Mechanical characterisation of AA7015 aluminium alloy reinforced with ceramics
ABSTRACT Manufacturing of metal matrix composites (MMCs) through powder metallurgy route and their characterisation are the objects of the present work. Thus a light alloy reinforced with 5% of ceramics is obtained after attrition milling of mixed powders, die pressing, lubrication of compacts and hot extrusion into 10 mm diameter bars. Since 7xxx series of aluminium alloys show high mechanical properties, AA7015 alloy was chosen as metallic matrix and B4C, TiB2 and Si3N4 ceramics were added. After process optimisation, the microstructure of these materials shows a uniform distribution of ceramics in the aluminium alloy matrix. Physical properties like density, conductivity and coefficient of linear dilatation were determined on extruded MMCs samples. Hardness and tensile strength properties on machined samples according to ISO 2740 standard were evaluated. Also wear behaviour using a pin-on disk test was studied, within a microstructure study, which was carried out using optical and scanning electron microscopy.
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ABSTRACT: In this study, a number of metal matrix composites were manufactured to determine their tribological properties. AA2124 matrix material, reinforced by SiC, B4C or Al2O3 (of different particle sizes), was used for manufacturing by powder metallurgy. The reinforcing particles were included at 10%, 20% and 30% volume fraction (vf). The matrix and reinforcement powders were compressed at 600 MPa and 615 °C for 30 min in an argon atmosphere. For comparison with the metal matrix composites (MMC), unreinforced AA2124 samples and GGG40 cam material samples (both induction-hardened and untreated) were also prepared for tribological tests. Tribological tests were conducted at 50 N loading with 900 rpm revolution for 30 min under dry conditions.The specific wear rates of the composites reinforced with 10% volume fraction of B4C or SiC are each lower than that of the GGG40 cam material. While the composite having 30% volume fraction of 20 μm SiC gives the best wear performance, the sample with B4C shows the best performance at 10% vf.Wear 01/2012; 289:73 - 81. · 1.26 Impact Factor
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ABSTRACT: Al-SiC composites were successfully produced with improved mechanical properties. Effect of SiC content, its particles size and shaping method were investigated. Three shaping methods of conventional powder metallurgy (PM), hot press (HP) and hot extrusion (EX) were used. The hardness of the samples was measured by Vickers method. Tensile and compression tests were performed for the characterization of mechanical properties. Microstructure was monitored by optical microscopy. Maximum relative density (RD) was obtained for hot pressed samples. Higher SiC content with smaller particles size had the best effect on the mechanical properties such as yielding point (YP), ultimate tensile strength (UTS) and hardness. Maximum hardness (6.57 GPa) and UTS (212 MPa) were obtained for Al-20%SiC with SiC mesh size of 1000. Maximum YP was obtained for Al-20%SiC in compression test (143.64 MPa) that is larger than it in tensile test (117.96 MPa). Remarkable difference exists between HP and extrusion methods at higher SiC contents. The YP of EX samples are larger than HP samples. Strains at known stress (562 MPa) of EX samples are smaller than HP samples.Materials Research 10/2013; 16(5):1169-1174. · 0.52 Impact Factor
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ABSTRACT: Fas ligand (FasL, CD95L, APO-1L, CD178, TNFSF6, APT1LG1) is the key death factor of receptor-triggered programmed cell death in immune cells. FasL/Fas-dependent apoptosis plays a pivotal role in activation-induced cell death, termination of immune responses, elimination of autoreactive cells, cytotoxic effector function of T and NK cells, and the establishment of immune privilege. Deregulation or functional impairment of FasL threatens the maintenance of immune homeostasis and defense and results in severe autoimmunity. In addition, FasL has been implicated as an accessory or costimulatory receptor in T cell activation. The molecular mechanisms underlying this reverse signaling capacity are, however, poorly understood and still controversially discussed. Many aspects of FasL biology have been ascribed to selective protein-protein interactions mediated by a unique polyproline region located in the membrane-proximal intracellular part of FasL. Over the past decade, we and others identified a large number of putative FasL-interacting molecules that bind to this polyproline stretch via Src homology 3 or WW domains. Individual interactions were analyzed in more detail and turned out to be crucial for the lysosomal storage, the transport and the surface appearance of the death factor and potentially also for reverse signaling. This review summarizes the work in the framework of the Collaborative Research Consortium 415 (CRC 415) and provides facts and hypotheses about FasL-interacting proteins and their potential role in FasL biology.European journal of cell biology 11/2010; 90(6-7):456-66. · 3.31 Impact Factor