Papers by Keyword: Nano-Precipitation

Abstract: The effects of Co contents on the microstructure characteristic and phase structure of Co_xCrCuFeNi high-entropy alloys were investigated by SEM, EDS and XRD. The microstructures consisted of dendrites and many nanoprecipitations in the interdendritic. Increase Co contents,the size of nanoprecipitated phase in the interdendritic firstly increased and then decreased slightly. According to XRD analysis, two simple FCC phases, dendrite phase and Cu-rich interdendritic phase were found. As a result of slow diffusion, supersaturated solid solution was formed during solidification and then nanophase was precipitated during the following cooling process. The results of EDS revealed that Fe、Co and Cr were rich in dendrites, while Cu was rich at the interdendritic. For element Ni, which was rich in dendrites when x≤1.0, but was almost the normal value in dendrites for x>1.0. The reason for segregation was related to the positive mixing enthalpy between elements. The contents of Co had little impact on the hardness of Co_xCrCuFeNi high-entropy alloys according to micro-hardness testing.

Abstract: The behavior of nanoprecipitates of 800Mpa grade high strength low carbon steel during tempering has been studied. Transmission electron microscope (TEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive spectrometry (EDS) were used to systematically analyze the morphology of precipitates and their grain orientation with matrix at different tempering temperatures. Experimental results confirm that the composition of these nanometer sized particles in the matrix was compound carbonitrides containing Ti, V, Mo and other elements. The precipitates of the as-received steel are (Nb,Ti)(C,N) at low tempering temperature, while those at high tempering temperature are composite carbides containing a variety of elements such as Mo, V, Ti and Nb. On the other hand, as tempering temperature increases, precipitates in the steel were slowly growing up and roughening according with the typical Oswald ripening mechanism; a sharp orientation relationship exists between precipitates and matrix.

Abstract: Dextran catches increasing attentions as a drug carrier because of its biocompatibility, biodegradability and ease of modification. In this study, we synthesized the derivated dextran by grafting with 1-(3-aminopropyl) imidazole. The dextran-based nanoparticles with sizes of 1H NMR, SEM, AFM and Zetasizer.

Abstract: The microstructure of high-entropy Alloys AlFeCuCoNiCrTix (x=0, 05, 1.0) with different titanium contents had been studied. The results showed that: (1) The microstructure of AlFeCuCoNiCrTix exhibited the trend from dendritic structure to eutectic-cell structure as the titanium contents increasing and spinodal decomposition, nanoprecipitation and amorphous phase can be also observed; (2) Composition segregation appeared (especially Cu) and Ti promoted the segregation of Cu; (3) Alloys was consisted of FCC and BCC, and phases gradually converted from FCC+BCC1 to FCC+BCC1+BCC2 with addition of titanium and BCC2 became the leading phase; (4) Both ordering and spinodal decomposition coincided due to the difference of atomic size and high entropy effect.

Abstract: Bi-doped Sr0.7Ba0.3TiO3 ceramics sintered at different temperatures were studied by analytical electron microscopy. Grain boundaries (GBs) with discrete Bi nano-precipitates (NP) were observed in both samples sintered at 1170°C and 1190°C. Dopants’ solutions as well as their segregations to GB were analyzed quantitatively to reveal the origin of NP. NP at GB contributed to the high dielectric constants of the materials.

Abstract: In the present work, low carbon low alloy submicro-steel sheet has been developed successfully by severe warm-rolling (SWR) at 500 °C through a single pass. The result shows submicro-structure can be fabricated by severe rolling. The formation of the submicro-structure is attributed to the grain refinement mechanism induced by the severe plastic deformation (SPD). The refinement involves the cutting and subdividing of the original micro-crystals into ultrafine grains by dense dislocation arrays. To a certain extent, dynamic recrystallization in ferrite during SWR also seems to contribute to the formation of the submicro-structure. The thermal stability of the submicro-steel was investigated by annealing the steel at different temperatures. The investigation indicated that the submicro-steel can be subjected to annealing at 550°C without apparent grain growth. The unusually high thermal stability can be attributed to the pining effect of numerous uniformly distributed nano-precipitates in the steel. The sizes of the nano-precipitates belong to two different orders. The average diameter of the large precipitates is about 30 nm and the smaller one less than 10 nm.

Abstract: Plain low carbon steel produced by compact strip production (CSP) process was analyzed using TEM, EELS and XEDS. Nano-sized oxides and sulfides were observed in the steel. The nano-oxides are mainly ferrospinel of <20nm in size, and the nano-sulfides are MnS and FeS particles with size of 20-100 nm. They distributed both in grains and at grain boundaries. These nano precipitates could form in cast slab before heavy deformation by rolling process. It is proposed that besides the grain refinement, the nano-pricipitation plays an important role in yield strength enhancement. This mechanism may provide a new approach to strengthen plain low carbon steels.