The aim of present work was to produce pure nickel aluminate （NiAl2O4） nanoceramic compound by high energy millingof nickel carbonate （NiCO3） and aluminum （Al） powders followed by annealing. Phase composition, t...The aim of present work was to produce pure nickel aluminate （NiAl2O4） nanoceramic compound by high energy millingof nickel carbonate （NiCO3） and aluminum （Al） powders followed by annealing. Phase composition, thermal behavior, morphologyand microstructure of powder samples were characterized by means of X-ray diffraction, differential scanning calorimeter,thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. The results showed that formationof NiAl2O4 spinel compound from NiCO3 and Al powders took place in three steps： oxidation of Al to Al2O3, decomposition ofNiCO3 to NiO and CO2, and finally the solid state reaction between Al2O3 and NiO. It was also demonstrated that single phaseNiAl2O4 spinel compound can be produced by 5 h of mechanical milling with subsequent annealing of NiCO3/Al mixture at 900 Cfor 2 h, which is 冾 500 C lower than the temperatures used in the traditional solid state methods. The particle diameter of theproduced NiAl2O4 spinel compound was found to be less than 100 nm as measured by transmission electron microscopy.展开更多
The microstructure and micro-texture in different areas of a friction stir(FS)-welded DP600 steel were investigated by means of electron backscatter diffraction.The volume fraction of martensite and non-polygonal ferr...The microstructure and micro-texture in different areas of a friction stir(FS)-welded DP600 steel were investigated by means of electron backscatter diffraction.The volume fraction of martensite and non-polygonal ferrite was evaluated based on the image quality(IQ)parameter.Analysis of grain boundaries revealed that the fraction of sub-grain boundaries as well as that of low-angle grain boundaries in the heat-affected zone(HAZ)and stir zone(SZ)was more than doubled compared to those in the DP600 steel base metal(BM).The micro-texture examination of the BM showed strong{112}<110>and{111}<112>components with an intensity 4.6 times of that random texture.The texture showed a memory effect in the HAZ,with a reduced overall intensity.Within the SZ,D_(1),D_(2) and E shear texture components together with a cube component were developed.Formation of these texture components of ferrite were attributed to the transformation of B and R texture components of prior austenite,which are evidences of continuous dynamic recrystallization mechanism in the SZ of the friction stir-welded DP600 steel.展开更多
文摘The aim of present work was to produce pure nickel aluminate （NiAl2O4） nanoceramic compound by high energy millingof nickel carbonate （NiCO3） and aluminum （Al） powders followed by annealing. Phase composition, thermal behavior, morphologyand microstructure of powder samples were characterized by means of X-ray diffraction, differential scanning calorimeter,thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. The results showed that formationof NiAl2O4 spinel compound from NiCO3 and Al powders took place in three steps： oxidation of Al to Al2O3, decomposition ofNiCO3 to NiO and CO2, and finally the solid state reaction between Al2O3 and NiO. It was also demonstrated that single phaseNiAl2O4 spinel compound can be produced by 5 h of mechanical milling with subsequent annealing of NiCO3/Al mixture at 900 Cfor 2 h, which is 冾 500 C lower than the temperatures used in the traditional solid state methods. The particle diameter of theproduced NiAl2O4 spinel compound was found to be less than 100 nm as measured by transmission electron microscopy.
文摘The microstructure and micro-texture in different areas of a friction stir(FS)-welded DP600 steel were investigated by means of electron backscatter diffraction.The volume fraction of martensite and non-polygonal ferrite was evaluated based on the image quality(IQ)parameter.Analysis of grain boundaries revealed that the fraction of sub-grain boundaries as well as that of low-angle grain boundaries in the heat-affected zone(HAZ)and stir zone(SZ)was more than doubled compared to those in the DP600 steel base metal(BM).The micro-texture examination of the BM showed strong{112}<110>and{111}<112>components with an intensity 4.6 times of that random texture.The texture showed a memory effect in the HAZ,with a reduced overall intensity.Within the SZ,D_(1),D_(2) and E shear texture components together with a cube component were developed.Formation of these texture components of ferrite were attributed to the transformation of B and R texture components of prior austenite,which are evidences of continuous dynamic recrystallization mechanism in the SZ of the friction stir-welded DP600 steel.
