Papers by Author: Gang Wang

Abstract: Three-dimensional graphene foam (GF) is synthesized by chemical vapor deposition (CVD) at ~1000°C under ambient pressure. Then it is characterized by scanning electron microscopy (SEM) and laser Raman spectroscopy, the results indicate that GF has changed the surface morphology of Ni foam, and ~ 98% of the GF are fewlayer. At last, the surface wettability of GF is investigated, which shows that it is hydrophobic. The special three-dimensional structure and excellent properties of GF make it a candidate for a range of applications.

Abstract: NiMnCoIn alloys are new-type magnetic shape memory alloys (MSMAs) in which a reversible magnetic-field-induced phase transformation was observed. They are ideal candidates of materials used in actuators and sensors. The polycrystalline NiMnCoIn alloys are generally brittle so that they can not be easily deformed into the shape applicable to actuators and sensors until now. In the present paper, the influence of hot deformation on the microstructure of Ni₄₅Co₅ Mn_36.7In_13.3 alloy was studied. The experimental results showed that second phase was observed after deformation at high temperature between 800~900 °C and at strain rate lower than 4×10^-3s^-1. The content of Co of second phase was higher than the matrix alloy, while the content of In was lower than the matrix alloy. It was determined by TEM measurements as γ phase with fcc structure which was popular in NiFeGa and NiMnGaCo alloys. It is possible to improve the ductility of Ni₄₅Co₅Mn_36.7In_13.3 alloy by control of amount and distribution of γ phase by hot deformation.

Abstract: A nanostructured surface layer was synthesized in a pure copper plate by means of surface mechanical attrition (SMA). The evolutions of microstructure and orientation were examined by using XRD, TEM and ODF. The microstructural evolution with the treatment time can be divided into two stages: the first is characterized by a formation of nc grains with small to medium misorientations in the surface layer and a texture transformation from rolling type to shear one in the near-surface layer, and the second by a significant increment of misorientations between the nc grains and a texture transformation from shear type back to rolling one. It might be reasonably deduced that shear stress can effectively induce grain refinement, and the combination of shear and compress stresses might be helpful for the increment of grain boundary misorientations.

Abstract: In recent years, there has been an increasing interest in magnetic shape memory alloys (MSMAs) due to their unique ability to produce very large output strains and rapid response frequency. NiMnCoIn is a new-type MSMAs in which a reversible magnetic-field-induced phase transformation is observed. The microstructural evolution in the process of dynamic recrystallization in polycrystalline Ni45Co5Mn36.7In13.3 was studied in the present paper. The experimental results showed that the high deformation temperature and slow strain rate were necessary to achieve perfect dynamic-recrystallizing microstructure in Ni45Co5Mn36.7In13.3 alloy. Precipitates with two sizes were observed. The content of Co in precipitates was higher than that in the matrix alloy, while the content of In was lower than that in the matrix alloy.

Abstract: The magnetic shape-memory alloy NiCoMnIn shows, in monocrystalline form, a large reversible magnetic-field-induced strain (MFIS). But it is difficult to achieve the properties in polycrystalline NiCoMnIn alloys. The technique of powder metallurgical preparation of NiCoMnIn foam was studied to improve the properties of polycrystalline NiCoMnIn alloys in the present paper. We introduced a processing route including choosing appropriate space-holding fillers, sintering NiCoMnIn alloy and the filling agent with appropriate grain size. The sintering temperature and time and the optimum volume fraction of the filling agent were determined by analysis of the structure of sintered bulk foams.

Abstract: Equal channel angular extrusion (ECAE) is an effective means of producing ultrafine-grained materials with extraordinary mechanical properties. Texture evolution and microstructure in pure copper single crystals processed by ECAE for up to five passes via route C are investigated to understand mechanisms of plastic deformation and grain refinement during ECAE. The experimental textures after the third pass ECAE process recovers that after one pass ECAE process. The main textures approaches a stable one after four passes of ECAE process via Route C while the intensity of main texture components decreases gradually. Local TEM-OIM measurements shows that grain subdivision in ECAE-processed samples occurs with the formation of many low angle grain boundaries.

Abstract: A specimen current heating sintering process was employed to manufacture SiC particulate reinforced iron matrix composite. The results show that mechanical properties of the composite can be improved significantly with increasing pressure level, voltage, sintering time. It is found that short sintering time, fast heating and uniformly heating, surface activation of particles can be accomplished in specimen current heating hot press sintering to avoid oxidation degradation of Fe powder, and to produce fine microstructure, which contribute the main reasons for achieving higher density and higher properties. The best properties achieved so far for the composite are: density is 99.90%, Brinell hardness is 416HB and tensile strength is 838MPa.

Abstract: Microstresses due to intergranular and inter-phase interactions in an austenitic-ferritic super duplex steel (SAF 2507) under uniaxial compressive deformation have been studied by in-situ neutron diffraction experiments. Lattice strains of several hkl planes of austenite respective ferrite were mapped as a function of sample direction at a number of load levels during loading into the plastic regime and unloading. The analysis of the experimental results has shown that during loading both grain-orientation-dependent and inter-phase stresses were generated under plastic deformation that was inhomogeneous at the microstructural level. Residual stresses depending on the grain-orientation and phase have been found after unloading. The results also indicate stronger intergranular interactions among the studied hkl planes of austenite than those of ferrite.

Abstract: The orientation evolution in Copper single crystal during ECAE (in Route C) has been investigated experimentally for 90° die angle by X-ray diffraction and TEM-OIM. It is shown that after the previous three passes of ECAE, orientation evolutes with similar mechanism to the simple shear deformation. The grain subdivision occurs with the appearance of many low angle grain boundaries. After four times extrusions the ED of the samples remains stable, their ND rotates around the ED by about 20°. After five times extrusions the main texture component remains stable.

Abstract: The microstructure of Ti+P IF steel were studied after warm rolling, cold rolling and recrystallization using X-Ray, TEM and SEM. The results show that the characteristics of warm rolled sheet are the same as that of the cold rolled, but the texture displays different characteristics in the subsequent cold rolling and recrystallization because of the numerous second-phase particles. In this work, a Ti+P IF steel sheet with high strength and plastic strain ratio was obtained.