Papers by Keyword: Micro-Porosity

Abstract: Ti₂AlC is one of the most promising MAX phase materials due to its combination of properties at high temperatures (> 800 °C) such as high strength, good oxidation and corrosion resistances, low thermal expansion, readily machinable, high thermal conductivity and nonsusceptibility to thermal shock. Porous structures based on Ti₂AlC are excellent candidates for diverse applications such as heat exchangers and filters, although more systematic studies are required to implement this material. In this work, porous Ti₂AlC material was obtained using a low cost and eco-friendly process, the space holder technique. Commercial Ti₂AlC powder was mixed with different contents (30, 50 and 70 vol.%) of ammonium hydrogen bicarbonate (NH₄HCO₃) as space holder. Afterwards, the obtained powder was uniaxially pressed, followed by elimination of space holder by a heat treatment at low temperature. Finally, porous Ti₂AlC structures were consolidated at 1350 °C under argon atmosphere. Processing, final microstructure and pore characterization of the consolidated materials are described in detail.

Abstract: This paper presents analysis of Micro-Porosity defect in product Crankshaft - Ductile cast iron (FCD 700/2), which has been carried out at one of Automotive Foundry Company in Malaysia. Systematic analyses like cause-effect diagram and defect diagnostic study approach were carried out to understand the root causes of the micro-porosity. From the data analysis there are two significant factors are identified that affect the formation of micro-porosity, they are mold factor and metal factor. Four remedial countermeasures have been proposed to prevent micro-porosity; increase squeezes pressure at molding machine, control sand moisture, increase radius at edge of mold, and reduce Magnesium (Mg) content. Result of the trials showed substantial reduction of micro-porosity defect in crankshaft (casting). The company has accepted the countermeasure and incorporated in the standard operation procedure.

Abstract: The effect of two heat treatment processes on microstructures and tensile behaviors of K465 superalloy was investigated and compared. The results show that hot isostatic pressing (HIP) process partly or completely eliminated the micro-porosity to densify K465 alloy, and can effectively reduce the size of γ′ phase and improve the tensile strength and plasticity of K465 alloy. Electron probe micro-analysis (EPMA) studies revealed that the element segregation ratio was smaller in the HIP process alloy than that in the ordinary process alloy. nanoindentation tests revealed that elastic modulus and the hardness in the interdendrite of K465 alloy for HIP process were higher than that for the ordinary process.

Abstract: Green sand casting and chill mould casting methods are representing the slow and fast cooling rates of the brass casting, respectively. The compositions of the raw material for this study were about Cu70 and Zn30, which falls under alpha (α) brass. Slow cooling rate casting shows coarse dendritric structures with large spacing between the dendrites. On the other hand, faster cooling rate casting shows finer grains with shorter dendrite spacing. The developed structure during solidification influences the properties of the cast samples. As grain size decreases, the strength of the cast brass increases; micro-porosity in the casting decreases and the tendency for the casting to fracture also decreases. However, the macro-examinations of fracture surfaces of these castings show the differences in the cast samples. Fracture surfaces of the sand cast specimen show larger dimples taking longer time to break indicating higher elongation. However, chill cast specimen shows smaller dimples and cleavage type fracture surface having higher strength and lower elongation.

Abstract: Calcium phosphate compounds, in particular HA and β-TCP, are the principal synthetic materials used for bone substitutes. To assess the feasibility for further grafting of drug delivery systems, a pure HA was elaborated with specific internal material porosities and then tested on its biological effectiveness. The cell viability tests with L132 cells confirmed the excellent cytocompatibility of HA and the graphite powder. MC3T3-E1 osteoblasts were grown on HA conditioned with culture medium and FCS for 2h. All HA samples produced a higher proliferation and vitality rates than the TCPS controls; the micro-porous HA inducing the highest cell growth near 150%. The macro/meso-porous HA is easily colonized by MC3T3-E1 osteoblasts As to the cell morphology, no significant differences are observed between control cells and those grown on the HA samples. Cytochemical staining of osteoblasts revealed a well developed cytoskeleton with strong stress fibres oriented in the cells in their longitudinal direction. Labelling of the focal adhesion contacts with anti-vinculin showed a less developed adhesion process in the cells on the different HA substrates, which may explain the above mentioned increase of proliferation.