Papers by Keyword: Microstructure

Abstract: In this work, tungsten inert gas cladding (TIG), is utilized to in-situ synthesize the (Ti,W)C based cermet cladding layers. The microstructure and microhardness of the cladding layers were analyzed by scanning electron microscopy (SEM) and microhardness tester. The grain abrasion resistance of the cladding layers is also discussed. The grain abrasion resistance of the coating is also discussed. The results showed that excellent bonding between the coating and the AISI 1045 steel substrate was uniform, continuous and almost defect-free. (Ti,W)C cladding layers have compact microstructure and high microhardness. The grain abrasion resistance of the coating is attributed by the compact microstructure.

Abstract: The effects of process parameters on evolution of microstructures of 7055 aluminum alloy in creep age forming were studied and the microstrucures were analyzed using transmission electron microscopy (TEM). Some important results are obtained: with the increasing of ageing time, the size of platelet shaped (known as Guinier-Preston (G-P) zones) precipitates and spherical shaped η' precipitates increased, the number of platelet shaped precipitates increased too, while the number of η' precipitates decreased; the precipitates with almost the same size distributed continuously and uniformly along the grain boundary with quite narrow precipitate free zones (PFZs) at 5 hours of ageing time, when the ageing time increases to 8 hours, the distribution of the precipitates along the grain boundary becomes discontinuous and the PFZs gets wider, while with the further increasing of the ageing time, the precipitates distributed continuously again along the grain boundary and the PFZs become more wider. From comparison of stress-aged alloy to stress-free-aged alloy, it was found that after 20 hours ageing, the precipitates in the stress-aged alloy are slightly coarser and the PFZs are wider, the density of retained η' is lower with the development of η phase.

Abstract: Ceramic foam is a class of materials with high porosity and three-dimensional network of struts. In this study, ceramic foams were fabricated by polymeric sponge method using commercial PVA foam as a replica template. The study focused on the effect of alumina content on the physical and mechanical properties of such ceramic foams sintered at 1500°C for different sintering times. It was found that ceramic composition with higher amount of alumina required higher sintering temperature than that used in the present study. Physical properties and mechanical strengths depended upon ceramic composition as well as sintering time. Microstructural analysis revealed the evolution of primary cuboidal mullite and needle-like nano-sized mullite phase in the sintered sample. This fine needle-like phase added to mechanical strengths of ceramics.

Abstract: The AlMn and AlMnSi foils were fabricated by rapid solidification technology. The phase transformation temperatures, microstructures and distribution of elements were characterized by Differential Scanning Calorimetry (DSC), Transmission Electron Microscope (TEM), X-ray Diffraction (XRD) and Energy Disperse Spectroscopy (EDS) respectively. The result shows that the phases of AlMn7 nanofoil conclude Al, Al6Mn and quasicrystal phase, the crystal size is about 120nm; the phases of AlMn5Si5 nanofoil conclude Al, Al4.01MnSi0.74 and Al9Mn3Si, the crystal size is about 60nm. The phase transformation temperatures of AlMn7 and AlMn5Si5 nanofoils are 543K and over 873K, respectively. The microstructure morphology of AlMn7 nanofoil are rod, block and petal-like, but the microstructure morphology of AlMn5Si5 nanofoil is homogeneous globular.

Abstract: Amorphous nickel hydroxide powders codoped with Ce and Fe were synthesized by the combined chemical precipitation and rapid freezing method. The microstructure and chemical composition of the samples was characterized by XRD,SAED and EDS. The electrochemical performance of the prepared samples was analyzed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge-discharge tests. The results showed that this amorphous nickel hydroxide codoped with Ce and Fe had more structural defects than those of Fe singly doped amorphous nickel hydroxide. These abundant structural defects with Ce and Fe codoped amorphous nickel hydroxide increased the thermal stability, decreased the charge transfer resistance, inhibited oxygen evolution reaction effectively and improved the electrochemical reversibility of the amorphous nickel hydroxide electrode.

Abstract: The solidification behavior of undercooled Cu98Cr2 alloys was investigated under different rapid solidification methods. The results shown that whole lamellar (α+β) eutectics appeared in melt spun alloys for the sample undercooled into the coupled zone. The microstructure of arc melted Cu98Cr2 alloys consisted of primary β(Cr) particles distributes on α(Cu) matrix and (α+β) eutectics set in cellular α (Cu) phase. However, due to the different thickness and different solidification rate, the microstructure of splat quenched Cu98Cr2 alloys shown that only cellular supersaturated α solid solution occurred for thin flake and primary β(Cr) particles and (α+β) eutectics occurred for thicker flakes.

Abstract: The effect of cooling rate on the microstructure of Cu80Cr20 alloys was studied by using vacuum non-consumable arc melting, vacuum induction melting, electromagnetic levitation and splat quenching. The microstructure evolution of the Cr-rich were analyzed by scanning electron microscopy (SEM) and optical microscopy. The results showed that nonuniform Cr-rich dendrite distributes on Cu-rich matrix for arc melted alloys and uniform Cr-rich dendrite distributes on Cu-rich matrix for electromagnetic levitation melted alloys and vacuum induction melted alloys. However, the Cr-rich phase show both dendrites and spheroids for splat quenched alloys. This means liquid phase separation occurred during rapid solidification.

Abstract: AZ91D alloy composites reinforced by CNTs/SiCp were fabricated using stir casting process. The mechanical properties of the composites were tested, observed and analyzed the microstructure, the fractographs were observed and analyzed via scanning electron microscope. The results showed that CNTs/SiCp could not only refine the grains of the composites, but also bear the load of resistance to deformation. Compared with the matrix alloy, the tensile strength, the elastic modulus, the micro-hardness and the elongation rate of the composites had been enhanced significantly. But the mechanical properties would be fell down with the more addition of CNTs/SiCp.

Abstract: Al-8.5Fe-1.3V-1.7Si/SiCP composite prepared by multi-layer spray deposition in different states were investigated. Ultimate tensile strengths of the composite sheets as-rolled tested at 315°C and 400°C are up to 300MPa and 186MPa respectively. The fine dispersoids and fine grains, and homogeneous SiC particles contribute to the excellent mechanical properties of the composite at elevated temperature. Specially, partial dissolution of SiC particles contributes to the stability of Al12(Fe,V)3Si phase.

Abstract: High velocity arc spraying (HVAS) process was used to deposit Al-Ni-Y-Co and Al-Ni-Mm-Fe amorphous/nanocrystalline composite coatings onto AZ91 Mg alloy substrate. Their microstructure was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The coatings are both about 500 μm in thickness with fully dense and low porosity. The microstructure of the coatings is classified into two regions, namely, a full amorphous phase region and homogeneous dispersion of fcc-Al and some intermetallic nanoscale particles in a residual amorphous matrix region. Vickers micro hardness of the coatings was also measured. The average Vickers micro hardness of Al-Ni-Y-Co and Al-Ni-Mm-Fe coating is about 311 HV and 340 HV, respectively.