نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 24 (بهار 1392)

In this study, the microstructure of dissimilar welding of super duplex stainless steel UNS 32750 to austenitic stainless steel AISI 304L was investigated. For this purpose, gas tungsten arc welding process (DCEN) and two filler metals including ER25104L and ER309LMo were used. The microstructure of the different zone in each joint, including weld metals, heat affected zone, interface were evaluated using optical microscopy was investigated. The investigations showed that austenitic and ferritic structure such as dendrite, weld metal 25104L, with secondary Austenite, 309LMo weld metal was observed as the primary ferrite with austenitic matrix. In addition microstructure was seen as skeleton ferrite morphology. The interface of 304L austenitic stainless steel by two filler metals with epitaxial growth and interface of super duplex UNS 32750 Was seen high ferrite content.

In this study the mechanical properties of bronze composites reinforced with basalt fibers were studied. Basalt fibers are sensitive to the strengthening of the bronze was used in powder metallurgy. Samples were sintered at 850 °C in reducing atmosphere (H2-% 25N2) for 30 minutes. The effects of basalt fibers volume fraction on the friction properties and tensile properties of the composites were investigated. The best tensile and wear properties of basalt fibers is visible in the samples containing 9%. The fracture surfaces of the samples were examined by electron microscopy.

In this study، the capability of methods stir casting، ultrasonic cavitation and combination of two stated methods for making of A356 - 1 wt. % SiC was examined. In all methods، the effect of addition of master powder instead of green nanoparticles into melt was investigated. Metallographic studies by OM and SEM show that fabrication of the cast nanocomposite by use of second or third method is practicable. The synthesis of cast nanocomposite by stir casting is possible only when master powder is used instead of nanoparticles (modified stir casting method). The highly uniform distribution for nanoparticles in matrix is achievable by use of the third method and master powder. The as-cast microstructure of nanocomposites is finer than that of base alloy. The results from hardness test indicates that hardness of nanocomposites is higher than that of base alloy and maximum hardness is observed in the nanocomposite prepared by modified stir casting method.

In this research، nanostructure calcium titanate (CaTiO3: CTO) has been synthesized via mechanical alloying without using heat treatment. Phase development، particle size and morphology of calcium titanate were investigated by X-ray diffraction pattern analysis (XRD)، zetasizer instrument and scanning electron microscopy (SEM)، respectively. XRD results showed the minimum time of calcium titanate phase after 70 hours milling without heat treatment، also the agglomeration a part of powder have shown in SEM images. The results showed the minimum time of calcium titanate synthesis via mechanical alloying without heat treatment is 70 hours that formed and the range of grain size (apparent size) is 69 nm.

In this study، after preparation of Li2O-Al2O3-SiO2-TiO2 base glass containing Cr2O3 dopant using casting method، the effect of different amount of dopant on spectroscopic and optical properties of glass has been investigated. Due to the spectroscopic، optical and structural properties of glasses، UV-Vis and FTIR spectrophotometers have been utilized. Hence، optical parameters such as absorption coefficient، extinction coefficient، Fermi energy level، optical band gap and Urbach energy have been calculated. According to results of calculations، augment of dopant to 1. 5% leads to the reduction of molar volume، optical band gap، Fermi energy، Urbach energy and enhancement of density. The mentioned changes could be attributed to the role of Cr3+ as the network modifier.

In this study the for survey effect of titanium on the microstructure and properties of steel adfield، 4 alloy composition based Containing 1. 2 percent carbon and 12 percent manganese and different amounts of titanium (0. 2، 0. 4 and 0. 6) and a sample without titanium for compared were foundery. Solution heat treated specimens were including austenitizing to 1100 ℃ temperature for three hours and then quench in water. To investigate the microstructure used of optical microscopy and scanning electron microscopy (SEM) and to determine the type of carbides was used elemental analysis (EDX). for wear test was used The pin on disk method. Results from observations and experiments showed that the structural heat threatment completely austenitized (in the sample of No titanium) and non-continuous carbides of titanium in austenitic background (in the sample contain of titanium) were obtained. Increasing titanium، fine grain structure and hardness has increased. In addition to the large difference in the wear resistance of titanium and non-titanium samples obtained. The best wear resistance obtained of the sample with 0. 6% of titanium.

Corrosion tests were conducted on St37 carbon steel and 316 stainless steel in three different molten zinc baths. It was found that، the corrosion rate of stainless steel sample was higher than that of carbon steel. Beside chemical composition of bath، steel chemical composition affected their resistance to corrosion. Available high carbon in steel resulted in forming thick layers on surface of St37 steel and reducing the corrosion. Thin behaviour come be attributed to the thinner intermetallic layer formed on S. S. than that formed on St37 stee which has been confirmed by microscopic examinations. Available lead in bath affected 316 steel coating. The presence of lead in the bath results in the dendritic structure of coating and growth of surface grains which cause to increase the more penetration of zinc into coating.

In recent years، much research in the field of mechanical alloying process for the synthesis of advanced materials has been done. In this investigation، Al2O3-TiN composite by mechanical alloying method were produced. Aluminum and titanium oxide powders was used as a raw materials and milling under N2 atmosphere with 5 atmosphere pressure were performed. The results showed that reduction of TiO2 by Al is the first step of synthesis process and then Ti with N2 were react. When Al/TiO2 molar ratio is equal to 1. 2 and 1. 3، after 20 hours milling، TiN peaks appears in the XRD results. Also، the result of investigation of nitrogen peressure variation with nitriding process promotion of milling showed that nitrogen peressure in the near of process end was drastic decreases.

In this study، the degree of sensitization was examined in AISI 316 type steel by DLEPR method whose experiments have been carried out on steels with different sensitization degree to examine and determine the detailed parameters; concentration and scan rate of the DLEPR method. In order to determine the degree of sensitization، oxalic acid، Huey and Streicher tests were carried out and revealed microstructures and measurements of weight loss by the acid tests were then correlated with DLEPR method results، as a first step towards standardization of DLEPR method for 316 steels. Best agreement was provided with test parameters which are 1M H2SO4 + 0. 005M KSCN at 3 V/hr scan rate with 30 °C solution temperature. Finaly، the Ir: Ia ratios were obtained to determine Ir: Ialimitations for every sensitized Specimen.

In this work، Z-type nano hexagonal ferrites (Ba3Co2Fe24O41) prepared using citrate method. In order to study particle size effects on absorption properties، the ferrite samples were synthesized in two different molar ratios group، CA: EG=6:4، 4:6 with different CA to nitrates molar ratios (Rc). Microstructures and grain size of the ferrites were characterized using XRD and TEM. The results showed ferrite particle sizes are different and 29-79 nm. The radar absorption of ferrite/polymer and ferrite/Ni/polymer composites with synthesized ferrites was measured using vector network analyzer. The nanostructure composite 60% ferrite + 40% polymer with molar ratio CA: EG = 6:4، Rc = 3. 5 and thickness 3 mm had a reflection loss 14 dB in frequency 11. 5 GHz. The reflection loss was increased to 16 dB by adding Ni powder to the composite.

In the present research، the effect of skin pass rolling on work hardening coefficient and normal anisotropy، representing deep drawability in sheet metals ecpecifically in automotive industries، are investigated. To do this، several samples of low carbon steel sheets were selected and the effect of cold reduction on and and grain morphologies was studied. The results showd that cold reduction less than 4. 8% and also elongation magnitude of skin pass do not affect on value. On the other hand، severely decreases with cold reduction and elongation percent of skin pass. The amount of decrease depends upon microstructure and process conditions of prior skin pass stages.

Cladding of steel with titanium alloys to improve corrosion behavior and reduce production costs، is used widely in aerospace، chemical and nuclear industries. Roll bonding is one of the solid state processes to produce this combination. In this research the high quality bonding of hot roll bonding of titanium on steel Substrate was investigated in terms of physical and mechanical properties، and the effect of copper interlayer to prevent interdiffusion was evaluated. The microstructure at interface was observed by an optical and scanning electron microscope and the presence of intermetallic phases in the reaction zone was examined by X-ray diffraction on the fracture surfaces of the joints. The experimental results showed that the volume fraction of intermetallic will be controlled effectively، because there is not enough time for interdiffusion of the elements. Total thickness of intermetallic layers and microhardness at the interface increased with increasing bonding temperature.