Showing 5 results for Shaeri
Mohammad Talafi Noghani, Mohammad Hossein Shaeri, Arezoo Esmaeili, Ahmad Razaghian Arani,
Volume 17, Issue 12 (2-2018)
Abstract
In the current research, the effect of severe plastic deformation on microstructure and mechanical properties of Al-7075 alloy focusing on toughness was investigated. For this purpose, the Al-7075 alloy was subjected to ECAP process up to 4 passes by route BC at room temperature. Microstructure and fracture surface of the specimens were analyzed by optical and electron microscopy and mechanical properties were studied by hardness, tensile and impact tests. Dynamic and static toughness of the alloy were measured from the area under the stress-strain curve and impact test, respectively. The experimental data revealed that after 4 passes of ECAP, the grain size decreased from 40 µm to about 600 nm, and the hardness and strength of the specimen increased about 2 times in comparison with initial material. Static and dynamic toughness decreased about 62% and 30% after the first pass of ECAP, respectively. While, by increasing the pass number, the static toughness increased and dynamic toughness remained approximately constant. The fracture surface of specimens revealed that the fracture of all specimens was ductile. ECAP process caused a considerable increase in strength of Al-7075 (more than 100 percent), whereas, the toughness declined slightly during ECAP process (about 30 and 5 percent in dynamic and static toughness, respectively). So, it can be concluded that one the most advantages of ECAP process in comparison with common forming process is the notable improvement of strength without considerable sacrifice of toughness.
Iman Ansarian, Mohammad Hossein Shaeri, Mahmoud Ebrahimi,
Volume 18, Issue 2 (4-2018)
Abstract
Commercial pure (CP) titanium has many applications in biomaterials especially in implants due to its excellent biocompatibility. The major weakness of CP titanium is low strength compared to that of other titanium alloys. One of the methods can be used to increase the strength of CP titanium are severe plastic deformation methods such as multi directional forging (MDF). Therefore, the aim of this research is the improvement of CP titanium strength by grain refinement in MDF process. For this purpose, after one hour annealing at 800°C, the CP titanium was forged by MDF process up to six passes at ambient temperature. Microstructural studies were performed by optical microscope and scanning electron microscope equipped with EBSD. Mechanical properties were also studied by Vickers’ microhardness and tensile tests. The finite element simulation by Abaqus software was also applied to predict the strain distribution during MDF process. The results of microstructural analysis showed that the average grain size decreased significantly after the MDF process and increasing the pass numbers of MDF led to an increase in grain refinement. After six passes of the MDF process, the average grain size decreased from 45 microns to 390 nm. Mechanical properties results showed that the strength and hardness of specimens increased with MDF process and increasing the number of passes. The hardness and strength of six passes MDFed specimen was about 2 times greater than those of annealed specimen. The strain distribution results obtained from the simulation showed good agreement with experimental results of microhardness distribution.
Z. Zarei, M. Talafi Noghni, M.h. Shaeri, I. Ansarian,
Volume 19, Issue 8 (August 2019)
Abstract
In this research, Cu-30Zn alloy was subjected to severe plastic deformation (SPD) by Multi-Directional Forging (MDF) process up to 6 passes at room temperature. After the samples fabrication, microstructure, mechanical, and electrical properties were investigated. Mechanical properties of the samples were measured by shear punch, tensile, and hardness tests at room temperature after each pass of MDF process. In addition, electrical properties of the samples were evaluated by Eddy Current method. The results of microstructure characterization by scanning electron microscopy equipped with EBSD attachment showed that the grain size of the initial annealed specimen reduced from about 230 µm to less than 1 µm, after 6 passes of MDF process. Furthermore, grain size reduction was accompanied by slip process, formation of twinning, and shear bonds in a specific direction. According to the results, mechanical properties were significantly improved after 6 passes of MDF. MDF process led to a 212% increase in hardness, enhancement of 105% and 73% in shear yield and ultimate shear strengths, and also improvement of 298% and 190% in tensile yield and ultimate tensile strengths, respectively. The results of the electrical conductivity showed that the electrical conductivity of the Cu-30Z alloy reduced slightly during the MDF process. Comparison of mechanical and electrical properties results demonstrated that high-strength alloys can be obtained in the MDF process without significantly reduction in the electrical conductivity.
I. Ansarian, M.h. Shaeri,
Volume 20, Issue 3 (March 2020)
Abstract
Commercial pure (CP) titanium has many applications in biomaterials especially in implants due to its excellent biocompatibility. Despite the importance of surface properties in bio-applications, limited research has been conducted to improve surface properties of CP titanium by improving the structure. Therefore, the purpose of this research is to improve the corrosion and wear properties of CP titanium by reducing grain size by multi-directional forging (MDF) process. For this purpose, annealed CP titanium samples were forged by MDF up to six passes at ambient temperature and 220°C. To investigate the corrosion properties of specimens, the tafel polarization test was performed in a simulated body fluid (SBF) solution. The tribological properties were also investigated by pins-on-disk test at sliding speed and applied stress of 0.2 (m/s) and 1MPa, respectively. The results of microstructure analysis of the samples using a scanning electron microscope (SEM) equipped with EBSD showed that the ultrafine grain structure was formed in titanium CP, after 6 passes of the MDF. The results of the investigation of the tafel polarization test showed that the corrosion resistance of the samples increased with applying MDF and increasing the pass number, regardless of the processing temperature. Also, the corrosion resistance of MDFed samples at 220°C temperature was higher than the MDFed samples at ambient temperature. Wear resistance of CP titanium was also increased, by decreasing the grain size. The results of the investigation of surface morphology of samples using a field-emission scanning electron microscope showed mainly the abrasive and delamination wear mechanisms.
Davood Yousefi, Reza Taghiabadi, M.h. Shaeri,
Volume 21, Issue 10 (October 2021)
Abstract
In this study, the effect of multidirectional forging (MDF) was studied on the microstructure and mechanical properties of Ti-modified SiP/ZA22 composite containing 4 and 8 wt. % Si. The forging process was performed at 100 °C by two and five passes. Based on the obtained results, Ti modification refined the coarse primary dendrites, and reduced the size of primary Si (SiP) particle as well as grains. Applying MDF also gradually eliminated the dendritic structure, promoted fine distribution of SiP particles, second phases, and porosities in the microstructure. According to the image analysis results, the average size of SiP particles in as-cast composite reduced from 25 and 30 μm to about 6 and 7 μm, respectively in 5-pass MDFed composites containing 4 and 8 wt. % Si. The mechanical properties results also showed work softening during the MDF where after two-pass MDF the hardness and tensile strength of the base sample reduced by 30 and 25%, while its elongation and toughness improved by 120 and 325%, respectively. In MDFed composites, the presence of SiP particles maintains the hardness and strength. According to the results, in the case of 2-pass MDFed composite containing 4 wt. % Si the hardness and tensile strength reduced by 18 and 2%, respectively, but the elongation and toughness increased by 25 and 175%, respectively.
