Nanostructured Ni/n-Al_2O_3 metal matrix composites prepared by Pulsed Electrodeposition

摘要

For several applications in aeronautics (e.g. paddles of jet engines), automotive and also in the field of mechanical engineering, materials with special mechanical features were required. Materials used for these applications should combine a low weight with a high wear resistance, hardness, stiffness, and yield stress. In some cases the materials have functionalizations like self-lubrication or anticorrosion properties. These requirements can no longer be fulfilled by a monolithic material, and hence there is an increasing interest in composite materials. Metal matrix composites (MMCs) consist of inert second phase particles, usually ceramic particles, dispersed in a metallic matrix. The inert particles can consist of hard oxides like Al_2O_3 (1-3), ZrO_2 (4-6), TiO_2 (7-9) or carbides like SiC (10-12), WC (13-15), TiC (16, 17) or even diamond particles (18-20). Self-lubrication coatings are equipped with Teflon~TM (PTFE) (21-23), graphite or MoS_2 (27-29). The advantage of particle reinforced MMC's compared to fiber-reinforced composites is the isotropic microstructure which offers an isotropic behavior in material testing. Metal matrix composites can be prepared in different ways: powder-metallurgical methods (28-31), squeeze casting (32, 33), physical and chemical vapor deposition (PVD and CVD) (28, 34), High Velocity Oxygen fuel thermal spraying (HVOF) (28, 35, 36), electrophoretic deposition (28, 37-39), and electrolytic deposition (2, 3,27,40). In this contribution pulsed electrodeposition (PED) is used (41,42). The advantage of PED is that apart from the type, shape and amount of the particles dispersed in the electrolyte the properties of the deposited composite can be tuned by the variation of the plating parameters (current density, duty cycle, pulse repetition rate, etc.) A great benefit of PED is the nanocrystallinity of the deposited metallic matrix.