Materials Science Forum Vols. 534-536

Abstract: TiB2-Cu composites in a nanostructured state are candidates for high-strength conductive and erosion-resistant materials. In this work, we studied formation of nanostructured TiB2-Cu composites under shock wave conditions. We investigated the influence of preliminary mechanical activation (MA) of Ti-B-Cu powder mixtures on the peculiarities of the reaction between Ti and B under shock wave. In the MA-ed mixture the reaction proceeded completely while in the nonactivated mixture the reagents remained along with the product – titanium diboride. The size of titanium diboride particles in the central part of the compact was 100-300 nm. This research shows that shock wave synthesis in mechanically activated powder mixtures with simultaneous compaction of the composite is a promising way to materials with submicron and nanostructures.

Abstract: Conventional powder metallurgy processing can produce copper green compacts with density less than 8.3 g/cm3 (a relative density of 93%). Performances of these conventionally compacted materials are substantially lower than their full density counterparts. Warm compaction, which is a simple and economical forming process to prepare high density powder metallurgy parts or materials, was employed to develop a Ti3SiC2 particulate reinforced copper matrix composite with high density, high electrical conductivity and high strength. In order to clarify the warm compaction behaviors of copper powder and to optimize the warm compaction parameters, effects of lubricant concentration and compaction pressure on the green density of the copper compacts were studied. Copper compact with a green density of 8.57 g/cm3 can be obtained by compacting Cu powder with a pressure of 700 MPa at 145°C. After sintered at 1000°C under cracked ammonia atmosphere for 60 minutes, density of the sintered compact reached 8.83 g/cm3 (a relative density of 98.6%). Based on these fabrication parameters a Ti3SiC2 particulate reinforced copper matrix composite was prepared. Its density, electrical conductivity, ultimate tensile strength, elongation percentage and tribological behaviors were studied.

Abstract: Conductive pastes have drawn significant interest due to their advantageous physical properties as well as their potential in electronic material industries. Conductive pastes consist of conductive fillers, organic binders, solvents and additives. Metal powders, such as Au, Ag, Ni, Cu, etc. are used for conductive filler. Filler dispersion is a very important and yet a difficult process in conductive paste manufacturing. Meanwhile, there are some metal powders such as copper, nickel etc that are used for pastes which have serious surface corrosion problems. This problem leads to change of the color and decrease in conductivity and affect storage stability of conductive pastes. To overcome these problems, we adopted two kinds of surface modification method. One is a method involving coating of silane coupling agent to conductive metal powders to overcome the corrosion stability and the other is a method involving addition of a dispersing agent to increase the degree of dispersion of metal powders. A coupling agent and dispersing agent are used to reduce the interfacial energy between filler and organic binder to enhance dispersion and its stability. By using silane coupling agent and dispersion agent, we can ensure both the corrosion stability and long term storage stability, and enhance the high performance electrical and mechanical properties of EMI shielding silicone sealant.

Abstract: In this paper, the whole temperature programmed decomposition (TPD) spectrum of titanium hydride was acquired by the special designed set-up. After separating and simulating the TPD spectrum by using Spectrum Superposition Method (SSM), Consulting Table Method (CTM) and differential spectrum technique, the kinetics parameters of titanium hydride and corresponding equations were obtained. Using these kinetics equations, the fabrication parameters of Al alloy foam can be determined and foaming process of Al alloy melt can be predicted.

Abstract: This work will report the deformation behavior of silicon carbide reticulated porous ceramics (SiC RPCs) under three-point bend test. SiC RPCs were fabricated by replication processing using an open-cell polyurethane sponge with cell size of ~ 13 pores per inch (ppi). It is shown that the deformation behavior strongly depends on the loading uniformity and the macrostructure. Using a compliant layer (0.5 mm paper pad), the uniform loading leads to a significant transition in the load-displacement curve of RPCs from the complex saw-tooth shape to the one similar to dense ceramics, despite the presence of some macrostructural flaws and partial clogged cells. However, this dependence of loading uniformity is alleviated by developing highly uniform macrostructure with fewer flaws and clogged pores. Even, this dependence becomes less important as the struts become thicker and stronger, leading to an increase in relative density, accordingly. The bend result of RPCs with highly uniform macrostructure is in excellent agreement with the GA (Gibson and Ashby) model, but the one with un-uniform macrostructure deviates from the GA model. This work shows that the macrostructure plays an important role in deformation behavior of RPCs under bend.

Abstract: Metal foams are not easy to use as materials as their manufacturing process involves all three, solid, liquid and gaseous phases occurring simultaneously at varying temperatures and moreever the morphology of the solidified foam is quite complex. There has not been any report on the stabilization of metal foams. To compare the stabilisation of metal foams using a different method, powder metallurgy and casting method using SiC and Ca alloy particle are required. Our investigation results showed deeply etched valleys with high oxygen content and secondary phases attached to line-shaped pores with higher SiC content than the matrix. These line-shaped pores - most probably oxide bifilms-form networks decorated with either secondary phases or oxide particle. We suspect that these decorated bifilms play a crucial role in the stabilisation of metal foams.

Abstract: Porous metal materials have been widely used in various industrial fields in the world. This paper describes the recent research achievements of CISRI in the development of porous metal materials. High performance porous metal materials, such as large dimensional and structure complicated porous metal aeration cones and tube, sub-micron asymmetric composite porous metal, metallic membrane, metallic catalytic filter elements, lotus-type porous materials, etc, have been developed.

Abstract: Plating of the sintered components has some problems due to interconnected porosities in those parts. In this research, iron-based sintered specimens infiltrated with copper were used. The pretreated specimens were then plated with nickel and the adhesion of coated layer to substrate was investigated. The results showed that the adhesion of coated layer in copper infiltrated iron sintered components is independent of substrate initial density.

Abstract: Defects of components as a result of entrapped gases during an injection process could be minimized with the utilization of a gas-permeable metal die material in the mold, due to its excellent permeability of air. Conventional gas-permeable die materials employ low temperature sintering of loosely packed steel powders with or without the addition of pore-forming polymers, whose microstructures are usually weak and their gas permeability values are also low. In this study, gas-permeable metal die materials are developed using tool steel powder, packed in a mold having the insertion of orthogonally arrayed polymer wires. Linear gas-permeable channels in orthogonal array are thus developed by the burning out of the polymer wires, which yield a large value of air permeability. The value of air permeability can be adjusted by changing the diameter and number density of the polymer wires. The tool steel powder can be made fully dense by supersolidus liquid phase sintering, yielding a microstructure with a wear resistance value much larger than that of the conventional gas-permeable die material.