activity process can be achieved. By reducing Al and Si amount in the pack from %10 to %5 in mass, the coating depth enriched by Si decrease from 50 to 20μm. In 1 hour, With %10 in mass pack hyperstoichiometric NiAl phase with more than %50 at of Al was formed while after 1 and 3 h aluminizing with %5 in mass pack, hypostoichiometric NiAl phase with less than %50 at of Al was formed. Micro hardness test results have shown that hardness of formed surface coating varies from 449 VHN in substrate to 1003 VHN in interdiffusion zone duo to presence of various carbides with complex composition.

Severe plastic deformation is one of the most effective methods for applying high plastic strain to metallic specimen. Constrained Groove Pressing (CGP) and Repetitive Corrugation and straightening (RCS) are preeminent in this field. There are several similarities between these two processes, however, there are some differences in applied strain. Consequently, the deformation process is really crucial in case of method. In this study, AA 1070 Aluminum alloy has been utilized in order to investigate the behavior of deformation using stated methods. Therefore, filling of the die, effective strain distribution and required load to perform the process were analyzed using Finite Element Analysis (FEA) for a single pass of deformation. To evaluate homogeneity of applied deformation, inhomogeneity index of effective strain was considered. The simulations are carried out using commercially available DEFORM-3DTM software and for validation, the results were compared to former reported researches. It was revealed that the amount of filling of the die was greater for CGP in comparison with RCS. As a result, it is feasible to repeat the process in order to obtain high plastic strain. Furthermore, the deformed specimen experienced more plastic strain for CGP. In addition, this strain distribution was imposed homogeneously thus the mechanical properties can be improved uniformly in the specimen.

In recent years, Ionic Polymer Metal Composites (IPMC) have been extensively used in various industries. They are new generation of smart materials for fabrication of actuators. IPMC is a layered polymer-metal composite with high technology processing. The objective of this project is production and processing of Polypyrrole - gold - Polyvinylidene fluoride (PVDF) composite. The porous PVDF membranes were first sputtered with gold as a conductive layer. The solution of propylene carbonate, pyrrole and lithium triflouromethane sulfonamide salt employed as electrolyte for electroplating of poly pyrrole on gold layer in controlled condition. The composite layers and the influences of temperature, current and time of electroplating electrolyte concentration and the thickness of gold layer on characteristics of IPMC were investigated with SEM and FTIR analysis. The results indicated that with increase of the thickness of gold layer and electroplating duration the thickness of polypyrrole layer increases in 0.1 molar concentration of pyrrole and lithium triflouromethane sulfonamide salt temperature of -25 °C.

Dual phase steels have unique properties such as continuous yielding, low ratio of yield strength to tensile strength, high work hardening rate and homogenous elongation percent which are applicable for vehicle industries. Triple phase steels are a developed type of dual phase steels which contains ferrite, bainite and martensite. In this study, triple phase microstructure with 34Vol.% ferrite was obtained for AISI4140 steel using appropriate heat treatment. Then, tempering was performed for triple phase microstructures at 250, 450 and 650oC temperatures for 90 min and microstructural studies and mechanical tests including tensile and hardness were used for the related microstructures. Microstructural studies using optical and scanning electron microscops revealed the three phases as well as tempered martensite and secondary carbides formed during tempering. The results of tensile test showed continuously reduction of yield strength and ultimate tensile strength and also increase of elongation with increasing tempering temperature. The fracture surfaces of tensile tested specimens showed more ductile behavior at 650oC tempering temperature which was in agreement with other mechanical properties.

In this research the main purpose was finding and improving a technical and practical process to produce aluminum based foam. As a result; aluminum-A356 foam was produced using melting process, the molten A356 was alloyed by adding 4%Wt of Copper(4%WtCu-Al) to be apt for aging, then foam was produced by using TiH2 Nano scale powder as foaming agent. Ageing heat treatment cycle was performed on alloyed foam then cell structure and mechanical properties for both alloyed and not alloyed foam was compared. Results was shown cell structure for the foam with Cu is spherical with smooth layer which is crooked and elliptical that for A356-foam. The uniaxial compressive yield strength, as a result of this heat treatment cycle, was increased from 10 to 27.5 MPa, about 170% increase in yield strength. The energy absorption, was measured by uniaxial compressive loading, was shown an increase of about 160% for the aged alloy in comparison to non-heat-treated specimen. So to achieve this final properties adding 4-5 percent of Cu following the heat treatment cycle is the main result of this research. The cycle, solution process at 510 °C for 12 hours and then quenching in cold water, carrying on the process by aging at 160 °C for 3 hours culminate in best mechanical properties for A356+4%wt.Cu.