Materials Science Forum Vols. 534-536

Abstract: During the last decade, the use of metal matrix composites (MMCs) materials such as Al/SiC or CuW for microelectronic devices have made powder modules more reliable. Today, due to the continuous increasing complexity, miniaturization and high density of components in modern devices, high power microelectronic industries are looking for new adaptive thin films with high thermal conductivity, low coefficient thermal expansion, and good machinability. This paper presents an original and new elaboration method (tape casting and hot rolling) which has been optimized in order to elaborate copper/silicon carbide thin film composite materials. The first part presents the optimization of the tape casting parameters used (powder mixing; optimization of the nature and concentration of organic additives; tape casting, debinding and pre-sintering conditions). In the second part, the main characteristics of thin film obtained are discussed, such as thermomechanical properties of the composite Cu/SiC thin films.

Abstract: The microstructure and mechanical property of hot-pressed Al2O3/Cu nanocomposites with a different temperature for atmosphere changing from H2 to Ar have been studied. When the atmosphere changed from H2 to Ar gas at 1450°C, the hot-pressed composite was characterized by inhomogeneous microstructure and low fracture strength. On the contrary, when the atmosphere changed at a lower temperature of 1100°C, a more homogeneous microstructure and higher fracture strength was observed.

Abstract: This paper describes a fabrication process of Al/CNT composites and investigated their mechanical properties. CNT is a very useful reinforcement for composites since it has a very high strength and very high Young’s modulus. However, it is very difficult to distribute CNT in a metal matrix. Natural rubber was used as an elastomer and mixed with Al powder and CNT precursors to improve the distribution of the CNT in Al matrix. The resulting powder mixture was filled into Al alloy billets and encapsulated in vacuum atmosphere. The billets were then extruded with different extrusion ratios of 5, 10 and 20 at 673K. The composites were observed under optical microscope and FE-SEM, and the mechanical properties were evaluated by Vickers hardness and tensile tests. We succeeded in obtaining fully densified and finely extruded rod of Al/CNT composites of well distributed CNT by hot extrusion process. Observation of post extrusion micro structures revealed that CNT were not damaged by the hot extrusion process and their Vickers hardness and tensile strengths obtained were about twice compared to pure Al.

Abstract: Carbon nanotube (CNT) reinforced hydroxyapatite (HAp) composites were fabricated by using the spark plasma sintering process with surfactant modified CNT and HAp nano powder. Without the dependency on sintering temperature, the main crystal phase existed with the HAp phase although a few contents of β-TCP (Tri calcium phosphate) phase were detected. The maximum fracture toughness, (1.27 MPa.m1/2) was obtained in the sample sintered at 1100 oC and on the fracture surface a typical intergranular fracture mode, as well as the pull-out pmhenomenon of CNT, was observed.

Abstract: In the present work, hot workability of particulate-reinforced Al6061-20%SiC composite produced by direct hot extrusion technique was studied. Uniaxial hot compression test at various temperatures and strain rates was used and the workability behavior was evaluated from the flow curves and the attendant microstructures. It was shown that the presence of SiC particles in the soft Al6061 matrix deteriorates the hot workability. Bulging of the specimens and flow lines were observed, which indicates the plastic instability during hot working. Microstructure of the composites after hot deformation was found to be heterogeneous, i.e. the reinforcement clusters were observed at the flow lines. The mechanism of deformation is determined to be controlled primarily by dynamic recrystallization.

Abstract: The type, volume fraction, size, shape and arrangement of embedded particles influence the mechanical properties of the particle reinforced metal matrix composites. This presents the investigation of the SiC particle and porosity distributions in various aluminum matrix composites produced by cold- and hot-pressing. The microstructures were characterized by optical microscopy and stereological parameters. SiC and porosity volume fractions, and the anisotropy distribution function were measured to establish the influence of the consolidation method. The results showed that SiC particles are arranged in a different way during the cold- and hot pressing. The amount of porosity in the hot pressed specimens is always lower than that in the cold pressed ones; however, cold pressed and sintered samples have few large pores whereas more fine pores develop in the hot pressed ones. In the cold pressed specimens, heating rate for sintering influences the final density, the amount of porosity increases parallel to the increase in the relative particle size; and coating of SiC particles with Cu lowers the porosity while Ni-coating does not result in such an effect.

Abstract: Bend tests were performed at temperatures between 273 and 363 K for W-19vol%Cu, W-22vol%Ag and W-19vol%(BAg-8) composites. Yield and/or maximum strengths and ductility of the composite were discussed in terms of microstructure and fractography. Results are summarized as follows. (1) Almost no difference was recognized in yield strength between the composites. In contrast, a large difference was recognized in maximum strength and ductility between the composites. Maximum strength and ductility of W-Ag and W-(BAg-8) composites were generally much inferior to those of W-Cu composite. (2) Inferior mechanical properties of W-Ag composite to W-Cu composite are attributed to heterogeneous distribution of Ag-phases, whilst inferior mechanical properties of W-(BAg-8) composite to W-Cu composite are attributed to large pores at grain boundaries.

Abstract: This paper presents a new approach for analyzing the microstructure of SiCp-reinforced aluminum matrix composites from digital images. Various samples of aluminum matrix composite were fabricated by hot pressing the powder mixtures with certain volume and size combinations of pure Al and SiC particles. Microstructures of the samples were analyzed by computer-based image processing methods. Since the conventional methods are not suitable for separating phases of such complex microstructures, some new algorithms have been developed for the improved recognition of the particles in the metal matrix composites. One of the most determining attribute of composites structure is anisotropy, but the measurement of this parameter is very difficult and slow. For this reason, the anisotropy of metal matrix composites was investigated by the newly developed algorithm which has an optimized speed.

Abstract: A 15 wt.% NbC particulate reinforced iron-based composite was prepared by using warm compaction PM technique. It possesses a high relative density of 98%, a tensile strength of 515 MPa, a hardness of HRC 58 and a remarkable tribological behavior. Warm compaction was used because it can provide compacts with high green density and also increase the formability of the mixed powder. Furthermore, it can provide green strength that is strong enough to handle compacts before sintering. Block on ring tribotester was employed to study the compact’s friction and wear behavior using GCr15 steel as counterpart. A load of 980 N was used. The friction coefficient was 0.085 when the number 20 engine oil as lubricant was used. The results showed that the sintered composite has excellent wear resistivity. This material was then applied in the valve-guide cup of a combustion engine and subject to 500 hour bench test. The cup showed good performance for this test and did not shown any severe wear on the working surface after the test was completed. Therefore, it is a suitable material for parts that are exposed to severe wear condition.

Abstract: Boron carbide is a very hard material with high abrasive wear resistance. It requires a very high sintering temperature of above 2200 oC to fabricate a monolithic B4C close to the theoretical density. However, the mechanical property of monolithic B4C is not good enough to use it directly to industrial applications. In this investigation, B4C based ceramic composites were fabricated by in-situ reaction hot pressing using B4C, TiC and SiC powder as starting materials. The reaction synthesized composites by hot pressing at 1950 oC was found to posses very high relative density. The reaction synthesized B4C composites comprise B4C, TiB2, SiC and graphite by the reaction between TiC and B4C. The newly formed TiB2 and graphite was embedded both inside grain and at grain boundary of B4C. The mechanical properties of reaction synthesized B4C-TiB2- SiC-graphite composites were more enhanced compared to those of monolithic B4C. The flexural strength and fracture toughness of these in-situ B4C synthesized composites were 400-570 MPa and 6-9.5 MPam1/2, respectively.