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Soltani N.,Sharif University of Technology | Bahrami A.,Razi Metallurgical Research Center | Moghimi F.M.,Islamic Azad University at Saveh | Pech-Canul M.I.,Islamic Azad University at Saveh | Hajaghasi A.,National Polytechnic Institute of Mexico
HTM - Journal of Heat Treatment and Materials | Year: 2012

This article investigates the simultaneous effect of extrusion ratio and T6 heat treatment on microstructure and mechanical properties of in-situ Al-15wt.%Mg2Si composite. his composite has already been introduced as a new class of light materials but the brittle structure of the primary Mg2Si which is formed during solidification limits its application. As-cast composite was directly extruded as rod by using three different dies. After T6 heat treatment on extruded samples, microstructure was studied by optical and scanning electron microscopy. Results demonstrated that extruded and heat treated composite possesses considerably higher strength and enhanced ductility in comparison with the as-cast samples. It was also found that heat treatment and extrusion processes change the primary Mg2Si morphology considerably and its size increases as extrusion ratio decreased. Fracture surface examinations revealed a transition from brittle fracture mode in as-cast composite to ductile fracture in heat treated and extruded specimens. his can be attributed to the changes in size and morphology of Mg2Si intermetallics and porosity content. Source

Soltani N.,Sharif University of Technology | Soltani N.,CINVESTAV | Jafari Nodooshan H.R.,Shanghai JiaoTong University | Bahrami A.,Razi Metallurgical Research Center | And 4 more authors.
Materials and Design | Year: 2014

Al-15wt.% Mg2Si composites were prepared by in situ casting and characterized in wear tests. Previous to the extrusion of specimens at 470°C - varying extrusion ratio (7.4, 14.1 and 25), the as-cast composites were homogenized at 500°C for 5h, followed by slow furnace cooling. The microstructure, hardness and sliding wear behavior were characterized for both, the as-cast and hot extruded composites. Results show that increasing the extrusion ratio causes a significant improvement in hardness and wear resistance. This is ascribed to the observed decrease in average size and better distribution of Mg2Si particles, in tandem with a remarkable decrease in porosity percentages, which goes from 5.63 in the as-cast condition, to 0.47 at the extrusion ratio of 25. It was found that abrasion is the dominant wear mechanism in all extruded composites, whilst a combination of adhesion and delamination appears to be the governing mechanism for as-cast composites. © 2013 Elsevier Ltd. Source

Molaei S.,Shiraz University | Molaei S.,Razi Metallurgical Research Center | Alizadeh R.,University of Tehran | Attarian M.,Razi Metallurgical Research Center | And 2 more authors.
Case Studies in Engineering Failure Analysis | Year: 2015

The purpose of this study was to investigate the main causes of the co-fracture of sixteen connecting bolts of a filter press cylinder-piston system. Stress state of the bolts during the service conditions has been analyzed and the failure reasons were determined from the fractography analysis and gathered information. According to the obtained results, it was concluded that the bolts had failed by the fatigue mechanism. It seems that insufficient torque was used during assembly. © 2015. Source

Soltani N.,Sharif University of Technology | Soltani N.,CINVESTAV | Pech-Canul M.I.,CINVESTAV | Bahrami A.,CINVESTAV | Bahrami A.,Razi Metallurgical Research Center
Materials and Design | Year: 2013

A zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite) can be a good substitute as reinforcement in metal matrix composites. In the present study, the effect of the amount of 10Ce-TZP/Al2O3 particles on the microstructure and properties of Al/(10Ce-TZP/Al2O3) nanocomposites was investigated. For this purpose, aluminum powders with average size of 30μm were ball-milled with 10Ce-TZP/Al2O3 nanocomposite powders (synthesized by aqueous combustion) in varying amounts of 1, 3, 5, 7, and 10wt.%. Cylindrical-shape samples were prepared by pressing the powders at 600MPa for 60min while heating at 400-450°C. The specimens were then characterized by scanning and transmission electron microscopy (SEM and TEM) in addition to different physical and mechanical testing methods in order to establish the optimal processing conditions. The highest compression strength was obtained in the composite with 7wt.% (10Ce-TZP/Al2O3) sintered at 450°C. © 2013 Elsevier Ltd. Source

Attarian M.,Sharif University of Technology | Karimi Taheri A.,Sharif University of Technology | Jalilvand S.,Razi Metallurgical Research Center | Habibi A.,Pardis Petrochemical Co
Engineering Failure Analysis | Year: 2016

In this paper, the failure of the reformer furnace tube, made of HP-Nb micro alloyed heat resistant steel is investigated. The failure was due to a longitudinal crack developing in the circumferential weld joint close to the outlet end of the tube, where the mean wall temperature had reached the highest value during service. According to the temperature records during the period of 7 years of being in service, the tube had experienced temperatures higher than the tubes designed temperature. This situation besides the occurrence of several sudden shutdowns caused the mechanical properties degradation.Macroscopic and microscopic examinations revealed that the failure had occurred due to the extensive fissuring initiated and developed from the heat affected zone (HAZ) adjacent to the root weld. The results of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) analysis, and the crack growth rate calculations indicated that the crack propagation rate was controlled by the overheating and the secondary thermal stress due to the sudden shutdowns.Moreover, the ductility at the tip of the crack had dwindled due to the nitrogen uptake at high temperature, which promoted the crack growth rate. Quantitative microstructural analysis performed at the uncracked and cracked sides of the weld joint showed that the area fraction of HAZ creep cavities were 0.3% and 0.7%, respectively, which were interpreted in turn as the accumulated creep damage level D and E. Finally, it was concluded that the creep cavities alignment and fissuring that took place at HAZ are the main causes of the cracking and failure of the tube. © 2016 Elsevier Inc. Source

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