The crystallization process of the eutectic composition of GdAlO_3-Al_2O_3 from the amorphous phase prepared by rapid-quenching of melt that leads to the formation of a cantaloupe skin-like microstructure was investig...The crystallization process of the eutectic composition of GdAlO_3-Al_2O_3 from the amorphous phase prepared by rapid-quenching of melt that leads to the formation of a cantaloupe skin-like microstructure was investigated using focused ion-beam scanning electron microscopy (FIB-SEM) and high-resolution transmission electron microscopy (HR-TEM).The amorphous films were heat-treated at temperatures between 1000 °C and 1500 °C for up to 30min to form the eutectic phases of GdAlO_3 and Al_2O_3.The GdAlO_3 and Al_2O_3 crystal phases that formed from the amorphous phase were identified by FIB-SEM and HR-TEM.Both components began to crystallize and grow from the amorphous phase separately at different temperatures.The formation process of these crystal phases was different from that of the ordinary eutectic microstructure solidified from the GdAlO_3-Al_2O_3 system.Therefore,the observed structure is termed "eutectic-like" for distinction.The microstructures formed from the amorphous phases at sufficiently high temperatures consisted of ultra-fine microstructures of individually crystallized components and were similar to ordinary eutectic microstructures.By heat-treating the amorphous films at 1500 °C for either 2 min,8min or 30min,the ultra-fine components of GdAlO_3 and Al_2O_3 were found to crystallize following a eutectic-like stage after 8min of heat treatment.展开更多
Cerium oxide has a great capacity to remove nonbridging oxygen atoms (NBO) from the glass network and serves as glass former units. The well formed CeO<sub>4</sub> units played the role of decreasing NBO f...Cerium oxide has a great capacity to remove nonbridging oxygen atoms (NBO) from the glass network and serves as glass former units. The well formed CeO<sub>4</sub> units played the role of decreasing NBO from the silicate network and cause a reduction in the concentration of tetrahedral boron groups (N<sub>4</sub>). The highest content of NBO in glass of lower CeO<sub>2</sub> (1 mol%) has a dominant role in constructing crystalline clusters in the glass. Higher CeO<sub>2</sub> concentration leads to formation of an amorphous glass network as documented by XRD and TEM-EDP spectra. Coordination of cerium with oxygen atoms gives uniform units of spherical morphology in the pure CeO<sub>2</sub> as well as in cerium rich glass. Clustered species has a great benefit in the field of application, used as a shielding material for ionized radiations.展开更多
Ce^（3＋） substituted Cu-spinel nanoferrites CuCe_xFe_（2-x）O_4（x=0.00, 0.02, 0.04, 0.06, 0.08 and 0.10） were synthesized via sol-gel self-combustion hybrid route. Single phase spinel ferrite of Cu nanoferrites we...Ce^（3＋） substituted Cu-spinel nanoferrites CuCe_xFe_（2-x）O_4（x=0.00, 0.02, 0.04, 0.06, 0.08 and 0.10） were synthesized via sol-gel self-combustion hybrid route. Single phase spinel ferrite of Cu nanoferrites were examined using X-ray diffraction（XRD） analysis whereas the multiphase structure was observed as Ce contents increased from x=0.06. Field emission scanning electron microscopy（FESEM）, Thermogravimetric and differential thermal analysis（TGA and DTA） and Fourier transform infrared spectroscopy（FTIR） were used to find out the morphology phase and metal stretching vibrations of Ce^（3＋） substituted nanocrystalline ferrites. The crystallite size was increased and found in the range of 25-91 nm. The agglomerations in Cu ferrite samples increase as the Ce^（3＋） concentration increases. The magnetic properties such as remanence, saturation magnetization, coercivity, Bohr magneton and magnetocrystalline anisotropy constant（K） were determined using M-H loops recorded from a vibrating sample magnetometer（VSM）. Saturation magnetization, remanence and coercivity are increased as the Ce^（3＋）contents increase in Cu nanocrystalline samples. Moreover, law of approach to saturation（LoA） was used to calculate the maximum value of saturation for Ce-doped Cu nanoferrites. The soft magnetic behaviour of the Cu nanoferrite is observed as compared to the samples substituted with the increased Ce contents in Cu nanocrystalline ferrite. Bohr magneton and magnetocrystalline anisotropy are found to increase with the substitution of rare earth Ce^（3＋） contents in Cu spinel nanocrystalline ferrite. Cedoped Cu nanocrystalline ferrites with excellent properties may be suitable for potential applications in sensing, security, switching, core, multilayer chip inductor, biomedical and microwave absorption applications.展开更多
Magnesium(Mg)alloys are ideal candidates for automotive applications due to their high strength to weight ratio,castability,recyclability etc.,however,they lack corrosion and oxidation resistance.Solid-state depositio...Magnesium(Mg)alloys are ideal candidates for automotive applications due to their high strength to weight ratio,castability,recyclability etc.,however,they lack corrosion and oxidation resistance.Solid-state deposition techniques,such as cold spray,have been demonstrated to enhance their corrosion resistance as it relies on the severe plastic deformation of powder particles upon impact with the substrate to form a metallurgical bond with the substrate and within the coating.At cold sprayed interfaces,a heterogeneous microstructure is formed that includes some porosity,oxides and intermetallics which can significantly affect coating performance.Thus,establishing a direct correlation between the interface microstructure and its properties can aid in designing optimal cold spray parameters.In this study,we investigated the microstructure and mechanical properties of a zinc(Zn)coating deposited on a high pressure die cast(HPDC)AZ91 Mg substrate via high resolution scanning transmission electron microscopy,in situ micro-tensile testing,and finite element method(FEM)modeling.Micro-tensile pillars fabricated using the plasma focused ion beam(PFIB)successfully isolates the coating-substrate interface within the gauge length.The average bond strength of Zn-Mg interface was determined to be∼140 MPa with failure occurring partially at the interface and mostly into the coatings.A detailed microstructural characterization revealed evidence of a strong metallurgical bonding at the Zn-Mg interface and formation of the C14 MgZn_(2)laves phase interlayer resulting in a mixed mode of fracture during the micro-tensile experiments.FEM modeling reveals the stress distribution along the interfaces and suggests that a MgZn_(2)layer thickness between 200–400 nm is optimum to increase the bond strength and minimize the triaxiality.Such a site-specific interfacial analysis with correlative computational modeling provides crucial insight into the overall performance of cold spray interfaces.展开更多
基金part of the study under the "Human Resource Development Center for Economic Region Leading Industry" Projectsupported by the Ministry of Education,Science & Technology(MEST)by the National Research Foundation of Korea(NRF)
文摘The crystallization process of the eutectic composition of GdAlO_3-Al_2O_3 from the amorphous phase prepared by rapid-quenching of melt that leads to the formation of a cantaloupe skin-like microstructure was investigated using focused ion-beam scanning electron microscopy (FIB-SEM) and high-resolution transmission electron microscopy (HR-TEM).The amorphous films were heat-treated at temperatures between 1000 °C and 1500 °C for up to 30min to form the eutectic phases of GdAlO_3 and Al_2O_3.The GdAlO_3 and Al_2O_3 crystal phases that formed from the amorphous phase were identified by FIB-SEM and HR-TEM.Both components began to crystallize and grow from the amorphous phase separately at different temperatures.The formation process of these crystal phases was different from that of the ordinary eutectic microstructure solidified from the GdAlO_3-Al_2O_3 system.Therefore,the observed structure is termed "eutectic-like" for distinction.The microstructures formed from the amorphous phases at sufficiently high temperatures consisted of ultra-fine microstructures of individually crystallized components and were similar to ordinary eutectic microstructures.By heat-treating the amorphous films at 1500 °C for either 2 min,8min or 30min,the ultra-fine components of GdAlO_3 and Al_2O_3 were found to crystallize following a eutectic-like stage after 8min of heat treatment.
文摘Cerium oxide has a great capacity to remove nonbridging oxygen atoms (NBO) from the glass network and serves as glass former units. The well formed CeO<sub>4</sub> units played the role of decreasing NBO from the silicate network and cause a reduction in the concentration of tetrahedral boron groups (N<sub>4</sub>). The highest content of NBO in glass of lower CeO<sub>2</sub> (1 mol%) has a dominant role in constructing crystalline clusters in the glass. Higher CeO<sub>2</sub> concentration leads to formation of an amorphous glass network as documented by XRD and TEM-EDP spectra. Coordination of cerium with oxygen atoms gives uniform units of spherical morphology in the pure CeO<sub>2</sub> as well as in cerium rich glass. Clustered species has a great benefit in the field of application, used as a shielding material for ionized radiations.
文摘Ce^（3＋） substituted Cu-spinel nanoferrites CuCe_xFe_（2-x）O_4（x=0.00, 0.02, 0.04, 0.06, 0.08 and 0.10） were synthesized via sol-gel self-combustion hybrid route. Single phase spinel ferrite of Cu nanoferrites were examined using X-ray diffraction（XRD） analysis whereas the multiphase structure was observed as Ce contents increased from x=0.06. Field emission scanning electron microscopy（FESEM）, Thermogravimetric and differential thermal analysis（TGA and DTA） and Fourier transform infrared spectroscopy（FTIR） were used to find out the morphology phase and metal stretching vibrations of Ce^（3＋） substituted nanocrystalline ferrites. The crystallite size was increased and found in the range of 25-91 nm. The agglomerations in Cu ferrite samples increase as the Ce^（3＋） concentration increases. The magnetic properties such as remanence, saturation magnetization, coercivity, Bohr magneton and magnetocrystalline anisotropy constant（K） were determined using M-H loops recorded from a vibrating sample magnetometer（VSM）. Saturation magnetization, remanence and coercivity are increased as the Ce^（3＋）contents increase in Cu nanocrystalline samples. Moreover, law of approach to saturation（LoA） was used to calculate the maximum value of saturation for Ce-doped Cu nanoferrites. The soft magnetic behaviour of the Cu nanoferrite is observed as compared to the samples substituted with the increased Ce contents in Cu nanocrystalline ferrite. Bohr magneton and magnetocrystalline anisotropy are found to increase with the substitution of rare earth Ce^（3＋） contents in Cu spinel nanocrystalline ferrite. Cedoped Cu nanocrystalline ferrites with excellent properties may be suitable for potential applications in sensing, security, switching, core, multilayer chip inductor, biomedical and microwave absorption applications.
基金the support of the U.S. Department of Energy Vehicle Technologies Office
文摘Magnesium(Mg)alloys are ideal candidates for automotive applications due to their high strength to weight ratio,castability,recyclability etc.,however,they lack corrosion and oxidation resistance.Solid-state deposition techniques,such as cold spray,have been demonstrated to enhance their corrosion resistance as it relies on the severe plastic deformation of powder particles upon impact with the substrate to form a metallurgical bond with the substrate and within the coating.At cold sprayed interfaces,a heterogeneous microstructure is formed that includes some porosity,oxides and intermetallics which can significantly affect coating performance.Thus,establishing a direct correlation between the interface microstructure and its properties can aid in designing optimal cold spray parameters.In this study,we investigated the microstructure and mechanical properties of a zinc(Zn)coating deposited on a high pressure die cast(HPDC)AZ91 Mg substrate via high resolution scanning transmission electron microscopy,in situ micro-tensile testing,and finite element method(FEM)modeling.Micro-tensile pillars fabricated using the plasma focused ion beam(PFIB)successfully isolates the coating-substrate interface within the gauge length.The average bond strength of Zn-Mg interface was determined to be∼140 MPa with failure occurring partially at the interface and mostly into the coatings.A detailed microstructural characterization revealed evidence of a strong metallurgical bonding at the Zn-Mg interface and formation of the C14 MgZn_(2)laves phase interlayer resulting in a mixed mode of fracture during the micro-tensile experiments.FEM modeling reveals the stress distribution along the interfaces and suggests that a MgZn_(2)layer thickness between 200–400 nm is optimum to increase the bond strength and minimize the triaxiality.Such a site-specific interfacial analysis with correlative computational modeling provides crucial insight into the overall performance of cold spray interfaces.
