Mehdi Shahedi Asl was born in 1981 in Khoy, west-northern Iran. He finished his primary and secondary education in Khoy and after being accepted in the entrance exam for state public schools, he attended Hedayat High School in Tehran. In 1999 he began his bachelor's in metallurgical engineering at Iran University of Science and Technology. He was ranked 5th in the entrance exam for the master's program and continued his education at the Sharif University of Technology in Tehran. In 2012 he began his studies in the doctoral program at the University of Tabriz and in 2015 finished his postgraduate studies as the first student to graduate the doctoral program at that university. Mehdi Shahedi Asl has been teaching and researching as an assistant professor at the University of Mohaghegh Ardabili in Iran since September 2015. From the beginning of 2020, Mehdi traveled to Canada for about 2 years to participate in a postdoc sabbatical leave and research at the University of New Brunswick. He was an Associate Professor at the University of Kyrenia in Cyprus from March 2022 to June 2024. He is currently teaching and researching as an Associate Professor at Xi'an Jiaotong-Liverpool University in China since July 2024. Mehdi is the Founder of Synsint Research Group (Publisher and Research Group) and Synthesis and Sintering (Journal).
Journal of the Taiwan Institute of Chemical Engineers, 2020
Abstract ZrB2-based composites were consolidated through reactive spark plasma sintering of the p... more Abstract ZrB2-based composites were consolidated through reactive spark plasma sintering of the powder mixtures containing relatively 5 vol.% of metallic Zr particles, and graphite flakes (GF) or carbon nanotubes (CNT) as the carbon source, with the aim of ZrC in-situ synthesis in ZrB2 matrix. Microstructural and phase analyses indicated that GFs cannot result in detectable ZrC in the final microstructure. Contrarily, it was found that CNTs promote the in-situ synthesizability of zirconium carbide in the composite system. However, the sample containing graphite flakes presented better densification outcomes. The mechanism of ZrC formation in the composites, based on the carbon source, was finally discussed and illustrated.
Abstract A TiB2–Ti3AlC2 ceramic was manufactured by spark plasma sintering at 1900 °C temperature... more Abstract A TiB2–Ti3AlC2 ceramic was manufactured by spark plasma sintering at 1900 °C temperature for 7 min soaking time under 30 MPa biaxial pressure. The role of Ti3AlC2 additive on the microstructure development, densification behavior, phase evolution, and hardness of the ceramic composite were studied. The phase characterization and microstructural investigations unveiled that the Ti3AlC2 MAX phase decomposes at the initial stages of the sintering. The in-situ formed phases, induced by the decomposition of Ti3AlC2 additive, were identified and scrutinized by XRD and FESEM/EDS techniques as well as thermodynamics principles. The sintered TiB2–Ti3AlC2 ceramic approached a near full density of ~99% and a hardness of ~28 GPa. The densification mechanism and sintering phenomena were discussed and graphically illustrated.
Abstract Solid solution formation, phase evolution, microstructure development, and mechanical be... more Abstract Solid solution formation, phase evolution, microstructure development, and mechanical behavior of ZrB2–TiC composites with/without carbon fiber additive were investigated. Fully dense composites were manufactured by spark plasma sintering route under 40 MPa load at 1900 °C for 420 s. FESEM and XRD studies were carried out to unveil the densification and toughening mechanisms in the sintered specimens. Results showed that the addition of only 1 wt% short carbon fibers increased the hardness from 21.8 GPa to 23.5 GPa. Moreover, a 3 % enhancement in the indentation fracture toughness was also observed due to the incorporation of short carbon fibers. The in-situ formation of ZrC and TiB2 phases were identified and related to a chemical reaction between the ZrB2 and TiC constituents. The solid solution development between the ZrB2 matrix and the in-situ formed TiB2 was also proved by the microstructural observation and the shifted peaks of ZrB2 in the XRD patterns.
Abstract A ZrB2–20 vol% SiC–5 vol% TaC ceramic was sintered through the hot pressing process. By ... more Abstract A ZrB2–20 vol% SiC–5 vol% TaC ceramic was sintered through the hot pressing process. By sintering for 60 min at 1850 °C under 40 MPa in a vacuum atmosphere, an almost fully dense specimen with a relative density of 97.5% was achieved. The phase and microstructural investigations revealed that alongside the ZrB2, SiC and TaC as the starting materials, two new phases of ZrC and TaSi2 were synthesized in-situ during the hot pressing. The oxidation behavior of as-sintered hybrid composites was investigated at three temperatures in an atmospheric furnace for 1-, 4- and 10-h cycles. Parabolic oxidation rate constants of 2.25, 30.69 and 1309.70 mg2/cm4.h were calculated for the samples oxidized at the temperatures of 1000, 1400 and 1700 °C, respectively. The activation energy of 178.7 kJ/mol was kinetically calculated for the oxidation of ZrB2–SiC–TaC ceramics. Four oxidized layers on the unaffected ZrB2–SiC–TaC matrix were also detected and microstructurally characterized.
Abstract The effects of processing variables on densification behavior of hot pressed ZrB 2 -base... more Abstract The effects of processing variables on densification behavior of hot pressed ZrB 2 -based composites, reinforced with SiC particles and short carbon fibers (C sf ), were studied. A design of experiment approach, Taguchi methodology, was used to investigate the characteristics of ZrB 2 –SiC–C sf composites concentrated upon the hot pressing parameters (sintering temperature, dwell time and applied pressure) as well as the composition (vol% SiC/vol% C sf ). The analysis of variance recognized the sintering temperature and SiC/C sf ratio as the most effective variables on the relative density of hot pressed composites. The microstructural investigations showed that C sf can act as a sintering aid and eliminate the oxide impurities ( e.g. B 2 O 3 , ZrO 2 and SiO 2 ) from the surfaces of raw materials. A fully dense composite was achieved by adding 10 vol% C sf and 20 vol% SiC to the ZrB 2 matrix via hot pressing at 1850 °C for 30 min under a pressure of 16 MPa. Moreover, the in - situ formation of interfacial ZrC, which also improves the sinterability of ZrB 2 -based composites, was studied by energy-dispersive X-ray spectroscopy analysis and verified thermodynamically.
Abstract The influences of adding SiC on the microstructure and densification behavior of ZrB 2 a... more Abstract The influences of adding SiC on the microstructure and densification behavior of ZrB 2 and TiB 2 ceramics, hot pressed at 1850 °C for 60 min under 20 MPa, were investigated. The sintered samples were characterized by SEM, EDS and XRD methods. A fully dense TiB 2 -based ceramic was obtained by adding 30 vol% SiC. The grain size of ZrB 2 or TiB 2 matrices in the final microstructures decreased with increasing SiC content. The XRD analyses, microstructural characterization as well as thermodynamical calculations proved the in-situ formation of TiC in the SiC reinforced TiB 2 -based composites. The interfaces between ZrB 2 and SiC grains in the SiC reinforced ZrB 2 -based composites were free of any impurities or tertiary interfacial phases such as ZrC. This result was consistent with the X-ray diffraction pattern and thermodynamics.
ZrB2 -25 vol. % SiC composites were fabricated by hot pressing with a various SiC particle size (... more ZrB2 -25 vol. % SiC composites were fabricated by hot pressing with a various SiC particle size (20 nm, 200 nm, and 2 µm) in order to scrutinize the densification process and mechanical properties. Microstructure analyses show that the grain size of the sintered samples highly depends on the SiC particle size. Consolidated samples using nano-sized SiC particulates, as the reinforcement phase, exhibit improved density and mechanical properties. In addition, intragranular SiC particles were monitored within the ZrB2 matrix.
Journal of the Taiwan Institute of Chemical Engineers, 2020
Abstract ZrB2-based composites were consolidated through reactive spark plasma sintering of the p... more Abstract ZrB2-based composites were consolidated through reactive spark plasma sintering of the powder mixtures containing relatively 5 vol.% of metallic Zr particles, and graphite flakes (GF) or carbon nanotubes (CNT) as the carbon source, with the aim of ZrC in-situ synthesis in ZrB2 matrix. Microstructural and phase analyses indicated that GFs cannot result in detectable ZrC in the final microstructure. Contrarily, it was found that CNTs promote the in-situ synthesizability of zirconium carbide in the composite system. However, the sample containing graphite flakes presented better densification outcomes. The mechanism of ZrC formation in the composites, based on the carbon source, was finally discussed and illustrated.
Abstract A TiB2–Ti3AlC2 ceramic was manufactured by spark plasma sintering at 1900 °C temperature... more Abstract A TiB2–Ti3AlC2 ceramic was manufactured by spark plasma sintering at 1900 °C temperature for 7 min soaking time under 30 MPa biaxial pressure. The role of Ti3AlC2 additive on the microstructure development, densification behavior, phase evolution, and hardness of the ceramic composite were studied. The phase characterization and microstructural investigations unveiled that the Ti3AlC2 MAX phase decomposes at the initial stages of the sintering. The in-situ formed phases, induced by the decomposition of Ti3AlC2 additive, were identified and scrutinized by XRD and FESEM/EDS techniques as well as thermodynamics principles. The sintered TiB2–Ti3AlC2 ceramic approached a near full density of ~99% and a hardness of ~28 GPa. The densification mechanism and sintering phenomena were discussed and graphically illustrated.
Abstract Solid solution formation, phase evolution, microstructure development, and mechanical be... more Abstract Solid solution formation, phase evolution, microstructure development, and mechanical behavior of ZrB2–TiC composites with/without carbon fiber additive were investigated. Fully dense composites were manufactured by spark plasma sintering route under 40 MPa load at 1900 °C for 420 s. FESEM and XRD studies were carried out to unveil the densification and toughening mechanisms in the sintered specimens. Results showed that the addition of only 1 wt% short carbon fibers increased the hardness from 21.8 GPa to 23.5 GPa. Moreover, a 3 % enhancement in the indentation fracture toughness was also observed due to the incorporation of short carbon fibers. The in-situ formation of ZrC and TiB2 phases were identified and related to a chemical reaction between the ZrB2 and TiC constituents. The solid solution development between the ZrB2 matrix and the in-situ formed TiB2 was also proved by the microstructural observation and the shifted peaks of ZrB2 in the XRD patterns.
Abstract A ZrB2–20 vol% SiC–5 vol% TaC ceramic was sintered through the hot pressing process. By ... more Abstract A ZrB2–20 vol% SiC–5 vol% TaC ceramic was sintered through the hot pressing process. By sintering for 60 min at 1850 °C under 40 MPa in a vacuum atmosphere, an almost fully dense specimen with a relative density of 97.5% was achieved. The phase and microstructural investigations revealed that alongside the ZrB2, SiC and TaC as the starting materials, two new phases of ZrC and TaSi2 were synthesized in-situ during the hot pressing. The oxidation behavior of as-sintered hybrid composites was investigated at three temperatures in an atmospheric furnace for 1-, 4- and 10-h cycles. Parabolic oxidation rate constants of 2.25, 30.69 and 1309.70 mg2/cm4.h were calculated for the samples oxidized at the temperatures of 1000, 1400 and 1700 °C, respectively. The activation energy of 178.7 kJ/mol was kinetically calculated for the oxidation of ZrB2–SiC–TaC ceramics. Four oxidized layers on the unaffected ZrB2–SiC–TaC matrix were also detected and microstructurally characterized.
Abstract The effects of processing variables on densification behavior of hot pressed ZrB 2 -base... more Abstract The effects of processing variables on densification behavior of hot pressed ZrB 2 -based composites, reinforced with SiC particles and short carbon fibers (C sf ), were studied. A design of experiment approach, Taguchi methodology, was used to investigate the characteristics of ZrB 2 –SiC–C sf composites concentrated upon the hot pressing parameters (sintering temperature, dwell time and applied pressure) as well as the composition (vol% SiC/vol% C sf ). The analysis of variance recognized the sintering temperature and SiC/C sf ratio as the most effective variables on the relative density of hot pressed composites. The microstructural investigations showed that C sf can act as a sintering aid and eliminate the oxide impurities ( e.g. B 2 O 3 , ZrO 2 and SiO 2 ) from the surfaces of raw materials. A fully dense composite was achieved by adding 10 vol% C sf and 20 vol% SiC to the ZrB 2 matrix via hot pressing at 1850 °C for 30 min under a pressure of 16 MPa. Moreover, the in - situ formation of interfacial ZrC, which also improves the sinterability of ZrB 2 -based composites, was studied by energy-dispersive X-ray spectroscopy analysis and verified thermodynamically.
Abstract The influences of adding SiC on the microstructure and densification behavior of ZrB 2 a... more Abstract The influences of adding SiC on the microstructure and densification behavior of ZrB 2 and TiB 2 ceramics, hot pressed at 1850 °C for 60 min under 20 MPa, were investigated. The sintered samples were characterized by SEM, EDS and XRD methods. A fully dense TiB 2 -based ceramic was obtained by adding 30 vol% SiC. The grain size of ZrB 2 or TiB 2 matrices in the final microstructures decreased with increasing SiC content. The XRD analyses, microstructural characterization as well as thermodynamical calculations proved the in-situ formation of TiC in the SiC reinforced TiB 2 -based composites. The interfaces between ZrB 2 and SiC grains in the SiC reinforced ZrB 2 -based composites were free of any impurities or tertiary interfacial phases such as ZrC. This result was consistent with the X-ray diffraction pattern and thermodynamics.
ZrB2 -25 vol. % SiC composites were fabricated by hot pressing with a various SiC particle size (... more ZrB2 -25 vol. % SiC composites were fabricated by hot pressing with a various SiC particle size (20 nm, 200 nm, and 2 µm) in order to scrutinize the densification process and mechanical properties. Microstructure analyses show that the grain size of the sintered samples highly depends on the SiC particle size. Consolidated samples using nano-sized SiC particulates, as the reinforcement phase, exhibit improved density and mechanical properties. In addition, intragranular SiC particles were monitored within the ZrB2 matrix.
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Papers by Mehdi Shahedi Asl