Abstract: The system components and the theory of jet electrodeposition orientated by rapid prototyping (RP) are introduced.The nanocrystalline copper parts with simple shape were fabricated by RP technology. The microstructure evolution of the nanocrystalline Copper layer was examined by means of the Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). The results show that the jet electrodeposition can greatly enhance the limited current density, fine crystalline particles and improve deposition quality. The copper deposited layers have nanocrystalline microstructure with average size of 55.6nm. The grain size decreases to 41.4 nm in crystal plane (311).
Abstract: The solidification characteristics of the immiscible alloys exhibit a unique opportunity in designing composites with spherical crystalline particles dispersed in the amorphous metal matrix. The multicomponent Al82.87Pb2.5Ni4.88Y7.8Co1.95 immiscible alloy has been designed. The ribbon samples of the multicomponent alloy were prepared by the rapid quenching. The microstructure was characterized and the phase constitution and transformation were studied. The as-quenched samples revealed the Al-based metallic glass matrix is embedded by the spherical crystalline Pb-rich particles. A method has been developed, based on the mechanism of the liquid-liquid phase decomposition in the miscibility gap of the multicomponent immiscible alloy, to produce spherical crystalline particles in the amorphous matrix. The microstructure evolution in the Al-based amorphous matrix composites has been discussed
Abstract: The effects of spheroidizing annealing process on SWRH72B heavily cold drawn pearlite steel wires were studied and the mechanisms of low-temperature spheroidizing annealing were discussed. The results show that, with increasing drawing strain, the spheroidizing annealing temperature and time decreased and uniformity of the spheroidizing increased; the mechanism of low-temperature spheroidizing annealing was different from the traditional one of heavily cold drawn pearlite steel wires. When the true strains were between 2.85 and 5.1, the spheroidizing process of carbide could be divided into two stages: partial dissolution of lamellar carbide, and the precipitation and accumulation of compulsory dissolved cementite. When the true strains were larger than 5.1, the spheroidizing process of carbide was only characterized by precipitation and accumulation of compulsory dissolved cementite.
Abstract: The preparation, mechanical properties, grain size and thermal property of bulk nanocrystalline Cu (BNC-Cu) were investigated in this paper. BNC-Cu can be produced by in situ consolidation of pure Cu powder with high-energy ball milling at room temperature; the average grain sizes of Cu samples decreased with the increasing of ball milling time before 9 h because the grain refining velocity was bigger than the grain growing velocity in this stage. When the ball milling time was beyond 9 h, the average grain size reached a steady minimum value about 27.5 nm. The microhardness of BNC-Cu samples increased with the extending of ball milling time in the first 9 h because the dominating factor was the hardening effect caused by grain refinement and work hardening rather than softening in this stage. BNC-Cu gained its highest microhardness about 1.59GPa when the ball milling time reached 9 h. Subsequently, the microhardness of BNC-Cu slightly fluctuated around this value. Because there were numerous triple grain boundaries and the interaction among different crystal defects in BNC-Cu, BNC-Cu showed outstanding thermal stability when it was annealed in the range of 100°C to 400°C.
Abstract: Equal-channel angular pressing (ECAP) is used to convert coarse grain into ultrafine grain (UFG). The characteristics of ECAP and the shearing patterns obtained when ECAP applied to metals are investigated. Then propose a series of procedures to verify the structure evolution of AZ31 Mg alloys after ECAP processing. The results indicate that parameters including route, die angular and pressing passes influence on the microstructure of the AZ31 Mg alloys. Route BC is the optimum processing route due to the largest slipping angular range.
Abstract: The temperature-dependent deformation and damage behaviors of ultrafine-grained (UFG) Cu and Ti produced by equal channel angular pressing (ECAP) were investigated and compared. It was found that ECAPed materials with different crystalline structures, e.g. the present fcc Cu and hcp Ti, exhibited significantly distinctive high-temperature deformation and damage characteristics. As the testing temperature is below recrystallization, small- and large-scale cracks or voids formed along the shear bands (SBs) on the surface of UFG Cu, whereas only a few fine shear lines and some non-propagation voids appeared on the surface of UFG Ti. As the temperature is above recrystallization, some small cracks (or voids) formed along grain boundaries and slip deformation took place in many coarsened grains, while only extrusions and intrusions instead of obvious cracks or voids are observable for UFG Ti. The corresponding microstructual changes after compressive deformation, e.g. grain coarsening, were also examined and confirmed by TEM observations.
Abstract: The Mg96Y3Zn1 alloy processed by equal channel angular pressing has been investigated. It was found that the Mg96Y3Zn1 alloy processed by ECAP obtained ultrafine grains and exhibits excellent mechanical properties. After ECAP, the average grain size of Mg96Y3Zn1 alloy refined to about 400 nm. The highest strengths with yield strength of 381.45MPa and ultimate tensile strength of 438.33MPa were obtained after 2 passes at 623K. It was found that cracks were preferentially initiated and propagated in the interior of X-phase during the tensile test. As a result, the elongation of alloy is decreased with pass number increasing.
Abstract: Mullite nanocomposite was synthesized using kaolin with different Si/Al molar ratios in the range of 1.1- 4.31. The synthesized samples were analyzed and characterized using XRD and SEM techniques and effects of Si/Al molar ratio on mullite nanocrystal morphology have been investigated. SEM results showed that the mullite nanocomposite synthesized from kaolin with different Si/Al molar ratios had different morphologies and distribution patterns of particle size. It was found that the mullite nanocrystals with relatively homogenous grain-size distribution, low aspect ratio, and little agglomeration were produced from the precursors made from kaolin with a Si/Al ratio of 1.1-2.33 at calcination temperature of 1100-1250 oC.
Abstract: Microstructures and properties of ultrafine grained (UFG) iron by different rolling processing are investigated. By applying the asymmetric rolling (ASR), the equiaxed UFG iron with the grain size of 0.9 μm has been obtained due to the shear strain induced by the mismatch of the two roll during ASR. With the same rolling reduction, the ASR processed iron shows higher yield strength than that of the symmetrically rolled one. When the ASR processed iron is further symmetrically rolled, the grain morphology maintains equiaxed and the grain size decreases to about 0.3 μm.