Materials Science Forum Vols. 492-493

Abstract: Layered double hydroxide(LDH) was synthesized from the mixture of magnesium hydroxide and aluminum hydroxide with microwave irradiation. It has been compared with that of conventional heating method in the respect of crystallization time, structure, morphology, particle size, and its anion exchange capacity. The microwave speeded up the crystallization rate of Mg-Al- LDH so that the XRD patterns of LDH was observed from the sample after microwave hydrothermal treatment, while the crystal phase was hardly observed from that prepared by conventional hydrothermal method before drying process. Mg-Al-LDH prepared with microwave irradiation seemed to have slightly higher Mg/Al molar ratio even with the same compositions of starting materials and the lower anion exchange capacity after 1 day exposure in 0.1N NaCl solution compared to the conventionally prepared one.

Abstract: The creation of three dimensional functional graded materials by powder processing methods requires the capability to arrange a sequence of two dimensional images that can be presented to a solid freeforming device. Planar stacking methods can only achieve a one dimensional gradient. We describe the acoustic control of powder metering and dispensing valves in which the flow rate and switching of powders from a capillary can be controlled using the frequency and amplitude of acoustic vibration from a computer sound card. An orchestra of such valves can be used to pattern layers of powder on the building platform which forms part of a 3-axis table in the Selective Laser Sintering (SLS) process. Patterns and gradients were prepared using copper and steel powders.

Abstract: The porous alumina tube with pore gradient along the radial direction was successfully fabricated, where PMMA particles were used as pore former agent. The specimen was expected as a filter subjected to high temperatures. Alumina and PMMA particle were mixed with water to form aqueous slurry, compacted using centrifugal molding technique. The green body was dried in partial vacuum atmosphere, calcinated at 273 K to remove the organic component, sintered at 1623 K to obtain sintered porous a-alumina tubes. The control on the pore gradient of porous tubes was attempted by two ways; lamination and continuous methods. The microstructure observation showed that the inner part of the tubes had higher porosity than the outer part irrespective of the method used. Porous alumina tubes were characterized by microstructure observation, porosity and air permeability. The binary pores of 10µm and submicron in diameter were visible, which were formed by the burning-out PMMA particles and lower sintering temperature, respectively. The influence of PMMA amount on the pore morphology of the tubes was investigated. Fracture strength was carried out by the O-ring diametral compression testing. An analytical formula subject to the diametral testing was introduced with considering the porosity gradient. The correlations between the fracture strength and pore gradient were investigated, where a reduction in fracture strength was observed with the increase in laminated layers, and minimum strength was found in continuous porous tubes.

Abstract: In this paper, we introduced research and development of technology of low cost production of FGMs. This research is designated for development of mass production technology for production of ceramic wares with induction heating (IH) function. Slurry lamination method has advantage in forming graded layers due to its simplicity and easiness. However, this method has a disadvantage to generate cracks during drying process. Therefore, freeze-dry in vacuum was introduced in drying process of slurry lamination. By doing so, mass production could be achieved. In this trial production, we adopted SPS sintering method to production technique. In the future, we will further develop other applications of FGMs into industrial products.

Abstract: The production method for metal components with micro sized porous structure has been developed by applying “powder space holder method” to metal powder injection molding process. In this study, a co-sintering process was utilized to make a plate of sintered metal with micro porous graded structure. The green compact sheets with various contents of space hold particles were prepared by hot press molding for simplification. The five layers of metal with symmetric structure, which the skin layer was formed with high density metal and the core was formed with open or closed porous structure, or with inverse symmetry, was obtained by changing stacking sequence in co-sintering process. Mechanical properties of the materials with plain homogeneous porous structure and porous graded structure were compared. The usefulness of proposed method for producing the metal components with micro porous graded structure and the effective of graded structure to compensate the deficiencies on the mechanical property of porous metals was shown.

Abstract: In the present work, oxygen-free-copper (OFC) and Ti-6Al-4V (TC4) were joined by diffusion welding at first and then the structural control of the joint interface was mainly analyzed. It was found that firmly welded OFC/TC4 joint was obtained over a temperature range of 1023K~1103K, and the temperature played the key role which mainly affected the thickness of the joint interface. The results also showed that the joining of OFC to TC4 was attributed to the mutual diffusion effect of elements Cu and Ti. The structure of the joint interface was further controlled by exerting restrictive pressure (10MPa), controlling heating and cooling rates, lower welding temperature and reducing welding time etc. Finally, under certain welding parameters and by employing rational structural control techniques, well welded OFC/TC4 joint without large distortion or damage was obtained.

Abstract: Mixtures of 12 mol% CeO2-stabilised ZrO2 with 5 to 20 wt % Al2O3 were prepared and densified through pressureless sintering in air at 1450° C for 1 to 4 h. The influence of the Al2O3 content and sintering time on the phase constitution, microstructure and mechanical properties of the as-sintered composites were investigated. Fully dense Ce-TZP/Al2O3 ceramics with a good combination of hardness and fracture toughness can be obtained by pressureless sintering in air for only 1 h. The addition of Al2O3 to Ce-TZP improves the mechanical properties and suppresses ZrO2 grain growth. The average ZrO2 grain size increases with increasing sintering time and decreasing Al2O3 content. This leads to an increase in toughness. An excellent fracture toughness of 14.3 MPam1/2 in combination with a Vickers hardness of 9.14 GPa was obtained for 12 mol % CeO2-TZP with 5 wt % Al2O3, sintered for 4 h.