Seksak Asavavisithchai

Microstructural examination and mechanical properties of replicated aluminium composite foams

Open-cell aluminium foams can be produced with the structural replication of dimensional accuracy from polymeric foam patterns through a pressure infiltration casting process. The strength of open-cell foam is much less than that of the closed-cell counterpart, and thereby subjects to mainly functional applications. An improvement in mechanical properties of the foams can be implemented with the addition of ceramic particles. In the present study, the composite foams were produced using AC3A alloy added with varying contents of SiC particles. The resultant foams have ceramic particles embedded in the alloy matrix and on the strut surface. Higher volume fraction of ceramic particles resulted in an increase in the compressive strength, energy absorption and microhardness of the foams. The improvement of these properties is due to the modification of the microstructure of the foams and the increased strength in the node and struts at which the ceramic particles reside.

Effect of Co Addition to Heat- Treated P/M 316L Stainless Steel on α′-Martensite Formation and Mechanical Properties

Abstract The effect of various Co additions to P/M 316L stainless steel on α ’-martensite formation and mechanical properties (bending strength and hardness) were investigated. Powder mixtures were compacted using a single action press at 498 MPa and sintered at 1,300°C for 30 min under hydrogen atmosphere, followed by heat-treating in air at 800°C and 900°C for 25 h, 50 h, 75 h, and 100 h, respectively. It is found that oxide formation in closed pores at high temperatures can induce the α ’-martensite formation and reduce the area fraction of porosities, resulting in higher hardness of the heat-treated specimens than that of the sintered specimens. The Co additions can also reduce the amount of α ’-martensite. Long-term heating results in a slight decrease of bending strength due to high connected oxide formation in the internal pores.

Multi-Level Porosity Silver Foams by Powder Processing Method

Abstract Silver foams with 70% porosity have been produced by the sintering and dissolution process (SDP) of fine silver powder. The powder was obtained from the reduction of rod-shaped silver sulfate, using glycerol mixed with sodium hydroxide as reducer and reaction accelerator, respectively. The foam shows three-level porosities, ranging from nanometer to millimeter level. The nanopores were created during the reduction process. The micropores were formed by the dissolution of remaining silver sulfate. The millipores were made from the removal of disaccharide powders. The pore architecture is unique and can be tailored by varying material and process parameters such as silver sulfate and disaccharide morphologies, reduction temperature and time as well as volume fraction of materials.

In-Situ Oxide Stabilization Development of Aluminum Foams in Powder Metallurgical Route

Abstract The development of stabilizing oxides during foaming process has been studied. The investigation of microstructure shows that the surface oxide films on the aluminum powder particles were ruptured after compaction. Pore nucleation results in a comprehensive shearing of oxides. After complete melting of powder particles at which a continuous liquid is dominant, the oxides move through the cell walls and Plateau borders by convection, due to pore growth, and connected to each other due to their tangled shape, forming strong local clusters or networks, leading to foam stability.

Structure and mechanical properties of ADC 12 Al foam–polymer interpenetrating phase composites with epoxy resin or silicone

Abstract Metal foam is a high-porosity engineering material which has many outstanding properties such as lightness, high specific strength and stiffness, large energy absorption during impact and good thermal transportation. Impregnation of metal foams with polymers produces new types of composites such as interpenetrating phase composites (IPCs) and co-continuous composites, due to an interconnection on the macroscopic level of individual phases as a co-continuous 3-D network. The coexistence of the metal and polymer phases allows each to contribute its prominent properties to the composite. This novel composite material is a potential candidate for applications in the automotive and aerospace industries. The present study aims to develop two IPCs from open-cell Al foams of 20 ppi impregnated with silicone or epoxy resin. The compressive behavior and energy absorption characteristics of IPCs are also examined and compared. The results showed that although both IPCs have a similar foam structure with similar density, the disparities in the properties of impregnated polymers lead to distinct mechanical properties. The combination of the Al foam and polymers, both silicone and epoxy resin, yield stiffer IPCs than either of the two individual materials alone. Higher stiffness was found in IPCs with epoxy resin, owing to the brittle nature of the resin. Energy absorption capacity was also increased when compared with the original Al foam.

Effects of Nickel and Chromium Additions on Microstructure of P/M 316L Stainless Steels

The present study aims to investigate the effects of Ni and Cr additions on microstructure of P/M 316L stainless steels. The optimum content of both elements to maximize the oxidation resistance of the stainless steel with minimum σ phase formation and microstructural development in various sintering times are also examined. The 316L samples were produced by homogeneously mixing Ni and Cr powders in various contents, followed by cold compaction at high pressure for 30 s. The solutioning process was performed at 1300°C for 45 s under hydrogen atmosphere. The sintering temperature was at 800°C and the sintering times were selected at 200, 400 and 600 hrs, in order to simulate working conditions. The development of microstructure was examined through optical microscope. It is found that the addition of Ni and Cr resulted in the formation of different porosity contents. The porosity increases when the content of the powders increases.

Developments of Metallic Foams in Thailand

Metallic foam is currently one of very active research topics in worldwide research communities, owing to its high potential to be employed in numerous industrial applications. Around 150 institutions are reported to be working in metallic foam research and development. In Thailand, it has been a research focus of universities and research institutes for many years. Most of them involve fabrication, characterization, improvement of metallic foam quality and process, and development of novel metallic foams. The majority of metallic foam research is conducted at Chulalongkorn University. The present article reports a review of metallic foam researches in Thailand.

Aluminum Foam Structures and Compressive Properties Produced from Multiple and Differently Arranged Precursors

Abstract Large closed cell aluminum foam components, produced through a powder metallurgical route, normally need multiple foamable precursors. The larger the size of components, the more precursors are required. The placement of precursors in the mold prior to sintering is important for a successful foaming. The present study shows that the initial precursor arrangement has a significant effect on the final foam structure and its mechanical properties. The largest foam expansion, close to the geometry of the mold, with more uniform pore distribution was found in the foam with the arrangement of four precursors, which were placed horizontally at the bottom of the mold in two layers. This was due to the delayed foam collapse as a result of the different onsets of individual precursor expansion. The difference in heat conduction of distinct precursor positions resulted in different cellular structural characteristics which strongly affect compressive behavior of the Al foams.

Microstructure and Compressive Properties of Open-Cell Silver Foams with Different Pore Architectures

Abstract Hollow silver particles with three different shapes, i. e., spherical, cylindrical, and octahedral, were used as raw material to produce open-cell silver foams. The shape difference of the particles resulted from the reduction of different shaped silver sulfates. Fabrication of silver foams was carried out using SDP process with disaccharide particles as space holder. The resultant silver foams show high porosity with distinctive pore microstructures. The examination of pore structure by SEM shows that there are three levels of porosities which are unique for each type of foam. The foams, using spherical and cylindrical silver particles, have a larger surface area and a higher density than the foam with the silver particle of octahedral shape. A control of pore architecture can be performed by tailoring material and process parameters. The difference in pore architecture resulted in a different compressive behaviour of the foams. As expected, the foam, using octahedral silver particles, has lower compressive strength than the others, mostly due to lower foam density.

Investigation of AC8A Scrap-Recycled Aluminum Foams

Open-cell Al foam has outstanding properties which are suitable for functional applications. However, a major drawback for widespread employment of Al foam is its high relative cost which can be several times higher than conventional metals. To reduce the cost, a recycled material waste is constructively used instead of expensive base metal. The present study aims to fabricate economical open-cell Al foams using AC8A alloy scrap from lathe machines. The Al foams were fabricated through pressure infiltration casting process at which the cellular pattern was made from commercial reticulated open-cell polyurethane foams with the pore size of 12 ppi. The compressive strength and microhardness of scrap-recycled Al foams are higher than those of pure Al foam. The increase in foam mechanical properties resulted from the change in foam microstructure as the formation of Si hard phase in Al matrix. The strength and microhardness of the foams increase with increasing scrap contents.