Materials Science Forum Vols. 546-549

Abstract: The metal elements, such as Fe, Mn, Co, Ni, Ni-Mn, Co-Mn and Fe-Mn, were mixed and milled with pre-cross-linked polysilazane Ceraset® and subsequent pyrolysis. The metals act as active fillers to increase the density of composite. The phases and microstructures of metal/ceramic composites were studied using XRD, SEM and EDS, and the magnetic property was measured with Magnetic Property Measurement System at –196oC. The results show that there are two main domains in composites, one is metal-rich domain and another is metal-poor domain. The density of composite is larger than that of polymer-derived SiCN ceramic, but the hardness varies little. The compound generated by the reaction between metal and matrix has great effect on the magnetic properties of composites, which are filled with different metals.

Abstract: A new cermet sinter with sweat-gland micro-pore structure has been developed by powder metallurgy technology in vacuum. The effects of the pore-forming materials on micro-pore structure and Y2O3 additions as well mechanical properties of TiC/FeCrWMoV cermets were investigated. Some typical sweat-gland micro-pores were formed while compound additives TiH2 and CaCO3 adding into the sinter matrix. The porosity of the cermet sinters changes from 20% to 28% with the compound additives from 6% to 8%, and the micro-pores of sinters exist a regularized and interpenetrated network structure just like human’s sweat-gland one and obeying to Rayleigh Distribution. As such the sinters could be easily infiltrated with high-temperature solid lubricant. For improving the property of the ceramet sinter, the elements Y2O3 of 0.6～0.8% (vol. fraction ) was also added into the sinter matrix and its effect on the sinter has been also discussed .

Abstract: A new resistance sintering method under ultra high pressure has been developed for fabrication of Mo/Cu (functional graded material) FGM. The consolidation was carried out under pressure of 8GPa, and input power of 15kW for 50s. The relative density of the FGM specimen was upwards 98% and the composition distribution was nearly the same as designed one. The micro-hardness and bend strength were measured to evaluate the sintering effects. The densification effect and microstructure of these FGM samples were investigated and the sintering mechanism was discussed.

Abstract: Cyclic extrusion is a new bulk deformation method. It consists of two steps. In the first step a part of the work piece will be indirectly extruded. In the second step the extruded part will be backwards pressed into the bulk again so that the original shape of the work piece is retained. Similar to ECAP, cyclic extrusion can be repeated many times without shape change. On the other hand, cyclic extrusion can be applied locally on a work piece so that local grain refining or work hardening is possible. Magnesium alloy AZ31 was cyclically extruded at 400 °C with different tools. The grain size was refined from 800 +m to 15 +m. The local grain refining in the surface zone with cyclic extrusion improved the rollability of cast AZ31. Pure aluminium specimens were cyclically extruded up to 2.5 times, which corresponds to a deformation degree of -7. The microstructure changes were examined with EBSD.

Abstract: Laser rapid forming (LRF) is a new manufacturing technology, which has been developed on the basis of multi-layer laser cladding. In the LRF process, the microstructure has important effects on the mechanical properties of the parts
but the control of microstructure is a problem. In this study, the influences of crystallography orientations of substrate and profile of solid/liquid interface on microstructure were discussed. Further, with the combining of the columnar to equiaxed transition (CET) model during alloy solidification, the growth law of microstructure of Rene88DT alloy was established. It has been found that the temperature gradient was lowest and the solidification velocity was greatest at the solid/liquid interface of the tail of molten pool, and hence the CET occurs easily at this position. The temperature measurement system of molten pool was developed by using a two-color infrared thermometer in this study. With the measurement of temperature gradient of the tail of molten pool by using a two-color infrared thermometer, the process parameters of laser multi-layer cladding were optimized. Finally, directional solidification even single crystal was achieved in laser multi-layer cladding.

Abstract: The dispersion of CNTs (Carbon Nanotubes) within polymer matrix is a big obstruction to restrict the application of CNTs. In this paper, the dispersion of MWCNTs(Multi-walled Carbon Nanotubes) within epoxy resin, which was improved by the coupling agent Volan and dispersing agent BYK, were studied. It showed that the best dispersing result of MWCNTs was obtained by combination treatment of Volan and BYK.

Abstract: The hot corrosion behavior of titanium alloy and AlCuFeCr quasicrystalline coating on titanium alloy in the presence of a solid mixture of NaCl and Na2SO4 deposit at 700°C was studied. The result shows that weight-gain kinetics for titanium alloy exhibited a linear rate law, while the kinetics of AlCuFeCr quasicrystalline coating displayed parabolic growth rate. The corrosion resistance of the titanium alloy was improved by applying the AlCuFeCr quasicrystalline coating. The corrosive oxide morphology formed on titanium alloy was porous. For AlCuFeCr quasicrystalline coating with the mixture of NaCl and Na2SO4 deposit, the scale formed on the coating surface was compact and uniform. Oxide formed on the surfaces of Al-Cu-Fe-Cr quasicrystalline coatings after hot corrosion consisted of Al2O3.