INTERNATIONAL JOURNAL OF INDUSTRIAL ENGINEERING AND PRODUCTION MANAGEMENT (IJIE) (INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE) (PERSIAN)
Year:2007 | Volume:18 | Issue:4 (SUPPLEMENT OF METALURGY AND MATERIALS ENGINERING)|Papers Count:14

Following to the repeated observations of leakage and failure-in service of the components manufactured via die casting route, in the stress much lower than their designed an expected level, they were studied and analyzed. Leakage is the sort of defects which frequently has been reported in the high pressure casting components. This study showed that possibility of the formation of air bubbles with and without trails in their wake in the castings is quite high in the high pressure die casting process. It seems that these defects, as special types of discontinuities, have a critical role in the leakage problems and low mechanical properties seen in the high pressure die castings. Bubble damage as frequently seen defects and bubble trail, as a special form of bubble damage defect which already has been reported in the sand casting process, was clearly seen in this study. Specifications of bubble trails observed in this investigation vary to some extent to what already reported in the conventional casting and thus are discussed in this work.

Properties optimization of alumina-spinel refractories via particle size distributing in order to prepare a proper system against corrosion in-service is the main aspect of present study. The particle size distribution (PSA) of aggregates is the main factor controlling properties and behavior of low cement alumina=spinel castable refractories. For this purpose formulations with different size distribution coefficient, q, in modified Anderasen model were chosen in this research. According to the results the samples with q=0.22 have shown better properties such as physical, cold and high temperature strength compared to others. The influence of different phases and microstructure on physical and mechanical properties of the samples was investigated using XRD, SEM techniques.

In this article, with the objective of understanding the reinforcing mechanisms of short steel fibers in ceramic matrix composites, the bond between the fibers and the surrounding matrix was studied by conducting single fiber pull-out tests on steel fibers bonded in high performance cementitious matrix. Two different fiber shapes (smooth and hooked) with three different surface conditions (without coating, zinc phosphate coated, and zinc-calcium phosphate coated) were investigated, and the effects of fiber shape and coating on the pull-out behavior of the fibers were quantified through pull-out load-displacement plots. To investigate the influence of the interface characteristics on the strength and fracture toughness of composite, different fibers were embedded in dog-bon shaped tensile specimens, and the tensile load-displacement plots were obtained. The microstructure of the interface between the fibers and matrix was also studied using a scanning Electron microscope (SEM).

The second phase hardening is the major strengthening mechanism in 2xxx series of Al-alloys. Accordingly the alloys behavior under warm deformation is influenced by the particles characteristics. In the present study, the particle characteristics (e.g., size and distribution) were changed through different heat treatment routs before applying the warm deformation cycle. The hot compression tests were carried out at different temperatures (200°C and 300°C) and strain rates (0.001, 0.01, and 0.1/s). The results indicated that the straining resulted in the strain induced dynamic precipitation of the second phase thereby increasing the rate of work hardening. However, applying further deformation gave rise to particle coarsening through assisting solute elements diffusivity. The latter resulted in the higher rate of dynamic recovery within the solute elements-free and fine particle-free regions, which these in turn led to flow softening behavior during warm deformation.

In the present study, the destruction reason of peykan engine valves has been investigated using elemental and structural analysis by optical and election (SEM) microscopes. EDX results show that the alloy used for seat coating is similar to Estellite 6. The presence of denderitic arms surrounded in a fine eutectic has been shown by optical and SEM images. This is a proof for similarity between coating alloy and Estellite 6.Composition of coating in a Co-Cr-W ternary diagram indicates that denderitic arms are Co(a) which has been surrounded by a Cr7C3/Co solid solution eutectic. Metallographic investigations showed that carbides in the most regions of coating have been spheriodized, and this indicates unsuitable production process. Erosion pattern of surface merely shows the effect of coating material yielding.

Ferritic-martensitic dual phase (DP) steels are a new class of high strength low alloy steels. The source of strengthening in DP steels derives from the presence of the load-carrying hard martensite in a soft ferrite matrix, the basis of ductility. The aim of the present work is to study the influence of pre-deformation and ferrite grain size on microstructure and mechanical properties of dual phase steel. So, low carbon steel were pre-deformed with different reduction of area (0%,29%,45%,62%) and then were held at 74°C, 78°C for 5, 10, 15 minutes, and finally were quenched in cold water to obtain a ferritic-martensitic microstructure. The tensile test, hardness test and metallography were also done on all specimens to understand their characterizations. The results showed that ferrite grain size decreased and the volume fraction of martensite increased by increasing in amount of pre-deformation. The increasing in amounts of yield .strength, UTS, hardness and the decreasing in amount of total elongation is accompanied by increasing in amount of pre-deformation and decreasing in ferrite grain size.

The alloys WE43 and WE54 are the new generation of Mg-RE alloys which in the T6 condition (solution treated at 525°C for 8 hours, quenched in hot water at 60°C and aged at 250°C for 16 hours) have recently being used in aerospace and automotive industries because of their light weight, high specific strength, good creep and corrosion resistance and excellent damping characteristic. In this study aging response and early stages of precipitation in both alloys have been studied over the temperature range of 150-300°C Chemical composition and crystal structure of various precipitates and their orientation relationship with the matrix have been determined. The ductility of the alloys initially in the T6 condition decreased during service at temperatures between 100 and 150°C. This was associated with the formation of GP zones from the matrix in equilibrium with the unstable b' and b² precipitates during the exposure time.

Due to light weight and good mechanical properties, ceramics have been used for ant bullet armor shields. A layered ceramic armor composite consist of a ceramic plate and a soft backing material such as a thick metal plate. There are various methods for bonding of ceramic layer to metallic one (1). In this research plasma spraying method has used for bonding and forming of a ceramic layer to the metal support. Alumina layers with 0.1, 0.2 and 0.3mm thickness were coated on aluminum base plates. In order to study the effect of intermediate layer on impact behavior, from a bond coat of 80%Ni-20%Cr with 0.1mm thickness was used and then a 0.2mm alumina coat was sprayed by a plasma torch. The hardness of the coating was measured by the Vickers method.The prepared layered composite plates were supported by Kevlar fiber and the whole assembled unit used as armor shield against 9mm caliber shot by a MP5 gun.Depth of bullet penetration, amount of fractured ceramic coating after bullet impact and the residual ceramic coating left after impact were measured. Interfaces in samples with and without intermediate layer, and also phase analysis of the coatings were examined by SEM and XRD. The best coating thickness was 0.2mm with a good performance in stopping the bullet and creating less damage to the ceramic layer.

The grind ability of ores has been introduced as work index (wi) by F.C. Bond. This parameter is equal to the energy required to break one short ton of ore, theoretically from infinite size, reaching to 80% finer than 100 microns. Work index is estimated for any type of ores, using standard experimental approach in laboratory. In order to study on the effect of control screen size on the work index values estimation, three ore samples from different copper mines, Sarcheshmeh, Sungun and Qaleh Zari were used. The experiments were performed in six different sizes of control screens, 600, 425, 250, 150, 90 and 53 microns. The obtained results indicated that the increase of control screen size increase the relevant work index. It was also shown that the trend of (Pi)0.5 which is control screen size with Gi (mass finer than control screen size), and P (d80 of product size distribution) with Pi are linear.

In the present study dissolution of magnesia-rich spinel refractory grain in a steelmaking slag is investigated. The interaction between magnesia-rich spinel aggregate and the slag was studied at 1600°C for 20 minutes. Also thermo-chemistry calculation was carried out by FACT software to study the thermodynamical interaction between the refractory and the slag within the dissolution process. Microstructural analysis and the thermodynamic calculations showed that some of the cations from slag, such as Mn2+ Fe2+ and Fe3+, diffuse in to the spinel structure leading to formation of a complex spinel boundary layer around the refractory aggregate. Then composition of the slag changes and the molten slag viscosity increases by reducing iron and manganese consequently, the slag penetration and corrosion of the spinel refractory reduced.

Following field investigations at News tan Colliery by the author, during a research program at Tazareh Colliery on P10 coal seam the role of the stratigraphy of the hanging wall in the roof behavior was studied the results being compared.There are several types of quantitative and qualitative classification of roof rocks most of which based on the stratigraphy of the roof strata. Observations carried out at the above coal fields and evaluations made using roof classification systems showed that in addition to the geotechnical characteristics of the roof rock, the stratigraphy of the roof strata has a significant impact on the capability of the roof in a long wall operation.In this respect it was recommended that special attention be paid to the geological and exploration information from roof strata and, if necessary, additional boreholes be excavated to obtain enough stratigraphic information during roof support design for strata control.

In this research, the friction and wear behavior of 7 samples of brake pad with different amounts of Steel and Bazalt fibers have been investigated by using friction test machine. The optical and scanning electron microscopy was used to study the formation of friction film on the worn surface of these samples. The results show that samples of Steel fibers have low friction coefficient and high wear rate. In addition a relatively poor quality was obtained for friction film of the surface of the former case. The use of Basalt and Steel fiber mixture causes an increase in the friction coefficient, and a decrease in the wear rate, as well as the formation of an acceptable friction film on the pad surfaces.