Summary In recent years, carbon nanotubes have raised scientific interest due to their unmatched ... more Summary In recent years, carbon nanotubes have raised scientific interest due to their unmatched properties and their numerous potential applications. Their exceptional mechanical properties especially make them candidates for superstrong and lightweight ...
Aluminum-and magnesium-based alloys were developed to investigate the possibility of forming ligh... more Aluminum-and magnesium-based alloys were developed to investigate the possibility of forming light-weight nanocomposite materials. Four nanocrystalline alloys with nominal compo-sitions Mg 40 Al 60-x Zr x (x = 0, 5, 20, and 35 at. % Zr) were prepared by mechanical alloying aiming to synthesize nanocomposite materials containing nanocrystals embedded in an amorphous matrix. The addition of Zr proved to be beneficial in refining and stabilizing the nanostructure of these alloys. However, traces of oxygen contamination were detected in the XRD diffractograms upon increasing Zr content. The mechanical behavior was investigated by microhardness tests and the results showed that upon increasing Zr, hardness improves.
The importance of aluminum nitride (AlN) stems from its application in microelectronics as a subs... more The importance of aluminum nitride (AlN) stems from its application in microelectronics as a substrate material due to high thermal conductivity, high electrical resistance, mechanical strength and hardness, thermal durability, and chemical stability. Yttria (Y2O3) is the best additive for AlN sintering. AlN densifies by a liquid-phase mechanism, where the surface oxide, Al2O3, reacts with Y2O3 to form an Y-Al-O-N liquid that promotes particle rearrangement and densification. Construction of the phase relations in this multicomponent system is essential for optimizing the properties of AlN. The ternary phase diagram of the AlN-Al2O3-Y2O3 was developed by Gibbs energy minimization using interpolation procedures based on modeling the binary subsystems. This paper aims at testing the resultant understanding experimentally at selected compositions using in situ high-temperature neutron diffractometry. These experimental results agree with the thermodynamic calculations of AlN-Al2O3-Y2O3...
ABSTRACT Microstructural and mechanical properties characterizations of nanocrystalline Ni–Al+M a... more ABSTRACT Microstructural and mechanical properties characterizations of nanocrystalline Ni–Al+M alloys were carried out. M represents the addition of transition elements such as Fe, Ga and Mo. Mechanical alloying (MA) and densification by hot-pressing techniques were used to produce and consolidate the alloys. The mechanical alloyed powders have a microstructure consisting of nanometer size particles. The main effect of these elements on the microstructure of the NiAl alloy is the refinement of the grain size since this process gives rise to crystallite sizes in the nanometric range. Also, the three minor additional elements form a solid solution with the intermetallic structure of the NiAl. Additions of Mo in the range of 2–6 at.% cause second phase formation of Mo2C. Mechanical properties (hardness, yield stress and strain) were obtained as a function of composition and sintering temperature. The highest hardness value is obtained for the NiAl+2Ga+6Mo (at.%) alloy and always corresponded to the highest densifications (98%) for the sintered samples at 1200 °C during 30 min. The Ni–Al alloys with different additions of elements lead to higher deformations than those reported previously.
ABSTRACT In this study open-cell reaction bonded silicon nitride (RBSN) foams with high and contr... more ABSTRACT In this study open-cell reaction bonded silicon nitride (RBSN) foams with high and controlled level of porosity have been produced based on the wet processing of Si-PMMA suspensions in the presence of iron disilicide (FeSi2) as an additive. The investigation focuses on the effect of FeSi2 on the mechanical strength, nitriding mechanisms, and microstructure of the RBSN foam. The nitriding reactions and the foam microstructures and properties were investigated under various nitriding conditions and for different FeSi2 contents.
Composites of a commercial Al-2024 alloy reinforced with particulate TiC have been produced by th... more Composites of a commercial Al-2024 alloy reinforced with particulate TiC have been produced by the pressureless melt infiltration route. Infiltration was carried out at 1200°C for 2 h and composite materials containing 52 and 55 vol.% TiC were obtained. The phases other than the matrix and the reinforcement were identified as CuAl2, AlTi3, Ti3AlC, and TiAl3. It was found that
Summary In recent years, carbon nanotubes have raised scientific interest due to their unmatched ... more Summary In recent years, carbon nanotubes have raised scientific interest due to their unmatched properties and their numerous potential applications. Their exceptional mechanical properties especially make them candidates for superstrong and lightweight ...
Aluminum-and magnesium-based alloys were developed to investigate the possibility of forming ligh... more Aluminum-and magnesium-based alloys were developed to investigate the possibility of forming light-weight nanocomposite materials. Four nanocrystalline alloys with nominal compo-sitions Mg 40 Al 60-x Zr x (x = 0, 5, 20, and 35 at. % Zr) were prepared by mechanical alloying aiming to synthesize nanocomposite materials containing nanocrystals embedded in an amorphous matrix. The addition of Zr proved to be beneficial in refining and stabilizing the nanostructure of these alloys. However, traces of oxygen contamination were detected in the XRD diffractograms upon increasing Zr content. The mechanical behavior was investigated by microhardness tests and the results showed that upon increasing Zr, hardness improves.
The importance of aluminum nitride (AlN) stems from its application in microelectronics as a subs... more The importance of aluminum nitride (AlN) stems from its application in microelectronics as a substrate material due to high thermal conductivity, high electrical resistance, mechanical strength and hardness, thermal durability, and chemical stability. Yttria (Y2O3) is the best additive for AlN sintering. AlN densifies by a liquid-phase mechanism, where the surface oxide, Al2O3, reacts with Y2O3 to form an Y-Al-O-N liquid that promotes particle rearrangement and densification. Construction of the phase relations in this multicomponent system is essential for optimizing the properties of AlN. The ternary phase diagram of the AlN-Al2O3-Y2O3 was developed by Gibbs energy minimization using interpolation procedures based on modeling the binary subsystems. This paper aims at testing the resultant understanding experimentally at selected compositions using in situ high-temperature neutron diffractometry. These experimental results agree with the thermodynamic calculations of AlN-Al2O3-Y2O3...
ABSTRACT Microstructural and mechanical properties characterizations of nanocrystalline Ni–Al+M a... more ABSTRACT Microstructural and mechanical properties characterizations of nanocrystalline Ni–Al+M alloys were carried out. M represents the addition of transition elements such as Fe, Ga and Mo. Mechanical alloying (MA) and densification by hot-pressing techniques were used to produce and consolidate the alloys. The mechanical alloyed powders have a microstructure consisting of nanometer size particles. The main effect of these elements on the microstructure of the NiAl alloy is the refinement of the grain size since this process gives rise to crystallite sizes in the nanometric range. Also, the three minor additional elements form a solid solution with the intermetallic structure of the NiAl. Additions of Mo in the range of 2–6 at.% cause second phase formation of Mo2C. Mechanical properties (hardness, yield stress and strain) were obtained as a function of composition and sintering temperature. The highest hardness value is obtained for the NiAl+2Ga+6Mo (at.%) alloy and always corresponded to the highest densifications (98%) for the sintered samples at 1200 °C during 30 min. The Ni–Al alloys with different additions of elements lead to higher deformations than those reported previously.
ABSTRACT In this study open-cell reaction bonded silicon nitride (RBSN) foams with high and contr... more ABSTRACT In this study open-cell reaction bonded silicon nitride (RBSN) foams with high and controlled level of porosity have been produced based on the wet processing of Si-PMMA suspensions in the presence of iron disilicide (FeSi2) as an additive. The investigation focuses on the effect of FeSi2 on the mechanical strength, nitriding mechanisms, and microstructure of the RBSN foam. The nitriding reactions and the foam microstructures and properties were investigated under various nitriding conditions and for different FeSi2 contents.
Composites of a commercial Al-2024 alloy reinforced with particulate TiC have been produced by th... more Composites of a commercial Al-2024 alloy reinforced with particulate TiC have been produced by the pressureless melt infiltration route. Infiltration was carried out at 1200°C for 2 h and composite materials containing 52 and 55 vol.% TiC were obtained. The phases other than the matrix and the reinforcement were identified as CuAl2, AlTi3, Ti3AlC, and TiAl3. It was found that
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